Rocket Planes: To the edge of infinity 9781909128729

Citation preview

FROM SOUND BARRIER TO HEAT BARRIER…

PLANES By David Baker

To the edge of infinity The story of the intrepid few who helped make today’s supersonic aircraft a reality

Contents Introduction

In October 1947 Chuck Yeager became the first pilot to exceed the speed of sound in level flight. What began as a research project became an all-out race for speed and altitude – all the way to hypersonic flight and the edge of space!

Chapter 1

Rockets and warfare

By the 1920s scientists were taking ‘simple’ war rockets and forging new tools for the exploration of space...

Chapter 2

Vengeance rockets

As the world waged war, German scientists were perfecting a method of propulsion which would form the basis for guided missiles and rocketplanes...

Chapter 3

Winged rocket planes

While engineers such as Wernher von Braun were building the world’s first ballistic missile, the aircraft industry was building high-performance rocketplanes...

Chapter 4

The search for speed

WBy 1945 the Americans had made up for a late start on jet aircraft, missiles and rocketplanes and picked up the pace toward penetrating the sound barrier...

Chapter 5

‘An unhesitating boldness’

Industry and government had come together to build a research programme that would underpin a bid to break the supersonic barrier. As the Bell X-1 emerged for its crucial test, military aviation was already knocking on the door to Mach 1...

Chapter 6

Bigger, faster, higher

With the sound barrier no longer an obstacle, the NACA and Air Force introduced new combat aircraft for test and evaluation, while the Navy’s Douglas Skyrocket began flying...

Chapter 7

Pushing the edge

With the Air Force having already achieved supersonic flight and a new generation of X-planes on the way, it was time to push higher and faster – with Mach 2 as the next prize...

Chapter 8

On the edge

For almost 10 years the X-1 series and the Douglas Skyrocket had the supersonic test run to themselves, probing faster and higher than ever. But then the X-2 came along, promising much but bringing catastrophe as it hit Mach 3...

Chapter 9

A very British approach

While the Americans were pushing hard on the speed and altitude barriers, engineers across the Atlantic here in Britain were developing a rocket-powered interceptor driven by the needs of the Cold War and capable of attacking Soviet bombers...

Chapter 10

Attacking the heat barrier – the X-15

The first generation of supersonic rocketplanes had pushed high-speed flight through Mach 3. Now it was time to take the next giant step forward – to Mach 6 and beyond...

Chapter 11

The final frontier

Rocketplanes took a back seat after the X-15, while test pilots and astronauts went to the moon and rode a winged spacecraft called Shuttle to build a giant space station – until a group of entrepreneurs and billionaires revived the concept...

In October 1947 Chuck Yeager became the first pilot to exceed the speed of sound in level fligh ght. h What Wh h began as a research project to discover the peculiari riti ities i of fligh ght h across the sound barri rier i became an all-out race for speed and alti titu itude u – all the way to hyp ypersonic p fligh ght h and the very edge of space its tself s lf! f!

E

ver since the aeroplane was invented, pilots have been trying to go faster and higher. Less than two years after the first flight fll by the Wright Brothers in December 1903 official bodies were set up in the United States and France to log flights fll and compile an official list of speed and altitude records. The first officially recognised speed in excess of 100kph was achieved on July 10, 1910, by Leon Lee Morane in a Bleriot monoplane at Reims in France. But not until February 1912 did a pilot fly faster than 100mph (161kph), when Jules Vedrines flew a Deperdussin at Pau. Fast forward 35 years and a veteran of the Second World War, nursing a broken rib due to a riding fall, strapped himself into the Bell X-1 rocketplane and flew through Mach 1 – breaking the sound barrier for the first time in level flight. It was October 1947. Fast forward a further 20 years and the more powerful X-15 carried its pilot beyond Mach 6 and to the fringe of space itself. In less than 25 years, aviation had gone from piston engine aircraft to rocketpowered planes capable of exceeding the wildest expectations of the pioneers who ushered in an era of flight fll and flying fll unlike anything seen before.

The desire to go faster and higher had a useful purpose. Stimulated by the need to maintain air superiority tyy in the postw twar w world, US scientists and engineers wanted to understand the challenges faced by the high speed and high altitudes which future aeroplanes were expected to reach. The invention of the jet engine in Germany and in Britain during the 1930s, and its availability tyy to US engine-makers in the 1940s, promised unprecedented performance which would push aircraft ftt into areas of physics which no pilot had visited. Research aircraft ftt were needed which would go in harm’s way to find out the limitations of engineering practice and to explore ways of going beyond the known limits of the day. There was no better way of doing that than by using rocket motors to propel aircraft ftt into areas of flight where there was no reliable scientific data. Aircraft Aii ftt powered by piston engines were restricted by the speed at which propeller blades could turn before

encountering a wall of increased drag, a resistance which increased with the rotational speed of the tip. Several aircraft ftt have been built where the blade tip is supersonic but if that were to be raised to several times the speed of sound the shockwaves would destroy the engine. In reality, most propeller blades have a maximum tip speed of Mach 0.9, about 690mph (1111kph) at sea level. Although some engines impart tip speed greater than Mach 1 and have a characteristic screaming sound as a result. However, because of unavoidable physical principles, the speed of the aircraft driven forward is much less than Mach 1.

The Bell X-1E is on display at the Neil Armstrong Flight Research Center at Edwards Air Force Base, California. NASA

Carried here atop a converted Boeing 747 in a fly-over of the Johnson Space Center in Houston,Texas, NASA’s Space Shuttle conducted 135 launches but two were destroyed – Challenger in January 1986 and Columbia in February 2003 – killing all 14 of the vessels’ crew members.The final shuttle flight was by Atlantis in July 2011. NASA

Today, the world’s fastest propeller-driven aircraft is the Russian Tu-95/142 Bear which has achieved a speed of Mach 0.82, about 575mph (925kph) from its turboprop engines in the 1960s. However, in a dive the thin wing of the Supermarine Spitfire was cleared to Mach 0.91. When jet engines came along they opened the possibility of providing the power to achieve supersonic flight, but engineers had no idea how to design aircraft to achieve that speed. Problems had already been encountered by aircraft flying close to the speed of sound and some which had crashed for apparently no known reason were believed to have succumbed to what quickly became a feared encounter with an invisible and impenetrable force. Several aircraft, presumed to have gone out of control, may have encountered this phenomenon. In such circumstances, very few pilots lived to explain the experience associated with what became known as compressibility. High-speed combat aircraft introduced during the latter stages of the Second World War were already encountering compressibility. The rocket-propelled Messerschmitt Me 163, operational from late in 1944, would frequently approach the sound barrier in a gliding dive back down to the ground. Even the jet-powered Messerschmitt Me 262 was running into difficulties when forced to flee at high speed or exceed its critical Mach number. These experiences only served to enhance the mystique of the sound barrier, which appeared to many pilots as a speed ceiling on aircraft and pilots alike. Yet even as the war was reaching its climax with the defeat of Nazi Germany and Imperial Japan seemingly inevitable, plans were laid to use rocket motors to propel an airframe through the sound barrier and explore the science of flight beyond Mach 1.

The US National Advisory Committee for Aeronautics was a powerful and highly respected arm of the government set up in 1915 for the specific purpose of investigating the science of flight and flying. Its specific mandate as defined by an Act of Congress was to “…supervise and direct the scientific study of the problems of flight with a view to their practical solution”. During the 1920s and 1930s the NACA had experimented using wind tunnels and research laboratories set up in Virginia, California and Ohio, with a flying field eventually set up close to Edwards Air Force Base, also in California. With these combined facilities the NACA provided a wide range of

aerofoil profiles from which designers could select appropriate wing shapes. With uniquely identified properties related to lift and drag, aircraft engineering grew at a phenomenal rate, enabling manufacturers to turn out large numbers of different types. By the 1940s, American aircraft manufacturing led the world and was well equipped to tackle the sound barrier. When the war ended in 1945 there was a great deal of enthusiasm for pressing ahead with aviation and aeronautical science and engineering, supported by an established range of university and college qualifications which opened new and exciting opportunities. Those were translated into possibilities by the large number of pilots coming back into civilian life looking for some of the youthful excitement that had enthused them in the skies over war-torn Europe and Japan. It was this group of young and aspiring pilots which provided a deep pool of resourceful talent which would take aircraft through the sound barrier and beyond. The use of rocket motors to push through the barrier was opportune. American physics professor Robert Goddard had first fired a liquid propellant rocket into the air on March 16, 1926. It flew only 184ft on a flight lasting less than three seconds. But it demonstrated the potential power from mixing a fuel and an oxidiser in a combustion chamber and releasing the expanded gas, causing a reaction which propelled the device in the opposite direction. The Americans lagged behind faster development of rockets elsewhere, the German rocket scientist Wernher von Braun being largely responsible for development of the V-2 which by late 1944 was being fired in large numbers against Antwerp and London. ➤

Much of the knowledge to build the Shuttle came from rocketplanes such as the X-15, which made 199 flights during the late 1950s and 1960s. Without this probing of the hypersonic and earth-space boundary, none of the Shuttle accomplishments would have been possible. NASA ROCKETPLANES 5

Only by the use of rocket motors could the ultimate high-speed and highhigh altitude flights be achieved. Propeller-driven aircraft ftt were limited to t altitudes of around 65,000ft ftt while a jet engine, which still relies on taking in air, is limited to a maximum altitude of about 100,000ft ft. t Rocket aircraft ftt take along both fuel and oxidiser and because they are independent of the outside environment environme they can operate ideally in a pure vacuum. The challenge of the sound barrier was difficult to understand and there was insufficient knowledge abou about how to design a supersonic air intake for a jet engine operating above Mach 1. A rocket-powered research aircraft ftt was ideal. It would be used to conduct research that would show design engineers how to come up with an aerodynamic shape, and a jet engine inlet, which could operate beyond the SpaceShipOne successfully achieved the first non-government funded flight into space on speed of sound. In an age before June 21, 2004. D Ramey Logan computers there was no way of knowing how an aircraft ftt would react at these speeds and altitudes and the ultimate promise of rocket first flight to Earth’s nearest neighbour. rocketplane to take the art of supersonic flight research was to push humans to the very An Another n X-15 pilot, Joe Engle would have into the hypersonic world of Mach 6+. edge of the atmosphere, perhaps even to commanded a moon landing mission had that The development span of X-plane space itself. not been cancelled in a cost-cutting exercise technology gyy embraced those two tw w distinct eras: That was at least the dream of pilots who in the early 1970s. Engle would go on to fly the early days on and around the end of the flew the X-series rocket powered research the Shuttle into space. Second World War, where rocketplanes were aircraft ftt betw tween w 1947 and 1968. Their legacy But test pilots such as Armstrong Arr and Engle designed without any real knowledge of the was not to blaze a trail to space but to were second-generation X-men, the original conditions they would encounter. relinquish wings for spacecraft ftt as some such group which included pilots such as ‘Chuck’ Characterised by the Bell X-1 series and the as Neil Armstrong, Arr the first moonwalker. A Yeager and Joe Walker were from the early Douglas D-558-II Sky kyrocket, y they pioneered civilian test pilot for the NACA, Armstrong Arr days when nobody really knew how to fly very the science of transonic and supersonic flight flew the X-15 on several missions to high fast and very high. Pilots such as Scott ttt laying a path for the second generation X-15, speed and extreme altitude, joined NASA as Crossfield represented that small group who designed a decade later and benefitt tting t from an astronaut and commanded Apollo 11 on the transitioned betw tween w the generations of several hundred research flights to write the

science and define the physical laws which enabled flight to the outer atmosphere and to hypersonic speeds. Paradoxically, the information obtained by the X-planes was not to be used in winged vehicles flying through space but to lay a path for high-speed flight with conventional jet aircraft. Every fast jet today bears some aspect of its design or its technology directly linked to information acquired by test pilots on the rocketplanes. Without the pioneering work on highspeed and high-altitude aerodynamics provided by the X-15, NASA’s Shuttle could not have been built. While not a rocketplane in the true sense, when it first flew into space in 1981 it represents the embodiment of all that was learned through the previous 35 years. The Shuttle flew 133 successful space missions in more than 30 years of sustained operations, carrying people, satellites and spacecraft. It was instrumental in launching the elements of the International Space Station and was retired in 2011. Building on the back of this extraordinary technology, where the science of rockets merged with the exotic design requirements of an orbiting spacecraft, it too has a legacy; one more closely akin to the design and technology of the X-series rocketplanes than anything before or since. That legacy had its origin in the X-Prize created in May 1996 by a foundation committed to stimulating space flight for everyone. The foundation offered $10 million to the first private organisation to demonstrate that it could conduct a trip into space twice within two weeks. More than 20 teams announced an interest and did some work to achieve that feat but it was won in 2004 by aerospace engineer Burt Rutan and Microsoft co-founder Paul Allen. Inspired by this remarkable achievement, the British

Taking the achievements of pioneering rocketplane engineers and gathering them in to a single endeavour to open up suborbital space flight to fee-paying customers,Virgin Galactic’s Richard Branson is confident he can fulfil the dreams of pioneers. Virgin Galactic

entrepreneur Richard Branson made space tourism his next ambition and created Virgin Galactic to put fee-paying passengers on suborbital flights to the fringe of space using a development of the rocketplane which had secured the Ansari X-Prize. Other contenders emerged and some, such as the XCOR Lynx, are strong competitors to Virgin Galactic. They all aspire to turn into a routine activity a form of flight which still

remains a unique activity in which experienced test pilots break down barriers and write new laws of aerodynamics. Rocketplanes are dangerous and flight by this means may never become routine. But there are men and women striving to make it so and while there are people lining up to pay money to make the ultimate high flight, there will be engineers and scientists striving to achieve that. ■

Rocket Planes Author: David Baker ProDuCtIoN EDItor: Dan Sharp DEsIgN: Holly Munro, Tracey Barton, James Duke rEProgrAPhICs: Jonathan Schofield, Simon Duncan MArkEtINg MANAgEr: Charlotte Park PublIshEr: Tim Hartley CoMMErCIAl DIrECtor: Nigel Hole PublIshINg DIrECtor: Dan Savage

PublIshED by: Mortons Media Group Ltd, Media Centre, Morton Way, Horncastle, Lincolnshire LN9 6JR Tel: 01507 529529 PrINtED by: William Gibbons and Sons, Wolverhampton

Member of the Professional Publishers’ Association

Independent publisher since 1885

ISBN: 978-1-909128-72-9 © Mortons Media Group Ltd. All rights reserved. No part of this publication may be produced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage retrieval system without prior permission in writing from the publisher.

FroM thE PublIshEr oF: Having trouble finding a copy of this magazine? Why not just ask your local newsagent to reserve you a copy

ROCKETPLANES 7

The father of liquid propellant rocket motors, Robert H Goddard, launched the first of its type in 1926, opening the possibility of flight above the atmosphere. Here Goddard poses in his workshop in October 1935. Smithsonian

Rockets and warfare After centuries of speculation and debate about how to reach above our planet’s atmosphere, by the 1920s scientists were taking ‘simple’ war rockets and forging new tools for the exploration of space, also leading to the first rocketplanes which would eventually carr y pilots beyond the sound barrier.

M

ore than 100 years ago the world was full of exciting discoveries. Science fiction writers such as Jules Verne and H G Wells had set alight human imagination with dreams of alien worlds, space travel and the exploration of planets beyond our own. In Russia, a school mathematics teacher, Konstantin Tsiolkovsky, had worked out the formula for rocket propulsion using hydrogen and oxygen to fuel powerful engines capable of sending humans beyond Earth’s thin atmosphere. And the new and exciting prospect of powered flight in heavier-than-air flying machines had become reality. Nothing, it seemed, could stop the march of progress and the promise of rocket flight seemed very real indeed. 8 ROCKETPLANES

Powder rockets had been invented in Asia more than a thousand years ago. The Chinese and later the Mongols and the people of India had worked out the formula for firecrackers, and war rockets were quickly developed by European nations – particularly the British – and developed into projectiles for hurling fire and destruction over distances of several kilometres. In the late 18th and throughout the 19th century, powder rockets found application not only for war-fighting but also for use as rescue rockets firing lifelines to stranded ships from wave-lashed rocks and even for sending mail across inhospitable terrain – at least in theory.

Powder rockets use a mixture of charcoal, saltpeter and sulphur, a chemical formula also known as gunpowder. It has the advantage of being a ‘slow-burner’ and can be used to provide energy for propulsion as well as its application as an explosive. The particular use depends on the chemical formula and how it is packaged. But powder rockets provide insufficient energy to do very much.

Packed into a relatively lightweight casing they can be made to propel a rocket considerable distance but they have no real load-carrying capacity. Nevertheless, powder rockets did find wide use as missiles and the British Army was the first in the world to have its own ‘rocket troops’. It was William Congreve, conducting experiments and tests at Woolwich Arsenal, London, during the 19th century who introduced what would be forever known as the Congreve rocket. His work was influenced by the use of rockets by the Indians against the British in the battle of Seringapatam in 1792. Local leader Tipu Sahib supported his father, Haidar Ali, in resisting British rule and attacked soldiers protecting the East India Company. Using age-old techniques of black powder packed into bamboo sticks, these crude weapons delivered disproportionate success compared with the crude and simple nature of their design. Battle-hardened soldiers were caught off guard and sent into a panic by the rain of fire that descended on them from above.

British rocket troops

In London, Congreve examined captured Indian rockets and in 1804 wrote A Concise Account of the Rocket System in which he described the way they worked, pointing out the advantages of a more scientific approach to what could, he mused, be a very considerable asset to the British Army. Thus was born the Congreve rocket which, within a few years had produced a wide range of optional projectiles in excess of 2km. They were used first against the French town of Boulogne in 1806 when more than 2000 projectiles were fired from ships, completely eliminating all opposition and spreading fire and destruction. The following year several thousand rockets were fired against Copenhagen, terrifying the Danish population, setting fire to buildings and burning down warehouses. Over the next several years, Congreve rockets were used with great effectiveness against Callao in 1809, Cadiz in 1810 and against the German city of Leipzig in 1813. But, it was perhaps in the war with the recently independent United States of America that British rocket troops achieved their most enduring legacy – immortalised within the national anthem The Star Spangled Banner. On August 24, 1814, the British used Congreve rockets to attack and subdue Fort McHenry, Baltimore, causing the Americans to retreat and burning down the White House in Washington DC. But the flag over Fort McHenry was never brought down. Written by Francis Scott Key, and set to music by Englishman John Stafford Smith, the anthem became a symbol of American resistance and national pride, one line that enshrined in the national memory of that day was “…the rocket’s red glare, the bombs bursting in air, gave proof through the night that our flag was still there.” Its symbolism is engraved in the following words: “O say does that star-spangled banner yet wave, O’re the land of the free and the home of the brave.”

A group of rocket pioneers at Pasadena, California, in 1936 prepare a rocket flight close to where the Jet Propulsion Laboratory will later orchestrate US flights to the planets. Smithsonian

The American Rocket Society readies a test launch from Marine Park, Staten Island, New York in 1933. At left is G Edward Pendray, a founding member of the ARS. Smithsonian

The development of powder rockets waned by the middle of the century, although the Americans quickly picked up on the technology and produced their own Hale rockets. Developed by Englishman William Hale they incorporated angled fins at the base of the projectile to spin-stabilize the rocket in flight. This did away with the need for long guide sticks extending far behind the cylindrical powder casing as was the practice with Congreve rockets. But whether Congreve or Hale, rockets were eclipsed by the development of field artillery which was to a very considerable degree spurred on by the Napoleonic wars at

the beginning of the 19th century and the better preparation of iron and steel during this period of great industrial development. Yet the big advantage with rockets was the absence of recoil, which made them suitable for use from small inshore and estuary boats where canon and artillery were impractical. The recoil from big guns made them unsuitable for use from small ships but their inaccuracy made them less suitable for the mechanisation and scientific development of war-fighting techniques of the 19th century. By the time the American Civil War was fought in 1861-65, rockets were out of favour. Powerful, new and accurate artillery pieces were in. ➤ ROCKETPLANES 9

The Opel RAK-2 rocket car before a run at on May 23, 1928. Smithsonian

Britain’s Naval Rocket Brigade during the Abyssinian campaign. British Army

10 ROCKETPLANES

the Avus Speedway, Berlin,

Wernher von Braun (in breeches behind the white-coated technicians) after a successful test launch on August 5, 1930. Smithsonian

The American Rocket Society launches its first test rocket 12, from a farm near Stockton, New Jersey, on November 1932. Smithsonian

Robert Goddard gazes up at the launch frame by which the world’s first liquid propellant rocket had been launched on March 16, 1926. Smithsonian

ROCKETPLANES 11

Rockets and aeRoplanes

A parachute is packed into a rocket during a demonstration at New York University in 1932. Smithsonian

12 ROCKETPLANES

Just as the powder rocket was going out of favour, smaller and lighter diesel and gasoline combustion engines were beginning to emerge and would take over some of the jobs done by steam for the previous century. The potential of the petrol engine was realised with the motor car and the aeroplane, while the latter, paradoxically, would briefly resurrect the potential of the powder rocket. The shift from an external to an internal combustion engine for small, lightweight machines was the key to the aeroplane and to the marriage of winged flight and rocket power. The first petrol-driven motor car was produced by Karl Benz in 1885 and it took 18 years before the world’s first heavier-than-air flying machine, powered by a reciprocating engine, took to the air at Kitty Hawk, North Carolina, on December 14, 1903. Aeroplanes evolved relatively slowly until European inventors and entrepreneurs produced a vibrant industry in the years leading up to the First World War. When conflict broke out in August 1914, the aeroplane was little more than a plaything for sport and recreation, dragooned into military service a few years earlier as a reconnaissance platform and a gunspotting observation post more manoeuvrable than balloons or man-carrying kites (which the French had developed). For two years, the war raged on with the ever-evolving use of aeroplanes for spotting, reconnaissance, bombing and fighting other aeroplanes. In 1916 a French Lieutenant, Yvres

Le Prieur, already known for his inventiveness and for testing ingenious, if not always practical, designs, produced a powder rocket for bringing down observation balloons. These Le Prieur rockets were little more than cardboard tubes filled with about 0.2kg (7oz) of powder and attached to sticks 4.9ft (1.5m) in length. There were suspicions at first that the rockets would, of their own accord, do more damage to the aircraft launch than to the offending target, so tests were required. These demanded firing trials with a mock-up wing installed on a Pic-Pic car capable of 120kph, which demonstrated that they could safely discharged. The rockets were attached in sets of four, one above the other, on both sets of interplane struts separating the outer sections of biplane wings, set at an inclination of 45º. Various aircraft carried Le Prieur rockets, each fitted inside a hollow tube and fired electrically from the cockpit. The rockets were most effective against German observation balloons but many were fired at German airships, against which they were not successful. The greatest exponent of attack using these rockets was the Belgian air ace Willy Coppens who destroyed 35 German Drachen balloons in just over five months during 1918. But against airships, the British had no success and the rocket, which had no explosive warhead, fell into disfavour after the introduction of more powerful guns and incendiary ammunition. Once again, the rocket was superseded by a better technology.

The American Rocket Society testing ground was at Crestwood, New York, here seen in 1935. Smithsonian

Calculationss and an flight fl gh logs ogs from Goddard’s Goddard s library meticulously record recorded corded the he detailed de a ed results of his work. Guggenheim Institu Institute e

Liquid rockets

After the war, powder rockets continued to attract interest for risk-takers and entrepreneurs keen to snatch daring opportunities for thrill-seekers to admire. Unstable, unpredictable and when used by amateurs likely to spontaneously combust, powder rockets were nevertheless, sought for propelling aircraft into the air, for serving as back-packs to launch intrepid aeronauts into the air and even to move boats across lakes at unprecedented speed! None of which were in any way effective or likely to succeed. The real development in rocketry came in the mid-1920s after many years of work by Dr Robert H Goddard into liquid propellant rocket motors. These had always been seen as the only truly effective way of sending objects above the atmosphere. While Goddard dreamed of space travel including flights to the moon, he veiled his work in conservative terms unlikely to offend the academic sources of his income.

Like Tsiolkovsky, Goddard realised that liquid propellants were the only practical means of propulsion for his ambitions and, quietly and without fuss, he worked away at perfecting the design of a series of motors which would help bring on that day when humans travelled through space. Goddard’s work reached fruition when, after almost a decade after starting work on his ideas, the world’s first liquid-propellant rocket took to the air on March 16, 1926. Launched from a deserted field in Auburn,Massachusetts, the rocket flew to a height of just 41ft and came down 2.5 seconds later in a cabbage patch, 184ft from its makeshift test stand. It looked about as different to the public concept of a rocket as it was possible to be. With a combustion chamber at the top supported by two thin pipes each side curving out to converge again below where they joined the liquid propellant tanks, Goddard’s rocket ushered in the era of rocket planes and spaceships.

Robert Goddard's rocket with turbopumps is prepared for assembly at Roswell in 1940. NASA

Why rockets?

The big difference between powder rockets, or solid propellant, and liquid propellant motors is that solids just do not have sufficient energy per given weight that liquids do when burned together in a combustion chamber. To get beyond the atmosphere, a rocket motor – whether in an aircraft or a rocket launcher – must take along the oxygen it needs to burn the fuel. So, both an oxidiser and a fuel are essential for flights beyond the edge of the atmosphere. In that, they are unlike a jet engine which takes in air, consisting of 21% oxygen and 78% nitrogen. It is the oxygen which allows the fuel to burn to create thrust. And so it is with a rocket engine but because it is not diluted with nitrogen, the oxidiser is in a purer and more densely stored form – usually at ‘cryogenic’ temperatures which means that to store it as a liquid it must be kept below –298ºF (–183ºC). Rockets work because of physical laws which were identified and described by Isaac Newton, one of which states that “to every action there is an equal and opposite reaction.” It is this, the third law of motion that drives the rocket. Combustion of fuel and oxygen liberates energy which is delivered in a single direction through the exhaust nozzle causing the entire rocket, or aeroplane, to move forward, in the opposite direction, by natural force. Rockets work better in a vacuum because there is less pressure pushing against the exhaust to slow it down and since the thrust is dependent, to some degree, on the speed of the gases escaping the exhaust, if there is no resistance to that force the speed is faster than it would be in the atmosphere. Hence, as rockets rise up through the air and the atmosphere gets thinner, the thrust goes up. They are the only means of propulsion where the air gives out and both reciprocating motors and jet engines become useless. ROCKETPLANES 13

Vengeance rockets As the world waged war, German scientists were perfecting a method of propulsion which would form the basis for guided missiles and rocketplanes in the mid-1940s.

Captured V-2 rockets returned to the US were test fired as shown here with this Bumper-WAC by the German missile. US Army

I

t was not long before the whole world learned of the work of Dr Robert Goddard and his experiments with rockets in the United States. Throughout the 1920s enthusiasts raised on the science fiction writers of the day thought this was a great leap toward the future. Liquid propellant rockets could achieve what no assembly of powder rockets could ever achieve – they just did not have sufficient energy to lift instruments, let alone people, beyond the atmosphere. Goddard himself 14 ROCKETPLANES

made great strides in developing more practical and realistic rockets in which he did propose to send instruments to the outer edge of the atmosphere. Ever the scientist, he wanted to know what the fringe of the atmosphere was like and what lay beyond the thin veil of air that supports all life on Earth. For others, across the Atlantic Ocean, it was an answer to their dreams. Inspired by Goddard’s achievements, organisations were set up to build their own rockets and carry out experiments into reactive flight.

Among these was the Verein fur Raumschiffahrt – the German Society for Space Flight – which included a young university student by the name of Wernher von Braun in its membership. Formed in 1927, just a year after the world’s first liquid propellant rocket flight, it would be the source of much enthusiastic research eventually leading to the world’s first ballistic missile. As work advanced in both America and in Germany, other groups too formed organisations to study and develop the new

Tests with German rockets in the early 1930s would lead to the V-2. Wernher von Braun is behind the technician holding a small rocket. Smithsonian

science of rocket flight. With an eye on space travel, the British Interplanetary Society was formed in October 1933. Among their founding members was a young Arthur C Clarke, a prophetic voice among engaged enthusiasts who would mix science with science-fiction. Among his great achievements was to describe how satellites placed in space at a certain distance would appear to remain stationary, relaying radio and television signals between continents. As a science fiction writer he would attract a global audience and achieve fame outside the genre with his 2001: A Space Odyssey, made into a film with the help of Stanley Kubrick. But the Europe of the 1930s played host to the fascist movements which took over Italy in 1926 under Benito Mussolini and Germany in January 1933, when Adolf Hitler became chancellor and the Nazi party quickly took over control of the government. Rearmament was a priority for the new German government and any potential advantage that the German Army could achieve was sought with enthusiasm. But the experimental test shots of small liquidpropellant rockets from a disused site on the outskirts of Berlin had already attracted the attention of Major Walter Dornberger, an artillery officer, which was why he offered von Braun a contract and almost limitless resources to build really big rockets before Hitler came to power.

The V-2 is born

From the time von Braun and a few colleagues had agreed to work for the German Army in 1932, attention was focused on developing a series of test shots to learn the basic principles which would allow them to build long-range missiles. As an artillery officer, Dornberger saw rockets as self-propelled cannon shells without the need of a barrel. As a man with his head already in the stars, von Braun saw them as the means to achieve interplanetary flight with humans.

The Army wanted a ballistic missile with a range of 200 miles carrying a one-ton warhead and for that it would have to be far bigger than anything conceived to date. There were challenges with this. The sheer audacity of ordering the expected performance would have been daunting to anyone with less than full confidence in their abilities. Development would push technology and engineering to the limit. No-one had built anything like this and the test facilities did not exist to try out the wide range of systems➤

Gerhard Zucker with the rocket brought to the UK for tests from Lymington. Fired toward the Isle of Wight it landed in Pennington to the west! Smithsonian ROCKETPLANES 15

A soldie rocket a V-2 rock

Above: Alfred Africano of the American Rocket Society designed a rocket in 1936 for atmospheric research, but it was never built. Smithsonian Below: Postwar, engineers were trained on the V-2. In the foreground, second from left, is the HWK rocket motor used for the Me-163 rocket fighter amid more conventional jet and reciprocating engines. NACA

16 ROCKETPLANES

The V-2 rocket motor was primitive and built for mass production. Nevertheless, it would form the basis of America’s first postwar rocket motors in much modified form. US Army

er of the German Reichswehr holds a one-stick Repulsor at Kummersdorf in August 1932, a far cry from the massive ket launched in 1942 to the edge of space. Smithsonian

The V-2 rocket became the iconic template for guided missile design after the war, its propellant tanks contained within a stiffened frame, stringer and skin construction. US Army

This adapted V-2 was designed by the Germans toward the end of 1944 to attempt lifting flight with a rocket-propelled missile. US Amy

➤and subsystems which would be essential to the proper working and reliability of the rocket. Those too would have to be built. At first work began on a series of smaller rockets, miniatures of the big missile, which would allow the team to test methods essential to reliable performance. They would need to know how to control large rockets in flight, using gyroscopes and tail fins acting like rudders in the exhaust from the rocket motor, how to measure the stability of the combustion process and learn how to develop reliable turbopumps to move the fuel and the oxidiser from their respective tanks to the motor itself. The pace picked up when von Braun and his men were moved from the suburb of Berlin to Peenemunde on the Baltic coast in 1936. Free from the prying eyes of intrigued Berliners and spying foreigners, the rocket team could set up test facilities for the big rocket engine and perform firings without attention.

The Baltic itself provided an ideal range with tracking facilities and optical observation posts as strategic locations. Test rockets could fall harmlessly into the sea and not interfere with life near towns and cities. The very remoteness of Peenemunde made it an ideal facility. Long before the scientists and engineers moved to Peenemunde they had built and flown a rocket designated A-1, for Aggregate (Assembly) 1. It had all the essential features of a missile but with a length of only 4.6ft it was tiny and was powered by a rocket motor giving a thrust of 660lb. With a similar length, the A-2 was used to test gyroscopes for stable flight and controlling the directional flight path of the large rockets to come. Late in 1934 tests with the A-2 were carried out from the island of Borkum on the North Sea coast where heights of 1.5 miles and more were achieved. But the next rocket was very different.

The plan for the big missile envisaged a single rocket motor with a thrust of 55,000lb but to get to that from the tiny A-1/A2 types was a big step which would require an intermediate test-bed designated A-3. The big missile was assigned the development number A-4. The A-3 had a height of 22ft and a diameter of 26in with a rocket motor delivering a thrust of 3500lb. Like its predecessors it ran on a mixture of alcohol and liquid oxygen. Unlike the A-1/A-2 which had the motor buried in the bottom of the fuel tank for cooling, the A-3 had the motor as a separate unit below the oxygen tank with the fuel tank above that. The first A-3 was launched in December 1937 and it, like others to follow, was a failure. A big step beyond the A-1/A-2, it had too much built into it without adequate test and analysis and while it was intended as a precursor to the definitive A-4, the A-3 was a leap too far. What was needed was a development rocket closely engineered to test and evaluate systems being designed for the A-4 and that became the A-5. Almost identical to the A-3, it had a muchimproved suite of systems and equipment more closely akin to those which would fly on the A-4. But much of the detailed research and development could make use of very small rockets launched from one of the islands of Peenemunde before they were built in to the big missile. From late 1938 a series of A-5 flights began which gave engineers operating experience with equipment being designed for the A-4. Results from those flights were fed back in to the final design of the big missile.

Ideally suited for mobile and rapid-fire operations, a battery of V-2 rockets stands ready for launch. US Army

18 ROCKETPLANES

To space!

When tests with the A-5 had demonstrated that the final designs for all the systems and subsystems in the A-4 were correct there was still an extensive test programme which only the A-4 itself could perform. With a length of 46ft and a diameter of 5.4ft, the A-4 weighed 28,000lb loaded with an ethanol and water (alcohol) mixture as fuel and liquid oxygen as the oxidiser. Powered by a single rocket motor with a thrust of 56,000lb, the A-4 would be under power for only 65 seconds before the propellants were consumed and the rocket was on its own travelling at a speed of 3580mph. As a weapon, the trajectory of the A-4 was optimised for maximum range. Arching over to the edge of space, 55 miles above Earth, the A-4 would begin a ballistic descent, slicing into the ground 200 miles from the launch site at 1790mph, detonating its 2205lb amatol warhead on impact. Flights of the A-4 began from Test Stand VII at Peenemunde in 1942. The first attempt on March 18 ended in disaster when the missile fell over and exploded. On the second attempt on June 13 it reached a height of almost three miles before falling out of the sky into the Baltic. An historic first was achieved on October 3, 1942, when the fourth A-4 reached a height of almost 56 miles and became the first manmade object to reach space. By the time the missile was ready for operational use, several hundred test firings had taken place from Peenemunde, and from Blizna and the Tuchola forest in Poland. Operating systems and equipment essential to the successful operation of the A-4 were conceived, designed and tested on these flights as gradually the missile was refined and made more reliable. For more than two years these tests were carried out involving vast resources and huge commitment from scientists and engineers forging a new technology in the white heat of war, developing a weapon which Nazi propaganda minister Joseph Goebbels would label the V-2 – Vergeltungswaffe zwei (Revenge Weapon No. 2).

The V-1 was the winged Fieseler Fi-103 cruise missile, or ‘buzz bomb’, which flew at subsonic speed propelled by a pulse-jet motor. These were the Nazi’s new wunderwaffen (wonder weapons) designed to terrorise urban populations if only through their indiscriminate targeting in dense cities. The first V-1 flying-bomb was launched in June 1944 and the V-2 was not far behind, the first rocket falling in Chiswick, near London, on September 8, 1944. Over the next seven months several thousand V-1s and V-2s were launched on London, south-east England and East Anglia, causing great damage and a loss of life on the scale of the Blitz in 1940. While fast fighters could intercept the flying-bombs, there was nothing that could be done to defend against the rockets, the population of London being hostage to attack without warning. When hostilities in Europe ended with the German surrender in May 1945 the Allies scrambled to salvage the highly advanced work conducted over the preceding 10 years. Far ahead of anything being developed anywhere else, rockets were now a plausible means of waging war across great distances but they also presaged a new age of rocketpowered winged flight to the very edge of the atmosphere and beyond. The Germans themselves had seen the advantage of this and on December 27, 1944, they launched a specially modified V-2 known as the A-4b with wings designed to extend the range of the basic missile. That particular flight failed owing to an error in the guidance system but the idea took hold elsewhere. The idea of using the V-2 for piloted research into high-speed flight occurred to the British in 1946 when a proposal was put forward for converting the nose section into a pressurised cabin where a single occupant could be propelled into space. Had this been implemented, it would have been possible to have shot a human on a ballistic flight to an altitude of more than 100 miles by the end of the decade using the basic technology uncovered by the Allies at the end of the war. Not until 1961 did the Russians and the Americans start flying people into space. ■

Above: The A-4b grew from an idea for a spaceplane using wings to create lift and extend the V-2 missile’s range. Smithsonian Below: German rocket engineers and scientists brought to the US in 1945 and 1946 to continue their work on missiles. US Army

ROCKETPLANES 19

Winged

rocket planes While engineers such as Wernher von Braun and the rocket pioneers at Peenemunde, located on the shores of the Baltic, were building the world’s first ballistic missile, engineers close to the aircraft industr y were building – and flying – the world’s first high-performance rocketplanes.

T

he development of jet aircraft, cruise missiles, rockets, missiles and rocket-powered aircraft in Germany during the period of Nazi rule from 1933 to 1945 had been staggering. It was arguably the greatest surge in the technology of weapons and their development ever recorded and was paralleled only by the development of the atomic bomb by the United States and Britain. All these weapons would underpin the Cold War and in the hands of both Russia and the US turn global nations into superpowers. When the Allies overran Germany at the end of the war therefore, rocket-powered aircraft were of particular interest. The drive to produce rocket-powered interceptors came as a result of the intense bombing campaign mounted by the British and the Americans from 1942. Within a year, the Combined Bomber Offensive was pounding German cities round the clock – the British by night and the Americans by

day. From 1944 single-seat fighters had sufficient range to accompany the bombers all the way to Berlin and back, defending the lumbering aircraft and fending off enemy attack. Urgently in need of a means by which the bombers could be brought down, the aircraft industry turned to a novel design of aircraft that dated back to the early 1930s. Aircraft designers had known from the early years of powered flight that while the wings and the tail-plane were crucial for control of an aircraft in flight, they contributed a lot of drag. As smooth air necessary for lift was transformed into waves of turbulent air, it reduced the efficiency of the aircraft and slowed it down. The eternal struggle between lift and drag could be won, said some designers, by eliminating the tail section altogether and shaping the wing into a delta or giving it a swept-back form. By doing this, they said, a given amount of energy from an engine would translate into higher speeds and manoeuvrability.

In 1932 Dr Alexander Lippisch began to develop tailless aircraft for the Focke-Wulf company but he was up against bureaucracy. As his aircraft had no tail it could not be given a certificate of airworthiness. For a while, tailless aircraft were banned by the German Air Ministry but this was later rescinded when the technology promised to produce winning designs. After moving to DFS, a company focused on developing gliders and carrying out research work on different wing shapes and profiles, Lippisch came up with a rocketpowered tailless aircraft which finally got the interest of the Air Ministry. Under the designation Project X, also known as the DFS 39, the company got a contract in 1937 to build a propeller-driven test aircraft followed later by a rocket-powered version. DFS was good with wings but lacked production capability so it would produce only the wings. The job of building the fuselage and integrating the rocket motor would go to the Heinkel aircraft company. ➤

The first liquid propellant rocket motor attached to an aircraft were tested in 1936 on the Heinkel He 72 Kadett, of which a pre-delivery production batch is seen here. RLM

“The sheer power of The rockeT moTor and The sTresses imposed upon The airframe of The he 112 ThreaTened To Tear The aircrafT aparT.” The firsT rockeT plane

Heinkel was the perfect choice for assembly and test of the DFS 39. It had already begun work on a converted He 112 adapted to carry a rocket motor designed by Wernher von Braun. The He 112 was a contender at the 1935 fighter competition which saw the Air Ministry choosing its rival, the Messerschmitt Bf 109. A He 112 airframe was donated to Heinkel and it was with this that tests were carried out with von Braun’s motor, which was installed in the rear of the fuselage, the propellant tanks being placed fore and aft of the cockpit. Tests with the rocket motor began in April 1937 but only after the aircraft had been taken into the air on the power of its Junkers Jumo 210C reciprocating engine. Burning alcohol and liquid oxygen propellants, the rocket motor produced 2200lb of thrust. This was not the first aircraft to carry a rocket motor into the air for tests but it was possibly the most dangerous. The sheer power of the rocket motor and the stresses imposed upon the airframe of the He 112 threatened to tear the aircraft apart. With Erich Warsitz at the controls, it did operate as planned but on one occasion the motor blew up and the aircraft crash landed. After getting another He 112 to work with, Warsitz made other, successful flights. The sheer power of the motor, and the use of liquid oxygen frozen to cryogenic temperature, made it a wholly impractical device. Instead, Heinkel turned to a less violent form of rocket propulsion. Only the year before these tests with the He 112, Heinkel had used its He 72 Kadett to test a small rocket motor designed and built by the Walter engine company. A tiny biplane trainer, in some respects the equivalent of Britain’s de Havilland Tiger Moth, the He 72 was fitted with a 300lb thrust Walter motor attached to the underside of the fuselage. The motor operated on hydrogen peroxide decomposed over a liquid catalyst. And it worked. The world’s first liquid propellant rocket motor carried in an aircraft; albeit one primarily driven through the air by a propeller. 22 ROCKETPLANES

The DFS 39 was designed as a tailless research aircraft which would lead indirectly to the rocket-powered Me 163. Robert Forsyth

Encouraged by these trials, Heinkel experimented with an improved version of the same motor producing a thrust of 660lb. It would be fitted to heavy Heinkel He 111 bombers to help them get into the air. This application was known as RATO – Rocket Assisted Take-Off – and the application would become common during the war. After these successful trials, and now with a greater familiarity with this type of motor, Heinkel decided to build an aircraft totally powered by a rocket motor – and nothing else. It would become the world’s aircraft powered solely by a rocket engine. Designated He 176, Heinkel wanted it for high-speed research and the power provided by a rocket motor gave the company an opportunity to reach the magical target of 1000kph – 621mph – sought by all German aircraft manufacturers. This was far beyond anything that had been attempted before and there was much debate about whether a reciprocating engine could pull an airframe through the air so close to the speed of sound,

which at sea-level is 767mph. At the time the h outright speed record of 380mph had been claimed by Hermann Wurster in a BFW 113R monoplane on November 11, 1937. Design work on the 176 began in Sonderentwicklung I, a secluded hangar at Rostock-Marienehe, during 1936. A year later construction began of what was designed to be the smallest possible aircraft capable of containing the pilot, and a small Walter rocket motor, and still provide wings and tailplane essential for stable flight. The fuselage of the He 176 had a diameter of 2ft 7in and a length of 20ft 4in. It was literally made to measure for Eric Warsitz, with an inclined seat and sufficient room for the main wheels to retract into internal bays. Two tanks within the fuselage contained hydrogen peroxide and methanol propellants with a Walter HWK R1-203 rocket motor in the back capable of being throttled to vary the thrust between 1102lb and 1323lb. Maximum thrust was only available for 50 seconds.

Heinkel was a specialist in high-performance wings. Denied full military aviation research and development capability after the First World War, the revitalised aircraft industry of the 1930s was built on a great deal of experience building gliders and sailplanes. For that, where the sporting enthusiasm in German youth took hold, wings were crucial to success. The 176 would benefit greatly from that work. Heinkel was already famous around the world of aviation for the elliptical wing, selected by R G Mitchell for the Supermarine Spitfire, and his new rocket plane would have wings with a span of 16ft 5in and a symmetrical profile with straight leading edge and dihedral. They were fitted with tip skids in case the narrowtrack main landing gear failed to keep it level. Unique, and giving the 176 a futuristic look, the cockpit canopy was a Plexiglass moulding conforming to the streamlined bullet shape of the forward section. The aircraft had a maximum take-off weight of 3570lb with 948lb of propellant on board. Calculations indicated a theoretical top speed of 466mph at 13,100ft with a ceiling of 29,500ft and a maximum range of almost 70 miles. Not long after completion the aircraft was moved to Peenemunde, which had just opened for tests with the V-2. This facility would rapidly become the home of top-secret German weapons development. The cockpit area of the 176 was designed to separate in an emergency

and deploy a braking parachute, enabling the pilot to bail out. Tests with this design involved a wooden mock-up complete with fully articulated mannequin dropped from a Heinkel He 111. In parallel, wind tunnel tests were undertaken at Gottingen in July 1938 and at Peenemunde the He 176 was towed at high speed behind a car along the beach at Usedom. Informal hops into the air under minimal rocket power preceded the official first flight which took place on June 20, 1939, a day before it was formally demonstrated before a group of Luftwaffe chiefs. Among the group was Ernst Udet who was distinctly unimpressed and ordered the project grounded, an edict which did not stop Adolf Hitler and associated Nazi leaders from witnessing another demonstration on July 3. The group included Hermann Goering, Wilhelm Keitel and others. Flight trials with the He 176 demonstrated what many suspected. It was heavy for its size, the wing loading was very high and the rocket motor had insufficient power. Heinkel had planned to build a second prototype and there was some interest on the art of the Air Ministry in adding armament. This was never fitted but blisters were added where the guns would be and instruments filled the void. Destined for a place in history, the only example was shipped to a Berlin museum where it was destroyed in a bombing raid in 1943. ➤

Above: The Opel Sander-Rak 1 rocket powered aircraft was built by Julius Hatry and first flown in 1929. Robert Forsyth Below: The Lippisch Delta I tailless aircraft was demonstrated at Tempelhoff airport, Berlin, by Gunther Groenhoff and Hermann Kohl in September 1931. Delta wings were extensively researched in Germany, a design adopted for the Me 163 rocket interceptor. DLR

ROCKETPLANES 23

A JET INTERLUDE

Heinkel was heavily involved in a wide range of projects and in parallel with the rocket-powered 176, the jet-propelled He 178 was starting its own tests. The first German turbojet engine was the work of Dr Hans Joachim Pabst von Ohain, who began bench running his demonstration turbojet, the HeS 1 engine, in December 1937. Within three months a much-improved He 3 engine was undergoing tests and with an axialflow impeller and a centrifugal compressor the engine was tested beneath a Heinkel 118 dive bomber. Emerging from the same hangar as the 176, the 178 was rolled out for taxi trials in August 1939. Warsitz was at the controls for a series of little hops along the runway and the first official flight took place on August 24, just over two months after the first flight of the rocket powered 176. Now Heinkel had a second achievement to his credit – the world’s first jetpowered aircraft flight. Not for a year and three days would another jet-powered aircraft take to the air when the Italian Caproni Campini C.C.2 made its inaugural flight. But this had a ducted fan engine and was not a jet in the true sense of the word. Not until nearly 21 months after the flight of the He 178 would Frank Whittle get Britain’s Gloster E.28/39 into the air as the first serious contender, making its first flight on April 15, 1941. By that time Heinkel had already flown the world’s first jet aircraft designed specifically as a fighter. German jet and rocket development would outstrip the rest of the world owing to the early start and massive investment from the government, spurred by the priority to develop a war machine capable of dominating future conflict. While jet aircraft were, in theory, a simpler solution to the problem of limitations with internal combustion engines, rocket powered flying machines were seen by many

The aesthetic lines of the Heinkel He 112 belied its potential as a fighter, some examples of which were used as a test-bed for Wernher von Braun’s rocket motors. RLM

24 ROCKETPLANES

An early design contender for the experimental He 176.

scientists and engineers in Germany at the time as potentially the supreme weapon of the future. It was for this reason that equal effort was afforded to key design teams like Ernst Heinkel and his design engineers. While outside the scope of this book, the sheer intensity with which the German Air Ministry pressed on with jet aircraft development was a key factor in producing what would become the world’s first operational jet fighter in 1944 – the Messerschmitt 262. The race for that prize began once again with Heinkel when, after there was disinterest in the rocket-powered He 176, the company turned its attention to the jet-powered designs. The first proposal for rocketplanes had been placed before the German Air Ministry by Major Wolfram von Richthofen in 1935. The idea only gradually gained ground among an overly conservative senior leadership, wedded to concepts they had been familiar with in the First World War, when many of them had been airmen. There were many competing ideas at this time, including the drive for a very long-range

bomber, which had been passionately supported by Luftwaffe General Walther Wever, chief of staff from February 1935. With massive injection of development money from seemingly limitless funds, this was a time in which bold new projects could be proposed. But Wever was killed in an air crash in June 1936 and real support for the strategic bomber died with him. It was simply too big a step from the Blitzkrieg warfare championed by Heinz Guderian and others to garner support. But jetpowered attack aircraft suited the mantra for lightning strike and persistent offensive action. Perhaps even with rocket planes too. By the end of 1939 the German Air Ministry had made up its mind to go all out for a jet fighter and for that several engine manufacturers were already producing what they each hoped would be a suitable design. Heinkel itself had the advantage of recruiting Max A Meuller, who joined the RostockMarienehe team from Junkers and introduced his own axial-flow engine previously developed at the Magdeburg factory where he had worked.

Meuller’s engine was given the Heinkel designation He 30 and his work ran parallel to von Ohain’s 1760lb thrust He3 3/6 series of motors, which had now matured into the 1540lb thrust HeS 8. Meuller was a powerhouse of ideas and also brought to Heinkel his own concept of the ducted fan engine, which Caproni had chosen for its own jet. There was certainly some resistance to the idea of jet engines, notably orchestrated by Wolfram Eisenlohr, directly in charge of engine development at the Air Ministry. Other manufacturers were in the running and Junkers had its own 109-004 and there was encouragement from the powerplant group of the technical department of the Air Ministry where Hans A Mauch and Helmut Schelp forged a new and effective plan for jet engine development. With this work under way by late 1938, another figure emerged to support, and orchestrate the joint and parallel development of airframes which would be adaptable for either jet or rocket engines – Hans M Antz. This combined drive, somewhat out of the limelight and in spite of resistance from older officials at the Air Ministry, produced a dual requirement which led on one branch to the Messerschmitt Me 262 jet fighter and on the other to the rocket-powered interceptor, the Me 163 Komet. But it was the jet fighter concept which had the biggest support, albeit reluctantly from some highly placed officials. Accordingly, plans had already been laid for Messerschmitt to get a clear run at a production concept. As early as December 1938, Messerschmitt had received a directive from the Air Ministry for a jet fighter capable of carrying any available engine. Early the following month an industry guideline specified a target speed of 560mph and the Messerschmitt design team began work on Projekt P.1065 which would emerge as the Me 262. Meanwhile, Heinkel was progressing with the He 280, certain that the airframe would be ready far ahead of any engine. Although

Although losing out to the Bf 109, the He 112 was a sound design and saw limited service in the Spanish Civil War. It proved useful as a high-speed test bed for rocket motors. RLM

the BMW 109-003 was considered the ideal powerplant, the simpler 109-004 from Junkers was considered adequate enough for early trials, while Daimler-Benz was progressing with the 109-007 and its advanced contra-rotating axial compressor. But at half the weight and only marginally bigger, the HeS 8 was considered a valid competitor for the 109-004 while Meuller’s HeS 30 was promising. This plethora of engine designs contrasts markedly with the situation in England, where leading jet engine exponent Frank Whittle received little government support and pushed hard against stumbling bureaucracy. In Germany, progress was rapid. The first He 280 was tested during glide trials towed by a Heinkel He 111B, those trials starting on September 22, 1940. After 40 such flights where little fault could be found either with the general design or the handling characteristics. Finally, test engines were ready to be installed in the 280, albeit without cowlings to improve cooling and prevent fuel pooling from leakages that

were all too common. The first prototype was fitted with two HeS 8 turbojets, although the engine itself had lagged behind the projected timeline and was still underperforming. Thrust was only 1102lb compared with the design prediction of 1540lb. Piloted by works test pilot Fritz Schafer, the He 280 V1 was taken into the air for the first time on April 2, 1941, the aircraft circling the Marienehe airfield at a height of about 980ft and landing minutes later. A full and very official demonstration flight was conducted on April 5 before an invited delegation of Luftwaffe officials and convinced the sceptical Eisenlohr of the aircraft’s virtue as a fighter. Just 10 days later the first flight of the experimental Gloster E.28/39 powered by a Whittle W.1 engine took place at RAF Cranwell, Lincolnshire. It would be nearly two years before the first British jet fighter would take to the air when the Gloster Meteor prototype was flown for the first time, also at RAF Cranwell, on March 5, 1943, a flight much delayed by problems with candidate engines. ➤

The only photograph of the Heinkel He 176 with tricycle undercarriage and tail wheel. Note the blended canopy line conforming to the elongation of the forward fuselage and glazed nose section for visibility. RLM ROCKETPLANES 25

“As if Angels were pushing…”

Engines were also the main reason why the Messerschmitt Me 262 was delayed. The first flight of the V1 prototype was completed on April 18, 1941, just 16 days after the first flight of the He 280. But unlike its competitor, the Me 262 was powered by a Junkers Jumo 210 piston engine mounted in the front of the fuselage and it wasn’t until July 18, 1942, that the Me 262 V3 flew on turbojet power alone. In the year that elapsed between the inaugural flights of these two jet fighter contenders jet engine manufacturers wrestled with problems over the development of this new form of power. Lack of demonstrated performance compared with theoretical prediction indicated a succession of unknown technical challenges which forced delay on all these fighter programmes, both in Germany and in Britain. But in the Meteor the RAF had an aircraft far superior in engine technology and manufacturing quality compared with the Me 262. 26 ROCKETPLANES

Superior in airframe design and aerodynamic performance, the Me 262 was bedevilled by bad engines and poor manufacturing standards largely as a result of the lack of skilled manpower and reliance on sweat-shop labour which frequently sabotaged the production line, often at the cost of their own lives. In Britain, no such flaws, either in quality or ethical work conditions, hampered the production of the Meteor. In the final comparative analysis between types, the German Air Ministry opted for the Messerschmitt design and the Heinkel He 280 was abandoned in 1943. Its demise was brought about by a string of minor, easily correctable, flaws and technical glitches but in the heat of war there was not time for lame ducks and the Me 262, had greater range and superior firepower from its four nose-mounted 30mm cannon. The Me 262 entered operational service in mid-1944, the first recorded air-to-air combat occurring on July 26. Within nine months it was all over and the world’s first jet fighter was consigned to history.

But the Me 262 had impressed fighter pilots on both sides of the conflict. Unlikely to be in a position to attack them in flight, American fighter pilots waited until they were coming in to land, loitering and circling behind hills and ridges adjacent to German airfields ready to pounce as they turned on finals. Discredited by the Nazis for criticising policy, Luftwaffe air ace and General of Fighters Adolf Galland was a tough man to impress. But when he flew the Me 262 for the first time he commented it was as though, “angels were pushing me!” More than 1400 Me 262s were produced during the war, accounting for more than 400 enemy aircraft for the loss of 100 in air-to-air Top: A three-view drawing of the He 176 with elliptical wings developed from the He 70. RLM Right: The He 280 was the first turbo-jet fighter to fly but wasn’t adopted by the Luftwaffe due to preference for the Messerschmitt works. Jet and rocket powered aircraft were competitors in the race for the super-plane. RLM

combat. But these engagements were with piston-engine Allied aircraft since no British or American jet aircraft would see combat before the Korean War in 1950. Nevertheless, in reaching speeds approach Mach 1 they presaged an age of supersonic flight. While it would be left to the Bell X-1 rocketplane flown by Chuck Yeager in October 1947 to claim the crown of glory for the first flight faster than the speed of sound, many American pilots who tussled with the German jet believed it had been there already. While no records exist to positively assert that the Me 262 flew through Mach 1, after the war US pilots who read the flight notes of German airman describing the response of the Me 262 to very high subsonic speed believed that they had encountered Mach 0.85. During flight trials before and during operational service several pilots had been killed in unexplained crashes flying high speed test dives and German aerodynamicist Prof Karl Doetsch was brought in to look at the reasons. He knew from theoretical calculations that close to Mach 1 the air becomes compressed, causing stress on the airframe and rendering aerodynamic control almost impossible in an aircraft not specifically designed for that environment. From his calculations and tests in wind tunnels he was able to duplicate conditions that occurred close to the speed of sound and he reached the conclusion that some of these pilots had indeed encountered compressibility in the transonic region and paid for the experience with their lives. ➤

The He 178 became the world’s first aircraft to fly solely on the power of a turbojet, the first true flight occurring on August 27, 1939.The British Gloster E.28/39 did not fly until May 15, 1941. RLM

Right: Me 262 prototype V74 was used for tests with the BMW 003A-1 jet engine, a hybrid type which had the unusual feature of incorporating a BMW 109-718 liquid propellant rocket motor for an advanced development of the Me262C. RLM

ROCKETPLANES 27

The first Me 262 (V1) being readied for flight.The initial design of the Me 262 was as a tail-sitter but erosion of Tarmac by the downward-angled jet effl fflux fl nudged the design into a tricyle layout. Robert Forsyth

“News of The jeT as well as rockeT aNd missile programmes had beguN To leak To briTish iNTelligeNce.” The rockeT choice

While Heinkel had been busy working away at the 176 rocket-powered experimental aircraft and the 178 candidate jet, the Messerschmitt works had, by January 1939, acquired the top-secret Project X in which Lippisch and his team had been developing the rocket-powered DFS 39. The stifling environment of a highly classified project and the division of work between the DFS company, building the wings, and Heinke building and integrating the rest of the airframe an rocket motor, caused confusion as work slowed. The situation was both intolerable and unworkable. Appealing to higher authority in the Air Ministry, Lippisch decided to manage the entire project himself but the Air Ministry got involved and moved him across to the Messerschmitt works at Augsburg, much to the disgust of Willy Messerschmitt himself. It was there that Section L was set up, initially with around 20 people, and the Ministry gave the project an official designation – the Me 163. To configure the programme for a more formal restart, work still remained to be done on the original DFS design concepts, which would be used for testing both wing configurations and motors. A development of the DFS 94, the 194 emerged quickly as a pure rocket design – the 94 had originally been designed for use with a piston engine, only being adapted to carry a rocket motor. By early 1940 the DFS 194 was moved to Peenemunde for installation of a Walter RI203, which was similar to the motor fitted to

28 ROCKETPLANES

the He 176 but modified to operate at a lower thrust level of 600lb running for much longer. While there at Peenmunde, DFS test pilot Heini Dittmar flew the 194 at speeds up to 342mph using cold propellants labelled TStoff and Z-Stoff. Propellants were key to efficient rocketplane motors and hypergolic chemicals, which ignite on contact, were preferable because they did away with the need for ignition systems, were simpler in design and could, in theory, be throttled for varying thrust output. T-Stoff was a high-test peroxide (HTP) and Z-Stoff was potassium permanganate. Each was toxic and highly volatile and when mixed they created a high-temperature chemical combustion producing manganese dioxide, which released energy proportional to the rate of delivery into a small combustion chamber. Materials technology was an important science since the temperature of this chamber could reach levels which would melt ordinary metals. This combination of T-Stoff and Z-Stoff was in common use in Germany for producing power for fuel pumps in aircraft as well as rockets. While the flight tests with the He 176 had produced a lacklustre response from officialdom, tests with the DFS 194 at Peenemunde went some way to restoring faith in rocket-powered aircraft. So much so that Messerschmitt felt encouraged to press ahead with development of a rocket powered interceptor, the Me 163. Now at last there

was some spur to the development of the new interceptor, which was already showing the influence of Lippisch and his desire for tailless aircraft. Over the winter of 1940-41, both the Me 163 and the jet-powered Me 262 came together in parallel and while each had a unique function and were destined for very different operational roles, together they epitomised the extraordinary progress that German scientists and engineers had made in development of aircraft powered by reaction-engines. Nowhere else in the world was this level of development seen, with the world’s first ballistic missile, the V-2, well on the way to becoming a reality. News of the jet as well as rocket and missile programmes had begun to leak to British intelligence community before the war began, and by a very unusual route. Disillusioned, a technician from the Heinkel works escaped to Britain and was interrogated by the Air Intelligence Branch of the Air Ministry. They learned of Germany’s fascination with reaction-engines for jet and rocket propulsion, the latter applicable to very fast interceptors – unstoppable by pistonengine aircraft – and ballistic missiles which were undetectable until they detonated on impact. A low-level programme began in which friendly sources in Germany were tuned to gather information which may be of help in finding out more about these wunderwaffen.

Very little progress was made until RAF photo-reconnaissance aircraft brought back film of test facilities for the He 280 in May 1942. Concern raised by some within the scientific intelligence community was not matched by those in authority. Churchill’s science adviser, Prof Lindemann, refused to believe in the practical possibility of rockets and interpreted photographic evidence of the V-2 from high altitude flights over Peenemunde as nothing more than propaganda – “sausages with fins” as he derisorily called them. Not until November 1942 did Air Intelligence get word on both Heinkel and Messerschmitt work on jet- and rocket-powered aircraft. When confirmation did come, the reaction was swift and decisive. On the night of August 17-18, 1943, RAF Bomber Command sent 596 aircraft, including 324 Lancaster bombers, to attack Peenemunde in a special operation that required a precision raid against a very small target. This was unheard of and was unique to the second half of the war. Much of the work being conducted by the German rocket engineers focused on this facility, which by this date had swelled to several thousand workers, specialist engineers and technicians, in addition to the security services of special Wehrmacht and SS units. The raid specifically targeted the living quarters of the scientists and engineers, the factory where components for rocket motors were built and the test facilities where engineering data was obtained. The raid involved a single master bomber leading the entire raid. That man was Group Captain J H Searby of 83 Squadron, 8 Group. Deliberately set for the night of a full moon, the raid was led by pathfinders, who initially dropped flare markers on the camp for forced labour workers but the raid was quickly brought back on track. A feint raid with Mosquitos streamed off toward Berlin to divert fighter attention and this largely succeeded. In all, the 560 aircraft that reached the target dropped 1800 tons of bombs killing 180 Germans and almost 600 foreign workers housed in flimsy buildings without bomb protection. Bomber Command lost 40 aircraft that night but the raid was judged a success. The attack caused the rocket research to shift to other places and while testing would reappear elsewhere, including areas of Poland, the shattered buildings and broken homes were left unrepaired to give Allied reconnaissance aircraft the impression that the place had been abandoned. It had not. The facilities that survived the onslaught were used for theoretical work, preparing all the drawing plans and analysing data obtained elsewhere. Not until after the war, when the Russians arrived, was it apparent that the place had continued to thrive as the centre of research and planning, directing work dispersed throughout the Reich. Manufacturing of V-2 weapons and jet fighters would take place in converted horizontal mine shafts and adapted facilities such as Mittelwerk production site near the Dora concentration camp. By the time this raid took place, much work had been done on the Me 163, although the programme was not affected in any significant

The Me 262 would encounter compressibility at speeds close to Mach 1 and give its pilots an unwelcome foretaste of the sound barrier. David Baker

way by the attack on Peenemunde. Already, by August 1943, the ‘Komet’, as it was called, was being brought into service and pilot training was about to begin. The raid itself served to endorse the role of the Me 163 as a high-speed interceptor launched against incoming Allied bombers in an attempt to halt the 24-hour round-the-clock bombing of German cities and production facilities. It was hoped that the sheer speed of this delta-wing aircraft would afford a higher level of survivability as it soared high above the box formations of bombers and sliced down to gun down individual aircraft as it descended. The technical capabilities of the Walter motor and the operational 11,800ft/min climb rate would allow the aircraft to achieve a speed of 590mph, nosing over at depletion of the rocket propellants and diving down close to the speed of sound as it attacked the bombers. For most of the flight the aircraft was unpowered, its finessed wing serving as a lifting surface affording sufficient control for it to conduct a controlled descent to the ground,

touching down at a speed of 137mph on a centrally mounted skid beneath the fuselage, deployed from a stowed position just before contact. The Komet had a ceiling of almost 40,000ft and a maximum powered endurance of eight minutes, after which it was a glider.

Rocket men

By early 1941 the DFS 194 had produced much of the research work needed to decide on the wing platform for the Me 163. But there were differences. The Me 163 had a larger fin and rudder area and the wing trailing edge had greater sweepback that reduced the wing area. Moreover, the fuselage had assumed a more rounded shape and lost its slab-sided profile. The wing itself benefited from the attentions of Alexander Lippisch, with compound sweepback on the leading edge and unique aerofoil sections designed to give the glider total control under a wide range of flying conditions. ➤ ROCKETPLANES 29

The triangular cross-section fuselage shape became an identifying aspect of the jet-powered Messerschmitt Me 262 interceptor, bomber and photoreconnaissance aircraft. David Baker

➤Automatic leading edge slots near the wing tips had been developed for the DFS 194, averting elevon reversal by ensuring the centresection stalled first. For the Me 163, Lippisch applied fixed slots providing low levels of drag and equal pressure levels at each end to inhibit flow through them. The first unpowered flights with the Me 163A V1 took place at Augsburg during the spring of 1941. Towed behind a Me 110, Heini Dittmar piloted the prototype as it was carried to heights of 13,000-26,000ft. Released for independent flight, the V1 demonstrated a descent rate of 1:20 and achieved unpowered speeds of 528mph, displaying excellent stability and good control responses. Some degree of flutter was encountered but this could be eliminated by careful balance control. The combined skills of Lippisch and Messerschmitt had produced a remarkable aircraft. These flight trials, all unpowered, greatly impressed Ernst Udet, a fighter ace from the First World War who had served under the famous Manfred von Richthofen and was a skilled and highly respected pilot to whom an aircraft such as the Me 163 had great appeal, if only because of its remarkable performance as a high-speed glider. While visiting on other business, Udet watched in disbelief as the unpowered V1 prototype made several circuits of the airfield without landing, finally touching down after 10 minutes. Doubting the word of the test team that the aircraft was not fitted with any form of propulsion, Udet had the ground technicians open every removable panel on the aircraft to prove that this was the case. 30 ROCKETPLANES

The significance of Udet in the fortunes of the Me 163 is not to be underestimated. Right at the time when Germany was rebuilding its military forces after appreciable losses during the succession of conflicts which began with the attack in Poland in September 1939, continued through the attack on France and the Low Countries in May 1940 and ended with the Battle of Britain and the Blitz in JulyDecember 1940, untried concepts were not in favour. There was a coming attack on Russia and all emphasis was going on mobilising resources for Operation Barbarossa and the biggest land assault in history. Yet for all that, beguiled by the remarkable handling and flying qualities of the Me 163, Udet, as Generalflugzeugmeister – director-general of equipment – could exert great influence over its selection for further development. Which was what he did. Fortunately for the Komet, his influence came quickly enough to take root within the Air Ministry at large for, on November 17, 1941, tired of the politics and the bickering of the Nazi regime under which he had been advantaged, he shot myself. Other factions had argued in favour of sustained research into very high performance aircraft. By late 1941 the German Army was pushing deep into the Soviet Union and there was every sign of imminent success in the complete defeat of Russia. Where outright production of equipment essential to the current war had taken priority on resources, it was time to invest in equipment for the next conflict – a potential war with America which Hitler imagined was inevitable.

Within a year, that confidence would have frozen and died on the timeless initiative of Russia’s two immortal generals – December and January of the Russian winter. By that date a new threat was beginning to emerge as, after the Japanese attack on Pearl Harbor in December 1941, after which Hitler declared war on the United States. The air war was bound to get more ferocious and rocket-powered interceptors were a welcome prospect. After the death of Udet, support for the Me 163 grew. The initial prototype, the Me 163A V1 had been taken to Peenemunde-West in July 1941 where it was fitted with a Walter RII-203, a version of the motor used on the He 176 and the DFS 194 but with the added advantage that it could be throttled in steps between 330lb and 1650lb thrust. The tests proved that handling T-Stoff and Z-Stoff had dangerous consequences for the unwary. When particles of calcium permanganate, used as the catalyst, clogged the jets into the combustion chamber the entire engine could explode without warning, as happened when a complete test building was destroyed. A similar occurrence was recorded at the test station at Trauen-Fassberg. In spite of these dangers, flight tests with the engine installed on Me 163A V4 began on August 13, 1941 with Heini Dittmar at the controls. Dispensing with a conventional undercarriage to save weight and reduce the size of the fuselage, the aircraft was supported on the ground by a dolly firmly attached below the lower fuselage.

The propellant was loaded shortly before starting the engine after which it made its takeoff run, releasing the dolly after it became airborne at a speed of 125mph, the unsprung, narrow-track carriage bouncing along before coming to a stop. After hugging the ground for several seconds the V4 slowly turned toward the sky and reached an altitude of 13,100ft in 55 seconds, the first time any powered aircraft had achieved this altitude in less than a minute. For a pure speed run and to test the rocket motor and the airframe to their limits, Dittmar made an air-launched flight on October 2, 1941. Towed into the air behind a Bf 110C to a height of 11,800ft, he was released for a powered flight which reached the phenomenal speed of 623.8mph – just exceeding the magical 1000kph set by aircraft designers and test pilots as the crucible from which to forge an assault on the sound barrier. But Dittmar’s flight came very close to catastrophe as he cut the motor when the aircraft was hit by a compression wave close to the transonic region at Mach 0.85 and the V4 went into what appeared to be an uncontrollable dive. The sudden change in pitch had destabilised the controls, caused largely by a wing which was still too close in design to that of the DFS 194. The wing on the Me 163A had a staggered leading edge sweep of 27º inboard and 32º outboard, compared with 19º and 27º

respectively on the DFS 194. Moreover the trailing edge sweep was 6º less than that of its precursor. This was causing problems close to the transonic region but the remarkable claims made about the flight of Heini Dittmar caused a stir. This already top-secret project was closed to the wider fraternity of German aviation companies and the information could not be shared or corroborated through independent analysis. Nevertheless, strongly doubting the claims, the Air Ministry asked Dr Göthert to check the figures captured by the Askana cinetheodolites which had been used in triangulation to gather data substantiating the claim. The highly respected Dr Göthert ran the DVL high-speed wind tunnel at Göttingen and his professional evaluation of the data was thought to be a determining factor in whether the Air Ministry believed Messerschmitt and the technical staff were controlling the flight, or not. It was through this analysis that the data was substantiated and the claim accepted but these were truly remarkable figures which even the jet-powered Me 262 was unable to achieve in level flight. At the time this record-breaking flight was made, in Britain the RAF was just equipping itself with the Supermarine Spitfire Mk.V, a type capable of 374mph, and the de Havilland Mosquito had not long made its first flight, with

the potential for a top speed of 380mph. A demonstrated speed more than 240mph faster than that was hard to countenance. Had the British known the full extent and potential of this work targeted raids such as those conducted against the Peenemunde facility in 1943 would doubtless have been organised for the Messerschmitt factories. But the flying skill and the technical performance that Dittmar gave that October was impressive too on a human level. In June 1942 he was presented with the Otto Lilienthal Award for Aeronautical Research.

A new breed

While the performance of the Me 163, still owing much in its design to the precursor DFS 194, was impressive, this was not the definitive rocket interceptor. But while the aircraft itself was being redesigned to take account of lessons learned during the flights trials with the experimental V-types, a total of six having been ordered, a further 10 were commissioned from the Wolf Hirth Segelflugzeugbau at Göttingen. There designated as Me 163A-0 types they would be used as nursery types for pilots converting to the rocket aircraft. First, they would learn to fly the delta-wing interceptor by rehearsing unpowered flight with the Stummel-Habicht, a version of the standard Habicht glider hangared at Gelnhausen in Hesse, 25 miles from ➤

The debate still rages as to why Hitler deployed the aircraft first as a bomber rather than leave it as a fighter as the Jagdwaffe preferred. Willi Messerschmitt ‘sold’ it as a multi-role combat type.This radar-equipped two-seat night fighter came too late for real advantage. Messerschmitt

ROCKETPLANES 31

Although designed as a jet fighter, the Me 262 had the smooth lines and sleek appearance of postwar jets. It would be equipped with R4M underwing solid propellant anti-aircraft rockets and some variants would be designed for rocket motors, none of which actually flew. David Baker

Frankfurt. There they would become proficient in handling an unpowered aircraft because the easy bit was going up, the most difficult bit about flying the Me 163 was getting down to the ground. They were some of the most efficient gliders ever built to that date and required some experience to cope with the unusual handling characteristics. In some respects the challenges faced by Me 163 pilots presaged the challenges designers of the NASA Shuttle would face 40 years later in bringing a powerless glider back from space. Only the extremes of performance were markedly different. With an operational range of 50 miles, and a powered portion of flight lasting no longer than eight minutes, descending at speeds in excess of 600mph and conducting a slicing attack through massed bomber formations, managing the energy left within the aircraft was daunting. Effective piloting of the Me 163 centred around ‘energy-management’, balancing the trade-off between lift and drag. It was difficult to slow down and this required a level of expertise for which, in wartime, there was all too little opportunity. The pilot had to arrive at the flare point to the landing strip with just the right amount of speed remaining to drop it down to the ground. But there were still challenges, once within the vicinity of the landing field the high lift-to-drag ratio meant that it wanted to keep on flying. It required special practice to be competent in putting it on the ground. The order for the definitive operational version, the Me 163B, was awarded on December 1, 1941. It would carry a fully developed Walter rocket motor using different propellants and with a much improved design it would also incorporate several modifications and changes to the airframe. Moreover it was to 32 ROCKETPLANES

be armed either with cannon alone or cannon and R4M rockets mounted on trays under each wing. The aircraft would look significantly different to the A-series with a major part of the redesign was in the wing, which incorporated changes brought about by the high-speed tests at Augsberg and Lechfeld. Instead of the cranked leading edge, the operational B-series would have a straight leading edge with a constant sweep of 23.3º at quarter-chord and a slightly reduced sweepback on the trailing edge. Designed by engineer J Hubert, the so-called C-slot was fitted to the outer 40% of the wing directly opposite the trailing edge elevons. Incurring only a 2.5% increase in drag, the slots prevented wing-tip stall making the aircraft impossible to spin, inducing instead only a gentle sideslip under crossed controls. A major change too was introduced with the Walter RII-211 (known in production as the 109509A-0-1) rocket motor that had been under development and test for some time and considered ready for use in flight. While the previous Walter motor used in the A-series adopted the cold system, the new engine would use the hot system of T-Stoff and C-Stoff. The T-Stoff was the same as before but the C-Stoff was a hydrazine hydrate mixed with methyl alcohol and water and this combination provided a greater exhaust velocity and a higher amount of energy per given volume of propellants. Moreover, the thrust of the motor could be controlled in sequential stages from 6603,300lb and therefore gave much more power than previously available with the RI-203. Regenerative cooling of the combustion chamber fed propellant through the walls of the chamber to remove excess heat

before it was recirculated back into the engine for combustion. The prototype Me 163B V1 was ready for flight trials by April 1942, the first of 30 to bear Versuch numbers indicating a test function. Originally six prototypes had been ordered but 24 of the 70 pre-production aircraft were also assigned this purpose. However, problems with the new rocket motor dogged the test programme and while the aircraft itself performed exceptionally well the programme was seriously delayed. By the summer of 1943, with almost twothirds of the 70 pre-production aircraft having been delivered, the programme went through a period of some turbulence when Alexander Lippisch had a difference of opinion with Willy Messerschmitt and left the company to take over the Luftfahrtforschungsanstalt Wien. Messerschmitt had not wanted the project from the outset and felt indignant that it had been foisted on him by the Air Ministry. Relations with Lippisch were fractious to say the least and Messerschmitt sought every means to discredit the Me 163 and boost the operational functionality of his jet-powered Me 262. It was within this highly competitive environment that a major misunderstanding would emerge after the war as to the operational use of the jet. While it is outside the scope of this book to give a detailed account of the Me 262, it illustrates one example of how political pressure can skew the use of an optimised aircraft. In trying to push the suitability of his Me 262, Messerschmitt had encouraged the senior Nazi leadership, as well as the Air Ministry, to think of it as equally suited as a fighter, a photo-reconnaissance aircraft and a bomber. Despite having been unable to defeat

the RAF in the summer of 1940, ex-fighter pilot and head of the Ministry, Hermann Goering had retained faith in his fighter pilots until the gradual erosion of his confidence under the incessant pounding of German cities. As the fighter pilots appeared unable to stop these round-the-clock bombing raids, Goering tuned his attention to the bomber pilots who were more attuned to Nazi ideology than the less reverential fighter boys. Hitler, as well as Goering, realised in 1943 that an Allied offensive on mainland Europe was only a matter of time and that defeat on the beaches was the only way the vast AngloAmerican war machine could be stopped in its tracks. To do that he needed bombers to hit the invasion force hard – right there on the beaches where they landed. Despite protestations from the fighter leadership, he recalled the fervent enthusiasm with which Willy Messerschmitt had encouraged use of the jet as a bomber and to settle the squabbling leadership of the Luftwaffe, Hitler intervened and ordered an end to the dispute and assignment of a bomber role as priority for the Me 262. After the war the belief that Hitler had intervened in destabilising the true role of an aircraft that armchair enthusiasts believed should have been prioritised as a fighter held traction and even today that myth is replicated in numerous books and publications. It was a myth encouraged and given impetus by the very man who had seen the Me 262 come too late and be too ineffective to make a real difference to the outcome of the Allied advance into Europe or to halting the incessant bombing raids on the towns and cities – Willy Messerschmitt chafed at the dispersion of his resources producing both jet and rocket aircraft. Unable to fill any role other than that of interceptor, the rocket-powered Me 163 was given the job of countering the bombers, a project he had not even wanted. Bitterness is the bedfellow of disillusionment.

The 19° swept wing of the Me 262 was not for aerodynamic reasons but because the initial BMW engines were too heavy and it was essential to sweep the outer panels to maintain the centre of gravity. German research to favour swept wings came after initial jet fighter design. David Baker

Into servIce

Bench tests with the new RII-211 did not begin until late in 1942 so with pre-production aircraft mounting up a wide range of trials and flight evaluations were conducted using the Me 163B as a glider only. These tests went as far as gun trials and Heini Dittmar was joined by Rudolf Opitz who would play a major role in getting the aircraft ready for operational deployment. The redesigned airframe had superb handling qualities and was a remarkably impressive aircraft with fine design qualities. But not until June 1943 was the first RII-211 motor delivered to Peenemunde and installed immediately in the V21 prototype for the first flight to take place with the hot engine on the 24th. A second flight followed on July 12. By this time Wolfgang Späte had set up a tactical training unit for the Me 163B, Erprobungskommando 16, stationed at Peenemunde-West, part of the rocket

The DFS 39 was designed as a tailless research aircraft which would lead indirectly to the rocket-powered Me 163... an initial version of which is seen here. Robert Forsyth

development facility operated by the air force, including the Fi-103 flying bomb, the V-1. The parallel work on the V-2 and other land-based missiles was under the auspices of the Army. The function of the unit was to train pilots for operational service on the rocket interceptor and to work with the Messerschmitt company at Augsberg in working out, with the cooperation of the Air Ministry and the Luftwaffe, a string of bases across Germany. Located at intervals of 93 miles so that their operational radii would overlap, they were positioned along Allied flight paths into and out of Germany for bombing raids. By the middle of 1943, EK 16 was moved to Bad Zwischenahn to escape the attention of the RAF after the bombing raid aimed at destroying the rocket research facilities at Peenemunde. Within a few months of the move around 30 pilots had been selected for operational duty, their training begun on the Habicht gliders ➤

DFS flying-wing design variants featuring tailless configurations from which useful aerodynamic performance was applied to the Me 163. RLM

and progressively transferring to unpowered and then powered flights in the Me 163A with the less powerful engine and finally the B-series type with the definitive powerplant. Only later would a two-seat version of the Komet become available but training was protracted because every flight had to be solo and cautiously planned – if only to reduce the probability of losing an expensive and valuable aircraft. Towards the end of 1943 the first operational unit – Jagdgeschwader 400 (JG 400) – was set up at Wittmundhafen under the command of Oberleutnant Olejnik. Three staffeln made up one gruppe (I/JG 400) which in June 1944 was moved to Brandis near Leipzig where it cooccupied facilities with EK 16. Inexplicably, Späte had been moved to the Russian front in early 1944 and deployment of the Me 163 to this location was made so as to protect the Leuna oil refineries. But this was counter to the methodical plan laid down for the defence of the Reich. The aircraft too was encountering administrative reversals as well as the plan for its use. In what seems to have been a counterproductive move, and one certainly not discouraged by the company’s owner, Messerschmitt relinquished manufacture of his unwanted Me 163 at Regensburg to the Klemm Technik GmbH facilities. But only manufacture and production was moved; the Air Ministry still wanted Messerschmitt to look after progressive improvements to the design and to modifications that the Klemm works would implement on the production line. Logical in theory, in practice it resulted in sub-contracting out to companies inexperienced in high-quality manufacturing of finely engineered components. 34 ROCKETPLANES

The definitive production model was designated Me 163B-1a, preceded by a batch of precursors designated Ba-1, and when they began to arrive at Lechfeld for flight testing they were found to be in dire need of attention. The B-1a was a refined aircraft and incorporated many modifications and changes to the basic design through data gleaned over the preceding two years. With the change to the hot engine the arrangement of tanks had been reconfigured. The highly toxic T-Stoff propellant was stored in a single, unprotected, tank behind the pilot with a capacity of 229 gallons, plus one 13gallon tank each side of the pilot’s position in the cramped forward section of the bulletshaped nose. The C-Stoff was housed in unprotected wing tanks, a single 38-gallon tank aft of each main spar and a single 16-gallon tank in the leading edge of each wing. The fuselage was of an oval cross-section in light alloy with wings made of wood and covered with plywood. A single main spar was carried at quarterchord and an auxiliary rear spar served to support the elevons and large trimming surfaces inboard. Two split flaps forward were balanced by these trim surfaces for pitch deflection when landing. The fuselage was split in two sections just aft of the wing, which allowed access to the Walter rocket motor after removal of the tail section. The motor was relatively small and weighed only 220lb. The T-Stoff tanks were interconnected and accessed via a single filler on the top of the fuselage just aft of the cockpit. The forward section of the rocket motor consisted of the turbine housing; the fuel pumps geared to the turbine shaft, pressurereducing valve and electric starter. Connected to the forward section by a configuration of

propellant feed lines to the appropriate nozzles, the aft section comprised the combustion chamber and exhaust orifice. Removal of the aft section allowed quick access to what was a highly lethal and extraordinarily volatile cocktail of highly poisonous chemicals.

Rocket men

Protection for the pilot, seated on what was a basic and standard seat with only adjustment for height, consisted of an asbestos suit which was designed to be acid proof, although this was not always effective. Although infrequent, when T-Stoff found its way into the cockpit there was little means of avoiding toxic fumes and on a few occasions the pilot suffered badly from the ensuing burns. Ground crew too had to wear these Asbestos-Mipolamfibre suits to protect them against spillage; the consequences of which can only be imagined as these hypergolic chemicals would ignite on contact. But these were not the only physical discomforts, as the unpressurised cockpit provided little relief from the extreme cold of high altitude. With only an oxygen mask for breathing, the human body can experience extreme pain as the pressure drops and the blood begins to react. If pressure drops too low the blood will boil and the body will be unable to sustain life. Biomedical research was a major science in the wartime Luftwaffe and many medical experiments had been conducted on concentration camp victims, many of whom lost their lives in de-pressurisation experiments. This information was used to balance performance against physiological need in fast, high-flying piston-engine aircraft, some of

which were designed for long periods on highaltitude reconnaissance missions. The mission of the Me 163 was brief and extremely violent for the pilot, who had to endure high G-levels during acceleration and high-speed manoeuvring and physical shocks to the body when landing on the unforgiving skid at the end of the short flight. It was widely accepted that if the landing skid could not be extended, the pilot would suffer a fractured spine on impact with the rough ground. The Americans got their first impression of a Komet in flight on July 28, 1944, when eight P-51D Mustang fighters of the 359th Fighter Group encountered two groups, of two and three rocket fighters each, attacking B-17 bombers near Merseburg. In the report submitted by Major General William Kepner the Komets were said to be in a highly organised formation with dense, white contrails allowing the Mustang pilots to track them visually. The Americans warned that future escort fighters were likely to encounter large numbers of these rocket interceptors and that the best defence for the bombers was for the escorting fighters to stay relatively close to their charges. But there would never be mass attacks by rocket fighters, as only 16 of the Me 163B-1a had been delivered to the Luftwaffe and 1./JG 400 had only the five at the time. Even if had there been a larger number of rocket interceptors available, their usefulness at the front was problematical. For the first time it was becoming apparent that too much speed and acceleration could be worse than not enough – the target was in sight for too brief a period to press home a meaningful attack. Diving into the bomber formations at 550-590mph, the attacking interceptors could be closing with an excess speed of more than 250mph with a closing speed of up to 500ft/sec under ideal conditions from the rear. With the 30mm MK 108 cannon and a Revi 16B gun sight, the pilot had a distance zone of 2000ft to 700ft from the target in which he could fire before he would have to break off – farther out and the cannon would not be effective, closer in and there was a real risk of ramming the bomber. The pilot would have less than three seconds to align the aircraft, secure the target with his gun sight and fire, what was in reality a gun with a notoriously slow response time. The combination of lightning reaction and extraordinary marksmanship afforded only a low percentage of probable success. By the end of July, 2./JG 400 had formed at Venlo close to the Dutch border, a part of the ‘defence of the Reich’ plan promulgated by General der Jagdflieger Adolf Galland. In this, a single Staffel of Komets would be deployed at every fighter station laid out across the incoming flight path of Allied bombers but Galland was replaced by the pro-Nazi Oberst Gordon Gollob, who favoured a concentration of Komets at a single location. This turned out to be Brandis where 2./JG 400 joined 1./JG 400 each equipped with 15 rocket interceptors. In September EK 16 was also moved to Brandis with a splinter group siphoned off to Udetfeld to form

The Me 163 under power immediately before dropping the two-wheel dolly, which supported it during the takeoff run. RLM

Ergänzungsstaffel/JG 400, a training unit. By the end of the year this was converted into two operational Staffeln of III/JG 400, which itself produced two Staffeln for II/JG 400. The first contact with the enemy took place during August 1944 but there was a very low level of success and the infrastructure and the special resources required to operate the aircraft was proving difficult to maintain. The MK 108 cannon was prone to jamming and pilots were tending to slow right down to increase their chance of hitting a bomber, rendering them highly vulnerable to attack and to being shot down. Some attempt was made to use the R4M rocket, which was fitted to the Me 262 jet fighter but a different solution was devised by Dr Langweiler, the inventor of the Panzerfaust, a highly effective, shouldermounted, anti-tank rocket. His idea was to mount a photo-sensitive cell to the upper surface of the aircraft which, on passing under the shadow of the target bomber, would trigger 50mm mortar shells, one to each of five vertical tubes in the upper part of each wing. With the mortars fired in salvo the Me 163 would rapidly escape while the bomber was struck underneath by the shells. The system was tested by Lt Hachtel of EK 16 on a Focke-Wulf Fw 190 and demonstrated that such a method would work. Only 12 aircraft were fitted with the SG 500 and it was never officially declared operational. However, Lt Fritz Kelb managed to shoot down a B-17G Fortress with this armament.

In its original calculations, the Walter works had estimated that the R II-201 rocket motor would have a thrust of 3750lb and that the T-Stoff consumption would be about 6lb/sec for which Lippisch had been asked to provide sufficient tankage in the operational version of the Komet for 12 minutes of powered flight. This was to include a 100% thrust for three minutes to reach 39,370ft, with 30 minutes of throttled power for a 150-mile combat range. As tests got under way this proved to be far too conservative and a consumption rate of 11lb/sec was the most which could be achieved. This meant that the tanks built in to the B-1a provided sufficient propellant for six minutes at full bore. Almost immediately, the company began further redesign of the engine to develop an auxiliary combustion chamber sufficient for a further 660lb of thrust in addition to the main chamber. With both chambers operating at maximum for takeoff and climb to altitude, the main chamber could be cut off with the aircraft flying on the thrust of the small chamber alone. Two aircraft were so modified and the first flight, in V18, took place on July 6 when Rudolf Opitz took off from Peenemunde for climb calibration trials. ➤

Below: The Me 163 V8 (Stammkennzeichen VD+ER) displaying the refined lines of the B model selected for production. RLM

ROCKETPLANES 35

Positioned beneath the wing of an Me 262, a Walter HWK-509 rocket motor for the Me 163 without its casing. David Baker

➤ Within seconds the aircraft was passing through 16,000ft and accelerating when Opitz shut down both motors and the aircraft went into an immediate dive, the pilot regaining control only just in time to prevent it slamming into the Baltic. The rudder had been almost completely shredded and careful analysis of the recorded data showed that this aircraft had reached a speed of 702mph. While the performance of the rocket motor had been outstanding, the airframe was revealing its own limitations. Nevertheless, development of the Me 163C began specifically to carry this motor, officially designated HWK 509C-1. Production of the Komet accelerated during the final two months of 1944, a total of 237 having been delivered by the end of the year. As the Allied armies pressed ever closer to the German heartland, resources, materiel and men began to run out and it became impossible to maintain planned delivery schedules. The Luftwaffe had been driven from the skies, and aircraft such as the Me 163 were available in insufficient numbers to make a difference. Even the jet fighters, epitomised by the Me 262, were unable to stem the tide of Allied superiority in sheer numbers. It is hard to see how the Komet could have been a truly effective fighter, it never was designed as such, and as a point interceptor it needed something which was not available to pilots of the Luftwaffe – an effective heatseeking guided missile or, better still, a radar guided anti-aircraft missile, because the cannon with which it was armed was unable to do the job. The Me 163 fell into the trap of providing a superior performance without the weaponry to 36 ROCKETPLANES

make it an effective war-fighter. Even aircraft designers are apt to overlook the reality that however exciting and attractive brute power and sheer performance can appear, the airframe and its engine are merely the platform for the weapons required to do the job. In all, fewer than 300 Komets flew in the skies over Germany and the official tally, while still contested, is no more than nine kills for the entire period of operational service. More pilots and Komets were lost in accidents than were extracted from the enemy. Like the Me 262, the V-1 and the V-2, it came far too late to make any difference and there was no time for reapplying the technology to a workable weapon of war. But the engineering behind the Me 163 would be captured by the Allies and the concept would be resurrected during the Cold War which was to follow.

The ulTimaTe rockeT

If the HWK 509C-1 came too late for practical application in the Me 163, it was in time to be chosen for what must rank as one of the most bizarre weapons to come out of the Third Reich. Known as the Bachem Ba 349 Natter, it emerged in 1944 as a potential counter to the sustained bomber offensive from Allied air forces now operating throughout the skies over Germany on a 24-hour basis. The destruction to German industry and the decimation of the manufacturing base was seen by many in the Air Ministry as a prime reason for Germany’s apparent inability to halt the tide of Allied advance. Provide a weapon which can act as a shield against this offensive from the

skies, they said, and Germany could yet turn this war around the push its enemies back – beyond the English Channel and back across the Urals. It was a vain hope but was the stimulus for what would become a last-ditch attempt to knock the bombers down. The concept used the Walter HWK 509C-1 and four solid propellant boosters to propel a piloted rocket launched vertically to high altitude. Once there it would discharge a cluster of forward-firing rockets to bring down the bombers, returning the Walter motor and pilot to Earth on separate parachutes while the expendable airframe was destroyed on impact with the ground. The idea of a vertically launched mancarrying rocket was not new. A similar proposal had been made by Wernher von Braun through a memorandum submitted to the technical arm of the German Air Ministry on July 6, 1939. In it, he envisaged an aircraft with a weight of 11,145lb propelled into the air by a 22,050lb thrust bi-propellant rocket motor. Launched up two vertical guide rails it was said to be capable of reaching an altitude of 26,250ft in 53 seconds. The idea was far too radical in 1939 but nearly five years later it was reassessed when extreme threats called for extreme measures. In the spring of 1944 the Air Ministry issued a requirement for a weapon to bring down the bombers using rocket-propelled interceptors. The Me 163 was nearing operational deployment but a simpler and less costly solution to the bomber threat was needed for production of an anti-aircraft system in sufficient numbers to be effective.

Four companies submitted proposals for what was designated the Jägernotprogramm (Fighter Emergency Programme), these being the Heinkel P.1077 Julia, the Junkers EF 127 Walli, the Messerschmitt P.1104 and the Bachem BP-20 Natter. The latter had not been solicited but was submitted uninvited. It grew out of a dialogue von Braun had sustained with engineer Dr Erich Bachem, who had previously been the technical director at Fieseler. When von Braun’s idea was rejected, Bachem maintained contact with von Braun and proposed his concept again but it too was rejected and Heinkel’s design was given authority to proceed. Not to be outdone, in August Bachem appealed directly to Heinrich Himmler, Reichsfuhrer SS, and received an enthusiastic response. Given immediate approval to proceed, the Bachem concept went into rapid development and was given the official designation Ba 349. To build the Natter, Bachem acquired a small factory at Waldsee in the Black Forest where he was joined by fellow engineer H Bethbeder, late of the Junkers works. Joining them was engineer Grassow from the Walter factory. Bachem’s original concept had been for the pilot to release all his nose-mounted rockets at one target and direct the aircraft to a collision course with another, ejecting shortly before impact, an event which would trigger release of the rocket motor, which would also return to the ground by parachute for reuse. Bethbeder worked the numbers and quickly came to the opinion that the ejection seat would be far too heavy to incorporate. Instead, the pilot would separate the forward fuselage after firing the missiles and this would automatically deploy the parachute. As the Natter would approach the speed of sound, wind tunnel tests were conducted at Braunschweig where speeds in excess of Mach

0.95 demonstrated stable aerodynamic properties. This was to be a very small aircraft, barely 20ft long and with a wing span of just under 12ft. It was the simplest aerodynamic form possible and was to be made of wood. The entire project was driven by a need for simplicity (each one had to be produced in less than 1000 man hours), reliability and cheapness. The stubby, rectangular wings had no dihedral or sweepback and the vertical tail extended in equal area above and below the fuselage. The elevators were set low on the upper fin and carried elevators, which was the only means of pitch control. The fuselage itself was of semimonocoque construction with formers and stringers supporting a laminated skin. The wing itself had a single laminated wooden spar which went through the fuselage but with no control surfaces, roll control being achieved through differential positioning of the elevators as elevons. The wing had a thickness/chord ratio of 12% with maximum thickness at 50% chord. The cockpit was simple but with substantial armour plating to protect the pilot. It had a single hinged hood which was attached to the

rear bulkhead. The T-Stoff propellant was contained in a 96-gallon tank above the wing spar where it passed through the fuselage, the 42 gallons of C-Stoff being in a similar tank below the spar. As the thrust of the Walter motor was slightly less than the weight of the Natter, Bachem adopted four Schmidding 109-533 solid propellant rockets each delivering a thrust of 1102lb for 10 seconds after which they were to be jettisoned. Combined, the two chambers of the HWK 509C-1 delivered a total thrust of 4410lb. With the four solids ignited for launch, thus equipped the 4920lb Natter would have a launch thrust of 8818lb generating a maximum 2.2G on the pilot. Control would be maintained for initial ascent via a 80ft vertical ramp with the upper rudder and outer wing tips running along three guide rails. ➤

The Me 163B ... including removable tail section and access panels. Refuelling ports were at the top of the fuselage immediately behind the cockpit. David Baker

➤The Natter had a calculated climb rate of 37,400ft/min, maximum speed of 620mph at 16,400ft and a range after climb of 36 miles. Homing in visually on the bomber formation, at a range of 1-2 miles the pilot would take over from an autopilot which would have been radiocontrolled from the ground at a height of 600ft. Until this point he was merely along for the ride until directing the Natter at the bomber formation, which was his sole function. The pilot would jettison the aerodynamic nose cone to expose the armament. Despite some initial reservations, the nose section had a hexagonal arrangement of firing tubes, all rockets to be released simultaneously in a salvo. It could house either 24 73-mm rockets or 33 55-mm projectiles. After firing all rockets, the pilot would release his harness, remove the control stick and release the latches that held the nose section. This would fall away, taking with it the windscreen, the forward section of the cockpit, the instrument panel and the rudder pedals. At the same time a parachute would be released from the rear fuselage, the sudden deceleration throwing the pilot forward and out of his seat whereupon his personal parachute would open. He would then return to the ground ready for another flight; this was one of the efficiencies of the programme. He need not be a qualified pilot at all. All he needed to do was point the Natter

at the bombers and fire the rockets, and that he could learn how to do in a rudimentary simulator on the ground. The pace of development was such that by the end of October, just 12 weeks after the goahead, the first 15 of 50 Versuch test airframes were being delivered. First, test flights towed behind a Heinkel He 111 took place, the first with Zubert, a test pilot, at the controls. The Natter was ballasted as though making a fuelled launch but the airframe demonstrated excellent stability at descent speeds of up to 435mph from an altitude of 18,000ft. The roll rate was 360º/min and at 250mph the pilot could make a complete 360º turn in 20 seconds. In fact, Zubert was so delighted with it that he judged it to have superior flying qualities to any other fighter in service. On December 22, 1944, the first of 11 unmanned vertical flights took place using the booster rockets alone and without the Walter motor. Because of the thrust decrement resulting from the absence of the 109C-1, the speed exiting the guide rails was a mere 37mph and far too low for aerodynamic stability. At times the solid rockets exploded without warning and at others one of the four suddenly fizzled out leaving the test model to cartwheel out of control. The first flight with the Walter motor attached got off the ground on February 23,

1945, but problems with control stability resulted in a decision to add small control vanes in the exhaust of the Walter motor, acting like rudders as did similar vanes attached to the motor on the V-2 ballistic missile. It is ironic that on the very day that the Natter demonstrated its first, successful, unmanned vertical flight the technical arm of the Air Ministry determined that neither this nor the P.1077 Julia programme, which had also been passed for development, held sufficient promise and that all plans for production and operational deployment should be dropped. Instead, the advice was to put all remaining resources into the Me 263, a developed version of the Me 163, and a version of the Me 262 with supplementary rocket motors to augment thrust. However, because the development of the Natter had progressed so well, the flight trials were to be completed after which the project was to be closed. The first manned flight took place on March 1, 1945, with Lothar Siebert at the controls. At a height of less than 500ft the cockpit cover and headrest became detached, the Natter arched up and over, turned over its back and dived into the ground from a height of 4920ft, killing Siebert instantly. Some 50 had been on order for the Luftwaffe and 150 for the SS, which by this time had taken over virtually all rocket research. As with all technical developments of the period, plans were being drawn up by Bachem for more developed versions of the Natter offering greater endurance, longer firing times and optional solid propellant rockets. With the end of the war only weeks away the Bachem Ba 349 Natter was doomed anyway but it was not the end of the story. As the Allies

Left: The Bachem Ba 349 Natter was designed to fly vertically, carrying its pilot on an intercept mission. Robert Forsyth Above: Interceptors showed performance capabilities which pushed research into high altitude pressure suits, as with this one designed for the Bachem Natter. US Air Force 38 ROCKETPLANES

rolled back the German army into the Fatherland and overran increasing numbers of factories and research facilities, the sheer magnitude of the technical developments funded by the Nazis became all too apparent. With rockets and flying bombs raining down on London and Antwerp for several months, there was little doubt that rich prizes awaited the victorious powers, weapons which could be of use in later wars. Teams equipped with specialists trained to tour important scientific and engineering facilities were crawling all over defeated Germany. On May 17, 1945, a special intelligence unit led by Theodor von Karman, a highly respected engineer and physicist, was sent to interview Willy Fiedler at the Bachem works. Fiedler had replaced Bethbeder at the end of February as the chief engineer on the Natter and he was at first thought to have been the designer of the manned rocketplane. He was a key target and within a few days he had been added to a list of highly valuable German scientists and engineers gathered up and taken to the United States under the Operation Paperclip programme, a group which included Wernher von Braun. Already, on May 7, a special report on the Natter was sent to the US Army aviation research centre at Wright Field, Dayton, Ohio, and by May 27 two complete Bachem Natters had been ‘liberated’ from Germany. This bizarre project was no footnote in the annals of military technology and it had already achieved one notable entry in the history books – it was the first time a man had been launched vertically on a rocket. The next time such an event took place an adapted Russian ballistic missile would launch a cosmonaut into orbit, the first man in space, on April 12, 1961. ■

Even as late as July 1944 German engineers were designing radical new ways of knocking down Allied bombers, as this sketch of a Natter concept displays. RLM

Displayed in Munich’s Deutsche Museum, the Bachem Natter had straight wings and four solid propellant boosters (red) attached to the rear fuselage. David Baker

ROCKETPLANES 39

The

search for

speed

With six rockets attached to the wing, in August 1941 an ERCO Ercoupe made the first jet-assisted takeoff in the United States. (NASA). US Army

By the end of the Second World War in 1945 the Americans had made up for a late start on jet aircraft, missiles and rocketplanes, but with the Cold War dawning and technical challenges from abroad, it picked up the pace toward penetrating the sound barrier.

T

he war years saw a rapid growth in the development of high performance aircraft, particularly in speed and altitude. When the war began in 1939, top speeds of 350mph were being achieved by the most advanced monoplane fighters such as the Spitfire, the Hurricane and the Bf 109. Within five years, as we have seen, jet and rocket fighters were capable of speeds in excess of 600mph. The Germans had made great progress in research and development of all manner of different highperformance aircraft and were far in advance of Allied countries in bringing these weapons into production. When the Americans carried back to the United States the fruits of their victory in 1945, the race was on to extract as much information as possible from captured scientists and engineers who had worked on these programmes and to translate all the documents and research results liberated from Germany by the truckload. 40 ROCKETPLANES

Tested in an NACA wind tunnel, the Bell P-59 Airacomet was an early entrant in the race for a high-speed jet fighter. Bell

Above left: Bell facilities in Buffalo, where the P-39 Airacobra was built, provided experience in building revolutionary aircraft. Bell Left: With an innovative layout placing the pilot between the engine and the propeller, the P-39 Airacobra brought in dollars to fund company expansion. Bell Above: Head of the US Army Air Corps in 1938, General ‘Hap’ Arnold was key to getting the funds to push American air power into the jet age. USAF

One area of great interest was the sound barrier, a seemingly impenetrable wall beyond which the normal laws of physics appeared to change, where all control would be lost and the aircraft destroyed. In reality, it was through studying the laws of physics that engineers gradually began to unravel the mysterious ‘wall’ and to find a way through.

A little help from friends

Paradoxically, the United States was far behind Britain and continental European countries in the development of atomic weapons, jet aircraft and rocket propelled fighters. British brains had unravelled the possibilities inherent in the nucleus of an atom and for several years had tried to interest the Americans. Only when they came into the war at the end of 1941 was progress made toward building a bomb. The British contribution was enormous. Work had been carried out at the Clarendon and Cavendish Laboratories at Oxford and Cambridge, and the United States was given access to this activity. It therefore got a major start on what would turn out to be one of the largest wartime endeavours of all time. But it was not just in the development of atomic weapons that the Americans lagged behind.

Before the war, an isolationist mood had set in across America in which politicians were loath to talk of getting involved again in a European conflict. They had joined the First World War in April 1917, 33 months after it began, and had returned US troops to America 19 months later, determined never again to get involved in such a conflict. This produced an apathy and a pacifism which left the American Army and Navy ill prepared to fight another foreign war. Consequently, while Germany had been pouring vast amounts of money into a militarised state since 1933, and Britain since 1935 had been engaged in the biggest escalation of arms spending in peacetime in a desperate attempt to catch up, the American armed forces were under-funded and under-equipped. So it was that when word leaked to the US that great technical developments were already producing results in Britain, there was a scramble to get their hands on the British inventions. Not that the American engineers and scientists had been idle, just that the will and the push to transform ideas and discoveries into useful applications for aviation had been lacking. A major factor in giving American aviation that ‘push’ was the appointment of Brigadier General Henry H ‘Hap’ Arnold to head the US

Army Air Corps in September 1938. There was no air force then, all military flying being under the USAAC until it became the US Amy Air Force in June 1941. Arnold knew there were three primar y organisations in America which could advance the state of the art in aeronautical science: the National Advisor y Committee for Aeronautics (NACA), which had been formed in March 1915; the Guggenheim Aeronautical Laborator y at the California Institute of Technology (GALCIT), set up in June 1926; and the Massachusetts Institute of Technology (MIT), a private research institute established in 1861 to accelerate US industrial growth. Of these organs, the NACA had laid down the foundations for aeronautical engineering design in the United States, providing design teams with a portfolio of aerofoil shapes tried and tested in wind tunnels, GALCIT was the keenest to develop rockets for a wide range of purposes (including jet-assisted take-off boosters), and MIT provided research into associated scientific inventions, particularly navigation and guidance equipment, for aircraft. Behind these were teams of industrial giants and lesser lights forging new highways to the skies. Commercial aviation had leapt ahead of military developments, airliners ➤ ROCKETPLANES 41

Unsuccessful as a fighter but valuable in giving Bell experience with building a jet aircraft, the Airacomet was eclipsed by more advanced designs. Bell

being faster than bombers and even some fighters by the end of the 1930s. Companies such as Lockheed and Douglas, with their transports and airliners, and Curtiss and Grumman with land-based and naval fighters, specialised in particular types of aircraft. Others such as Boeing had a more diverse product range while new companies such as Bell Aircraft were looking at high performance and could afford to concentrate on speculative concepts which did not suit the larger companies seeking big production contracts. Bell would figure largely in the story of rocket planes but prior to the Second World War this new company was short on orders and long on debt – until President Roosevelt asked the well-connected Larry D Bell to report on the state of the aviation industry in Germany, France and Britain. Reports reaching America of great strides in aeronautical science were of concern to this country in a hurry and Roosevelt was keen to tap in to new developments which could bolster US opportunities. Bell reported back that Germany was a hive of activity, forwardthinking engineers and a mighty surge in war productivity and weapons. France and Britain, he said, were floundering and falling behind. Bell had been established in 1935 to build wing panels and parts for mainstream manufacturers followed by a decidedly unpromising long range escort fighter known as the Airacuda. But in 1936 Bell responded to 42 ROCKETPLANES

a call from the Air Corps for a new generation of combat aircraft with the P-39 Airacobra, a highly unusual design in which the engine was placed at the centre of the fuselage with the cockpit between it and the propeller. With the pilot seated high above the fuselage visibility was outstanding and with a

“Lindbergh returned from a trip of europe awash with ideas and concern at the sLuggish performance of american aviation.” 37mm cannon firing through the propeller hub and two machine guns it had powerful armament. Being such a novel design the development investment was great and too few orders were coming through to sustain the company’s liabilities. It looked as though Bell, and its P-39, would go the way of many bright ideas. Then in September 1939 war broke out in Europe and things changed rapidly. The Anglo-French Purchasing Commission made a shopping trip to America and ordered 200 export versions of the P-39 with a down payment of $2 million; both countries needed large numbers of defensive fighters and the Bell Airacobra was one of those chosen for rapid delivery. Then in June 1940 the

High-speed photos of shock waves off a bullet (upper) and an aircraft at transonic speed.

Germans overran France and the order collapsed, only to be taken over by the British and added to the 675 P-39s they had ordered two months earlier. The P-39 entered service with the RAF in 1941 but it was never a success and only 80 were ever deployed, the rest were absorbed into orders for the USAAC with whom it did achieve some success and was widely produced for service in many parts of the world, with some sent to Russia to support the war effort. It had given Bell the boost it needed. With a massive injection of cash, expansion was essential to fulfilling the orders and new factories were opened, providing Bell with the resources to take on additional work when it came. And that was not long in arriving, largely due, again, to events on the other side of the Atlantic Ocean. When Hap Arnold became head of the Army Air Corps in 1938 he had a barrel-load of projects, proposals, technologies and devices which were proudly paraded by companies, inventors, engineers and scientists lacking a proper military market for their wares. Everything from rocket packs to help heavy aircraft get off the ground to radar and from windscreen de-icing sets to new remotely controlled guns. Arnold formed opinions quickly, made friends, rejected others and set about deciding

what the Corps needed to catch up with progressive developments in Britain and Europe. One friend in particular helped frame Arnold’s thinking: Charles Lindbergh, the first man to fly solo across the Atlantic. Lindbergh returned from a touring trip of Europe awash with fresh ideas and concern at the sluggish performance of American aviation. But the Americans missed the real developments and focused instead on the mundane, incremental developments being applied to conventional aircraft. No talk here of jet engines or rocket motors – felt by Lindbergh to be too speculative, unproven and risky. But Lindbergh did lend his very popular profile to a new research facility for the NACA at Moffett Field, California, and campaigned to keep America out of the European war when it started not long after his return. But it was Arnold’s firm conviction that America would have to get involved at some point but not, he thought, by using speculative, highly controversial and untried weapons. “For us to have expended our effort on future weapons to win a war at hand,” he said, “would be as stupid as trying to win the next war with outmoded weapons and doctrine.” What Arnold wanted was large-scale volume production of aeroplanes and for the

next five years the army focused its air arm on progressive and incremental steps. But developments abroad did concern him. In April 1941, with the United States still not in the war and with the combined approval of Lord Beaverbrook in charge of aircraft production, Sir Henry Tizard who had masterminded the radar programme, MooreBrabazon from the transport ministry and Air Chief Marshal Sir Charles Portal, American Air Force General Hap Arnold was given the secrets of Britain’s jet engine. With the Whittle W.1 engine and the E.28/39 experimental jet aircraft already at an advanced stage, the American delegation in Britain was witness to one of the most important developments of the war as they saw first-hand what the British had been developing. In September, with the approval of Winston Churchill as part of a broader ‘softening up’ of the isolationist Americans, Arnold negotiated a deal allowing them to take a Whittle engine back home and use it for trials in an aircraft of their own making before manufacturing it under licence. ➤ Below: Incorporating a low thickness ratio, swept-back wing and with a new generation of J-47 jet engines, the Boeing B-47 introduced the age of the mass-produced all-jet bomber. Boeing

ROCKETPLANES 43

Douglas’ D-588-1 Skystreak was built to research high speed flight close to the transonic regime powered initially by a GE TG-180 turbojet engine.

Meteors and shooting stars

By the middle of 1941 the NACA had begun work on research into jet engines but the availability of the Whittle engine dramatically cut the time required to develop a domestic jet engine industry. Arnold had lost faith in the NACA, thought by him to be ponderous, slow and too conservative in grasping new opportunities. He wanted action and found it through industry, with a top secret plan set in motion on September 4 which included Larry Bell, Donald ‘Truly’ Earner of General Electric (GE) and only 15 additional employees. GE was noted for radical and pioneering engine design and had been working on a supercharger. The company was perfect for reverse-engineering of the Whittle engine and coming up with a version of its own – to save paying the British a licence fee. The engines was to be put together at Lynn, Massachusetts, under the title Super-charger Type 1. Larry Bell’s connections got his company the job of designing an aeroplane for this new engine, although the company was perfectly sized for such work; never capable of large mass-volume production, it was skilled at using small and complex new technologies, of which the Airacobra was an example. And it was located near engine-maker GE. The work was so secret the tasks were segmented and kept separate so that only a handful knew what it was all for. Internally it was known as Bell Model 27 and officially it was given a designation which appeared to relate the work to a single-seat pusher-engine design known as the XP-52 (Bell Model 16). 44 ROCKETPLANES

The D-558-1 was a product of government-industry cooperation with the NACA providing valuable information on thin-wing design.

Because of difficulties with the availability of the Continental XIV-1430 engine originally intended for the XP-52, it was redesigned for a Pratt & Whitney R-2800-23 engine as the XP-59. But this was never built and so the new jet aircraft adopted this designation – XP59A – supposedly relating the work to that small-scale effort. It did not even have an allocated serial number. It would be disingenuous to say that Arnold rejected advanced and futuristic ideas, rather to explain that he wanted to win the

present war and not the next, on which basis he rejected anything which could not deliver within two years. Early, steady, work at the NACA coupled to preliminary work at GALCIT, linked to what he returned with from Britain convinced him that the jet qualified under that time bar. But not everyone was persuaded and Arnold went out on a limb to fight for the new technology. Eager to obtain all the secrets of the Whittle’s engineering work, Arnold traded NACA work on high-temperature turbine

blades for every piece of research and test data, including design drawings the British held. Thus the Americans got a head start on their own reaction engine technology. The Bell XP-59A was a conservative design, with a straight mid-wing configuration set on a slender, tapered fuselage carrying two GE I-A engines of 1300lb thrust each, buried in nacelles below the wing roots. Of allmonocoque design, the all-metal airframe had a flush-riveted light alloy skin, a wide-track main landing gear and nose wheel. The fabric covered control surfaces were manually operated, but the flaps and the landing gear were electrically operated and the cockpit was pressurised with ducted air from the engines. Although a concept design, the Air Corps wanted it to be configured as a fighter, so the XP-59A was equipped with two 37mm nose cannon. The aircraft was ready long before the engine and it did not make its first flight before October 1, 1942, with Robert Stanley at the controls, four flights being made that day from Muroc on the edge of Rogers Dry Lake, three miles from Edwards, California. Remote, far from prying eyes and with almost limitless takeoff and landing space, it was an ideal location from which to flight test new and revolutionary types, the future site of Edwards Air Force Base from where many rocketplanes would be flown. Only after flight tests began did the type receive a serial (42108784) and it was two years before Stanley’s wife learned that he had made the historic first flight of an American jet aircraft that day. As flight tests progressed, the engine posed problems from failed turbine blades and overheating with fuel pump failure not

uncommon. Progress was slow even after a second prototype joined the first in and by the end of April 1943 the third aircraft had begun flight tests. Only a month earlier the Air Corps had placed an order for 13 preservice trials aircraft and the first two YP-59As were delivered to Muroc in June. With slightly improved I-16 engines installed the aircraft could reach a speed of 409mph at 35,000ft. The third YP-59A was sent to Moreton Valence in Britain for trials alongside the Gloster Meteor. Suitably painted in grey-green RAF camouflage and with a bright yellow underside befitting all experimental test ➤

Above: Conceived specifically to carry out research at and around the speed of sound, Bell’s X-1 was shaped like a bullet with a conformal glazed canopy and an instrumentation spine running along the top of the fuselage. Bell Below: The X-1’s wing carry-through structure provided a structural mount for the circular cross-section fuselage and associated systems. Bell

ROCKETPLANES 45

aircraft in British skies, it made its first flight on September 28, 1943, piloted by Frank H Kelley Jr. The Gloster F.9/40, precursor to the Meteor and almost identical, had made its first flight from RAF Cranwell on March 5 that year but the YP-59A was flown only nine times between November 5, 1943, and April 1944. It was returned to the US in early 1945. As part of a reciprocal exchange, the first Meteor F.1 (EE210/G), which made its first flight on January 12, 1944, was crated and sent to Muroc in February 1944. With a top speed of 415mph at 10,000ft, the Meteor F.1 was slightly faster than the YP-59A. While all this was going on, other jet fighters were in the development stage. After initial trials with the XP-59A, on May 17, 1943, the US Army had invited Lockheed’s Clarence ‘Kelly’ Johnson to submit a design for a jet fighter. Exactly one month later the invitation was turned into a formal requirement and a contract for the XP-80 was signed on October 16, by which date the aircraft had been delivered. Powered by a British Halford H.1B engine the XP-80 took to the air for the first time on January 8, 1944. It would go on to become the famous F80 Shooting Star from which a range of derivatives would emerge. The navy, despite being almost totally obsessed with conventional carrier-based fighters in the Pacific War, began to get in on the act and between January 1943 and January 1945 awarded development 46 ROCKETPLANES

contracts to McDonnell, Vought and North American for different types of jet fighter. In Britain, as early as late 1941 the de Havilland Aircraft Co was putting together the design of a single-seat fighter which would emerge as the DH.100 Vampire, making its first flight on September 20, 1943. The pace of development was staggering, exemplified by the government decision made in June 1943 to proceed with development of the world’s first four-jet airliner, the de Havilland Comet.

War work prioritised military production and the first flight of the Comet would not be made before July 27, 1949, but long before the war ended the performance of military, and potentially civilian, aircraft was approaching the limits of theoretical knowledge about high-speed and high-altitude flight. Nowhere was this more evident than in the United States, where development of conventional piston-engine aircraft was outpacing the theoretical calculations by aerodynamicists on conditions closer to the speed of sound.

The Airacomet was instrumental in providing the manufacturing examples from which Bell matured the design for the transonic research project. Bell

Opposite, top: The heritage of Bell’s work on the Airacobra would endure into the jet and rocket era, a sequential evolution achieved by no other manufacturer. Bell Right: The Reaction Motors XLR-11 was the first rocket engine developed in the United States for use in an aircraft and it benefited from the clustering concept of four separate chambers. David Baker Below right: As installed in the Bell X-1, the individual rocket chambers could be fired separately, progressively increasing thrust from 1500lb to 6000lb. NASA

KnocKing on ‘the wall’

By the end of the war aeronautical development was beginning to catch up with the known laws of physics. The pistonengined Republic P-47M Thunderbolt was capable of speeds in excess of 470mph while the nimble little North American P-51H Mustang could fly at more than 480mph in level flight. Frequently, these and other types were reporting conditions where they were suspected of encountering compressibility. Clearly, much more information was needed about the effects on an airframe of encountering the speed of sound, even passing through it if possible. The ‘wall’ though, was looking decidedly daunting so in great secrecy a completely separate effort was under way to challenge that wall in a very direct way – simply by shaping an aeroplane like a bullet – and flying straight at it! Jet engine development, largely sparked off by the efforts of the Frank Whittle against an entrenched and stagnant bureaucracy, was directly responsible for the resurgence in rocket planes which was about to open unprecedented opportunities for aviation and aeronautical engineering. Had it not been for the jet, the push to learn more about the effects of transonic speed on an aircraft in flight might have been delayed for many years. The urgency now was driven by projections from engineers and scientists that the development of jet and rocket motors was moving so fast that very soon the wall would be encountered as a very real threat to the safety of pilots. The basic physics of compressibility state that as an object moves through the air the temperature and pressure changes which it encounters are propagated by a pressure wave which moves ahead of the object. This effect begins to change with speed until, at the speed of sound, the air ahead of the object, an aircraft, is unable to move away and cannot be influenced by a pressure field in advance of that object. This forms a compression wave at the front of the aircraft and at the leading edge of the wings with sudden changes in pressure and temperature. These effects vary with altitude in a standard atmosphere unaffected by significant meteorological phenomena. ➤ ROCKETPLANES 47

The turbopump assembly for the X-1 located in the aft fuselage. NASA

The relationship between the speed of an object and the speed of sound was defined by the 19th century Austrian physicist Ernst Mach, who expressed the speed of sound as unity and all measurement relating to this speed as a ‘Mach’ number. The man is less remembered for having developed the Mach Principle, something altogether different and to do with the relationship of matter in the large scale universe and that here on Earth and which inspired Albert Einstein to develop his Theory of Relativity. Accordingly, speeds approaching that of unity are expressed as fractions and speeds above unity as multiples. Hence, an object moving at half the speed of sound is said to be moving at 0.5 Mach and one

With the end fuselage enclosure the four XLR-11 barrels reveal the injector plates with ‘shower-head’ orifices for spraying propellant into the combustion chamber. Bell 48 ROCKETPLANES

at twice the speed of sound as moving at Mach 2, and so on. Actually, by popular vote the commonest way to express this is as Mach 0.85 and Mach 2, even though it is wrong, but we will use that here. It is said, therefore, that an aircraft below the speed of sound is ‘subsonic’, an aircraft between Mach 0.75-1.3 is in the ‘transonic’ region and an aircraft in excess of that is ‘supersonic’. With the development of powerful engines during the 1930s and 1940s, engineers were beginning to encounter compressibility when they studied the tip speed of spinning propellers. The length of the propeller is determined by the amount of air it is required to move and by the surface area of the blade. The longer the blade the higher the tip speed, which can cause an increase in drag and reduce the effectiveness of the propeller. The rotational speed of the propeller is also linked to the amount of thrust it produces. Moreover, as the tip approaches the speed of sound the drag increases and the thrust imparted by the propeller reduces. The ideal tip speed for peak efficiency is Mach 0.88-0.92. It was this encounter with the speed of sound which first drew attention to the theoretical limits aerodynamicists believed they were confronted with when jet and rocket power appeared to promise unlimited speed. And as new and faster piston-engine aircraft entered service, pilots were encountering compressibility in a dive and paying for it with their lives. In America the first serious student of this had been Theodore von Karman who attended a conference in 1935 on high-speed flight at Campidoglio held in Italy. While there, listening to aerodynamicists theorise about the problem, he became convinced that it was possible to fly through the barrier. Another scientist equally convinced was Ezra Kotcher, at the time an instructor at Wright Field, Dayton, Ohio. Converted while listening to a lecture on supersonics he became convinced aircraft could fly in the transonic region and survive intact and under control. But while von Karman was working on theoretical calculations

and hoped to develop ways of getting through the barrier using wind tunnels, Kotcher recognised building the tunnels needed more information and there was no adequate method for avoiding reflected shock waves from the walls bouncing back on the models under test. The NACA had been used to building wind tunnels but not for supersonic flight. Only the Germans had got to that level and at this early stage the Americans were not even in the war. Kotcher worked hard to convince the Air Corps that it needed to develop a full scale research aircraft to test in flight methods by which an aircraft could safely pass through the sound barrier. That meant building an aircraft suitably shaped to have the best chance of going through the transonic region and getting a pilot to try it out. In 1940, this was a high-risk concept and few were prepared to back it, although

Kotcher did provide Arnold with a copy of his proposal. Kotcher felt it would be necessary to use jet or rocket propulsion for these tests and emphasised the need to do real tests rather than simulated studies using ground equipment, such as wind tunnels, especially since the lack of real understanding about this phenomenon would make it virtually impossible to design and operate a satisfactory wind tunnel. Added support came from Robert Wolff who worked for Bell Aircraft. With experience on the XP-59A there was keen interest among engineers at Bell to keep doing the interesting things and this appealed to the company, where it saw most of its potential. What really baffled scientists at the time was that the calculations could reasonably explain what happened to an aircraft at subsonic and at supersonic speeds but not in the transonic region.

Most analysts appeared to believe that drag would increase by several orders of magnitude but ballistics experts who had been studying the flight of supersonic bullets for many decades disagreed and testified to a minimal drag increase at the speed of sound. Clearly, it was an aerodynamic problem related to the design and the shape of the aircraft and Bell’s engineers were excited by the prospect of getting to grips with the design of an aerodynamic shape which could confound the sceptics. Another figure in the move toward a supersonic research aircraft was John Stack, an aerodynamicist like Kotcher who made conceptual studies of possible aircraft shapes for getting across the transonic region. In 1943 Wolff began to lobby for an agencywide development programme to tackle compressibility quite literally, head-on. During a

conference in Washington DC that December he suggested that the army, the navy and the NACA co-fund, and develop, a research aeroplane for such a purpose. He wanted the government to fund it and industry to build it and the message appeared to have got through when the army issued a technical instruction calling for “possible development of an experimental article (aircraft) for the purpose of investigating aerodynamic phenomena in the range of 600 to 650mph”. by now the Army Air Corps had become the Army Air Force and the Air Materiel Division was to handle it. ➤

Above: Sunlight shining through the conformal canopy of the Bell X-1 lights the interior and shows the cramped cockpit with seat and side hatch. NASA ROCKETPLANES 49

The converted Boeing EB-50A mothership for the X-1 transonic research programme was raised on jacks to allow the rocketplane to be positioned beneath the fuselage, where it would be attached in the adapted bomb bay. NASA

Mach 0.999

Work began almost immediately on a possible configuration but undecided as to whether it should powered by be a rocket motor or a jet engine. Kotcher was responsible for putting this together and for the rocket motor he selected a design from the recently formed Aerojet Engineering Corporation which offered a thrust of 6000lb. As a candidate jet engine, Kotcher selected the GE TG-180, of 4000lb thrust. Developed alongside the centrifugal-flow J33, the TG-180 was to become the air force’s first axial-flow engine and would be known in service as the J35, the manufacturing contract going to Allison. Also under consideration was the optimum shape for an aircraft designed to go where none had gone before. Instead of designing for lift and controllability, it was felt from all the evidence that the shape should be driven by the need to overcome the compressibility inevitably encountered and the fact that bullets had been happily crossing the transonic zone seemed to be a good starting point. During the first few months of 1944 the shape was fixed as circular in cross section with a faired canopy shaped as a glazed portion of the forward fuselage. There were to be no bulbous cockpit humps protruding into the airstream. The aircraft would have a thin wing mounted mid-fuselage, 50 ROCKETPLANES

with a straight planform and squared tips, and a vertical fin and horizontal stabiliser located at the rear fuselage. At the time Theodore von Karman was director of GALCIT and served in an advisory capacity to Hap Arnold. He calculated the lift/drag ratio of this winged bullet at 3:1 and, half in jest, Kotcher dubbed the project the Mach 0.999 proposal. By general consensus, in April 1944 a rocket motor was selected over the jet engine to power the research aircraft. The rocket was also preferable because of its very high power-to-weight ratio and because it would avoid the necessity of having to accommodate an air inlet and all the complications of flow patterns and shock waves that would ensue. Having agreed on the general shape and means of propulsion, further levels of test were now essential. It was at this time that, as advocated by Kocher, the army and the navy came together in a combined effort to develop a research programme for transonic flight that would benefit both land-based and sea-based aircraft of the future. Both services recognised that with jet aircraft under development it would only be a matter of time before combat aircraft would be flying supersonic – assuming that such a thing was possible. But there were differences, both in what each service wanted from this research

programme and how it went about obtaining those results. Because they felt rocket motors were very new, inherently unreliable and risky, the NACA favoured a jet engine and the navy concurred. Its own research programme would proceed along that path and adopt a more conservative approach. There was some merit in that. The emergence of a jet aircraft programme had flouted a fundamental law of aircraft development – never develop both a new engine and a new airframe at the same time. But of course with such a new form of propulsion there was no alternative. Going one step further and adopting a rocket motor was, for the navy, a step too far. Throughout the remainder of 1944, the navy and the air force diverged along separate research paths and in the type of aircraft they wanted. While each was developing its own approach, and its own aircraft, they were both working toward the same objective. The jetpowered navy aircraft would be shaped by 1st/Lt Abraham Hyatt and he would focus on a methodical path resulting in a research programme aiming for 650mph (Mach 0.85) at sea level; Kotcher would set the target as Mach 1.1 at 35,000ft. Primary responsibility for the general design and layout of the army aircraft was assigned to an engineering team at Wright Field

consisting primarily of Capt F D Orazio and Capt G W Bailey. They argued long and hard with the NACA about the choice of a rocket engine but held their ground and Kotcher received permission from his boss, von Karman, to start work on the defined concept as MX-524, which only left the job of selecting a contractor to build the aircraft. Getting someone to build it was not all that easy, especially as the established ‘big names’ in aircraft manufacturing wanted nothing to do with exotic, one-off projects which would sink company cash and time when they preferred to spend resources on churning out standard combat aircraft for the War Department. The decision was made by chance. Along with Larry Bell and Ray P Whitman, one of the founders of Bell Aircraft was Robert Woods and on a whim, at the end of a day discussing other projects at Wright Field, he stopped by the office of Ezra Kotcher for a casual chat. Woods knew nothing about the transonic project and only during incidental conversation did Kotcher regale Woods with his dilemma. Not suspecting Woods might be interested, when the Bell executive showed real surprise, Kotcher kept him talking and by the end of the evening he had agreed to give Bell the contract for an aircraft which was guaranteed to be safe and controllable up to Mach 0.8 with no comeback on what happened after that. The air force had found its industrial partner and Woods returned to Bell to mobilise Robert Stanley to the task ahead and to choose a group to work on the project which included Paul Emmons, Benson Hamlin, Roy Sandstrom and Stanley Smith. To forestall accusations of an anticompetitive stance, the NACA looked at a proposal from McDonnell (MCD-524) and in fact took the air-launch concept from that proposal and applied it to the Bell design (MCD-524). Bell was intrigued to get the work because it specialised in unusual and challenging tasks and with the experience of the XP-59A it was a natural for the transonic project. At this time Bell was bidding for work on several unique high-speed piston engine fighter requirements and Woods was himself immersed in starting in to helicopter work, which would turn out to be the type of aircraft for which the company would come to be most popularly known. Nevertheless, late in 1944, the company was gearing up deliver 100 P-59 jet fighters, now named Airacomet, which although far less than Bell had hoped would be ordered, did come with an expectation of an order for a further 250. By the end of 1944, with the end of the war now inevitable, that initial order was cut back to 50 with no prospect of any more. The army liked the Lockheed P-80 better and it did have more attractive performance, but the transonic project was a new challenge. Although the general shape of the transonic aircraft had been decided, the refinement of its profile and planform could be crucial to its success – and survival. To get these matched as closely as possible to objects they knew had flown supersonic, i.e. bullets, they obtained Schlieren photographs of fired rounds travelling far beyond Mach 1. Schlieren

photographs are a means of photographing the motion of fluids of varying density and provide a clear indication of shock wave attachment and movement on and around the speeding projectile. They were named by their inventor, a German physicist named August Toepler who first demonstrated the technique in 1864. Tests with .50 calibre slugs demonstrated that this was a very stable shape for transonic flight. Bell looked at several optional configurations for MX-524 and toward the end of 1944 examined a jet engine-powered version, a dual engine mix of jet and rocket or a rocket alone and decided, as had the air force, on the latter. The NACA was adept at designing wing shapes for a wide variety of aircraft types and roles. It held an index of available shapes and structural forms which an aircraft designer could pluck virtually off the shelf, by its NACA reference number. Designed to have a thickness/chord ratio of 5%, the NACA did not like the thin wing of MX-524 and preferred a thicker wing. It compromised and suggested two separate sets for flight testing on the real aircraft as it progressively made its way toward

“...the ‘big names’ wanted nothing to do with exotic, one-off projects which would sink cash and time ...” Mach 1. One set at 8% and a second set at 10%. But the required 8G tolerance demanded by the NACA was thought by many to be unachievable. Bell wanted 7G tolerance but the NACA insisted and this was finally achieved on the built aircraft. But the wing skins were thick, tapering from a root thickness of 0.5in to more normal thickness at the tip. But NACA engineers were highly suspicious of even the 10% wing being able to test out at 8G, the calculated requirement for transonic flight and they still continued to wrangle about the design of the wing itself. Some attention had been paid to advantages from a swept-back wing. In 1935 Adolf Busemann attended the very same conference at Campidoglio at which von Karman discussed transonic flight and presented a paper suggesting that one way of reducing high drag in the transonic region was

to sweep the wings back in the form of an arrow. Electrified by the possibilities, von Karman rushed back to the United States imploring the NACA to build a supersonic wind tunnel to test these theories, to no avail. In Germany, meanwhile, aerodynamicists had a tunnel geared to Mach 4.4 by 1941. But all this was unknown to the Americans and discussion about swept wings was resurrected by the idea that it could help alleviate drag rise in the transonic region and that this would help get the bullet-shaped plane through the barrier. The NACA objected to this because it saw MX-524 as a research tool not so much for pure scientific research but rather for supporting current jet projects already in development. The P-80 had straight wings and so MX-524 would have to have straight wings too. In this way the decision was made to use a straight wing adopting the NACA-66 aerofoil section and not as some accounts have claimed because the Americans did not discover the advantages of swept-wing aerodynamics until they overran the German research facilities where a considerable amount of work on this concept had been conducted. Another contentious issue about the new aircraft concerned the Aerojet engine. Designed to use red fuming nitric acid (RFNA) and aniline, the Rotojet, as it was called, was temperamental. These highly toxic and very dangerous chemicals were hypergolic, they would ignite on contact, and so any leaks or accidental spillages could wreak havoc in an uncontrolled situation. The dangerous cocktail of hypergolic propellants were being employed on the Messerschmitt Me 163 in Germany even as their application on MX-524 in America was being rejected as an unacceptable risk for ground crew and pilot. The engine selected instead was the RM-1 from Reaction Motors Incorporated, a company formed right after the Japanese attack on Pearl Harbor in December 1941, by members of the American Rocket Society. This engine was ➤

Below: The British research effort into transonic flight had many twists and turns but the first aircraft from this country to officially exceed Mach 1 did so on September 9, 1948 in the third of three DH 108s (VW120). De Havilland

ROCKETPLANES 51

The cramped X-1 cockpit resembled more a Second World War fighter rather than a specialised research aircraft.The Machmeter is the right-hand dial of the two uppermost in this view.

designed to run on liquid oxygen (LOX) and an alcohol-water mix, much the same as the German V-2, but it differed in many regards from other rocket motors. Instead of one single combustion chamber it had four, each providing as thrust of 1500lb, and was of welded stainlesssteel construction. Because of the total thrust output from all four cylinders it had the company designation 6000C4. This was a super-safe engine and because the propellants would not spontaneously combust on contact it required an igniter to start the motor. It had a very efficient regenerative cooling system. When the internal combustion temperature was running at more than 4500ºF the exterior of the chamber was a relatively cool 140ºF. None of the four chambers could be throttled and each had a fixed thrust. However, the overall thrust could be graduated from 1500lb to 6000lb in three increments simply by igniting additional combustion chambers. This was a safe, if undramatic, motor with safe propellants providing at least the thrust of the most powerful jet engine then under development.

The Bell X-1 iS Born

As the customer for the transonic project, the Army Air Technical Services Command informed the NACA on March 10, 1945, that it was giving Bell the contract to build the aircraft and just six days later a contract was signed with the contractor. Bell was to have a free hand in designing the aircraft, within the constraints of the specification, which also included precise positioning of the tail assembly, considered crucial perhaps to maintaining stable control of the aircraft. NACA wanted the tail to have a lower thickness/chord ratio to the wing. It was 52 ROCKETPLANES

postulated that in the event the latter ran into compressibility problems, the tail (with a different section) might not. Another design preference was for the elevators to be used for pitch control as on a conventional aircraft but with the ability for the entire horizontal tail to pivot as a single piece, not only for research purposes but for extra surface area. When the transonic project was moved to the contract stage it got a new designation, MX-653, and the type was designated XS-1, for Experimental Supersonic No. 1. In 1947, when the independent US Air Force was born out of the Army Air Force, under the new designation system the ‘S’ was dropped and so we will do that here to avoid confusion, what Bell designated as factory Model 44 being the X-1. Designations for US military aircraft hide an array of information and while seeming to be confusing at first, can locate a type within its place from experimental to production. It was a convention that began in the 1920s and migrated through the progression from Air Corp to Air Forces (1941) and on to independent Air Force (1947) and helps explain the system for the X-1 and its successors. When ordered as prototypes from a manufacturer, the type bore a number preceded by a letter indicating its role. For instance the Bell XP-59A fighter was the 59th type designation allocated by the War Department for this type of aircraft. The ‘P’ indicated that it was a Pursuit (or fighter) type, a descriptive noun adopted from the French by the Americans in the First World War. From 1947 this changed to ‘F’ for logical reasons. But the ‘X’ prefix indicated that it was a prototype, without any commitment to production. Successive orders for pre-production aircraft bore the prefix ‘Y’, any form of prefix being

dropped for full-scale production where the convention was for the letter sequence to follow the number as a suffix: the P-59A in this example being the initial production version, and so on with each new variant receiving the next letter in the alphabet. Because the Army Air Force was the customer, it retained the ‘X’ as an indication of an experimental type but had no functional allocation of purpose other than it was to attempt supersonic flight. The ‘X’ series was retained for successive experimental air force projects, which by 2014 has reached 56, many of which have pioneered innovative or groundbreaking technologies for existing or future aircraft designs. Three Bell X-1 were ordered, bearing serial numbers, 46-062, -063 and -064, but while the air force was moving swiftly to be first through the transonic region, the navy was taking a more conservative approach with a programme designated D-558 and named Skystreak. The navy had its own unique system of nomenclature, more complex and often more confusing than the air force. The ‘D’ stood for Douglas, the name of the contractor selected to build the type, but this aircraft is of only passing concern here as it was powered by a turbojet and not a rocket motor until a developed version, the D-558-II Skyrocket appeared in 1947. Suffice it to say that the navy contracted with Douglas for six aircraft in June 1945 but two months later the rocket-powered type was begun as a separate programme and the last three jet-powered Skystreaks were built as Skyrockets. Meanwhile, work progressed rapidly on the Bell X-1, now declared a secret project with top priority.

Super-weaponS

The pace at which MX-653 moved was not driven by the demands of research alone but rather by a determination to project the capabilities of an independent air force separated from the army. As discussed earlier, the US Army Air Forces (USAAF) grew out of the Army Air Corps and since that shift in 1941 there was a deeply held conviction among US airmen that the return of peace must not bring a retrenchment of capability as it had after the First World War. By forming the USAAF the air power element of the War Department had granted a degree of freedom to the air forces but they wanted more. To insure against retrenchment, in the middle years of the war the example of Britain’s RAF was a great influence over the next major decisions about the structure of America’s fighting force which had a direct relationship on a continuing move toward increasingly more capable rocket planes. The RAF had become effective on April 1, 1918, combining the Royal Flying Corps and the Royal Naval Air Service, and that consolidation had effectively prevented the disbandment of British air power in 1919 after the Treaty of Versailles had supposedly presaged an end to major wars. But largely at the urgings of Maj Gen Hugh ‘Boom’ Trenchard (the ‘father’ of the RAF) and Winston Churchill, Secretary of State for War and Air, the RAF was retained as a redefined

Snugly attached to the underside of the mothership, the Number 2 Bell X-1 affords little ground clearance during takeoff. NASA

“The AmericAns becAme convinced ThAT The nATion wiTh The superior Technology would win The nexT wAr.” aerial police force against insurrection in British territories. It was this that the US air leadership looked to as a template for their own independence from the army and saw in it perhaps a similar postwar role. In May 1944 the Joint Chiefs, which had imported Hap Arnold to its membership, appointed a committee to work out the optimum arrangement for administrative control of the military among three options: two departments for war and navy; three departments for war, navy and air; or one department covering all defence matters. In March 1945 they recommended one department for managing defence with three coordinating branches for land, sea and air. With tacit acceptance a separate air force was inevitable, consolidation of an intention to make it so was uppermost when the air leadership pressed for a technical leap into the unknown by having an air force aircraft break the sound barrier in level flight and under full control of the pilot for the first time. Thus stamping a firm grip on the new age of high-speed flight. Several historians, and those left aside by the decision, have sought to claim that pressure to break the sound barrier was increased by this desire for service prestige, a not unlikely effect of liberation from army control, but the pressure was already great enough to explain the urgent need to find out about transonic flight for the generation of upcoming jets. There was pressure too from the emerging administrative organ which would replace the War Department, although it would not be formalised until September 1947 when it would set in train a shift to what

became the Department of Defense based at the new War Department building on the outskirts of Washington DC, known around the world as the Pentagon – purely because of its shape. Ironically, the determination to press ahead with technological developments and to embrace rocket planes as a means of leaping ahead of the fast-paced upward development of high-flying, fast jets, was itself stimulated by a deepening view that wars are won by the best weapons and that superior technology had defeated Nazi Germany and Imperial Japan. The Americans became convinced that the nation with the superior technology would win the next war. This view would be propagated to the general public at large, with examples of how British radar had defeated the Luftwaffe in the Battle of Britain, of how the Navy’s Grumman Hellcat had outclassed the Mitsubishi Zero and how the atomic bomb had defeated Japan as an Imperialist nation. Because of this, much later during the Cold War a suspicion that the Russians were making great technological strides had a more empowering influence on American public opinion than might otherwise have been the case. In fact, this view of a technology-led superiority is not true, as Vietnam and countless minor wars since 1945 have proven. As President Eisenhower was only too well aware, what won the Second World War was manpower, mass production and vast resources overwhelming an enemy already awash with superior technology and as said on many occasions, the Second World War was won in Detroit, not on the battlefield.

But all this was of no account in 1944, when pressure began to build for the X-1 to be precursor to a rocket fighter which could be adapted for service. No less a person than Bell’s Robert Woods pursued this, no doubt with a view to turning a triple-buy research aircraft into a major production contract which had all the indicators of a truly revolutionary capability. But there were other factors as well which factored in to whether this remained a pure research vehicle or somehow had within its design the makings of a production-based interceptor. Benson Hamlin proposed that instead of taking off from the ground and wasting rocket fuel climbing to altitude, a minimum approach should be adopted with the X-1 carried into the air beneath a mother ship – perhaps an adapted Douglas C-54 Skymaster – which would drop the plane for its high-speed run. Benson Hamlin and Stanley preferred the air-launch approach and proposed a set of skids for it to land on but this was opposed by Woods but company president Lawrence Bell played Solomon and decided in favour of the air-launch method. The X-1 would be heavy with fuel and starting a rocket motor was never a sure-fire thing so carrying it first into the air would provide space and time for it to jettison propellants and make a gliding descent to the runway, should anything go wrong after the drop. Woods got transferred up to corporate headquarters and when the Nazis surrendered in May 1945 he was sent to Germany to support an intelligence swoop on technical booty from the defeated country. n ROCKETPLANES 53

“An unhesitating

boldness…” Industr y and government had come together to build a research programme that would underpin a bid to break the supersonic barrier. As the Bell X-1 emerged for its crucial test, militar y aviation was already knocking on the door to Mach 1.

Bearing photo-interpretation ‘X’ marks on the fuselage to distinguish it in the air, the second Bell X-1 had thinner wings and more horizontal tail than the first and third examples. NASA

M

ost of 1945 was spent on the detailed design and assembly of the first X-1. The initial calculations were for an aircraft weighing 13,034lb loaded with 8160lb of propellant, from which the four-chamber RM-1 rocket motor would push the aircraft to a speed of 1100mph at an altitude of 65,000ft from a ground launch. If carried into the air by a mother ship, it was believed the aircraft could reach a speed of 1600mph. It was in this flight regime that the rocket plane excelled. Without the complex air intakes and compound geometr y required for an air-breathing engine, the internal propellant supply minimised physical protuberances outside of the ideal aerodynamic shape and permitted the aircraft to sustain flight in a more rarefied atmosphere than

possible with a piston-engine aircraft. Moreover, the lower air pressure meant a higher thrust and greater efficiency from the rocket motor. One early decision was to adopt a pressurised propellant deliver y system, using nitrogen gas forced into the spherical tanks to push the liquids into the propellant deliver y lines and thence to the rocket motor. The optimum loading was initially designed as 311 gallons of liquid oxygen and 293 gallons of the alcohol-water fuel mix. In the early design, 12 nitrogen gas bottles were to be located in the bottom of the fuselage between the LOX tank, for ward of the main wing carr y-through spar, and the fuel tank aft. A compartment in the fuselage above the spar carr y-through was provided for the 500lb of in-flight instrumentation required by the NACA for sending and recording data during each flight.

The decision to use a pressurisation rather than a pump-fed propellant delivery system, which had been experiencing serious development problems, meant that the extra weight would reduce the propellant load to 4680lb, cutting engine time from 4.1 to 2.5 minutes, removing any possibility of early test flights from the ground as this would be insufficient time to push it to the transonic region. But with an air-drop it was still believed to be capable of reaching 900mph although the absolute ceiling would be reduced from 140,000ft to 87,750ft. Nevertheless, to get the maximum potential out of the aircraft, it was decided to complete the first two X-1s with pressure-feed and hold back on the third in the hope that a turbopump system could be ready when that airframe was eventually completed. This was eventually finished but not until five years’ development time had been absorbed. ➤

“It requIred an unhesItatIng boldness to undertake a venture so few thought could succeed.” It had capacity for 437 gallons of LOX and 498 gallons of ethyl alcohol and carried 31 gallons of hydrogen peroxide for the pump system itself. In finalising the details of the aircraft, there were some changes along the way to the wing profile selected; Bell, the air force and the NACA agreeing to a 65-108 aerofoil at 8% thickness ratio, although the third aircraft had a 65-110 section of 10% thickness. The leading edge sweepback was just over 5º and the wing had an aspect ratio of 6.03, reflecting the ratio of the half-span to the root chord. The 8% ratio wing had a root thickness of 5.9in while the 10% wing had a depth of 7.4in and the NACA, for whom in-flight measurements were a crucial part of the project, required installations of 12 strain gauges in the port (left) wing to obtain pressure measurements and air loads data. The airframe was fabricated from 24ST aluminium and one of the biggest headaches in engineering the aircraft was in the nitrogen pressurisation system. In redesigning the system, they placed one tank in the nose of the fuselage, seven tanks directly behind the cockpit around the circumference of the fuselage, two behind the LOX tank and below the wing carry-through spar and two aft of the alcohol tank. Welded high-pressure joints connected manifold lines from the 12 tanks to the LOX and fuel vessels and the entire system was pressurised at 4500psi. Regulators reduced this to 1500psi for lowering the landing gear and operating the wing flaps and to 340psi for pressurising the two propellant tanks, all three with the option of being controlled from the cockpit. Intriguingly, a completely new method of producing liquid nitrogen had to be found, 56 ROCKETPLANES

as the commercial availability at 2200psi was too low and the possibility of contamination with tiny oil droplets ran the risk of an explosion when mixed with liquid oxygen. A special process was developed which used an evaporator which boiled off the gas at high pressure which could then be piped directly into the tanks aboard the aircraft from a double-walled sphere which was proof tested to 9000psi. The cockpit had a few unusual features. Instead of the traditional control column, it was equipped with a wheel so that the pilot could exert greater force by gripping it with

both hands if the forces became excessive. This was fitted with controls for thrust selector, instrument switches, stabiliser control, and cutoff switch so that the pilot could operate these critical items without removing his hands from the wheel. The angle of the attack of the stabiliser was controlled by a screw jack worked by an electric motor and capable of moving through 15º in 15 seconds. Access to the cockpit was through a square hatch in the side of the fuselage, which would be secured from the inside. The cabin was pressurised with nitrogen requiring the pilot to wear an oxygen mask and with a pressure decay rate of 1% in an hour; this was considered quite acceptable for the short flights anticipated. The detailed technical design of the aircraft was completed on August 1, 1945, and thoughts turned to an appropriate mother ship to carry the X-1 to altitude. Early ideas of using a C-54 were replaced with a now burgeoning abundance of retired Boeing B-29 Superfortress bombers made redundant by an end to the Pacific War. With greater lifting capacity and with a ready-made opening for carrying the X-1 in a modified bomb-bay, the B-29 was ideal and over the course of the Xprogramme, both B-29 and B-50 types were used for mother ship duties, the latter differing from the B-29 most notably in being equipped with more powerful engines. With the war over, progress was rapid, although the impact of the conflict and its cessation was completely outside the experience of those working on the X-1, focused as they were on achieving the first transonic flight. The air force and the NACA got to see a full scale wood mock-up of the aircraft on October 10 and it was passed without changes. The first aircraft was rolled out of the Bell facility at Wheatfield, New York, on December 27. Sleek, starkly devoid of any major impediments to what was a perfectly clean shape, it looked very different

The second X-1 with air data probe attached to the nose on the dry lakebed at Muroc. NASA

to any other aircraft built to fly. Painted a deep yet bright orange, it bore the stencilled number 6062 on its tail, an abbreviated form of the air force serial number 46-062. The emotional sight of such a completely different aircraft, lost now after decades of so many extraordinary and unconventional flying machines, is hard to capture. In writing later about the magnitude of this endeavour, Bell engineer J van Lonkhuyzen would write: “It required an unhesitating boldness to undertake a venture so few thought could succeed; an almost exuberant enthusiasm to carry across the many obstacles and unknowns, but most of all a completely unprejudiced imagination in departing so drastically from the known way.” When the first X-1 was rolled out, it had no engine, and several months of subsonic flight test, a lot of it unpowered, lay ahead. Yet, even as the X-1 was shown off, design work was already under way on its successor – the swept-wing X-2, which would not make a powered flight until 1955.

Left, top: Charles ‘Chuck’Yeager with the first X-1 named after his wife Glennis. NASA Below: The original term ‘computer’ was applied to the women who worked the data into reports and put them on to readable charts for engineers and analysts to work with. NASA

Although the Americans fully understood the advantages of swept-wing aerodynamics, they were uncertain about the overwhelming advantage if afforded a transonic aircraft and not until the German data swung the balance was there detailed confirmation of this. The NACA had been receiving this information for much of 1945 but, in the belief that it was too radical a departure from the conventional to risk designing into the X-1, withheld from the air force and Bell critical information which could have given the project greater performance potential.

INTO THE AIR!

On October 24, Brig Gen Alden R Crawford, then the chief of the production division of the Army Air Force, told Dr Jerome Hunsacker, chairman of the NACA, that the withholding of this information had critically damaged development of the XP-86 fighter and XB-47 bomber programmes. These two projects were to underpin the air force’s transition from prop to jet powered combat forces. Design work on what would become the F-86 Sabre, eventually to achieve fame for its role in fighting Russian-built MiG-15s in the Korean War of 1950-53, had begun in late 1944. It was designed with a straight wing much like the P-80 Shooting Star, but a year would elapse before the general availability of German transonic research resulted in a

decision by the Air Force on November 1, 1945, to give it a swept wing. This did indeed delay production. The XB-47 was the prototype for what would enter service as the B-47 Stratojet. Design work on a straight-wing concept began in 1943 but not until the air force had its own technical teams in Germany late in 1945 did it become aware of the significant advantages for wing efficiency at high speed. The B-47 would be subsonic, but the advantages of wing sweep were evident enough to give the Stratojet a better performance and in October the air force ordered Boeing to immediately change the wing, giving it a 35º sweep. With this data in hand and the NACA becoming increasingly aware that it required a swept-wing test aircraft; on December 14, 1945, it was in attendance when the air force signed a contract for development of the X-2. But it would be a long time coming, and a disappointment when it did. The price for an overconservative approach during the latter war years was that the burgeoning development of operational jet combat fighters of the late 1940s and early 1950s would threaten to overtake the research efforts of the NACA. Which is why the air force was keen to use the X-1 as quickly as possible. Shortly after being rolled out at Wheatfield, NY, the first X-1 (46-062), was mated to the underside of a Boeing B-29 ➤

ROCKETPLANES 57

➤(serial #45-21800) and flown to Pinecastle Field, Orlando, Florida, arriving there on January 19, 1946. Bell engineers had cut out a portion of the B-29’s lower fuselage forward of the bomb bay and fitted an extendible ladder so that the X-1 pilot could climb down into the cockpit while in the air. On drop-flights, the amount of time taken to reach altitude would require the pilot to wait in the bomber until the time came to prepare for free flight. The secrecy surrounding this project was high; no word was leaked to the press and the aircraft was covered and disguised whenever it was moved from one place to another where there was the possibility of a public viewing. The NACA had wanted the aircraft flown from its Langley Laboratory in Virginia where there was a large military base but the air force decided otherwise. Bell was in charge of the flight tests to high subsonic speeds and pilot selection for both the mother ship and the X-1 until it was handed over to the customer and the air force began flying it for transonic trials. The NACA would have responsibility for monitoring the flight data for both sets of tests. The first captive flight (where the X-1 remained under the belly of the B-29) was completed on January 19, 1946. With ballast in place of a rocket motor, the first glide flight took place on January 25, with Bell test pilot Jack Woolams at the controls. The bulletshaped aircraft dropped away cleanly and Woolams liked the way it handled, gliding down to test the stall speed, which he found to be 120mph, or 110mph with flaps and undercarriage extended, and to check out the general feel of the aircraft. Woolams reported 58 ROCKETPLANES

that he was so content with the benign behaviour of this unpowered glider that he almost forgot and undershot the runway! Between January and March 6, Woolams made 10 glide flights in all, some of them exposing minor problems and unfortunate weaknesses, such as the collapse of the landing gear on flights four and five, before the aircraft was sent to Buffalo, NY. Its 10% thickness ratio wing was replaced with one of 8%, together with a tail of 6% thickness, for the first transonic trials. With the thicker set of wings (10%) and tailplane (6%), the second X-1 (46-063) was delivered straight to Muroc at Roger Dry Lake, Edwards, California, on October 7, 1946.

SuperSonic

Woolams had expected to join the first aircraft at Muroc for tests leading up to a supersonic run, but on August 20 he was killed flying a souped-up P-39 racing plane named Cobra 1. His place was taken by Chalmers ‘Slick’ Goodlin, a pilot of a youthful 23 years but with considerable experience in his late teens as a Spitfire pilot with the Royal Canadian Air Force. In September, Stanley Smith was moved from his position as project engineer on the X-1 to run the X-2 programme, his place taken by the controversial Richard Frost who was also a Bell test pilot. The NACA assigned management of the flight test programme to Walter C ‘Walt’ Williams, who would go on to great success with the hypersonic X-15 and eventually with NASA’s one-man Mercury space programme. Just as the X-1 team was gearing up to conduct a complex run of tests before making

Above: The second X-1 displays the high tail located to as to eliminate any airflow disturbance coming off the wing. NASA Right, top: The classic shot of the first X-1 under power as it is viewed from a chaseplane early in its powered run. NASA

an attempt on the sound barrier, grim news arrived from Britain. Geoffrey de Havilland Jr, son and test pilot of the famous aircraft designer and founder of the de Havilland Aircraft Company, was killed when the DH 108 he was flying on September 27, lost control and crashed during a high-speed dive from 10,000ft near Gravesend, Kent. The DH 108 was a tailless, jet powered, aircraft with a swept-back wing designed to obtain data for the DH 106 Comet jet airliner and the DH 110 Sea Vixen naval fighter. The forensic analysis judged that it had succumbed to very great aerodynamic loads imposed at a speed of Mach 0.9. There was nothing to link any of the technology in the DH 108 to that of the Bell X-1, but the news brought a reminder of the grim price paid for the high stakes at play in pushing through the sound barrier. The first glide trial with the second X-1 took place at Muroc on October 11, with Slick Goodlin at the controls and three more glide flights were completed, the last on December 3 and all involving air-drops from 25,000ft and a top glide speed of 230mph. Muroc had been slowly developing as a major military base since the early 1930s, indeed this general geographic location with Palmdale in one sector and the vast expanses of the Nevada deserts in the other direction

would form the test area in which many highly secret projects would be flown and evaluated. The first US turbojet, the XP-59A, had been flown from there and now the first rocket plane designed to crack the sound barrier was about to follow in its contrails. Observing the mated B-29 and X-1 #2 from the ground, test engineers and technicians monitored tracking information and voice communication as the aircraft made its first powered flight attempt on December 9. This time the X-1 was released from a height of 27,000ft and the drop came at 11.54am local time. It had been released from the B-29 many times but this time in place of ballast there was a fully fuelled propulsion system and a rocket motor primed to make the first powered flight. It felt heavy, weighing 12,012lb. Goodlin lit up the first of the four chambers with a long orange glow coming from the exhaust. With the first still running he ignited the second chamber, then shut it down and on the 1500lb thrust from the first chamber alone climbed slowly at 330mph. At 35,000ft he re-ignited the second chamber producing a total 3000lb of thrust and quickly reached Mach 0.79 before shutting down both chambers. Descending in a shallow dive to 15,000ft Goodlin ignited all four chambers simultaneously and on 6000lb of thrust surged forward outpacing piston engine and jet aircraft visually observing events.

A specially converted FP-80 Shooting Star (designated F for ‘Photographic’) was flying chase, monitoring the appearance and the behaviour of the X-1 as it sped away, rapidly out-accelerating the jet. A P-51D carrying Richard Frost was left standing – he successfully lobbied for a P-80 to replace the ageing Mustang for later flights. Shortly after firing all four chambers, a red fire warning light came on the in the cockpit and Goodlin shut the motor down and descended to a landing. None of the chase planes could see

anything wrong but burned wiring revealed there had in fact been a very small fire. The second powered flight occurred on December 20, attaining Mach 0.82 (554mph) at 35,000ft with Goodlin reporting minimal vibration and NACA strain gauges indicating very little compressibility effect. The little thinwing bullet was proving a winner already. Powered test drops continued with 10 completed by the end of January 1947 and then began a series of flights to examine the performance of the aircraft during buffet tests ➤

Test pilots Robert Champine (left) and Herbert Hoover pose by the No 2 X-1. Note the seat detail seen through the hatch. NASA

ROCKETPLANES 59

Technicians fuel an X-1 with propellant before it is finally winched up into the bomb bay of the mothership. NASA

➤which required pull-ups to 8.7G and Mach 0.4-0.8. Both aircraft and rocket motor (designated XLR-11 by the Air Force) passed with flying colours and although it had only been guaranteed for one hour of accumulated flight time it was already well past that level. Meanwhile, the X-1 #1 ship was converted with its thinner wing and tail and fitted with its own XLR-11 and flown to Muroc on April 5. Goodlin made a glide test with it five days later and although it was heavier than ship #2 and

had different lift surfaces, it appeared to behave almost identically to the second X-1 although the stall speed was calculated to be a little higher. Next day, Goodlin made the first powered flight in #1 and achieved Mach 0.77. All went well until the landing when the aircraft lifted back into the air, coasted for 100ft and landed again heavily in its main gear which brought the nose leg down hard, shearing it off and giving the underside of the forward fuselage a dusting as it scraped along the desert floor.

A Northrop YB-49 bomber of the type Capt Glen Edwards was flying when it crashed killing all crew members. Edwards Air Force Base bears his name. NASA 60 ROCKETPLANES

Repairs took two weeks before the X-1 was back in the air, the pause giving NACA engineers time to fit the instrumentation crucial to getting data about the transonic runs. Back in the air on April 28, it resumed flight trials toward the all-important attempt on the sound barrier as Bell worked its way through the 20 contractor flights required by the air force. These flights were completed on May 29, Bell’s work done, having proved the aircraft could accommodate 8G and reach Mach 0.8 in controllable condition. But thoughts were already turning to the allimportant attempt – only the air force would make those runs, Bell’s job was to deliver a product and not take it through the sound barrier. In June 1947 the air force made its decision about the flight crews which would be involved in the transonic and supersonic tests. The aim was not merely to produce a racing stunt through Mach 1 but to characterise the aerodynamics of this new and untried place and to see what happened beyond the speed of sound. For that, highly competent test pilots were essential, exceptionally brave pilots but ones who could work within a team to extract data and scientific information – heroes would be hindrance. The men who would run operations were selected from the Air Materiel Command and included James Voyles as the project engineer, Paul Bickle as head of the Flight Test Division’s Performance Engineering Branch

and Col Albert Boyle, chief of the Flight Test Division. Three pilots were selected from a shortlist of volunteers to fly the X-1: Capt Charles E ‘Chuck’ Yeager who would function as project pilot, Lt Robert A Hoover as his back-up and Capt Jack Ridley as the flight-test project engineer. These men were sent to Bell’s facility at Niagara Falls, Buffalo, to learn about the X-1 project, to experience an XLR-11 in action and to receive briefings on the X-1’s performance and flying characteristics. The NACA chose its own civilian pilots for its unique science flights: Herbert Hoover and Howard Lilly. Robert Frost briefed all five pilots on the challenge ahead. The official start of the air force test programme began on July 27, 1947, when the pilots arrived at Muroc. Walt Williams was in charge of the NACA Muroc Flight Test Unit as it too geared up for the coming work. Yeager was the first air force pilot to put the X-1 through its paces when he was air-dropped for a powered flight on August 29, with successive flights over the next several weeks nudging ever so slightly faster until Mach 0.92 (616mph) was achieved on September 12. He had the nose of the X-1 painted with the words ‘Glamorous Glennis’ in red and white, in honour of his wife. It was distinctive and typical of this ace pilot from the Second World War, who had shot down a Messerschmitt 262 jet fighter as well as 10 piston-engine aircraft. As the day approached when the best data available was in from previous flight trials and wind tunnel tests, there was still speculation on the reaction the aircraft would have to flight in the transonic region. There

was only limited information to go on. The air force knew from its wind tunnel data that all appeared well up to Mach 0.85 but it had nothing beyond that – the lag behind the Germans was very evident and everyone was still trying to catch up with ways to simulate supersonic flight. Wing flow data was available up to Mach 0.93 but the results were inconclusive. Just where information was needed most, it disappeared. ➤

Above: Just some of the equipment installed in an X-1 for research flights, which could take several weeks to prepare for. NASA Below: The ill-fated third X-1 had a steamdriven turbopump instead of the nitrogenpressurisation system used on the first two. It completed only one glide flight before being destroyed in a ground explosion. NASA

ROCKETPLANES 61

Named after Cpt Glen Edwards who was killed while test flying, Edwards Air Force Base quickly became the home for the NACA’s high-speed and high-altitude test programme. In the foreground is a restored North American P-51D chase plane. NASA

The compact arrangement of the Dryden Flight Research Center, named after Hugh L Dryden, gives a unique feel to the facility.

➤Yeager’s second flight was on September 4, reaching Mach 0.89 and on September 12, he nudged it up to Mach 0.92 (616mph) but tests were halted for installation of a faster reacting stabiliser actuator. This gave Yeager the chance to fly to Wright Field where he was fitted with a special pressure suit for flights at 50,000ft where the transonic runs would be made. Back at Muroc, flights resumed on September 25, with a single flight in the #2 aircraft before he took up with #1 and flew an evaluation flight with the new actuator on October 3. The standard procedure for the test

flights had Robert Frost flying his P-80 chase plane at low altitude, Robert Hoover on highchase in another P-80. Frost flew 1000ft behind the B-29 until the countdown began for the X-1 drop, then cut away below the mother ship and off to Yeager’s wing for the release, then climbing slightly in a vain attempt to keep up with the rapidly disappearing X-1 after light-up. Hoover was positioned 10 miles in front of the B-29 and at 48,000ft ready for Yeager to close rapidly, passing him just as the motor was shut off. Peering down against the dry yellowed Mojave desert below, he would try to keep the slowly descending X-1 in sight as it went in for landing.

A run on October 8, calibrated the instrumentation as Yeager reached Mach 0.925 (620mph) and two days later a second run nudged the X-1 to Mach 0.997 (658mph). After the drop he had fired all four motor chambers and climbed to 38,000ft, shut down all four chambers in sequence and stalled off 2000ft in altitude, reigniting two chambers for a climb to 40,000ft and an indicated speed of Mach 0.94. After the chambers ran out of fuel the X-1 coasted up to 45,000ft before arching over for a gradual descent. At which point frost began to build up on the window. But Yeager was unable to clear it and now flying blind he had to be talked down by Hoover and Frost flying chase, executing a perfect touchdown on the lake bed. There was some surprise when the ground tracking radar results were in and the X-1 had been seen to fly at Mach 0.997 without any real indications that it was so close to the sound barrier. There was now nothing more to do other than go for the barrier. Over the weekend Yeager took his wife Glennis to Pancho Barnes’ Fly-Inn, a mock ranch where pilots gathered to let their hair down, to eat and to drink – a lot of each! Afterwards, late at night, he took a horse and rode in the desert but collided with a gate, spooking the horse which bolted and threw him, Yeager breaking two ribs as he hit the ground hard. Unwillingly to relinquish his seat in the X-1 for the all-important flight, Yeager went to see a civilian doctor in nearby Rosamund and was strapped up with tight bandages without anyone at Muroc knowing about the incident, or the unconventional treatment. These were

Left: The new age of jet bombers and advanced technology peaked in the 1960s as a result of air- and ground-based research conducted during the 1950s. Here a YB-49 displays the flying-wing concept that would only emerge operationally 30 years later with the B-2. USAF Below: Flight research was not confined to Edwards.This P-80 test aircraft carried cannon angled upwards in the nose. USAF

64 ROCKETPLANES

The new Century-series fighters of the 1950s were a product of aeronautical research from rocket powered X-planes. From top, clockwise: F-101 Voodoo, F-102 Delta Dagger, F-100 Super Sabre and F-104 Starfighter. NASA

days before pilots had physical examinations prior to special test runs and Yeager was silent about the broken ribs as well as the pain. When dawn broke on Tuesday, October 14, 1947, he alone knew what he was nursing along with expectation in the cramped cockpit of the X-1. Preparations for the flight attempt began early with technicians preparing the bulbous aircraft but word had leaked out about the thrown ride, although not about the cracked ribs. Senior managers gathered round and discussed the flight as the pilot of the B-29, Maj Robert L Cardenas, chatted with Yeager about final flight plan details. This was a unique and tight-lipped little group who spoke very little to anyone about the type of work which paid their salaries, let alone the details of this super-secret project. In the broader world outside the bubble in which the X-1 and its team thrived, events were overtaking intentions as a new chill blew in around the increasingly frosty relations between the United States and the Soviet Union. Nobody wanted to give the ‘commies’ an advantage and even the newly formed and independent United States Air Force was unable to make publicity mileage about its pet project and events which were to unfold. Not for a long time would any of this become public knowledge, and then only because of leaks to the trade press.

The giant B-29 took off at 10.02am and slowly climbed to its drop height as down on the ground two SCR-584 radar units were switched on by a team led by Gerald Truszynski, their cathodes glowing, as the 27-man contingent representing the NACA

“There was now noThing more To do oTher Than go for The barrier.” gathered round the loudspeakers squawking with garbled voice chatter between the crew of the mother ship and the ground and between the ground and the chase pilots, up as usual on station in their respective positions behind and in front of the mother ship. It took barely 30 minutes for the B-29 to reach altitude and for Yeager to prepare for the drop. At 5000ft altitude he had slowly climbed down the ladder from inside the converted bomb bay and across through the square hatch in the side of the X-1. This was the moment of truth. He had already decided that if this effort was too much for his broken body, he would abort and give the ride to Hoover. But it was not too painful as he slid on to the seat and closed

the hatch and as he settled in, the final checks were made to make sure the ground tracking equipment was in place. Confirmation of success would not rely on Yeager’s word alone, claiming afterward that the needle had gone past Mach 1. It would have to be measured very precisely to the third decimal place of unity, to confirm any such success, or not, and only the ground trackers could provide that kind of detail. This was an age before telemetry and before vast bursts of data would be sent down from the test aircraft to the ground. That was space-age stuff and this was long before that. In fact, paradoxically, it was almost 10 years before the world’s first artificial satellite would be orbiting the Earth. It was 10.26am and the lumbering mother ship was doing a steady 250mph. Everything was ready. “You all set?” yelled Cardenas down the mike from his position across in the spacious pressurised forward cabin of the giant B-29. Already apprehensive but fuelled with anticipation, locked now in his sealed bullet, Yeager snapped back: “Hell yes! Let’s get it over with.” Releasing the clamps that held the X-1 firmly beneath the mother ship, Cardenas let loose the bright orange rocket plane set for a place in history. As the bullet fell, Yeager lit up No. 4 chamber followed by ➤ ROCKETPLANES 65

One of the North American P-51D chase-planes used for escorting outbound and inbound research flights. NASA

➤ No. 2. Then he shut off No. 4 and fired up No. 3, shutting off No. 2 and firing No. 1. With two burners now streaming little white diamonds out the back of the accelerating bullet, the X-1 streaked toward the blackness of the upper atmosphere, quickly leaving behind Richard Frost in his P-80. Then Yeager ignited the other two rocket chambers and the shock diamonds got brighter as the white streak in the sky held grounded technicians watching breathless with expectation, the thin line marking out the flight path of the world’s first transonic rocket plane. As the X-1 accelerated through Mach 0.83 toward 0.92, Yeager carefully set the

“Ground crew had liberally spread drene shampoo across the interior of the screen to prevent it icinG up and that had worked.” stabiliser as the rudder and the horizontal elevator lost grip. With the speed now at Mach 0.95 Yeager was still in relatively familiar territory, his previous flights having taken him thus far. At 35,000ft he shut down two chambers, levelling off at 40,000ft to horizontal flight before reigniting a third chamber and accelerating toward the magic number. Passing through Mach 0.98, and with the stabilizer set at 2º above horizontal, Yeager found that rudder and elevator control returned and at 0.99 it appeared to quieten down into an almost blissful smoothness. On through the speed of sound, Yeager kept an eye on the Mach meter as it nudged right through the mystical ‘1’ and 66 ROCKETPLANES

on to 1.02. The X-1 was supersonic – in level flight and under perfect control. For the moment the Mach meter stopped and then jumped to 1.06. With almost one-third of propellants remaining, Yeager cut off the three rocket chambers and the X-1 sank back down into the subsonic region but with a sharp and momentary bump at 0.98 as it decelerated. As recorded by the tracking radar and optical measuring devices and radio equipment on the ground, the X-1 had soared to 43,000ft and achieved a speed of Mach 1.06 – 700mph – and come back down under perfect control. The frosting that had plagued his earlier flight did not recur. Ground crew had liberally spread Drene shampoo across the interior face of the screen to prevent it icing up and that had worked.

As Yeager descended, a quiet came upon the slowly decelerating aircraft and Yeager said afterwards that he could hear the cockpit clock ticking! Just 14 minutes after being released from the B-29 the X-1 was back on the dry lake bed at Muroc, landing at 160mph and rolling out for almost three miles as it slowly came to a stop. It was a little while before confirmation came in that Yeager had indeed achieved the programme goal of the X-1. But it was not an end in itself. The X-1 was not about a single goal but rather a continuous effort to push speed and altitude to the ultimate, using rocket planes to make the leap from Earth to space and thus usher in a new age of excitement and adventure. On the day Yeager slipped through Mach 1, he was the fastest man alive, but he would not

remain so for very long. The Th h highly secret work would go on and even accelerate as more rocket planes were in development and even more spectacular successes were to be achieved. But for one day, there was a great sense of satisfaction and fulfilment as the work of three years came to fruition. Word went out to a very select few on a ‘need to know’ list within the air force, the NACA and industry. For the general public it was another day like any other and it would be a long time before they discovered what had been achieved on October 14, 1947. That Th h humans can build a machine to fly faster than the speed of sound. For the air force, now a fully independent arm of the newly formed Department of Defense, it was a very proud day. The Th h sound barrier had been broken. Were there any other barriers lying in wait? Oh yes there were and they were about to reveal themselves. n

An estimated flight plan for the second-generation X-1 series aircraft being planned even as the full potential of the first-generation had yet to be fully realised.

Research aircraft of the 1950s display the involvement from several US manufacturers. From left: second-generation Bell X-1; Douglas D-558-I; Convair XF-92A (background); Northrop X-4 Bantam (foreground); X-1 firstgeneration; Bell X-5. NASA

ROCKETPLANES 67

Bigger,

faster,

higher

With the sound barrier no longer an obstacle, the NACA and Air Force introduced new combat aircraft for test and evaluation, while the Navy’s Douglas Skyrocket began flying.

H

aving achieved the goal set when the X-1 programme began in 1944, success was not allowed to breed complacency. Flight tests would continue at a brisk pace and there was still much to probe and many aspects of transonic flight, as well as truly supersonic flight, to investigate. Manufacturers picked over the results of intelligence information coming back from Germany about advanced airframe and propulsion systems including both jet and rocket engines. There was an urgent need for investigations at the transonic boundary, and of flight dynamics of different types of airframe and aerofoil shape in pure supersonic flight. From mid-1944 there emerged a prolific array of new jet-powered bombers when the US Air Force issued a requirement which resulted in four types, designated B-45 to B48, being selected by the air force for prototype construction and flight evaluation. Ordered in 1945, flight trials were already under way at Muroc with America’s first fourjet bomber, the North American B-45 Tornado. That somewhat conventional looking aircraft had lifted into the sky over the desert floor on March 17, 1947, seven months before Chuck Yeager blasted through the sound barrier. ➤

America’s first jet bomber, the North American B-46 Tornado, inspired a new generation which would require transonic capability. NAA Right: With rocket-assisted take-off, a Boeing B-47 demonstrates a rapid climb to altitude. USAF

ROCKETPLANES 69

Above and opposite page top: Only two Convair XB-46 bombers were built but the frantic period of postwar rearmament presaged a requirement for high-speed aerodynamic data. Convair

It was followed on April 2, 1947, by the sole Convair XB-46, on June 22 by the first of only two XB-48s and on December 17 by the XB-47, which would achieve great fame in service. The B-45 was a subsonic aircraft, reaching a top speed of only 570mph at low altitude or 506mph at 32,000ft. Largely ignored by history, it would, however, serve with the air force with great distinction from 1948 to 1959, providing the US’s first airborne nuclear deterrent and serving as an effective spyplane. But the real pressure to get transonic and supersonic data was pressed upon the air force and the NACA by the new breed of fighter. The next generation to succeed the F-80 (formerly the P-80 in the old designation) was the North American F-86 Sabre and that made its first flight on October 1, 1947, before the X1 transonic flight. Yet the rate of progress was so great that within a few months it had become the first operational jet fighter anywhere in the world to perform a controlled and measured flight through the sound barrier during a shallow dive. What made the F-86 so special was its swept-back wings, inclined 35º to the fuselage. These wings had been fitted to the emerging fighter design after detailed study by the air force and North American Aviation of German wartime research into various wing shapes and configurations and their influence on performance. The X-1 had straight wings and derived its design from a conservative approach which maximised the research role of the aircraft but which did not take into account any operational role for the type. 70 ROCKETPLANES

But the adoption of swept wings for the F86 came only at the latter stage in its design. The Sabre emerged from dual contracts awarded in May 1945 for a US Navy jet fighter, which would become the Fury, and for an air force fighter, the Sabre. Both designs were conventional with straight wings and a mockup of the Sabre was shown to the air force on June 20 that year. It was calculated to have a top speed of 582mph at 10,000ft, short of the air force requirement for 600mph. The air force ordered another jet in early 1945: the straightwing F-84 Thunderjet fighter-bomber but the F-86 was meant to be an interceptor and a dogfighter and speed was essential for its role. Between mid-1945 and early 1946 L P Greene, North American’s project aerodynamicist, investigated the many different wing shapes coming out of Germany and opted to try swept-back wings in an attempt to improve the performance of this apparently sluggish little fighter. On November 1, 1945, the air force approved RD-1369, a North American Aviation study which proposed a major design change for the F-86 giving it swept wings. While the navy’s Fury continued in fast-track development with its conventional straight wings, the air force accepted a slower and more protracted development programme for the swept-wing Sabre. And so it was that a major step forward was taken which would see the F-86 a capable match for the equally swept-wing Russian MiG-15 when it tangled with the Russian jet in the skies over North Korea from 1950.

While the air force was cautious, and may be thought to have been over conservative in going along with the NACA in defending the straight-wing configuration for the X-1, it must be remembered that events were moving rapidly. A closer examination of the timelines involved in these decisions shows that 1945 was a turning point in accepting the performance value in swept wings, by which time the X-1 was about to make its first captive flight. But the reality that emerged during 1945 sparked development of the X-2, a swept-wing successor to the X-1, for which a contract was signed with Bell on December 14, 1945, for two aircraft. Just six weeks later, on January 29, 1946, Douglas Aircraft was given preliminary authorisation to build the D-558-2 rocket powered research aircraft – with swept-back wings. It was to be a successor to the straight-wing D-558-1. While the future pointed to swept-back wings, derivatives of the basic X-1 would explore the supersonic flight regime and push far beyond that initial flight by Chuck Yeager on October 14, 1947. Exactly one month after that historic event, the air force placed a contract with Bell for a second-generation rocket research X-1. Initial plans were for four aircraft designated X-1A, -1B, -1C and -1D but X-1C was eventually cancelled. The contract was formally signed off on April 2, 1948, and work ran in parallel with flight tests on the two first-generation X-1 types which continued unabated.

GoinG public

The world got to learn about Chuck Yeager’s historic flight through a leaked report in America’s premier aviation trade magazine Aviation Week. The issue dated December 22, 1947, broke the news and informed the world and the air force saw no reason to hide the fact any longer, its legal team believing that it was useless to pursue litigation against the publisher. Soon everyone would be flying supersonic. But the incident, and the alarm it caused in the upper echelons of the Pentagon, demonstrates how tight-lipped the air force had been about this feat. Far from being a branding iron for a new breed of air power, the transonic flight of the X-1 was a closely guarded secret until the press broke the story. Not until June 15, 1948, did the air force officially confirm the rumour when it announced that the X-1 had repeatedly broken the sound barrier and that by this date five pilots had performed that feat.

The RB-45C had the advantage of speed and high-altitude cruising which made it an excellent reconnaissance platform. USAF

Yeager was awarded another oak leaf cluster to his Distinguished Flying Cross and was named as the recipient of the 1947 Mackay Trophy awarded most years to the pilot who had performed the most outstanding flight in a given year. Established in 1912 by Clarence H Mackay, it had not been awarded in 1916, 1917 and not since 1939. It has since been awarded every year, often for outstanding personal skill under difficult conditions. Yet it was a glorious time for the brandishing of the newly independent United States Air Force, since September 18, less than four weeks before breaking the sound barrier, master of its own administration, America’s fourth fighting arm after the army, the navy and the Marine Corp. And if initial fury at the blundered release of this historic achievement was unconstrained, the air force was quick to capitalise, seeing in it fulfilment of the Air Force Song, with its rallying introductory chorus line: “Off we go into the wild blue yonder.”

If America had been slow to adapt to the jet engine imported from Britain, it had been quick to invest in the new technology. With four jet bombers to evaluate and new secondgeneration fighters already in the air, the research establishment and the NACA would have their hands full probing the new frontier and opening a path to the stars – for the US Air Force of the late 1940s knew no bounds and saw no ceilings. And if a little information bled out through ‘Aviation Leak’, as the magazine was dubbed, so much the better for the recruiting drive which would quickly adapt to the demand for air crew and ground crew alike as the chill winds of the Cold War blew in. But for the Bell X-1 team, it was science and engineering that mattered on the sunbaked sand of Rogers Dry Lake. Yeager’s transonic-busting flight had been the 50th drop in the X-1 programme and its 24th powered flight. To date only Woolams, Goodlin and Bell test pilot Alvin M ‘Tex’ Johnson had flown the stubby, bullet-shaped rocket plane. Johnson had checked out the No. 2 X-1 after it returned to Muroc on May 9, 1947, Bell’s Buffalo engineers having fitted a thicker wing and horizontal tail. His powered drop, on September 22, was his only flight in an Xplane, pulling 8G to verify the changes. Further flights with the X-1 explored areas where there was still a clear understanding of the conditions combat aircraft would have to face when the power of jet engines caught up with that of the rocket motor in pushing the X1 through the sound barrier. That need was well stated in the words used by Hugh L Dryden, the newly appointed head of the NACA’s aeronautical research department when Yeager received the Mackay Trophy: “The XS-1 is a small research airplane, flown at high speed at high altitude where the air loads on the structure are small. “Between it and tactically useful military aircraft of larger size flying at lower altitude and where air loads are much greater there remains much research and development on many difficult problems.” ➤

The relative advantages of straight or swept-wing geometry were balanced by performance requirements, as with the North American FJ-1, precursor to the Navy's Fury and the swept-wing F-86 Sabre. NAA

SuperSonic flight

The transonic region was the focus of research involving the design and objectives of the X-1. But that was only a part of the story. In popular understanding the word ‘supersonic’ applies to anything moving in air faster than Mach 1 (the speed of sound). In aerodynamic terms the supersonic regime is defined a little more precisely and precision was at the heart of what the Air Force and the NACA was doing with this X-plane family. The transonic region was loosely defined as Mach 0.85-1.2, while the supersonic region would eventually be determined as extending from Mach 1.02 to Mach 5. Above Mach 5, aerodynamic flight was said to be hypersonic – the thermal barrier where heat became a potential limit on how fast an aeroplane can fly. On these definitions, Yeager had pushed through the transonic region and gone supersonic. Research was at the core of the work which awaited the NACA, yet to make its first flight on the type. One week after Yeager’s record-breaking flight, on October 21, 1947, NACA test pilot Herbert Hoover took the second X-1 for his, and the agency’s first flight on the type, reaching Mach 0.84 (568mph). On landing the X-1 showed its Achilles heel and snapped its forward landing leg, pressing the nose down on the lake bed and necessitating repairs which kept it grounded until mid-December. Meanwhile, Yeager was back in the air on October 27 with the first of four flights before the end of the month, blending in as just another ‘X’ type aircraft, all the others 72 ROCKETPLANES

flying at Muroc being prototypes of potentially successful military aircraft or lame-duck ‘wannabes’ commissioned from leading manufacturers, types which promised much on paper and left it all back on the drawing board, never to be seen again. Flights with X-1 No. 1 gave Yeager the opportunity to push on to a new record of Mach 1.35 (905mph) on November 6 before Hoover was again in the air with X-1 No 2. On January 9, 1948, another NACA pilot, Howard Lilly made his first flight on No. 2, with Hoover for the NACA and Yeager for the air force alternating in each aircraft over the next several weeks.

On that day too top brass from the air force, the navy and the NACA met at Wright Field for a conference on results to date, many of those who would populate future programmes covering research aircraft of the future being in attendance. This seminar, closed to all but the invited, brought in Bell as well as the pilots from the X-1 air force team. News of the contract for four second-generation X-1 planes was welcomed, proposals being raised for use of these to research thermal effects at high speed, for the development of special weapons for supersonic combat aircraft and for development of crew safety devices in this new high-speed and high-altitude realm.

As the test programme unfolded, none of these schemes were implemented, the two research aircraft continuing to fly in support of aerodynamic research. But there was much talk at the seminar of the heat barrier, of supersonic flight at low altitude where the atmosphere was densest and where friction with the air produced unique stresses on the airframe. Throughout the early months of 1948, flights progressed with detailed flight profiles exploring minute fractions of the performance envelope. But a lot of other test flying was going on at the same time. Muroc came alive with a wide range of prototypes for flight evaluation and the NACA pilots were required to fly other aircraft as well. In November 1947, Hoover leapt from a Republic XF-84 which caught fire in the air and hit the tail, breaking both of his legs. That accident put him out of action on the X-1, his seat for the No. 2 NACA aircraft taken by Capt James T Fitzgerald Jr. But his first flight on February 24, 1948, was nearly a disaster when the motor caught fire forcing him to jettison propellant and complete the flight as a glide drop. Still the No 2 aircraft used for NACA tests had yet to make it through the sound barrier, and that was an important step for aerodynamics because this aircraft had the thicker wing and tail. Hoover corrected that on March 10 when he dropped from the B-29, lit three burners, levelled out at 40,000ft and lit the fourth. Accelerating in a level flight he reached Mach 1.065 (703mph), NACA’s first supersonic flight. Just 16 days later Yeager made the fastest run in a firstgeneration X-1 when he hit Mach 1.45 (957mph) at 50,000ft.

A pause to NACA flights was occasioned by a major accident on April 16. When Howard Lilly was landing the No. 2 aircraft it began to porpoise, collapsing the nose leg on contact with the ground which induced a sensor to signal the main gear to retract as well. The left leg did so but only partially, causing the aircraft to skid round to a stop resting on its nose wheel, the right wheel and the left wing tip. The aircraft needed significant repairs and would not fly again until November 1. A sequence of air force tests began with the No. 1 aircraft to evaluate stability and control conditions, the buffet boundary and carry out pressure distribution investigations. These flights were carried out by Fitzgerald and Maj Gustav W Lundquist who had joined the team.

Pilot Bob Champine straddles the cockpit sidewall of a Douglas D-558-I Skystreak.

Lunquist’s sixth and last flight ended when the left main landing gear door opened during a low-altitude flight at Mach 0.94 on June 3. It too had a nose leg collapse on landing which required it to be returned to WrightPatterson Air Force Base (formerly Wright Field) for repairs. The first-generation X-1s were prone to landing gear failures and the nose leg in particular was vulnerable to the nose coming down sharp after the main gear made contact. This was a consequence of the narrow band of elevator sensitivity to touchdown speed. At 130mph the elevators had good grip on the air but just 5mph below that speed they became virtually ineffective, the pilot losing pitch control. On a typical bounce following main gear contact the speed of the aircraft would bleed away, leaving the nose to slap down unchecked. The only way for the pilot to counter this was with a sharp jerk back on the stick, pulling the elevator up as though the aircraft was going into a climb. Intuitively, pilots do not like this manoeuvre, which in free flight is likely to induce a stall. Even on touchdown this action is counterintuitive. By the time the pilot reacted, usually with too little movement on the stick it was too late to arrest the motion. For almost five months the two X-1 aircraft were in repair, flight operations resuming with the NACA aircraft at the beginning of November and with the Air Force X-1 precisely one month later. During October the NACA aircraft was painted white for better visibility during the upcoming research flights and to make tracking a lot easier. But the life of a test pilot was often all too brief and another pilot joined the programme to replace the seat previously occupied by a pilot who had been killed in the line of duty. ➤

Swept wings were applied to the F-86 Sabre when newly acquired research from Germany added to an existing study of wing geometry indicated a favourable performance advantage. NAA ROCKETPLANES 73

Late of the Langley Aeronautical Laboratory, Robert A Champine joined the NACA X-1 test team at Muroc with his first flight in the type on November 23 and the year ended with Yeager making the 104th flight of the X-1 with a flight to Mach 1.09 (737mph) at 60,000ft the day before Christmas Eve. Lilly had been killed in an accident with the Douglas Skystreak in May 1948 and Hoover checked out the repaired No. 2 aircraft before handing it over to Champine. Test flying was taking its toll and none of it was routine. That fact, and the contribution made by the air force/NACA X-1 team was recognised by the fraternity when President Harry S Truman presented the Robert J Collier Trophy to John Stack, Lawrence Bell and Chuck Yeager in the Oval Office. Instituted in 1911 as an annual award for the “greatest achievement in aviation in America”, the citation for the award of the 1947 Collier Trophy recognised the supersonic flight as “an epochal achievement in the history of world aviation – the greatest since the first successful flight of the original Wright Brothers’ airplane 45 years ago.” At the dinner acknowledging the award of the Collier Trophy, it was suggested to Yeager that he might like to think about a ground 74 ROCKETPLANES

Top: An early 1950s scene showing NACA research aircraft (left to right: D-558-I, D-558-II, X-5, X-1, XF-92A (background), and X-4. NASA Above: Scott Crossfield, who would become the first man to exceed Mach 2. NASA

take-off under full rocket power. Not for a supersonic or high altitude flight but as an evaluation of the characteristics of the aircraft under those conditions. The air force was keen on this and Lawrence Bell was enthusiastic – after all, the X-1 had at first been envisaged for ground take-off – discussing the idea first with Gen Hoyt S Vandenberg, the Air Force Chief of Staff. Several modifications were made to the No. 1 aircraft, including different tyres, landing gear struts, brake pads and with partially full tanks to keep the weight under 10,000lb. The flight was planned for early in the morning so that the ambient temperatures would be low reducing the amount of oxygen boil-off, which could seriously affect the centre of balance of the airframe. Yeager had control of the stabiliser settings for his own preference but the method of getting into the air was rigidly determined by careful engineering analysis. The aircraft would be held on brakes until all four rocket chambers had been lit to ensure stable running, only then starting the take-off run. The attempt was made on January 5, 1949, when Yeager ignited first two chambers and then all four, the X-1 leaping away as soon as the brakes were released. Within one minute

50 seconds of starting the rocket motor, the X1 had reached a height of 23,000ft at which point Yeager shut down the motor and glided back to earth. Rolling to a stop without stressing the nose leg by touching the brakes, Yeager successfully completed the only groundlaunched take-off run for an X-series rocket-powered research aircraft. But success here was mixed with tragedy elsewhere, when Fitzgerald died 11 days after a serious crash in a training version of the F-80 Shooting Star the previous September.

HIGH FLIGHT

The first few months of 1949 saw new pilots join the air force segment of the programme. Making his first flight on X-1 No. 1, Jack Ridley had come across from test flying the XB-47 six-engine bomber prototype at Moses Lake, Washington, taking to the air at Muroc on March 11. He was followed five days later by Col Albert Boyd, making his one and only flight in the type. Both flights encountered small engine fires. On March 21, Maj Frank K ‘Pete’ Everest had his first flight in the X-1 and on three burners took the aircraft to Mach 1.22 (825mph) during a familiarization flight with a maximum altitude of 40,000ft.

The arrival of Frank Everest coincided with air force plans to switch from high speed to high altitude runs and he volunteered to start those using a new high altitude pressure suit. Col Boyd, who was himself a respected test pilot, ran the flight test activity at Air Materiel Command, the department of the air force which was responsible for the X-1 tests at Muroc. He had personally selected Chuck Yeager for the programme as well as Ridley as test engineer and Hoover as chase pilot. Boyd specifically requested Everest conduct these high altitude flights and found in him a willing volunteer for the job. The first attempt on March 25 ended abruptly when an engine fire and automatic shutdown aborted the attempt. Everest had been wearing the new suit and reached a maximum speed of Mach 1.24 (838mph) at 48,000ft. Everest’s next attempt was on April 19 but only two chambers ignited although the X-1 reached a height of 60,000ft. Devoid now of any coy secrecy, the air force wanted to use its rocket plane to snatch the altitude record for humans from an army team which, in co-operation with the National Geographic Society, had ascended to an altitude of 72,395ft in the balloon Explorer II on November 11, 1935.

During his first run Everest had experienced an over-pressure in his eardrums which, due to the new suit with its fixed faceplate, he was unable to relieve by the standard procedure of blowing against a pinched nose. Pressurised with nitrogen, the cockpit was lethal for an exposed man and Everest suffered a ruptured eardrum which, although minor, prevented him from getting back into the X-1 for several weeks. Sadly for him, his next flight on May 5 also ended abruptly when he lost rudder control. The chase pilot flew close during the glide back down and noticed that one of the four rocket chambers, which Everest had reported as not firing, had in fact exploded, jamming the rudder! X-1 No. 1 went back went to Wright-Patterson for repairs. The Air Force X-1 was back at Muroc in June and technicians reinstalled instrumentation removed for repairs to the engine section and tail before another altitude attempt was made on July 25, 1949. The Air Force wanted records but it also needed data on high lift coefficients so it was not all about glamour and glory, despite the fact that the NACA aircraft was quietly accumulating most of the data on transonic flight across a wide spectrum. But the third attempt by Everest to snatch the height ➤

X-1 pilot John Griffith hands his flight gear to Dick Payne, holding the hatch door) as crew members Ed Edwards (left) and Clyde Bailey look on. NASA

ROCKETPLANES 75

A flight test package for the Douglas D-558-II Skyrocket included the converted B-29 Motherplane, two F-86 chase planes and a host of crew, technicians and engineers required to support each flight. NASA

record fell short when the X-1 attained an altitude of only 66,846ft. The next effort was made on August 8 when Everest entered a steep climb after a clean drop and soared toward the edge of the atmosphere on three chambers of the rocket motor. Levelling off at 45,000ft he accelerated through Mach 1 and using the horizontal stabilizer trim for control pointed the X-1 upward once again. The fourth chamber failed to fire as intended however, and the little rocket plane reached a height of 65,000ft before the chambers shut down, starved of fuel. Arcing ever upwards on a ballistic trajectory the X-1 topped out at 71,902ft, short of the previous record, and slowly began to fall back toward the denser layers of the atmosphere. The next attempt on August 25 would be more memorable. All seemed well when Everest crawled down from the B-29 and into the cramped cockpit of the X-1 but as he settled in he noticed a tiny crack in the inner shell of the double-layered Plexiglass canopy. This time the flight progressed well but as he screamed through 65,000ft with all chambers firing a hissing sound began to fill his eardrums – the cabin was depressurising and the nitrogen in 76 ROCKETPLANES

the cockpit was fast leaking to the near vacuum of the outer atmosphere. The special pressure suit he had been pioneering suddenly inflated, constricting his body to the point where speech was impossible. As the chase planes and the technicians listening to the communications on the ground heard only grunts, they feared the worst. Everest immediately shut off the rocket chambers and threw the X-1 into a dive. Passing through 30,000ft at supersonic speed he pulled back on the stick and reduced the sink rate, opening the pressure dump valve at 20,000ft and depressurising the suit. Only then could he explain the situation. The crack had grown with altitude, the internal pressure of the cockpit too much for the stressed canopy. Had he not been wearing the special pressure suit, Everest would have died. The air force X-1 was grounded until a new canopy could be provided and installed and during this period the Air Materiel Command decided that they would cease altitude attempts. The aircraft, like its NACA equivalent, had pressure-fed propellant delivery systems and this was considered too dangerous when calculations indicated that the X-1 could only marginally exceed the balloon record set in 1935.

Other considerations were coming in to play. Four second-generation X-1s had been ordered and were shortly to be delivered and the X-2 was well into assembly. With the aircraft coming to the end of its design life, it was time to retire the Air Force X-1 although a few more flights remained.

The end of The beginning

The No. 2 aircraft had rejoined the flight research programme on May 6, 1949, when NACA pilot Robert Champine checked it out with a flight to Mach 0.92 (607mph). During the previous five months it had been specially instrumented for targeted stability and control tests and during planned research flights the pilots would conduct induced motions and pullups to gather unique data in these areas. As flights with the No. 1 aircraft were beginning to wind down in preparation for flights with the first of the second-generation X-1s, the No. 2 first-generation aircraft continued with an additional 10 research flights before the end of the year. Several changes took place at Muroc Air Force Base during the second half of 1949. Col Boyd replaced Col Signa A Gilkey in command of this desert outpost of frontier aviation and

A hangar shot showing just a few of the numerous types employed for test and research purposes, including (from left) the three Douglas D-558-II Skyrockets and the D-558-I Skystreak. Half of a B-47 and the wing of a YF-84A are to the right of the frame. NASA

three new pilots checked out on the X-1: John H Griffith flying the No. 2 NACA aircraft; Lt Col Patrick D Fleming and Maj Richard L Johnson flying the No. 1 Air Force aircraft. Johnson was chief of the fighter test section and was holder of the world air speed record in an F-86A at 670.981mph which he achieved on September 15, 1948. On December 8, Muroc, the place where that record was achieved, was renamed the Edwards Air Force Base in honour of Capt Glen W Edwards who had been killed on June 5, 1948, when the second Northrop YB-49 flying wing he was piloting crashed on that base. And as if to stamp a permanent presence on the freshly named air force facility, the NACA too changed the name of its own facilities there to the High Speed Flight Research Station. By the end of 1949 the X-1 programme had logged 132 flights and the NACA aircraft had been temporarily retired to the hangar for extensive installation work fitting a new suite of instruments for wing load measurements and for data on pressure distribution. This information was vital for transonic fighters and for as full mapping of the aerodynamics of high-speed flight. Essential to the next generation of combat aircraft. The NACA was leading the new frontier with ground breaking research and sustained transonic flight which would provide the basis for future aircraft design. With its thinner wing and horizontal tail, the No. 1 X-1 would always be faster than the NACA’s aircraft but the latter was

providing the depth and breadth of knowledge required to advance aeronautical science to the next level. The last flight made by the Air Force with its X-1 was on May 12, 1950. Flown by Chuck Yeager it provided camera footage for the John Wayne film Jet Pilot, and from there it was offered to the NACA. But it never flew again and was retired to the National Air and Space Museum in Washington DC where it occupies pride of place today. In total, X-1 46-062 had made 59 air force glide and powered flights, 35 of them with Chuck Yeager at the controls. In joining with

the Wright Flyer in the nation’s capital it represented an extraordinary period in which aircraft engineering evolved from the first powered flight, at little more than running pace, to rocket flight through the sound barrier in less than 44 years. Research involving hard pitch movements was crucial in understanding how to control these rocket planes at transonic and supersonic speed and from tests conducted with the NACA aircraft, during the second half of 1950 and the first half of 1951, the effectiveness of the moving stabiliser became apparent. ➤

Initially, the Skyrocket had the conformal cockpit canopy of the first-generation X-1. Douglas

ROCKETPLANES 77

Up-ship! The converted B-29 motherplane is raised on hydraulic rams to admit the No 2 D-558-II, this one equipped solely with a rocket engine, the aircraft which would be the first through Mach 2. NASA

The research carried out by Champine was particularly successful and helped feed information to the design teams working on supersonic fighter projects, especially with the all-moving tail-plane. As early as February 1949, North American Aviation had started design work on its Sabre 45 concept, a thinwing supersonic fighter with a thin wing swept back at 45º and with an all-moving tail. It would be known as the F-100 Super Sabre and during its first flight on May 25, 1953, it became the first fighter in the world to go supersonic in level flight. But, while the No. 2 aircraft (46-063) continued to research the flight environment, what of the No. 3 aircraft (46-064) which had been built at the same time as the first two? Painfully delayed for several years by the inability of the rocket engine manufacturer to produce a safe and reliable turbopump to handle the propellants, it did represent a major technical development and paid the price by remaining grounded while the engineers worked to fix its foibles. For three years it languished as the ‘hangar queen’, before finally it was delivered to Edwards AFB in April 1951. Albert Scott Crossfield (always known as Scott Crossfield), a pilot whose name would be synonymous with the X-15, made his first checkout flight in the No. 2 X-1 on April 20, 1951, reaching a speed of Mach 1.07 (706mph). Crossfield made nine more flights before the NACA aircraft was retired after 78 ROCKETPLANES

completing clean stalls, performing pull-ups, measuring wing loads and testing aileron effectiveness over a variety of flight conditions. But Crossfield had his moments. On the first flight he experienced the problems caused by inadequate data informing well-intentioned engineers. As usual, ground crew had set the horizontal stabiliser for the relevant flight plan but on this occasion 1º higher than usual. After dropping away from the mothership, the

X-1 went into a vertical pitch, stalled and rolled over on to its back. Recovering, Crossfield stabilised the aircraft, lit the four rocket chambers and completed the preplanned flight plan. On the way down the windscreen frosted over and Crossfield had to remove the sock from his right foot and wipe a clear patch large enough to see through, talking with the chase pilots all the while to safely make it back to the ground. Carefully does it! Technicians move the Skyrocket into position beneath the converted B-29, operating as NACA-137.

The decision to retire the X-1 was forced upon the NACA by circumstances. In May a new engine had been ordered for the aircraft after a malfunction and when it rejoined the flight programme it began a series of research flights on wing loads and aileron effectiveness. But the No. 3 aircraft had at last joined the programme with a glide test on July 20 piloted by Joe Cannon. With its new turbopump, the thin wing of the No. 1 aircraft and larger propellant capacity made possible by the elimination of pressurising tanks, calculations indicated it should be capable of running all the way to Mach 2.44 (1612mph) at 70,000ft. Much had been anticipated for this aircraft and a flight was scheduled for November 9 to check out the operation of the hydrogen peroxide turbopump system and to rehearse jettisoning procedures during a one hour captive flight. The jettisoning of the propellants had to be aborted when the nitrogen lost pressure due to Cannon mistakenly throwing switches in the X-1 cockpit to jettison the alcohol fuel. Not all of it was lost, however, and the decision was made to return to Edwards, land and remove the fluids from respective tanks. After the B-50 and its still attached X-1 had taxied to the loading area, Cannon went down into the X-1 cockpit to manage switches for purging the tanks. As the pressure began to build in the propellant tanks there was a sudden and unexpected thud, with a wisp of white vapour followed by a loud explosion and yellow flames producing black smoke. A succession of cascading explosions ripped through the X1 and began to engulf the wing of the B-50 as Cannon made his way back into the mothership and out. Crawling through liquid oxygen at supercold temperatures Cannon got freeze burns on his hands and knees producing scars which he carried for life. The No. 3 aircraft was totally destroyed and the B-50 was written off and scrapped. Only several years later was the cause discovered to be decomposition of leather Ulmer gaskets, a product of aging and chemical combustion.

The cockpit displays and flight controls for the D-558-II Skyrocket with Mach-meter (top centre) and propellant pressurisation dials (right). NASA

The last flight made by the X-1 took place on October 23, 1951, when Joe Walker made his second flight in two months on the type and brought the programme to a close but even that had its drama when two rocket chambers failed to ignite and the landing had to be made without flaps when they failed to deploy. In the previous months inspection by Bell engineers proved that the rocket plane was well past its operational life. The fuel tank was rusting badly inside and the multiple nitrogen pressurisation spheres were deteriorating. Moreover, the batteries were leaking acid into the lower fuselage and the structural frame of the aircraft was in urgent need of repair. In all, the NACA had made 54 flights with its X-1, the second aircraft delivered, and while it had lost the No. 3 aircraft in the ground explosion on November 9, 1951, before any powered flights could take place, the second generation X-1s were expected on the ramp soon enough to maintain continuity of research. And the air force too expected to gain from the second-generation rocket ships on order as well as the X-2.

Engineers fitted a wing chord extension to the D-558-II in attempts to improve lateral handling at transonic speed. NASA

The Douglas rockeT plane

For several years the US Navy had been working up toward its own rocket plane research flights, via the jet powered Douglas D-558-1. As early as August 1945 the idea for a rocket powered version of the subsonic Skystreak was discussed with Douglas. When the Naval Technical Mission in Europe reported back in May 1945 about the work the Germans had done on swept-wing research, the NACA saw in the D-558-1 the means of providing a swept-wing variant of an existing aircraft. In this way, by taking an existing airframe designed for transonic flight it could make the transition to a rocket powered research aircraft for supersonic flight. Douglas engineers fixed initially on a 4000lb thrust rocket motor which could fire for two minutes and first considered a sweptwing version of the D-558-1. But the NACA approved a plan to install the rocket motor as a supplement to the existing jet engine, which would be used for takeoff and landing. But the fuselage of the Skystreak was not big enough for both powerplants. It would require a complete redesign of the fuselage and, with a new wing that demanded a completely new aircraft. Douglas got approval to design what would become the D-558-2 Skyrocket on January 29, 1946. Douglas lost little time in getting a mock-up ready for inspection, which was looked over by the NACA and the navy, who was sharing the development cost, on March 18-19. On January 27, 1947, the navy issued a contract substituting three D-558-2 Skyrocket aircraft for the last three of six D558-1 Skystreaks. The design team was led by aerodynamicist Kerwin E Van Every and managed by Ed Heinemann, one of the iconic figures of early naval jet fighter design and who would take many laurels before finishing his career. The new fuselage was larger and longer than that for the transonic Skystreak and contained a more powerful rocket motor than had been planned. ➤ ROCKETPLANES 79

The Douglas Skyrocket with its motherplane, a converted US Navy Boeing P2B-1S. NASA

The essential design philosophy for the rocket plane was that it should retain as many of the low-speed handling characteristics of the Skystreak but that the intakes would be in the side and not in the nose, as with the D-558-1. At first, Every proposed a blended cockpit canopy like the X-1 but this was changed to a conventional V-shaped windshield affording greatly improved visibility. The Reaction Motors A6000C4 fourchamber rocket motor was identical to that used in the X-1, except that the Navy redesignated it the XLR-8-RM-5; it would produce the same thrust output of 6000lb. The TG-180 turbojet used in the Skystreak was replaced with the 3000lb thrust Westinghouse J34-WE-40 turbojet engine, installed in the centre section with air intakes blended into either side of the fuselage. The exhaust from the jet engine passed out through a ventral pipe in the rear, canted slightly downwards. Lacking aerodynamic data which would shift design preference toward a wing/fuselage fillet blending the two structures, the wing carried straight through into the circular cross section fuselage. Two tanks located above the wing centre section contained 250 gallons of gasoline jet 80 ROCKETPLANES

fuel, not kerosene. For the rocket motor a single 180 gallon LOX tank was situated in the forward section of the fuselage above the intake ducts with a 195 gallon alcohol tank above the jet pipe in the rear. There was an 11 gallon tank of hydrogen peroxide for a turbopump together with seven helium tanks for pre-pressurising the propellant tanks and the peroxide tank. The precise location and distribution of tanks was based on the desirability of maintaining the centre of gravity under most flight conditions. The turbopump was a first choice for Douglas, unlike Bell whose efforts to develop and install this weight-saving method of propellant tank pressurisation were fraught with delays and disaster. The Skyrocket was a sleek, well contoured design with a wing sweep of 35º and a tail sweep of 40º. Unusually, the wing had a thickness/chord ratio of 10% at the root and 12% at the tip and the leading edge was fitted with Handley Page slats in addition to fences. Douglas adopted the NACA 63-series aerofoil section for the Skyrocket which retained good slow speed handling and slow stall numbers but retained high-speed qualities. The wing area was increased on the sweptwing Skyrocket to retain the same stall speed

as the Skystreak. The sweep of the horizontal stabiliser was selected so as to optimise the tail stall and flow with the same 63-010 aerofoil section as the wing. The horizontal stabiliser was set high on the vertical tail to prevent interference from the wing wake. The design load was lowered from 18G for the Skystreak, Douglas opting for a 12G load factor at 11,250lb weight and 7.3G at 13,500lb. Like the D-558-1, the Skyrocket was designed for Mach 1 at sea level, unlike the X-1. Both external shape and design considerations were much closer to potentially operational aircraft than the X-1 and Douglas retained the tricycle landing gear of the Skystreak. The structure of the Skyrocket was of semi-monocoque design with aluminium frames covered with heavygauge magnesium sheet. The wings and tail surfaces were of aluminium skin and stringer construction, controlled by a wheel in the cockpit. Like the Skystreak, the Skyrocket had no aerobalances, power boost or tabs on the ailerons, elevators or rudder. The same instrumentation which Douglas had developed for the Skystreak was retained for flight research with the Skyrocket. Known as the 30-channel Miller oscillograph it was

Pilots for the mothership and the rocketplanes. Standing: Payne, Butchart and Walker; squatting: Litleton and Moise.

coupled to 904 strain gauges at various locations across the wings, far greater than with the Skystreak. Altogether, the Skyrocket had four miles of instrumentation wiring and three miles of pressure tubing across the wing and tail surfaces. It also had 400 pressure cavities in the wing and tail surfaces for measuring pressure distribution. The Miller instrument package handling these measurements was installed in the upper part of the forward fuselage. Even when the unmodified mock-up was shown to the customers in March 1946, the aircraft made a great impression with its sleek and streamlined appearance, looking more like an aircraft than a bullet and possessing a long aerodynamic instrument boom projecting forward from the nose of the aerodynamically shaped fuselage. Its gloss white finish too embodied speed and reflected light in a way the original orange colour of the X-1 had not achieved. Walter Williams had passed information to Douglas to the effect that the orange colour made it difficult to identify the X-1 in flight and that white was a visually preferable colour, as well as being, quite incidentally, aesthetically more attractive.

The ride of The SkyrockeT

The three Skyrockets had been given navy serials, known as Bureau of Aeronautics (BuAer) numbers: 37973, 37974 and 37975. The first of these was finished in November 1947 but without a rocket motor. Douglas wanted to hold back installation to the second aircraft so as to complete ground tests, while the navy got on with flying the aircraft on its turbojet engine alone. The X-1 had just pushed through the sound barrier and there was a wide range of research proposals for flight tests under consideration, a considerable amount of research activity to which the Skyrocket would be assigned, even without its rocket motor. The urgency to get the Skyrocket in the test programme, and to have it flying with a rocket motor to push it beyond the sound barrier, was impressed upon the navy team when George Welch flew an Air Force F-86A Sabre fighter jet through Mach 1 in a shallow dive on April 26, 1948. The swept-wing fighter had become the third aircraft, after the two X-1 rocket planes, to go through Mach 1. But the Skyrocket, with its swept wing planform, would carry up to 1100lb of scientific instrumentation. It

would fly far faster than the F-86 Sabre in pressing ahead of the new generation of jets with meticulous measurement of the aerodynamic environment of supersonic flight, exposing the pitfalls which lay ahead. Information which was becoming urgent, if not vital, to the numerous design teams all wanting to produce the ultimate fighter jet. Powered only by its Westinghouse jet engine, the first Skyrocket took to the air on February 4, 1948, but underpowered and denied its potential the aircraft was sluggish and limited to a top speed of Mach 0.9. To improve matters, Douglas fitted JATO – Jet Assisted TakeOff packs which were in fact solid propellant rockets – to the sides of the fuselage to assist it into the air. While flight trials were progressing a few design problems emerged, including the need for better visibility, accommodated by a raised cockpit, and a slightly taller tail. During this period Douglas was finishing up assembly of the second aircraft, albeit without its rocket motor, and it was flown for the first time by Gene May on November 2, 1948. It was handed over to the NACA on December 1. Problems with the engine on the No. 2 aircraft prevented the NACA from getting it into the air for flight research before May 24, 1949, when it began to investigate a long ➤ ROCKETPLANES 81

Test pilot Scott Crossfield (centre, white shirt) leans forward to examine the leading edge of the Douglas Skyrocket as it is prepared for flight – a process requiring several hours of meticulous care. NASA

suspected flaw in swept-wing aircraft, that of longitudinal instability. Severe and violent pitch-up motion and unpredictable sideways yaw and roll responses warned of potential catastrophes avoided only by rapid responses from the pilot and a lot of head scratching among aerodynamicists and engineers. Meanwhile, the third Skyrocket had been rolled out fully equipped with its rocket motor and it made its first flight on January 8, 1949, again with Gene May in the cockpit. With rocket motor installed the top speed was Mach 0.99 at 20,000ft but at 40,000ft it was calculated to be capable of attaining Mach 1.08. On June 24, 1949, it flew through the sound barrier for the first time with May noting that it was the smoothest flight he had ever known. But the potential of the Skyrocket could not be realised until it had been converted for air-drop launch without having to take off from the ground, for that was a hazardous endeavour in itself, but the NACA wanted to acquire some flight data on rocket power before making that decision. Like the first Skyrocket, to get into the air the second aircraft was also equipped with JATO, all the more essential with not only a full pair of gasoline tanks for the jet engine but LOX and alcohol propellants for the rocket motor too. Getting the Skyrocket into the air under these conditions was an extremely hazardous affair. At first the fully fuelled, and heavy, aircraft began its take-off roll on jet power alone, then two of the four rocket chambers were ignited followed by the four JATO bottles. In this bizarre configuration did the No. 2 Skyrocket become the first aircraft to fly with six rocket motors in full bore plus a turbojet at full throttle! With air-drop launch the Skyrocket would save precious rocket propellant used during take-off and in addition would have the advantage of its inertial speed as it separated from the mother-ship. Furthermore, by removing the jet engine altogether and adding 82 ROCKETPLANES

additional rocket propellant, Douglas calculated that the thus modified Skyrocket could reach Mach 1.6. This would place it in the same speed band as the straight-wing X-1 and allow it to evaluate swept-wing performance in time to feed this in to the X-2 programme, which sought a truly supersonic capability. With flight data in hand, when the second aircraft was returned to Douglas in January 1950 to have its rocket motor installed, the decision was made to convert it for air-drop operations. By 1950 the NACA had built two large slotted-throat wind tunnels, one capable of testing to Mach 1.08, the other to Mach 1.15. Results from the two X-1 aircraft had proven the worth of building simulators and wind tunnels capable of taking research to the next level. The X-aircraft had been necessary because the ground facilities did not exist and it was better to build rocket planes which could provide early data sufficient to provide the remedy: transonic and eventually supersonic wind tunnels to play a key part in helping design much faster rocket planes to carry out the next level of research.

Without its Westinghouse J-34-WE-40 turbojet, the modified No. 2 Skyrocket had two tanks each for 345 gallons of liquid oxygen and 378 gallons of the alcohol-water mixture to power its single Reaction Motors LR-8-RM-2 rocket motor which would deliver a thrust of 6000lb. Technicians smoothed over the two jet air inlets, now no longer required, with flush panels and removed the jet tail pipe. When it returned to Edwards on November 8, 1950, the hybrid turbojet/rocket-powered No. 3 Skyrocket had already completed four airlaunched flights, the first on September 8. All were successful and demonstrated that the swept-wing research aircraft could, like the X-1, be dropped for high-speed runs. Two more air-drops were flown, all six piloted by Bill Bridgeman, before Douglas handed it over to the NACA High Speed Flight Research Station at Edwards on December 15.

Below: During the final stages of flight preparation technicians attend the Skyrocket as it vents liquid oxygen.

Fertile Myrtle!

The two Skyrockets were air-launched by a Boeing B-29A acquired from the Air Force, the Navy redesignating the former bomber as the P2B-1S (number 84029). To Douglas ground crew preparing the adapted Superfortress for its bulbous baby in the converted cargo bay, and to NACA technicians at Edwards, the aircraft was affectionately known as Fertile Myrtle. Test pilot George Jansen was assigned to fly the mother-plane, a volunteer and formed crop duster who had flown B-24 Liberators during the Second World War. On one raid he had wrestled the giant bomber down to chimney height during a daredevil raid on the Ploesti oil refinery over Rumania. His job was to knock out a specific boilerhouse in the maze of machinery fuelling Nazi Germany and he did it. No-one doubted he was perfect for the Skyrocket role! But Skyrocket pilot Bill Bridgeman was no slouch either. Tired of plying the empty airways between Pearl Harbor and Australia in the first 18 months of the Second World War, he mysteriously acquired stomach ulcers, treatment for which was followed by him being mandatorily recycled back for other duties.

Equally mysteriously, Bridgeman was assigned to a combat squadron and flew Consolidated PB4Y Liberators on anti-shipping strikes all across the Pacific Ocean, achieving the rank of lieutenant commander and getting two DFCs, four Air Medals and a Purple Heart. Most mysterious of all, he never got ulcers again! But when the war ended he wound up as a civil airline pilot – until one day he had had enough of driving trucks around the sky and went to work for Douglas as a test pilot. Attempts to get the No. 2 rocket-powered Skyrocket to a successful air-drop were frustrated by poor weather and minor technical problems but that was finally achieved on January 26, 1951, although not without its drama. After entering the cramped cockpit, Bridgeman began powering up the equipment and noticed that fuel pressure was falling off and barked a “No drop – this an abort!” into the microphone. But Myrtle’s pilot George Jansen was unable to hear Bridgeman, his finger firmly pressed on the ‘transmit’ button as he counted down to the drop. Frantically, Bridgeman prepared the Skyrocket for flight, realising that if he dropped from the B-29A and only lit up with one fuel tank, the offset centre of gravity

would spin his aircraft out of control. As he fell away, and Jansen finally took his finger off the transmit button, Bridgeman hit the first rocket switch and felt the surge of acceleration pushing him back into the metal seat. The other chambers ignited as they should and the Skyrocket soared upward before flipping into a ‘Dutch roll’ – a continuous yawing and rolling motion – above Mach 1, surprising the pilot. Finally reaching Mach 1.28 at 38,890ft, he ran out of fuel and began the long glide back down to the lakebed. Thereafter, the Skyrocket was equipped with an electrical hook-up to the mother-plane so the pilot could indicate with a green light when everything was ready for the drop. Which was just as well as the next four drop attempts resulting in a wave-off due to problems in the final few seconds. One flight ended when Bridgeman could not dump all the rocket fuel and oxidiser and Jansen had to land the overweight combination overladen with explosive propellants. On a successful drop on April 5, 1951, Bridgeman experienced wild oscillations causing him to shut off the motor but not before hitting Mach 1.36 at 45,600ft. Rocket flight was never going to be easy. ➤

The all-rocket powered No 2 D-558-II accompanied by its F-86A chase plane descending from a powered flight. NASA

ROCKETPLANES 83

The Skyrocket executes a perfect free drop from the bomb bay of the converted B-29 motherplane. NASA

Above: Skyrocket pilot Joe Walker (left) chats with Butchart and Jones prior to a test flight. Right: New shapes at Edwards, courtesy of Douglas: the X-3 (foreground) conducted research into thin-wing flight; the F4D-1 Skyray was developed for the Navy using the aerodynamic theories of Alexander Lippisch who designed the Me-163; the Skystreak (left) and the Skyrocket. NASA

But things got better and the rocket plane nudged ever higher in altitude and speed. To keep external temperatures within reasonable limits, the No. 2 aircraft was taken to 62,000ft for a high-speed run, touching Mach 1.72 on May 18. At 1130mph, at the time it was the fastest aircraft in the world. Less than a month later Bridgeman nudged it up to Mach 1.789 at 64,000ft – 1180mph – but these two flights revealed an oscillation which, while controllable, did cause worrying concern. Nobody quite knew why it was happening and that in itself was worrying but to find out they suggested that instead of nosing very gently into level flight if Bridgeman pushed over hard it might reduce the G-loading and increase acceleration, wiping out the effect. On June 23, Bridgeman did just that and nearly lost his life. After igniting all four rocket chambers and barrelling up to 60,000ft he pushed over but as the Mach needle hit 1.5 the Skyrocket bucked wildly, throwing Bridgeman against the sides of the cockpit. With the roll rate approaching 90º a second, he used the ailerons to regain control and that only made it worse. With the gyrations getting wilder Bridgeman decided to shut off the rocket motor with almost a minute still left in the tanks. This too only seemed to make the bucking worse with the gyrations preventing Bridgeman turning back toward the lake in what was now a plummeting glider heading in the opposite direction. ➤ 86 ROCKETPLANES

ROCKETPLANES 87

Cleaned up and ready to go, the Douglas Skyrocket displays its clean lines and high fineness ratio (ratio of of body length to diameter). NASA

Running out of all other options, Bridgeman pulled a heaving 4G pull-out by hauling on the stick and the rocket ship started to climb again, the ride smoothing out with decreasing speed. Finally under control, he turned for home and rejoined the F-86 chase-plane from a roller-coaster ride that had seen him hit Mach 1.85, around 1220mph. Never again would a Skyrocket pilot attempt a hard pushover to level flight, and on the next flight on August 7 Bridgeman hit Mach 1.88 – 1260mph – at 67,000ft. Only one more flight remained before Douglas would hand over the No. 2 Skyrocket to NACA and for this Bridgeman was cleared for an altitude shot which had been cleared by Charles Pettingall, the chief aerodynamicist for Douglas. Both men knew the significance of this last industry flight before the NACA took it over. Skyrocket was already the fastest plane in the world having out-flown the Bell X1, now it could also become the aircraft to reach heights no other aircraft had attained. The flight was made on August 15, 1951, and shortly after Jansen dropped the diminutive rocket ship, Bridgeman lit the burners and roared toward the blackness of space, accelerating to a maximum Mach 1.35 and going for height. At 63,000ft the Skyrocket began a slow roll to the left but still it kept on climbing, ever higher as Bridgeman used the aileron to restore level flight. 88 ROCKETPLANES

Still climbing when it ran out of gas, the soaring rocket ship, silent now, reached the peak of its climb and started back down from a place where Bridgeman said he saw “a vast relief map” beneath him, with “papier-mache mountains and mirrored lakes and seas”. On the ground, radar tracked the tiny dot and when Bridgeman returned to land he was told that he was not only the fastest man on Earth but the one pilot who had climbed higher in the sky than any other had ever done – 79,494ft.

On August 31, 1951, the No. 2 Skyrocket was handed over to the Government and the NACA would now make a bid for the next big prize – Mach 2, twice the speed of sound, a number Bridgeman had himself come close to achieving but which would await another day and another pilot. Perhaps, in fact, for another rocket plane altogether for the air force and its industry partner Bell Aircraft had not exactly given up on achieving that record themselves. ■

The Skyrocket was unique in that it matured out of a jet-powered research type and proved flexible to changing requirements. Note the absence of wing fences seen on the aircraft above.

Destined for a desert graveyard, the Bell X-1A was the first of the second generation to make it into flight, a significant upgrade on the three X-1s. NASA

Pushing the

edge

With the Air Force having already achieved supersonic flight and a new generation of X-planes on the way, it was time to push higher and faster – with Mach 2 as the next prize.

J

ust one calendar month after ‘Chuck’ Yeager blasted the sound barrier, on November 14, 1947, the US Air Force had ordered four more X-1 rocket ships from Bell Aircraft. They wanted a better high-speed/high-altitude test plane and Bell came up with the Model 58, which would bear the Air Force designation MX-984. The new ships would be designated X-1A, B and -D. There were to have been four derivatives but the Bell 1-C was cancelled before the contract was awarded on April 2, 1948. These aircraft were specifically designed to push through Mach 2 and beyond using advances in technology from developments with the three original X-1 aircraft and improvements brought about through the challenging new environment where they would operate.

Whereas the X-1 had been designed with a single purpose in mind – to prove that an aircraft could safely fly through and beyond the sound barrier – the four successor types would measure the ‘heat barrier’, so called because the temperature would reach levels at the limit of materials used to fabricate the outer skin. Beyond Mach 2 the kinetic energy of the vehicle causing friction with air molecules would raise the temperature beyond anything experienced by powered aircraft to this time. The air force also wanted to test new means of controlling an aircraft at high altitude where atmospheric density was so low that pressure on the flying control surfaces – ailerons, elevators and rudder – would be so low as to render them useless. At extreme heights the aircraft would start

to float around and be uncontrollable until it descended to a denser part of the atmosphere where, if it was not in the proper orientation, it could break apart. To maintain control in this air, the new X-1s would carry pilot-induced reaction thrusters operating like tiny rockets to substitute for the conventional control surfaces for stabilising pitch, roll and yaw. Only in this way could the pilot maintain control of the aircraft in very thin air. The three new X-ships were noticeably different to the original X-1, the most visible feature being the stepped windscreen canopy, which was hinged for pilot ingress and egress, replacing the conformal canopy and sidehatch access with the earlier type. They were also longer so that larger propellant tanks could be fitted but the ➤ ROCKETPLANES 89

Chuck Yeager transfers down into the bomb bay of the motherplane before squirming into the cramped cockpit of the X-1A. NASA

stretch was limited by the restrictions of the bomb-bay in the mothership which allowed only a 4.5ft extension in fuselage length, extending this to 35.55ft. With the new cockpit adopting a more conventional design, the pilot would climb in to the aircraft from above and while it was protected from the slipstream. He would have a better means of escape by opening the canopy and moving up into the adapted bomb-

Angled for a deflective shot, the X-1A ejection seat is given a live ground test.

90 ROCKETPLANES

bay rather than clambering through the side hatch and up a ladder into the mother-plane. The first X-1 design had been ultraconservative in its approach, uncompromising in replicating the shape of a bullet and devoid of any unnecessary protrusion. The ejection seat, only installed after initial flight tests, was standard and the pilot had a conventional control stick rather than the H-shaped control yoke of the X-1.

The NACA 65-108 aerofoil section fitted to the first and third X-1 was standard on all four derivatives and elevator and rudder were identical. The ailerons were of 3.21sq ft each compared with 3.15sq ft for the earlier X-1s but the flap area was reduced from 11.6sq ft to 11.46sq ft. The flight control system was unchanged and unboosted, with the horizontal tail adjustable in pitch from the cockpit. Both ailerons and elevators were dynamically balanced and the conventional rudder was a direct carry-over from the original series. Construction benefitted from experience with the three original X-1s and while retaining the comparatively simple manufacturing choices and layout configuration they did incorporate changes recommended by engineers and technicians working the flight line. These changes allowed better access to panels and inspection hatches and were a general improvement to ease maintenance and reduce time between flights. All six X-1 types were test aircraft and needed frequent attention, to install or remove instrumentation and associated plumbing and wiring connecting sensors to signals boxes. These jobs were not easily achieved with the original three aircraft.

Maj Arthur Murray, USAF, demonstrates the new full pressure suit for high-altitude tests as he poses by the side of the X-1A. NASA

Power for the derivatives came from the same XLR-11-RM-5 (Model E6000C4) rocket motor which powered the #3 X-1 and consisted of four identical chambers to produce a total thrust of 6000lb. Midway through its flight test programme, the X-1B was refitted with an XLR-11-RM-9, the only difference being in its low-tension interrupter ignition system rather than the high-tension igniter in earlier variants. Like the #3 X-1, the new variants had a turbopump for propellant delivery, but with 37 gallons of hydrogen peroxide versus 31 gallons. Thrust was not the limiting factor in X-1 speed or altitude. Extending the duration of the burn was key to that, so to achieve higher performance the larger propellant tanks held increased quantities of oxidiser and fuel: 500 gallons of liquid oxygen and 570 gallons of diluted ethyl alcohol. Combined, this was an increase of 14.1% over the propellant capacity of the original X-1 series. These gave the motor a burn duration of 4.65 minutes and the new X-1s a theoretical top speed of Mach 2.47 (1635mph) at 70,000ft. The derivative X-1 had an empty weight of 7266lb, a launch weight of around 16,487lb (up 12% on the original type) and a landing weight of 7266lb. A clear objective was not only to study the behaviour of rocket-powered aircraft at high

“A cleAr objective wAs not crAsh And burn – twice only to study the behAviour The spread of research tasks singled out for of rocket-powered AircrAft the three new X-1 derivatives was written the contract was awarded. The X-1A but Also the physiologicAl when (serial number 48-1384) and the X-1B (48reActions of A pilot.” 1385) would be used for dynamic stability and speed and extreme altitude but also to study the physiological reactions of a pilot to these unprecedented flying conditions. The X-1 series were specifically designed with the technical and engineering performance of the machine in mind. However, as design engineers worked to match increasingly complex jet powered combat aircraft to the environment in which they would be flying, pilot performance was an unknown area. The reaction of combat pilots to these conditions was just as important. There was an added motivation. With an independent air force formed in 1947, there was a growing belief that the job of flying into space using winged rocket-powered aircraft was down to them. How pilots reacted, and how well they could control aircraft in the same way that they had muscled proppowered fighters around the skies during the Second World War, was all part of the knowledge base to inform a new generation of fighter jocks.

load testing while the X-1D (48-1386) would conduct research into heat transfer, measuring both the load (the total amount of heat absorbed by the airframe) and the heat rate (the peaks and troughs of when the heat built up and dissipated). This was crucial to understanding how materials used for the manufacture of supersonic combat aircraft would be affected by different flight regimes. Previously, in the piston era, only engine components and structural elements were affected by extremes of temperature. Now the airframe itself would be manufactured from a new generation of heat-tolerant materials and the X-series were flown to map those affects at different speeds and altitudes. The ability of the pilot to function in these conditions required special protective clothing and a new study of aerospace medicine grew alongside the technical requirements of the aircraft. The ability of the X-1 to contribute to the new generation of aircraft influenced the ➤ ROCKETPLANES 91

The X-1A coming in on finals attended by the ever-watchful F-86A chase plane. NASA

studies conducted by the air force, the NACA and the manufacturers. Plane-makers were to be given access to these test results to inform their design decisions and choice of materials. Industry was already catching up with test aircraft such as the X-1 and the Skyrocket. North American, famous already for its F86 Sabre, had begun design work on a supersonic successor, the F-100 Super Sabre. Work on this project began in February 1949 with company funds and at the instigation of Ray Rice and Ed Schmued, when it was known as the Sabre 45 – for the sweep angle in degrees of the wing leading edge. Weapons testing at high speed was a new science as well and at first the air force thought that it could use these rocket powered research aircraft to develop both the weapons and the techniques for high-speed combat. Originally the cancelled X-1C was to have been used for testing weapons and fire-control systems at high speed. But the idea was made redundant by the more sensible decision to use jet fighters, then coming on line, to do this work, since the effects and the operating procedures would be specific to aircraft uniquely designed to carry weapons. 92 ROCKETPLANES

“There was an eagerness To challenge The navy,which was keen To be The firsT Through Mach 2.” Within a year of getting the contract, Bell had a full-scale mock-up of the secondgeneration X-1 series ready for inspection by the air force. It passed with flying colours and only a few changes were recommended. By the end of 1950 the first of these, the X1D, was almost complete. The design team had been led by Robert Frost and following a near flawless checkout and inspection, an EB50 mother-plane (47-006A) carried it to Edwards Air Force Base ready for testing. The X-1D was carried into the air on July 24, 1951, for a glide flight to test its handling qualities. Bell’s chief test pilot Skip Ziegler was at the controls. The flight went well following the air-drop and a nine minute glide down to Rogers Dry Lake as the pilot evaluated its low-speed handling qualities. On touchdown the nose leg collapsed and the X-1D slid for more than 1000ft before

grinding to a stop on the underside of its nose. Bent metal and a smashed nose leg had to be replaced and for several weeks Bell worked feverishly to get the aircraft back in the air for a powered run. There was an eagerness to challenge the navy, which was keen to be the first through Mach 2 and had its Skyrocket primed to accomplish that. The competition was hotting up. On August 7 Douglas set a record of Mach 1.88 with the No. 2 Skyrocket and eight days later achieved a record altitude of 79,494ft. The elusive Mach 2 was getting closer. The newly independent air force was still a member of the US armed forces and the fight for funding depended on performance. The navy was battling the air force for the major strategic role of nuclear attack, seeing its carrier force as the instrument of retribution in the event of a Pearl Harbor-style attack and wanted to display a preparedness for that. A bitter and acrimonious conflict between the air force and the navy had broken out over two hugely expensive programmes: the giant B-36 hemispheric bomber and the proposed giant super-carrier.

The government could not afford both and the air force got the B-36. The navy never forgave it and pushed hard to demonstrate pre-eminence in combat aircraft, deployed anywhere in the world on its already capable flat-top fleet. Research flights with the Skyrocket attracted useful publicity. But the air force knew that it too had to stay ahead for maximum publicity surrounding its claim to get the biggest slice of the national defence budget. So it was with some degree of urgency that Bell reworked the X-1D following its inglorious landing. On August 22, 1951, just one week after the navy Skyrocket shot to its record altitude, the air force got the X-1D back in the air under the converted bomb bay of the EB-50A. Frank Everest was the pilot and as the combination chugged its way ever higher into the California sky, at 7000ft he worked his way down and in to the cramped cockpit of the tiny bullet-shaped rocket ship. Instrument checks and pressure gauge readings occupied his immediate attention but something caught his eye. The nitrogen pressure was falling and had gone from 4800 psi to 1500psi. Bottled nitrogen was used to operate the fuel tank regulators, the flaps and the landing gear, without which those elements could not work. Everest made his way out of the cockpit and back up into the mother ship were he set about discussing the problem with Jack Ridley and Wendell Moore. Moore was from Bell and knew about these things. There was no way they could do anything about the pressure drop with the aircraft still attached and the combination airborne. Nothing for it but to get back down on the ground and rectify the problem ready for another shot. Everest climbed back down into the cockpit to jettison the propellant from the fuel and oxidiser tanks in the rocket ship. You would not want to run the risk of a landing with all that rocket fuel on board. Everest slowly opened the pressurisation valve and then closed it to check the oxygen tank gauge working. Reassuring himself that it was working correctly, Everest reopened the pressurisation valve to bring it up to 46psi so that it would force the unwanted liquid oxygen out into the atmosphere. At that instance there was a loud explosion which rocked the X-1D and the mothership too. In an instant, Everest looked back to see flames engulfing the bomb bay of the EB-50A and heard Gust Askounis in a chase plane scream into his intercom “Pete! Drop her, drop her! She’s on fire!” As Everest lunged bodily upward and flung himself into the bomb bay he knocked down Jack Ridley who was a split second away from pulling the emergency jettison handle which, had he done so would have killed all on board. The lock pins holding the shackles gripping the rocket plane were still in place and if that handle had been pulled it would have jammed the X-1 against its restraints. Realising his error, Ridley pulled the normal release handle instead and the X-1D fell away, a

Some studies were made of giving the X-1 a swept-back wing with tests of a model at the Langley Research Laboratory.

“EvErEst lookEd back to sEE flamEs Engulfing thE bomb bay and hEard gust askounis scrEam into his intErcom ‘PEtE! droP hEr, droP hEr! shE’s on firE’!”

The X-1A displays a bare aluminium skin to evaluate thermal emissivity across the liquid oxygen tank. NASA

burning torch all the way down to the desert floor. Recovering their composure, the bomber crew confirmed their safe situation to the chase planes as well as the ground and made a landing back on the runway at Edwards. Scratch one very much needed second generation X-1. A review board initially judged that a stray electrical signal had ignited a fuelair mixture causing a fire which engulfed the rocket plane. Later it would become known that there was another, more insidious reason for the fire, but more on that later. While technicians, engineers and air crew were recovering from the near fatal accident, the third X-1 was prepared for a possible

attempt on Mach 2 and on November 9, less than 12 weeks after the loss of the X-1D, it was carried aloft by the same EB-50D which had narrowly escaped destruction. The flight was a precursor to the speed attempt by testing the jettison system. Fully loaded with fuel and oxidiser, the X-1 was a captive bomb and the pilot, Joseph Cannon, tested the hydrogen peroxide jettison procedure using distilled water as a substitute for this test. Again a gremlin struck and as nitrogen pressure fell, as it had with the X-1D, the attempt was called off. Still fully loaded with propellant, unable to jettison the volatile cocktail due to pressure ➤ ROCKETPLANES 93

Instrumentation checks on the X-1B in the hangar where most of the pre-flight installation of dedicated equipment took place. NASA

loss, the EB-50A made what airline pilots call a “heavy-heavy” approach, greasing the laden mothership gently back down on to the concrete runway. Turning off the landing strip the mothership taxied to the propellant loading area to take on nitrogen to pressurise the tanks and offload the propellant. Suitably topped up, a tow truck hooked up to the bomber’s nose leg and moved it out to the east end of the runway where the oxygen and alcohol propellants could be drained off. There was nothing unusual about the procedure, although fire trucks were on hand as standard practice – just in case. Cannon got aboard the No. 3 X-1 and raised the pressure in the LOX tank. As it got to 42psi there was a very loud but muffled ‘thump’ and Cannon leapt for his life as the X-1 began to hiss and boil, liquid oxygen gradually enveloping the encapsulated rocket ship partly hiding it in a fog. Just as Cannon was out of the cockpit there was a loud explosion which blew him to the ground. As he tried to get up, repeated blasts sent shock waves which held him to the ground. Nearby, and seeing Cannon held 94 ROCKETPLANES

in the grip of these ballooning pressure waves, William Means and Walter Myers ran to get him out of the area around the blazing wreck. Pulled free and saved from serious injury, Cannon was rushed to a medical centre and although burned made a full recovery. The No. 3 X-1 was totally destroyed along with the mother plane. Nobody would be getting close to Mach 2 for a while... and in fact it would be almost two years before that boundary was eventually crossed. And the reason for the explosions? The official answer came when it was discovered that the nitrogen storage bottles were manufactured from 410 stainless steel which has the unpleasant characteristic of failing at low temperatures. The nitrogen was not super-cold but the supply lines were next to the liquid oxygen tanks and those shattered when the tanks was pressurised. To test the reaction of 420 steel to extremely low temperatures, test pilot Scott Crossfield dropped a 1lb weight from 2in on to a bottle of cold nitrogen and it exploded like a bomb.

Trial by flighT and fire

With the loss of the third X-1, the first generation of Bell’s sonic-shattering research planes was gone. The first aircraft had made its last flight on May 12, 1950, and the second on October 23, 1951. The loss of two X-1 aircraft tore up the plan to use the No. 3 X-1 and the new X-1D to conduct advanced flight research activity and changed the way the entire supersonic research programme was conducted. Instead of carrying out specific flight research trials on stability and control tests for the Cornell Aeronautical Laboratory, the new X1A would be seconded into service with the NACA for carrying out tasks previously assigned to the two aircraft now lying in pieces on the hangar floor. But that was some time off. No X-1 aircraft would fly again for more than a year and as 1951 ended the year ahead would be dominated by the Douglas Skyrocket flying routine tests. The No. 2 Skyrocket had been delivered to the NACA’s High Speed Flight Research Station on August 31, 1951, for a preparatory series of four familiarisation and proving flights, Scott Crossfield cruising the swept-

wing research aircraft up to a maximum Mach 1.65 before the annual rains closed the base for flight operations. A fresh package of research tools was added to the increasingly complex business of flight and test with a 36-channel oscillograph being added to the expanding inventory of ground support equipment. Test flights resumed when Crossfield took the Skyrocket into the air on June 13, 1952. It was the first in a sequence which aimed to evaluate the longitudinal stability and control characteristics, wing and tail loads and lift, drag and buffet characteristics at different speeds. Crossfield took the Skyrocket up through Mach 1.36 and was able to pin down the onset of pitching motions resulting from a general loss of longitudinal stability at around Mach 1.2. Not all flights attempts were successful. On one flight the engine malfunctioned and the aircraft failed to achieve its flight Mach target and on another the primary liquid oxygen valve stuck and the powered phase had to be aborted after the drop.

“The miliTary brass wanTed records To wave before Their poliTical masTers responsible for allocaTing funds.” In all, by October 23, 1952, Crossfield had completed a total of 13 drop flights with the No. 2 Skyrocket since its delivery to the NACA and the ship was again grounded by rains until the following March. During the grounded winter and spring months of 1953, engineers planned a meticulous series of flights where Crossfield would study lateral stability and control responses at supersonic speeds and increasingly high Mach numbers. They wanted to hunt down the root cause of the severe rolling oscillations that nearly caused Bridgeman to lose his life in contractor flights during 1951. These methodical and precisely planned research flights were essential to answering questions raised by aircraft designers anxious to obtain as much data as possible on high speed flight. The military brass wanted records to wave before their political masters responsible for allocating funds. And the scientists and engineers were not about to be rushed into record-breaking stunts just to appease public relations personnel raising public awareness campaigns on how well their defence dollars were being spent. To each and every one of those groups there was a new urgency. On June 25, 1950, the communist forces of North Korea, encouraged by China and using weapons supplied by the Russians, invaded the South. Rushed into action on a United Nations mandate, American, British and Commonwealth forces landed on the southern tip of Korea – territory on the brink of falling completely to the communists. By mid-1951 the communist forces had been driven back to the 38th parallel where the fighting would remain until a ceasefire in July 1953 froze hostilities at what would

The X-1B cockpit displays a major change in layout over the original X-1 series, with a conventional stick. Propulsion controls are above flight instrumentation. NASA

thereafter divide North and South Korea – but without a peace treaty. Coming just after the Berlin Blockade of 1948-49, where Russia cut off all ground supplies to the western sector of the city, and with France fighting a defensive action against communist forces in Indo-China, the pressure was on to develop new and effective ways of defeating Russian aircraft in foreign skies. Not much of this was on the minds of engineers and NACA scientists as they plumbed the hidden secrets of supersonic flight but the pressure was on to push ahead with flight research in areas where exotic and futuristic combat aircraft could dominate the skies over battlefields and across enemy air space. Basic, fundamental research was essential to achieving that capability. The darkening skies across a world divided ideologically, becoming increasingly violent and locked in the race for nuclear supremacy ensured that money and resources would continue to flow to the supersonic research projects under way at Edwards Air Force Base. As 1953 dawned a new aircraft arrived at Edwards in the form of the Bell X-1A, air-lifted

across from the manufacturer on January 7. It was to be an eventful year for many different reasons. For several years the air force had been waiting to get this secondgeneration X-1 on the ramp and since the sudden loss of the X-1D 17 months the new arrival was all the more welcome. As indicated earlier, because of the loss of the X-1D the flight programme for the X-1A had been rewritten and it was now in the hands of Bell test pilot Jean Ziegler to put it through its paces before the company handed it over to the air force pilots. Zeigler was an experienced pilot and had already flown other X-series aircraft, notably the X-5, an aircraft with variable geometry wings which would eventually provide data from which General Dynamics would develop the F-111 ‘swing-wing’ fighter-bomber. On January 24 he flew a captive flight on the motherplane and with a full load of rocket propellants took the X-1A on glide flights down to the lake bed on February 14 and 23. The second free flight had been planned as the aircraft’s first under power but a problem with the propellant system converted it into an unpowered descent. ➤ ROCKETPLANES 95

The second-generation X-1 displayed advances including turbopumps for driving propellants into the four-chamber engine and increased fuel capacity facilitated by a 4.5ft increase in the length of fuselage. NASA

The following day Ziegler fired up one of the rocket chambers on the XLR-11 followed by the second and third but he stopped short of igniting the fourth combustion chamber when a fire warning light came on. False alarm. On March 26, Ziegler gave a full four-chamber demonstration of the X-1A’s readiness for flight tests but in two more flights on April 10 and 23 he encountered a low-frequency buzz when approaching Mach 1. On the second of these he shut down the engine and jettisoned remaining fuel when the turbopump went into over-speed. None of the flights exceeded Mach 0.94 and while the aircraft was instrumented for special examination of this phenomena Ziegler returned to Bell’s Buffalo facility to carry out flight tests on other aircraft. The air force would take over flights tests with the X-1A when the X1A was ready to return to the air. In the meantime, another catastrophic event put the entire rocket research programme into high-gear and changed the flight schedules once more. Since 1945 Bell had been working on a completely different rocket research aircraft, the X-2, designed to crack the speed barrier and exceed Mach 3. Eschewing warnings of dire consequences for humans trying to fly faster than the speed of sound, the air force was boldly planning to go where no other pilots had been before. Coming two years prior to the first flight through Mach 1, the decision to press ahead with a much more powerful rocket plane was bold indeed. The story of the X-2 comes later but suffice to say here that it was a fated programme from the outset and the second 96 ROCKETPLANES

aircraft, the first to be delivered, was not ready for captive flight tests from Bell’s Wheatfield facility before July 1951, using EB-50A 46-011 as the motherplane. As Bell’s chief test pilot, Jean Ziegler was the pilot for flights from Edwards Air Force Base after the X-2 arrived with the NACA on April 22, 1952. Starting on June 5 with an initial captive flight followed by a second 10 days later, the first unpowered glide flight occurred on June 27. Although NACA instrumentation had

The three second-generation aircraft had a similar NACA 65-108 aerofoil section with the airframe stressed to 18G.

failed to work, Wright Air Development Center approved the aircraft for powered flights to begin. Ziegler clambered aboard the X-2 as the motherplane climbed through 5000ft with technicians and crew helping strap him in and ready the aircraft for locking down the canopy. Operating without oxygen they had to have that process completed before they reached 10,000ft. The cockpit was very cramped and Ziegler was virtually sitting on the floor, jammed in between side consoles, his legs bent high to

The most distinctive visual recognition feature of the X-1A, X-1B, X-1D and X-1E was the teardrop shaped canopy which afforded the pilot a better view forward and sidewards. NASA

get his feet on the rudder pedals. The mothership levelled off at 31,500ft and 206mph and the X-2 was dropped free to fly on its own for the first time. Ziegler started on the downwind leg at 6500ft and 223mph and raised the trailing edge flaps, decelerating to 210mph before getting in on the landing approach. With the speed down to 183mph he lowered the flaps 28º and began his final approach at 1000ft, greasing the X-2 on to the runway at 142mph, the aircraft supported by two skids lowered from each side of the centre fuselage. It was believed that once contact had been made the aircraft would be stable in pitch and that the pilot could control vertical oscillations. This proved not to be the case and the X-2 slammed its nose wheel down on to the desert strip with an impact deceleration of 3.8G – outside the stress level of the leg. As the aircraft dug grooves in the strip, the nose wheel gouging furrows as it went, Ziegler applied left aileron which caused the X-2 to tip slightly, the port wing making contact with the ground causing the aircraft to slew round. Modifications to get the aircraft back in the air included redesigned skids and a strengthened nose leg, plus some refinements to the landing system with a wider main skid assembly and thin ‘whisker’ skis placed mid-way under each wing to prevent a tip contact on rollout. The second glide flight on October 10, 1952, was flawless and set up the flight schedules for air force test pilot Frank Everest, fresh from the X-1 programme, to pilot the X-2 on a familiarisation flight, which

took place successfully on October 10. During his descent from 30,000ft, Everest carried out pull-ups, stall manoeuvres, ailerons rolls and other test routines. Eight days later the No. 2 X-2 was returned to Wheatfield for the rocket motor to be installed. As related later, the rocket motor for the X-2 had serious problems and delayed the entire project far beyond its original schedule. However, on May 12 the No. 2 X-2, complete with its motor, was finally mated to the EB-50A carrier plane and flown from Bell’s Wheatfield facility toward Lake Ontario where liquid oxygen top-off and propellant jettison procedures were to be tested prior to a powered flight. Ziegler was pilot for these trials which envisaged a series of liquid oxygen topping off systems, LOX and fuel temperature readings and jettison and pressurisation systems. First a 25% propellant load would be used followed by increasingly loading the tanks on successive flights until a 100% loading was applied. Only then would powered flights commence. This first flight was to check initial topping-off procedures whereby the boil-off was compensated by adding additional LOX to the X-2’s oxidiser tank to ensure a completely full capacity at the drop – which of course would not be attempted on this first captive-active flight, defined as a fully mated flight where the X-2 was powered up and ‘actively’ part of the tests. Flying the EB-50A (46-011) were pilot William Leyshon and co-pilot David Howe with six other personnel in addition to Ziegler.

Everything went well and the first top-off run was successful. The second top-off operation was completed and nitrogen pressurisation of the tank began. Little more than a minute later, right over the centre of Lake Ontario the X-2 exploded throwing Ziegler out into the air. Crewman Frank Wolko baled out. Their bodies were never found. The official report picks up the story: “The exact time of the explosion was 13.05 EDT and the sky was overcast. The B-50 was flying at 200mph indicated air speed at an altitude of 30,000ft and in level flight. The liquid oxygen tank had been topped off for a second time. “The pressure was permitted to rise in these tanks by closing the vents after which they were pressurised with nitrogen. The explosion took place approximately 1.5 minutes after the start of pressurisation when the pressures had reached approximately the normal operating values. “As described by the chase pilot who was flying (a F-47 Thunderbolt) near the left wing of the B-50 a large ball of red flame originating below the B-50 engulfed all of the X-2 and part of the B-50. There was no sustained fire of any magnitude aboard the B-50. The ensuing blast rolled the chase plane violently into a left bank and the B-50 was seen to rise approximately 100ft. The chase pilot described the X-2 as having disintegrated. The largest piece he saw leaving the B-50 was apparently the outer half of a wing panel which passed (him) within 50ft. “As described by the crew, one or perhaps two explosions occurred in quick succession. The B-50 experienced violent positive and ➤ ROCKETPLANES 97

then negative accelerations and rose between 200ft and 650ft. The bomb bay was first engulfed in a grey fog and then by small particles of burning debris for a short period after the explosion. “The test pilot of the X-2 who was in the bomb bay observing instruments within the cockpit of the X-2 was not observed again after the blast. A scanner, having a position in the rear compartment of the B-50, baled out through an aft side door. The chase pilot saw a body leaving the B-50 at about this time but did not see any others. Immediate search for the missing crewmembers by the chase pilot and a continued search by Bell and government aircraft proved fruitless.” The initial explosion blasted the inboard landing flaps and engine nacelles with shrapnel but the pilots managed to muscle the big bomber back down to the ground, landing at Niagara Falls Airport. The aircraft never flew again. The review board met quickly and on June 9, 1953, a conference was held at WrightPatterson Air Force Base to review the findings and determine the next steps. It was 98 ROCKETPLANES

concluded that a stray electrical signal had ignited combustible materials in the oxygenrich mixture which blew the tanks. The remaining No. 1 X-2, by now complete and ready to fly, would be grounded along with the X-1A and X-1B until further investigation recommended a set of procedures to mitigate risk. Bell noted that they all used 410 stainless steel and the highpressure nitrogen tubes were replaced on all rocket ships.

Mach 2

With three X-series aircraft destroyed the air force was even more determined than ever to preserve its existing assets – two second-generation X-1 and the sole remaining X-2. Frank Everest pushed for assignment as the X-2 project pilot and was accepted while the air force Flight Test Center at Edwards AFB assigned Chuck Yeager to fly the remaining contractor flights with that type. But that was not nearly enough for the research-hungry engineers and scientists.

The NACA was keen to push on much faster and higher and to explore unique combinations of aerofoils, wing sections, wing sweep and other variables which would doubtless prove fruitful in the search for the ultimate supersonic configuration. In June 1952, a full year before the tragic loss of the X-2, the air force had signed a contract with Bell for a complete rebuild of the second first-generation X-1 (46-063) as the X-1E, while the NACA had begun formulating a research programme for an aircraft capable of exploring the Mach 4-10 region and at altitudes up to 50 miles (264,000ft). The new NACA requirement would create what was arguably the world’s first spaceship, a piloted machine sufficiently powerful to reach speeds hardly conceivable in the early 1950s and a technology which would eventually make possible NASA’s Space Shuttle of the 1970s. It would be known as the X-15 and achieve recognition as the fastest winged aircraft of all time. Meanwhile, almost six years on from Chuck Yeager’s flight through the sound barrier in

Above: Scott Crossfield in the cockpit of the D-558-II Skyrocket after his first run at Mach 2 on November 20, 1953. Left: Beaten to Mach 2 by the Douglas challenger, the Bell X-1B was to achieve Mach 2.3 on December 2, 1954. NASA

level flight, nobody had managed to reach Mach 2. But that was just about to change as NACA engineers wrestled with stability problems encountered with the Douglas Skyrocket on its way toward that goal. But none of that discouraged Scott Crossfield, who by now, along with US Marine Corps pilot Marion Carl, had come to know the Skyrocket well. Marion Carl had conducted several flights with the jet-powered Douglas D-558-1 Skystreak and had set a speed record of 650.606mph in that aircraft on August 25, 1947. No mean achievement given that he had the greatest difficulty squeezing his 6ft 2in frame into the cramped cockpit of the Skystreak. Crossfield resumed flight tests with the No. 2 Skyrocket on March 26, 1953, making the 14th NACA air-launched flight with that type, each with Crossfield at the controls. On through the summer months he flew on lateral stability tests and temporarily handed over to Carl for navy flights beginning on August 14. By September 2, Carl had made four flights, not all successful, and vacated the Skyrocket’s seat for Crossfield to resume NACA flights. But the NACA engineers had

made a modification to the LR-8 rocket motor by providing a nozzle extension to carry hot exhaust gases clear of the rudder during high altitude supersonic flight. It is a characteristic of rocket exhausts that the plume balloons into an expanding bowlshape as ambient pressure is reduced with altitude and the expansion is unrestrained by the denser atmosphere at lower altitude. This can cause serious heating effects as the exhaust flares and impinges on structural or control surfaces. With the nozzle extension this effect was reduced but the modification provided an added advantage in giving the motor a 6.5% thrust increase at Mach 1.7 and an altitude of 70,000ft. Scott Crossfield was not only a natural pilot but an intuitive engineer and could visualise ways to improve performance. To achieve higher thrust levels from the theoretical performance of the rocket motor, he added tank regulators in the cockpit which allowed him to raise the pressure by 10-15psi after the chambers ignited. With the nozzle extensions and the regulators affording some degree of throttling effect overall thrust was raised from

6000lb to 9000lb and burned the fuel appreciably faster. Crossfield was also fanatical about parasitic drag – the kind that causes air molecules to pull and tug at the little niches and panel lines, slowing the aircraft by a fractional amount. So they taped up the small protuberances and smoothed the cracks between panels, polishing and sanding them to a seamless finish. Two fuel jettison pipes were attached to the rear of the Skyrocket to keep the streaming liquid away from the tail of the carrier-plane. Engineers made aluminium replacements which burned away after the drop and motor ignition, reducing a few ounces of unnecessary weight! There were other ways of extracting the last ounce of speed too. An overboard vent line was there to get rid of excess fuel back up into the bomb bay but after separation from the motherplane it was no longer necessary so Crossfield had the technicians reattach it so as the aircraft fell away it remained with the carrier-plane and leave a flush surface on the Skyrocket. ➤ ROCKETPLANES 99

Scott Crossfield tells a film crew what it was like to become the first human to pass through Mach 2. NASA

On September 17, Crossfield made his first flight with this configuration, the rocket plane streaked to Mach 1.85 at 74,000ft and eight days later he made another flight. But on pushing over, he encountered a severe rolling motion which resulted in the Skyrocket becoming inverted at Mach 1.7. With ineffective ailerons, Crossfield had to perform a split-S manoeuvre to get the aircraft right way up and return to a safe landing. But there was always the spectre of some anomaly which would ruin a planned flight and so it was again on October 29 when the No. 2 rocket chamber failed to ignite and the engine shut down prematurely relegating the flight to a subsonic speed. Aerodynamic loads, lateral and longitudinal stability were the focus of attention but even the most attentive test pilot is prone to the seductive promise of a record-breaking flight. Denied that opportunity, the air force could only wait as modifications to the X-1A and X-1B could return those types to the flight line – the X-2 would not be in the air again for a year. As for the Skyrocket, not everyone was convinced it could push on through Mach 2 but that goal became a fixated target for Crossfield who suggested to a navy official it would be ‘neat’ to beat the air force at its own game! And that was that – Crossfield was cleared to go for Mach 2. By early November the various flights had achieved all that was necessary to go for a special high-speed run. Although Crossfield came down with a heavy bout of flu he was not 100 ROCKETPLANES

about to give up the opportunity and special preparations were made for the attempt. The night before the drop, mechanics chilled the fuel using a large refrigeration unit, slightly compressing the diluted ethyl alcohol which allowed the tanks to carry an extra 10-15 gallons. They cold-soaked the airframe by filling the LOX tank and continuously replenishing the liquid throughout the night. That effort almost backfired. When loading the hydrogen peroxide the following morning the airframe was so cold a vent line froze and leaked the toxic fluid through another outlet, spraying mechanic

“By NovemBer the flights had achieved all that was Necessary to go for a special high-speed ruN.” John Moisie with the freezing liquid. Standing nearby, Gil Kincaid grabbed a hose and washed him down before Moisie was trucked to the nearby medical centre. Crossfield went across to see for himself that he was none the worse before returning to find Kincaid sweating profusely in the chill morning air from peroxide-soaked clothing that was acting chemically and converting them into an intense thermal blanket! Tearing off his outer garments, Crossfield got down to Kincaid’s bare legs – spotted with peroxide burns. Any longer and the peroxide,

and Kincaid, would have spontaneously combusted. The medical centre quickly received another patient. So began November 20, 1953, the day when the first serious attempt at Mach 2 was made, ingloriously and with not a little farce to dine out on for decades to come. It would all come down to Lady Luck, the weather and everything working as planned. The flight plan had been meticulously written up by Herman O Ankenbruck, the project engineer on the Skyrocket project. He calculated it should be possible to slightly exceed Mach 2 by climbing to 72,000ft, levelling and entering a very shallow dive. Crossfield had sufficient trust in this brilliant aerodynamicist that he believed every step in the planned sequence. But it had been a long and winding road for the little research aircraft that began life as a jet designed to fly through Mach 1 and was now configured, with rocket motor, for an attempt at Mach 2. The potential was due in no small measure to the systematic nature of flight preparation which, over the years, had honed the pre-flight preparations into a formalised series of checklists and timed countdown events. It was even determined, by Crossfield himself, that one person, preferably a pilot, should have sole responsibility for talking to the man in the air. This was adopted as standard, its legacy being in the function of a ‘capsule communicator’ or capcom during NASA’s manned space flight operations from the

Walter C Williams (left), director of the High Speed Flight Station, and Joe Vensel, director of flight operations, discuss the successful flight with Crossfield. NASA

Mercury programme of the early 1960s to today’s sophisticated space operations. NACA pilot Stanley Butchart was at the controls of the P2B-1S as it climbed skyward with the No. 2 Skyrocket held in the grip of its modified bomb bay. It was a cold and blustery morning, wind from the east but the conditions were right for the Skyrocket. At 10,000ft Crossfield climbed down into the cockpit of the diminutive rocket ship and went through the limited checks necessary prior to free flight, monitoring gauges and instrument readings all the while. As the motherplane climbed, one job that Crossfield feared was pressurisation of the cabin. When activated the inlet blasted oxygen into the cabin threatening to blow ear drums and wreck sinus tubes. Like all test pilots, Crossfield had shattered sinuses and with a very heavy bout of flu he flinched at the prospect of this sudden and painful pressure blast. So, taking along a piece of cork he plugged the outlet tube, turned on the supply valve and only gradually released the cork, oxygen flowing out at a painlessly slow pace and avoiding excruciating pain. It took more than an hour to reach 35,000ft but this was height enough and almost at the ceiling of this adapted bomber-cummotherplane. Sometimes Crossfield had wanted to get to a height of 38,000ft but that would take an extra 30 minutes and Ankenbruck’s flight plan did not require that. Calmly counting down to the drop, Butchart

“Like aLL test piLots, CrossfieLd had shattered sinuses and with a heavy bout of fLu he fLinChed at the prospeCt of this sudden and painfuL pressure bLast.” released the Skyrocket from his position in the left seat of the P2B and instantly Crossfield’s vision was blinded by sunlight. As the rocket ship rolled off to the right, Crossfield trimmed the aircraft and one by one lit the burners, his eyes fixed to the airspeed and altitude instruments, all the while getting confirmation from Butchart that he was on course, streaking up and to the right of the motherplane. For three minutes and 27 seconds the four rocket chambers continued to fire, seven seconds longer than would otherwise been the case had not that process of meticulous chill-down not taken place before dawn that day. At 72,000ft Crossfield gently nosed the Skyrocket into a very shallow dive and for precious seconds the rockets continued to fire, flaming out just as the Mach needle on the instrument panel read 2.04. Suddenly, the Skyrocket began to decelerate and Crossfield pulled back gently on the stick, levelling off at Mach 1.8 as it slid down into the denser layers of the atmosphere. Decelerating through Mach 1 the inert rocket ship shook violently for a moment and settled

back down into a familiar flight pattern. Crossing the edge of the lake bed at 15,000ft, Crossfield did a victory roll, picked up the chase planes and let down between two lines on the runway exactly as he had planned and precisely at the pre-selected spot, rolling to a stop a mere 12 minutes after dropping from the motherplane. Dead-stick landings were becoming a fine art and the sustained demonstration of skill in managing energy between lift and drag in unpowered descents from the outer edges of the atmosphere augered well for the future of even more demanding research aircraft. There was nothing of great significance in achieving Mach 2, it being much the same aerodynamically as Mach 1.9 or 2.1 but the public relations affect was palpable. Great claims were made for the achievement of the Skyrocket and Douglas, the navy and the NACA lost no time in claiming their own specific role in bringing that about. It mattered a lot to the morale of the High Speed Flight Station and the boss, Walter C ‘Walt’ Williams was there at the side of the Skyrocket when Crossfield came to a stop. Williams would play an important role in the next generation of supersonic and hypersonic rocket ships and influence the way the first manned space missions would be managed and operated as a flight-line level. In several ways, the future was being written on the desert skid strips at Edwards Air Force Base. ■ ROCKETPLANES 101

edge

On the

For almost 10 years the X-1 series and the Douglas Skyrocket had the supersonic test run to themselves, probing faster and higher than ever before. But then the X-2 came along, promising much but bringing catastrophe as it hit Mach 3...

S

cott Crossfield was now the fastest man alive, but that would not last long. The day after he cracked Mach 2, Chuck Yeager began a series of requalifications flights with the X-1A, now released from a grounding brought on by the fatal accident to the X-2. It was with the X-1A that the air force hoped to push beyond Mach 2 and explore control phenomenon in that exotic flight region. The X-1A had been delivered from Bell’s Buffalo plant on October 16 and air force mechanics had installed replacement nitrogen storage tanks while NACA engineers fitted the bulbous rocket ship with special instrumentation. Yeager managed Mach 1.15 on that first flight on November 21 and on subsequent flights experienced severe control problems while nudging up to Mach 1.9, achieved on 102 ROCKETPLANES

December 8. The air force was anxious to press ahead with high speed trials and Yeager was convinced he could handle the vicissitudes of the seemingly temperamental rocket ship. But there was nothing to indicate significant risk to a high speed run, or to the survival of the aircraft and its pilot, and preparations were made to go for that on the very next flight, scheduled for December 12. Major Harold Russell was at the controls of the B-29 motherplane when it took off clutching the X-1A in its belly. As the giant bomber clawed its way to altitude, two F-86 chase planes flown by Major Arthur ‘Kit’ Murray and Colonel Jack Ridley formed up on it. Piloting the rocket plane, Yeager was dropped at 30,500ft and fired the three combustion chambers on the LR-11 motor, speeding away from the bomber’s contrails. At 45,000ft Yeager fired up the fourth

burner and soared ever higher, reaching 70,000ft where he began a pushover, levelling off at 76,000ft. As the rocket ship passed Mach 2, Yeager was now the world’s fastest pilot and heading for what NACA engineers had defined as the safe performance limit of the X-1A: Mach 2.3. As Yeager exceeded that theoretical limit the X-1A began to tip and roll to the left as if homing in on some unseen guide wave. Correcting with the aileron and rudder input, Yeager was unable to stop a violent snap to the right as the aircraft began to tumble. Shutting down the rocket motor, he hit Mach 2.44 and the X-1A fell completely out of control. Thrown around against the restraints of his harness, Yeager seemed helpless to correct the violent motions and could find no combination of stick or rudder application to save the situation. Radio contact was lost and Murray and Ridley tried desperately to raise Yeager by voice. By this time Yeager was literally fighting for his life, thrown with such force that his helmet had smashed into the cockpit canopy and almost shattered it as the X-1A fell at a sickening pace toward the ground several miles below. At 34,000ft the aircraft was upside down

and spinning toward the solid earth. At 29,000ft, barely conscious, Yeager recovered to a controllable spin and at 25,000ft brought the X-1A out of that into stable flight, controls benefitting from the denser atmosphere biting the aero surfaces of wings and tail. Understanding his situation and recovering his awareness, Yeager called the chase pilots, told them his position and began to manage the flight path once again back down to the ground. On landing, Yeager tossed the comment over his radio that if the aircraft had been equipped with an ejection seat “you wouldn’t still see me in this thing!” Battered and bruised from a 50,000ft uncontrollable plunge, Yeager had encountered in very real and physical form what the engineers had calculated – the second-generation X-1 was unsafe much above Mach 2 and it was to that limit that the aircraft was fixed in all future research flights. After all the data traces were analysed and the flight analysed in minute detail, the NACA engineers calculated that the X-1A had reached a speed of 1612mph and an altitude of 74,200ft. Yeager had experienced ‘coupled’ motion with longitudinal and lateral motions combining to decrease directional stability and roll-damping. That this would happen at high Mach numbers had been predicted by NACA scientist William H Phillips as far back as 1948 and Yeager’s flight had proved him right. The one design decision that emerged from this near-death experience for Yeager was that future aircraft, intended for speeds above Mach 2, would require large tail surfaces to combat the effect. It was a lesson Scott Crossfield would carry with him when he joined North American Aviation and played a significant role in the configuration of X-15. The X-1A continued research flights seeking information about high altitude controllability but here too it flew to the very edge of survival. The air force persuaded the NACA to let it fly the X-1A on these tests with Murray assigned to fly the rocket ship. On May 28, he exceeded Marion Carl’s altitude record with a flight to 87,094ft and little more than a week later he raised this to 89,750ft. On that flight Murray ran into the same kind of coupled motion experienced by Yeager the previous year but on this flight the air was

An early wind tunnel model of the Bell X-2 as it appeared in 1947 at the NACA Langley Aeronautical Laboratory.The ventral tail fin was tested on the X-1E. NASA

thinner and the speed much slower and Carl was able to recover the aircraft after dropping 20,000ft. On August 26, 1954, Murray nudged the X-1A to 90,440ft. The following month the NACA accepted the X-1A for its own flight research programme and the aircraft was immediately returned to Bell for an ejection seat – taking Yeager’s quip as a prescient warning that the next time that way may be the only means of the pilot getting back alive. The X-1A arrived back at Edwards with its new ejection seat on February 23, 1955, and Joe Walker made a familiarisation flight on July 20, 1955, experiencing severe aileron ‘buzz’ around Mach 0.90-0.92 before continuing on up to Mach 1.45 at 45,000ft. A second flight was attempted but had to be aborted due to technical difficulties. The next flight on August 8 had Stanley Butchart and Jack McKay pilot the B-29 launch plane and the X-1A to altitude for another go. Flying chase that day was Kit Murray and another NACA pilot in an F-51 Mustang – Neil Armstrong. As the B-29 climbed through 8000ft, Joe Walker entered the X-1A’s cockpit and settled into its ejection seat before closing the canopy. At 31,000ft and in level flight, with one minute

to go to the drop, the liquid oxygen tank blew, sending a white cloud of evaporating liquid oxygen into the bomb bay. The sudden shock jolted the rocket plane and settled it a few inches lower as it deployed the landing gear as Walker flung open the canopy and catapulted himself back across into the B-29. The shock had been so violent that debris struck Murray’s canopy and shattered it. Having dropped slightly and deployed its landing gear, the X-1A would have to be emptied of fuel if there was any hope of getting it back intact. The crew chief Richard Payne went down into the bay and looked inside the cockpit to see that the landing gear handle was still in the retract position. First job was to get rid of the fuel using the hydrogen peroxide and the remainder of the nitrogen supply but the chase pilots reported only a small amount had been released from the vent tubes before it stopped. Left with no alternative, Butchart turned the B-29 across over to the Edwards Air Force Base bombing range and jettisoned the rocket plane. Unbalanced by the blown oxygen tank and partially jettisoned fuel, the X-1A assumed a nose-up attitude as it slowly fell, gently spiralling around, to the desert floor. ➤

“The design decision which emerged from This near-deaTh experience was ThaT fuTure aircrafT, inTended for speeds above mach 2,would require large Tail surfaces.”

Under power for a speed run, with its sweptback wing the X-2 had all the promise of a valid contender for Mach 3. NASA

ROCKETPLANES 103

Exploding into a ball of flames it started a small brush fire, an ignominious end to a promising series of test flights that could have kept the X-1A making a valuable contribution for several more years. The X-1A was the fourth rocket plane to blow up with no single verifiable reason, only supposition and an educated guess to link these events to transient electrical shorts or faulty tyy circuits. There had always been a suspicion that the tube-bundle nitrogen system had caused the previous explosions due to an incorrect steel used in their manufacture. But the X-1A did not have those, being fitted instead with three cylindrical storage tanks of a completely different material. The wreckage was retrieved from the bombing range and was meticulously reassembled in the High Speed Flight Station alongside its identical twin, tw w the X-1B, for comparative analysis. As the X-1B was comparatively disassembled some residue oil was found inside the tank and along the oxygen supply tubes. The liquid was taken away for analysis and found to be tricresyl phosphate, usually used to impregnate leather. This material, known as Ulmer leather, had been used on all X-1 and X-2 aircraft ftt as gaskets in the liquid oxygen tanks.

After achieving Mach 2.3 in the Bell X-1B, US Air Force test pilot Frank ‘Pete’ Everest made a special point of flying the X-2 and achieved Mach 2.9, seizing for a while the title of ‘fastest man alive’. USAF 104 ROCKETPLANES

Only when they consulted with specialists was it revealed that this material should never be used where liquid oxygen was around as it was likely to explode at extremely low temperatures when subject to shock or vibration. The very act of pressurising it could produce sufficient energy gyy to blow the tank. So now at last the real reason why the No. 3 X-1, the X-1D, the X-2 and the X-1A had been lost was discovered. Never again would Ulmer gaskets get anyw ywhere w near liquid oxygen. The record speed flight of Mach 2.44, which very nearly took the life of Chuck Yeager, and the altitude record of 90,440ft ftt represented the very peak of X-1 performance and never again would the air force or the NACA use the remaining X-1B, or the emerging X-1E rebuild, to go near these limits. Except for one flight carried out on December 2, 1954, which involved the X-1B. The X-1B had been delivered to Edwards on June 20, 1954, and was taken up for a glide flight with Jack Ridley Rii at the controls on September 24. Two more shakedown flights were completed without any anomalies and various pilots were given the opportunity tyy to familiarise themselves with the type, tyy including General Haltoner, the first officer of this rank to fly a rocket ship, on November 26. Because Frank Everest had volunteered –

and been accepted – for the X-2 programme, he convinced his air force superiors that it would be useful for him to get experience with a couple of flights in the X-1B. On his second flight, on December 2, 1954, he attained a speed of Mach 2.3 (1550mph) at 65,000ft ftt and here too he experienced unexpected attitude excursions as the wings dipped by up to 70º. The following day the X-1B was delivered to the NACA’s Langley Laboratory in Virginia where it was fitted with special instrumentation and returned to Edwards for flight operations on August 1, 1955, where it joined the X-1A. At that time the X-1A was assigned high-speed/high-altitude research while the X-1B would conduct research into heat effects at various altitudes and speeds. The events of August 8 and the loss of the X-1A changed all that and the X-1B focused on its own dedicated and fully instrumented programme of exploring thermal effects. The NACA carried out 17 flights with the X-1B betw tween w August 14, 1956, and January 23, 1958, all but four piloted by John B McKay, the last few by a relatively unknown pilot – the same Neil Armstrong Arr who had piloted the chase plane when Joe Walker nearly lost his life and who would rise to world fame as the first man to walk on the moon. It fell to Arr Armstrong to make the last landing of a second generation X-1 aircraft ft. t Affter Aft t the 17th flight the X-1B was withdrawn for installation of a pair of ventral fins for greater stability tyy at high speed and high altitude, where it was hoped the aircraft ftt could make further contributions. A new XLR-11 engine was also to be installed. During the modification engineers discovered cracks in the liquid oxygen tank and an attempt to weld them to an acceptable standard failed. In mid-1958 the decision was

The X-2 had a tricyle landing gear but instead of main wheels the rear fuselage held two wire skids. USAF

made to permanently ground the X-1B and it never flew again. By this time the X-15 was well into its assembly phase and a much more potent research tool was about to arrive at Edwards. By this time the sole remaining X-2 had come and gone and the reworked No. 2 X-1 was on its way out.

END OF AN ERA

From the outset the Bell X-2 had been a difficult programme. Conceived in 1944 when the air force wanted a test vehicle for studying compressibility near to the speed of sound, the design requirement for the X-2 arose from German-led research into swept-wing aerodynamics. The air force had originally expected to be able to adapt the basic X-1 to carry straight or swept wings but early analysis revealed that this was not just impractical but impossible to achieve with a common airframe. So it was that a totally new aircraft was sought and a decision was reached on December 14, 1945, by the air force and the NACA to go with a proposal from Bell, which was awarded a contract for two X-2 airframes on July 3, 1947. As with the X-1, the initial designation was XS-2, the “S” for supersonic being dropped early on. The two aircraft would bear the serial numbers 46-674 and 46-675, with the primary objective of conducting research into heating effects at high speed. Internally, Bell assigned the project designation Design 37D and proposed a leading edge sweep of 40º. Engineering design was at the Bell Wheatfield facility, New York, and the military designation was MX-743. Formal design began at the company on September 11, 1945, before the formal goahead, with Stanley Smith assigned as chief engineer an Bell engineers Jack Strickler, Paul Emmons, Jack Woolams, Harold Hawkins and Robert Stanley. The formal design proposal was submitted on October 1, leading to the decision by the air force to proceed. Much debate surrounded the swept-wing concept, which had been proposed and studied by a wide range of aerodynamicists in several countries. In Germany during the 1930s Adolph Busemann was renowned for his pioneering theoretical work on such designs and had published papers convincing in their implications. In the United States Robert Jones had convinced the air force engineers at Wright Field that the idea was a winner for highspeed flight. Jones had teamed with Ezra

The X-1E was flown successfully 26 times and made the last flight of the X-1 series on November 6, 1958. NASA

Kotcher who argued the case for a swept-wing version of the X-1, which was how the requirement emerged to warrant the X-2. During the design development phase of the X-2, the navy managed the Skystreak and Skyrocket programmes, the latter with swept wings which were still a point of contention. Not until late 1949 did the Skyrocket begin flight trials and there was concern that not enough was known about this aerofoil configuration to guarantee a design for the X-2. To add data two Bell P-63A Kingcobra fighters were adapted and redesignated L-39, each equipped with a 35º swept wing replacing the original straight wings. Tufts on the wing surface were applied to measure flow across the aerofoil and internal instrumentation recorded responses in roll, pitch and yaw to various control inputs. Various high-lift devices were tried and slots and flaps tested in various shapes and sizes. The Navy sponsored these flight trials with the L-39s and one of these was transferred to Bell in 1946 so that it would apply lessons learned from this aircraft. Numerous flight tests were undertaken with Jack Woolams flying the aircraft to evaluate different wing sections. From there the aircraft was taken to the NACA’s Langley Field for extended evaluation. It all came down to justifying three essential reasons for a swept-wing research aircraft: delayed onset of compressibility; significant gust relief due to its inherent flexibility; and greatly reduced lift and drag

coefficients for a given Mach number. So advantageous were the benefits, and so responsive were different sweep angles to specific phases of flight, that some consideration was given to providing the X-2 with a variable-sweep wing – one in which the degree of sweep could be changed in flight according to the Mach number. But Bell was already involved in the X-5 programme to study just that kind of design so the need to focus attention on the use of the X-2 for its primary function, research into heating effects at high speed, eliminated that as a sound possibility. Power for the X-2 would come from a single Curtiss-Wright XLR25-CW-1/3 regeneratively cooled rocket motor consisting of two combustion chambers with a centrifugal turbopump operating at 12,000rpm, producing a thrust throttleable between 2500lb and 15,000lb. Fuel was an ethyl alcohol mix at a ratio of 75/25 and the oxidiser was liquid oxygen. A single large tank held 860.3 gallons of fuel and two tanks which together held 755.8 gallons of LOX. The fuel tank was positioned across the top of the wing carry-through structure with the oxygen tanks positioned at each end of the fuel tank. Aft of the rear oxidiser tank was the turbopump, behind which was the rocket motor. Forward of the front oxygen tank was a pressurised compartment for instrumentation and ahead of that was the cockpit and nose section. ➤

A minor landing accident brought the first X-2 to fly to a close encounter with the lake bed on its first unpowered glide. NASA

ROCKETPLANES 105

Flight tests with the X-1E began in December 1955.The cockpit incorporated a high-altitude ejection seat scavenged from the second Northrop X-4. NASA

Iven C Kincheloe with the X-2 and its flight support crew. He became the first man to fly above 100,000ft when he achieved 126,200ft on September 7, 1956. NASA

“Various concepts for pilot escape were eValuated and formed an important part of the aircraft’s oVerall design strategy. it was difficult to enVisage the dynamic forces to which an escaping pilot would be subject.” The rocket motor was built at the CurtissWright Propeller Division, Rocket Department, at Wood-Ridge near Caldwell, New Jersey. It was beset with significant development problems and was the primary reason why the X-2 was delayed several years beyond its original schedule. Much like the X-1, with a fineness ratio of 9.5 the fuselage was essentially one large collection of propellant tanks and rocket motor with wings and a tail section. In some bizarre aspect it appeared no dissimilar to plans for a piloted winged version of the V-2 which had been proposed in Germany by von Braun during the war. A major feature of the X-2, and one which drew considerable pride from the engineers working on the project, was the pioneering role it had in using exotic alloys. For the first time, substantial use of K-Monel alloy and stainless steel provided high strength at high temperatures, good structural rigidity, 106 ROCKETPLANES

resistance to corrosion from propellants and ease of assembly and spot-welding. Most of the fuselage was fabricated from K-Monel over bulkheads and stringers for stiffening and the propellant tanks were integral with the fuselage. All the aerodynamic surfaces were covered with stainless steel skins, tapered on the wings and tailplane for maximum strength and minimum weight. The wing had a sweep of 40º with a taper ratio of 5.0 and a mean aerodynamic chord of 8.379ft and a wing dihedral of 3º. The wing had slab-type ailerons with blunt trailing edges and a surface area of 10.8sq ft, the trailing edges half the thickness of the aileron leading edges. This was designed to eliminate flow separation at high speed and increase effectiveness. The wing also had flaps and small leading edge fences, the flap having a surface area of 12.2sq ft and a total downward travel of 15º.

The instrument display panel of the X-1E was painted ‘crackle’ black. Bell

Another pioneering feature of the X-2 was the flight control system which had screw-jacks powered by the electrical flight control system moving the ailerons and stabilator. This is the first known application of a ‘fly-by-wire’ control system. With the design goal of Mach 3.5 and an altitude capability of 120,000ft, the aircraft would be required to withstand extreme forces during high-speed manoeuvring and load distribution in the design of the structure was provided by calculation and extrapolation and not by measurement or data. The aircraft was designed for a maximum acceleration of 8G at the design gross weight of 24,910lb with a safety factor of 1.5. Various concepts for pilot escape were evaluated and formed an important part of the aircraft’s overall design strategy. It was difficult to envisage the dynamic forces to which an escaping pilot would be subject, without some further information about the environment into which this aircraft was to operate. The flight objective for the X-2 was more than three times the speed of sound and the aerodynamic consequences of departing from a tumbling aircraft at anything like that speed was problematical. It was never imagined that a pilot would leave his aircraft at this speed,

remaining with the aircraft in an emergency until it had reached slower speed and denser atmosphere. The final escape design incorporated a detachable nose section containing the pilot which would pitch forward and away from the main body of the aircraft. At a specified distance a ribbon parachute would open and through a static line stabilise the section and decelerate it to a velocity of around 120mph. After reaching a terminal velocity and descending through 10,000ft, the pilot would bail out manually and descend to the ground on a standard 28ft diameter personal parachute. Plagued by a succession of frustrating delays, the first X-2 to fly was the second aircraft and, as related earlier, this was lost in a catastrophic accident over Lake Ontario on May 12, 1953, the consequences of which were long lasting and far reaching. It would take the loss of more aircraft and intensive forensic analysis to unravel the complexities of the chemistry that explained why these losses kept occurring. But the loss of the No. 2 X-2 almost brought about the cancellation of the programme. On July 15, 1954, the No. 1 aircraft (46-674) was slung under a new EB-50A (48-096) and carried to Edwards Air Force Base. On

August 5, Frank Everest conducted his first glide flight but on landing the nose veered away to the left and then back to the right, again repeating the cycle as the X-2 slammed first one wing tip and then the other into the ground, denting metal and damaging the landing gear. The second glide flight did not take place until March 8, 1955, after repairs had been completed back at Bell’s Wheatfield plant. Again a rollout problem occurred and back it went to Wheatfield again for more repairs. The third glide flight on April 6 ended with the same oscillations, despite efforts to solve the uncompromising nose leg. Back it went yet again for further repairs and for installation of the rocket motor. The touchdown problem was as much a fault with the landings skids as it was with the nose leg and Bell engineered a complete redesign in which the leg was much shorter and less likely to invoke oscillations. The air force had insisted on a shockabsorbing oleo leg similar to those fitted to fighter aircraft and Bell had argued the flaw with that coupled to under-skids. Finally, the air force accepted the logic and approved the design of the much shorter leg it should have had from the outset. The first attempt at powered flight took

place on October 25 but this had to be abandoned when some more technical problems arose. The X-2 was running out of time and the NACA was getting frustrated. The air force was concerned at the manpower and resources the project was consuming with no apparent success in sight and it was generally agreed that unless a successful powered flight took place before the end of the year the project would be scrapped. That flight took place on November 18, just six weeks short of the deadline, in which Frank Everest achieved a speed of Mach 0.992 at 35,000ft. A small fire in the tail area marred an otherwise flawless flight. Over the next few months several more powered flights took place, with Everest achieving Mach 2.53 at 58,370ft on May 22, 1956. Three days later Ivan Kincheloe made his first flight on the X-2 and would make three more flights after a brief gap in which Everest returned for two flights of his own. At last the X-2 seemed to have puts its woes behind it as the air force planned to crack Mach 3 and begin a productive cycle of heat tests which were long overdue and which could feed in to the emerging X-15 programme. First it was necessary to evaluate the performance and handling of the X-2 ➤

The second X-1 was reworked into the X-1E with a substantial redesign of the cockpit area.The wing had an extremely thin 4% thickness/chord ratio and on later flights a ventral fin was added to the rear fuselage. Bell ROCKETPLANES 107

Inspired by the advantages of a more conventional canopy and windscreen, the reworked X-1E took on a distinctly unique appearance.

before turning it over to purely engineering and scientific research. A high speed run was flown on July 23 in which, briefly, Frank Everest became, in his own words, “the fastest man alive”. The drop occurred at 30,000ft over Victorville and his description of the flight displays an engineer’s instinct for technical performance: “The drop was made in a westerly heading because the winds aloft would not give us an appreciable increase in speed. “Immediately after drop both chambers were started at full power and a climb was initiated to altitude. Because of the high acceleration the X-2 gained speed too rapidly for the pilot to maintain best climb speed and a speed of 360 indicated was used throughout the climb. “Upon reaching 50,000ft, a slow push-over was started with level flight apparently being obtained at approximately 65,000ft. Airplane accelerated up to 2.85 Mach number at which time rocket shutdown was experienced apparently due to fuel starvation. “An aileron pulse was made immediately after shutdown and although it appeared that the directional stability was positive, there was a definite decay in lateral stability as the airplane continued to roll after pressure was released from the control stick. “After shutdown the airplane drifted up to 70,000ft which may be an indication that the airplane was still in a slight climb during the acceleration to 2.85 Mach number. A turn and dive was initiated at this time back towards the base from the vicinity of Bakersfield with a normal landing being made on the dry lake shortly thereafter”. Displaying an innate sense of situational awareness, Everest concludes his report with 108 ROCKETPLANES

There were no armrests on the sides of the X-1E cockpit and the right subpanel to the main display console sat above the oxygen feed system. Bell

some aspects of the flight and displays the manner in which the pilots themselves were an integral part of understanding the behavioural characteristics as influenced by design factors, and what was necessary to improve performance from a flight planning stance: “It was noticed during the climb that longitudinal control was quite sensitive which is primarily the reason for the difficulty in maintaining proper climb schedule. “The pilot feels that this sensitivity is because of the high breakout forces and low static forces causing the pilot to over-control any time he pulses the stick. The pilot used both hands in an attempt to fly smoothly but even then some over-control was noticed. “It is recommended that either the breakout forces be reduced by approximately 50% or the static forces be increased by approximately 50% to prevent longitudinal sensitivity. In concluding, it is felt by the undersigned that perhaps another Mach number could be realised from a better climb schedule and with some aid from the upper winds, but conditions would have to be fairly ideal.” Iven Kincheloe’s last three flights on the X-2 included two familiarisations runs with an attempt on the high altitude capability of the aircraft occurring on September 7. After a conventional climb to altitude and a drop at 30,000ft, the X-2’s rocket motor was ignited six

seconds after release and aligned with a flight path angle of 30º. A speed of 350mph was maintained to retain a balance between the optimum lift coefficient for the minimum drag condition as the aircraft flew toward the point where it would start the high-speed run. At a height of 56,000ft and a speed of Mach 1.2, Kincheloe put the X-2 into a nose-up attitude of 38º and continued accelerating to 1.2G. The propellant ran out at an altitude of 104,000ft where acceleration had increased to 1.45G, the aircraft now flying a semi-ballistic trajectory to peak altitude. As he drifted higher, Kincheloe could not see the Earth’s horizon but at Mach 1.7 in the rarefied air he coasted to a height of 126,000ft where static pressure was a mere 9.4lb-sq in. By using the stabilator, Kinchekloe held attitude and began to re-encounter the denser layers of the atmosphere while accelerating to 3.5G, pullout occurring at 40,000ft and Mach 1. From then on the pilot flew a normal recovery profile and returned to an uneventful landing. The X-2 had demonstrated high-altitude capability and the next flight would be the first for air force test pilot Milburn Apt, who had recently been assigned to the X-2 programme. Keen to extract as much performance as it could from the swept-wing rocket ship before handing it over to the NACA for flight

“Because the Naca imagiNed it could accomplish all its test flight requiremeNts with the X-1d,the first X-1 had BeeN retired to the smithsoNiaN iNstitutioN iN washiNgtoN dc while the third X-1 was fitted with a New turBopump aNd iNcreased fuel capacity.”

A technician adjusts the cryogenic flow control for the liquid oxygen fill pipes, suitably lifted above the supercold fluids on grip extenders. NASA

research, the air force wanted one more crack at the Mach record. It clearly had an eye on achieving Mach 3 to reclaim the record from the navy-based Skyrocket which, almost three years earlier, Crossfield had achieved in an aircraft designed for only half that speed. This was Apt’s first flight in any X-series aircraft and his only awareness of the bizarre characteristics of these temperamental rocketships was conversation with other test pilots and through a crude flight simulator known as the Goodyear Digital Analyser. Set for September 27, initially the flight went well and Apt dropped away from the EB-50D at 31,800ft and a speed of 230mph. Without prior experience, Apt was remarkably successful at following precisely the flight path mapped out beforehand and set the X-2 precisely on course for its goal. Maximum altitude came at 72,000ft with a slight nose-over to 66,000ft where the high speed run began. The engine ran for a few seconds over its expected duration and at shutdown the X-2 was in a 2.5º left bank and nose down by 6º, factors caused by a slight misalignment of the engine combustion chambers which had not been corrected and, because of that, had been a characteristic of all previous flights. As the motor cut off Apt began a turn and began a roll to level off before inexplicably reversing the ailerons to increase left bank while pulling back on the stick. The X-2 was

suddenly in a steep bank, acceleration forces built up to more than 2G. The X-2 was now moving at Mach 3. Left sideslip began to build up a a result of these unusual inputs and an exclamation was heard from Apt over the radio as the X-2 continued more quickly into a sideslip. Rolling violently, the forces built up to 6G and oscillated as the aircraft swung wildly for several seconds, the pilot being thrown around against his restraints. Coming up on 45 seconds after engine cutoff the aircraft was inverted and in negative G the airframe had survived intact and Apt began manoeuvres to start spin recovery. Then, on-board film showed him move to eject the nose section, which came away from the fuselage at an altitude of 40,000ft, 68 seconds after the engine had stopped. The normal procedure would have been for the pilot to have released his seat belt and taken to his personal parachute but when the capsule was recovered his body was found still partially attached to the seat. The aircraft struck the ground five miles from the nose section causing a small fire. It was over. Both aircraft had been destroyed. The X-2 was a shattered dream but Mel Apt had achieved his objective, the official verdict crediting his flight with having achieved Mach 3.196, or 2094mph. Frank Everest was still “the fastest man alive” and by a bitter irony could still retain his title which he would still

hold for more than three years. But it was quite the end of the original X-series, for the rebuilt No. 2 X-1 (46-063) had already begun test flying as the very much modified X-1E.

Last of the bunch

Because the NACA imagined it could accomplish all its test flight requirements with the X-1D, the first X-1 had been retired to the Smithsonian Institution in Washington DC while the third X-1 was fitted with a new turbopump and increased fuel capacity. The second aircraft was scheduled to follow the first into retirement and a museum. When the X-1D and the third X-1 were destroyed those plans changed and the second aircraft, instead of being put out to public admiration, was instead to be rebuilt as a completely new aircraft. Apart from acquiring the completely redesigned forward fuselage section and its more conventional layout with forward windscreens and flaired upper decking, there were more research-orientated changes. But first, an engineering switch. As early as 1951 it was discovered that the nitrogen spheres were likely to explode after more than 700 cycles and two bottles were removed from the No. 1 X-1 in the Smithsonian and tested – they burst. It was partly because of this finding that the second aircraft had been retired in October 1951. Because of this the modifications built in to ➤ ROCKETPLANES 109

The X-2 on its transportation dolly prior to being matedwith the mother plane. Plagued by delays and technical difficulties, both aircraft were lost in tragic accidents. NASA

the third X-1, but never tested out, were applied to the rebuild and the X-1E also got a new engine fuel system. The new system was designed in 1952 by engineers at Edwards on similar systems already flying in the Skyrocket and the X-1D and the third first-generation X-1. In addition, and because the NACA was keen to conduct research into very thin aerofoil sections, the X-1E would get a new wing. Designed by Robert Stanley and assisted by Richard Frost, the new wing was built by Stanley Aviation Corporation, a company founded by Robert Stanley himself, the former vice-president of Bell. The new wing would have a span of 22.79ft, a root chord of 7.62ft and a tip chord of 2.81ft. Stanley selected the NACA 64A-004 aerofoil section for a maximum root thickness of 3.37in and a thickness/chord ratio of 4%. Aircraft manufacturers were being asked by their design teams to consider ultra-thin wings for high performance. The X-1E was the first aircraft to fly supersonically with such a thin wing. An example was the Lockheed F-104 Starfighter which was being designed in 1952 and causing a stir. With a thickness/chord ratio of 3.36% it had a root thickness of only 4.2in, the F-104 had astonishing performance for its day. With a top speed in excess of Mach 2 it was knocking on the door of the X-series 110 ROCKETPLANES

“The manufacTuring meThods adopTed by sTanley pioneered a new way of building such wings and merely by being fabricaTed in This way iT conTribuTed much To The fuTure design of high load-bearing, buT Thin, aerofoil secTions.” and was projecting a performance the research pilots could only dream of. The F-104 would not fly before March 1954 but it was proving to be a classic case of the practical application outdistancing the research. Of greater concern than the aerodynamic performance of the thin wing, the aeroelastic properties were addressed by creating maximum torsional stiffness by designing the wing structure to have multiple rectangular cross-sections spars and tapered milled wing skins bolted directly on to the spars and ribs. Added to which was a requirement from the NACA for the wing to have 200 orifices for pressure distribution mapping and points for 343 gauges to measure load factors and heating characteristics. The manufacturing methods adopted by Stanley pioneered a new way of building such wings and merely by being fabricated in this way it contributed much to the future design of high loadbearing, but thin, aerofoil sections. The newly designed cockpit and forward windscreen was modelled after the aesthetically

shaped Douglas D-558-2 Skyrocket and incorporated an ejection seat as standard. Other than that the aircraft was essentially the same although it did play a part in contributing to technology for the X-15 by accommodating a redesigned low-pressure turbopump for the XLR-11 engine. The tail and landing gear were the same as those employed on earlier firstgeneration X-1 types and the propellant tanks and capacities remained the same. The rebuilt X-1D arrived at Edwards in mid-1955 and it was taken for a captive flight on December 3 with Joe Walker in the cockpit. The motherplane was the old reliable B-29, 45-21800, which had first carried it nine years earlier on its first flight. A glide flight followed on December 12 followed by the first powered flight three days later. Problems with an overspeed on two chambers and a premature shutdown on the others terminated the original flight objectives. Joe Walker would make 21 of the X-1E’s 26 flights, five by John McKay. On through 1956 the X-1E demonstrated

impeccable performance, Walker passing Mach 2 on August 31 that year. Modest damage was suffered after a similar flight on May 15, 1957, when Walker landed hard and broke the nose leg, his vision distorted by his faceplate. While in for repairs, engineers replaced the nitrogen pressurisation equipment with an air system so that the pilot could remove his faceplate for better visibility and several papers were published by the NACA on results of its heat tests in the preceding year. The X-1E was back on duty in August 1957 and on October 8 it reached Mach 2.24, about 1480mph, after which it was stood down for further modifications to improve directional stability by adding two ventral fins. Walker made the first flight with these installed on May 14, 1958, and noted a marked improvement busy sluggish manoeuvrability as a price. But there were other changes which the engineers wanted to make in an attempt to take the aircraft beyond Mach 3, which, with the loss of the X-2 in September 1956, was a target deemed unassailable until the X-15 came about. To give the X-1E a performance boost, back in November 1957 Hubert M Drake and Donald R Bellman of the NACA High Speed Flight Research Station proposed increasing chamber pressure in the LR-8 motor from 250psi to 300psi. They also proposed switching to a more high-energy fuel, replacing the diluted alcohol with a mixture of 60% UDMH (unsymmetrical dimethyl hydrazine) and 40% diethylene triamine, a combination known as Hidyne and one which was being tested on the rocket motors designed for missiles. After a flight on June 10, 1958, when the nose leg again suffered, these changes were introduced and time taken to install a new bell-crank in the horizontal tail to increase its travel and compensating to some degree for the lack of manoeuvrability caused by the ventral fins. John McKay made his first checkout flight on the X-1E in September and during October he completed two flights with increased chamber pressure. On November 6, 1958, McKay climbed aboard the X-1E and launched from the B-29 motherplane. It was the first flight to use the new Hidyne fuel and was a relatively simple and benign flight to check out the engineering changes and validate the new propellant.

Neil Armstrong flew the last mission of the X-1B on January 23, 1958.The X-1B is now in the National Museum of the US Air Force. NUSM

Joe Walker with the X-1E which he piloted for all but four of its 26 flights before the type was retired at the end of 1958. He was killed in June 1966. NASA

Following this flight the aircraft was returned to the engineering shop for installation of a new ejection seat, the old one had been incapable of supporting a fully suited pilot. The following month a routine x-ray inspection of the fuel tank revealed a crack. Two months earlier, on October 15, the first of three X-15 rocket planes had been rolled out to much publicity at North American Aviation’s Los Angeles facility. It would be flying within a year, promising hypersonic flight beyond Mach 6 and to heights three times greater than anything which had been achieved to date. It was the end of the era which had paved the way for rocket planes which would soon carry pilots out of Earth’s atmosphere and into space. The X-1B had stopped flying in January 1958 and now it was time to retire the X-1E. The No. 1 X-1 is in the National Air and Space Museum in Washington DC and the X-1B is on permanent display at the US Air Force Museum, WrightPatterson Air Force Base, Ohio. The X-1E was placed on a pedestal at the

Dryden Flight Research Center. These are the only surviving examples of the early X-series supersonic research aircraft. The No. 1 X-1, the X-1A and the X-1D together with both X-2 were lost in accidents. But it was not just the X-series which opened a new door on speed and altitude. The Douglas Skyrocket had its place in history too. Having made 122 flights with Douglas test pilots since February 4, 1948, the No. 1 aircraft was handed over to the NACA on August 31, 1951, from where it was sent to Douglas in 1954 for conversion to an all-rocket powerplant. It returned to Edwards on November 15, 1955, and a familiarisation flight was completed by John McKay on September 17, 1956, but it never flew again. It resides today at the Planes of Fame Museum, Chino, California. The No. 2 Skyrocket is on display at the National Air and Space Museum in Washington, DC, and the No. 3 aircraft is on a pylon at Antelope Valley College, Lancaster, California. They all have their place in history. ■

The first aircraft to exceed Mach 2, the No 2 Skyrocket, is preserved in the National Air and Space Museum, Washington DC. David Baker

ROCKETPLANES 111

A very

British approach

The first of two Saunders Roe SR.53 rocket powered interceptors (XD145) leaving diamond exhaust trails.

While the Americans were pushing hard on the speed and altitude barriers, engineers across the Atlantic here in Britain were developing a rocket-powered interceptor driven by the needs of the Cold War and capable of attacking Soviet bombers.

I

t is perhaps hard to imagine today but in the early 1950s Britain was a world leader in aviation. Not as a product of being a member of a vast international consortia but as a country in its own right. Having played a major role in the development of the jet engine in the 1930s, it had produced the world’s first jet passenger transport, the de Havilland Comet, in the 1940s and for a while held the world air speed record. Britain was active in rocketry of all kinds and in the early 1950s it was planning to develop an independent ballistic missile to go with its independent atomic weapons. Perhaps more important to the story of rocket planes, also in the early 1950s Britain was building the world’s first postwar manned rocket interceptor. Contrary to a widely held belief that postwar dabbling in rocketry was all about replacing manned aircraft with ‘push-button’ missiles, unlike the Americans the British were keen on the idea of rocket power for fighters and interceptors. Heavily impressed with the Messerschmitt Me 163, in the late 1940s de Havilland produced the Sprite with a thrust of 5000lb running on High Test Peroxide (HTP), while Armstrong Siddeley came up with the Snarler. With a thrust of 2000lb the motor ran on more conventional methyl/alcohol, water and liquid oxygen. The Snarler was installed in a converted 112 ROCKETPLANES

Hawker P.1040 (VP401), precursor to the sweptwing Sea Hawk, redesignated P.1072. Retaining its Rolls-Royce Nene turbojet it carried the Snarler under the tail section which provided two minutes and 45 seconds of burn time. With phenomenal acceleration and a top speed of Mach 0.82 it impressed officialdom who sought a target defence interceptor supplemented by rocket power. The result was a requirement issued

on February 2, 1952, by the then Ministry of Supply for an interceptor capable of reaching 100,000ft. While not being included in the invitation to bid, Saunders-Roe submitted a proposal which by the end of the year resulted in an instruction to proceed with three prototypes under the project designation SR.53 (XD145, XD151 and XD153). The aircraft would carry a turbojet for conventional subsonic cruise and

A mock up of the SR.177 with air-interception radar cone and clamshell cockpit canopy. This rocket interceptor would have had a top speed over Mach 2.2.

an 8000lb thrust de Havilland Spectre rocket for high-speed chase and combat. With a level speed of Mach 2 the aircraft was small and could not carry the advanced air-interception radar required. While the SR.53 was in development, in May 1955 the Ministry accepted a proposal for a larger and more capable operational version, the SR.177, which would have a 10,000lb thrust throttleable de Havilland Spectre 5A rocket motor giving the type a top speed of Mach 2.35 and a time to 70,000ft of three minutes, 51 seconds. It would carry two Red Top anti-aircraft missiles and two 1000lb bombs on underwing pylons. Nine pre-production aircraft were ordered but none were built and XD153 was cancelled, killed off by the 1957 Defence White Paper which made the colossal mistake of asserting that the days of the manned aircraft were over.

The aft fuselage section was removable for access to the rocket motor.

XD151 on static display at the 1957 SBAC Farnborough air show, where XD145 did the flight displays.

The SR.53 bequethed its propulsion geometry to the far more powerful SR.177, with the turbojet engine mounted above the rocket motor.

Nevertheless, the first SR.53 (XD145) made the type’s initial flight on May 16, 1957, and in early flights achieved Mach 1.33 during the test programme at Boscombe Down, Wiltshire. Both XD145 and XD151 wowed the public during the 1957 Farnborough Air Show but the latter crashed during a take-off attempt on June 15, 1958, when the rocket motor cut out just before rotation. Unable to lift off on turbojet power alone, the aircraft was destroyed and its pilot, John Booth, was killed. Ironically, the Ministry of Supply had tried

to keep the SR.177 project going and 300 were to have been procured, split between the Air Force and the Navy. With the Kriegsmarine interested as well, the Government had cleared production in Germany. But with the Government firmly opposed to any uniquely British combat aircraft surviving the axe, it went the way of many brilliant designs conceived and built in the UK by world-class aeronautical engineers. The sole surviving example of the SR.53 (XD145) is preserved in the RAF Museum Cosford.

Attacking the heat barrier –

X-15

the

B

y the end of 1958 the world was changing fast. Responding quickly to Russia’s Sputnik 1, the first artificial satellite launched on October 4, 1957, the US Congress had decided that it needed a dedicated agency to run the nation’s space programmes – such as they were. President Dwight D Eisenhower insisted, against fierce opposition from the air force, that this should be a civilian organisation. So was born NASA – the National Aeronautics and Space Administration – metamorphosed out of the old NACA, which had managed supersonic research since the mid1940s. The NACA officially became NASA on October 1, 1958. In the new world order, previous 114 XXX

rocket plane tests were known as Round One, operations with the upcoming hypersonic X-15 would be known as Round Two while Round Three would focus on a suborbital spaceplane called Dyna-Soar – an amalgam of Dynamic Soaring – ver y much an air force project. The X-3 to X-14 programmes were a mixture of experimental jet aircraft, vertical take-off aircraft and even the Atlas missile was given an ‘X’ designation in the transformed use of that classification. On June 24, 1952, the NACA decided that it should move its research and development up a notch and explore the aerodynamics of hypersonic flight, loosely defined as speeds in excess of Mach 5, and at altitudes of up to 50 miles. As early as 1945 the air force had defined the need for

The first generation of supersonic rocketplanes had pushed highspeed flight through Mach 3. Now it was time to take the next giant step for ward – to Mach 6 and beyond.

a Mach 3 research aircraft and that emerged as the X-2, which made its first glide flight only three days after the decision to go for a completely new research aircraft, later designated the X-15. The requirement was daunting. In June 1952 the record stood at Mach 1.45. Nobody really knew how an aircraft would behave at six times the speed of sound. All the engineers, scientists and aerodynamicists could say with certainty was that heat through friction at high speed would be ever y bit as daunting as the sound barrier had been a decade earlier. To test the best design engineering against a defined target speed of Mach 6.6, help from industr y was sought to provide the technical detail for a sufficiently robust airframe. In fact, work

carried out by Bell Aircraft’s Robert Woods assisted the NACA in writing the specification. What Woods proposed was a design concept from Bell employee Walter Dornberger, former head of the Peenemunde V-2 rocket facility and the man who had recruited Wernher von Braun to work for the German Army on ballistic missiles. The Dornberger hypersonic research aircraft was one of several proposals which had already been discussed at conferences and seminars presented by industry and to the air force and the research leadership at the NACA. Nevertheless, it was the Woods/Dornberger proposal which galvanised the NACA into action spawning a series of proposals from various bodies and industrial contractors. Throughout 1953 a series of committees examined the problems, looked at the requirement and made recommendations on the optimum approach. Study groups were set up to focus direction and these converged on the Air Force Scientific Advisory Board during October in which chairman Clarke B Millikan confirmed that it was time to develop such an aircraft. On February 4-5, 1954, a NACA Research Airplane Panel met under the chairmanship of Hartley Soulé to formally ask the three NACA laboratories (Langley, Ames and Lewis) and the Muroc Flight Test Unit at Edwards Air Force Base to support the bid for a hypersonic aircraft. Most of 1954 was spent wrestling highly complex aerothermal, aerodynamic and aerofoil challenges, most focusing on stability and control and the possible heating effects, as each of the NACA facilities applied their individual areas of expertise. Langley’s C H McLellan found a solution to the challenges of directional instability by suggesting a 10º wedge-shaped tail rather than the thin structure built on to the X-1 and the X-2. Others studied the complex interference patterns of air flow between the main wing and the horizontal tail; if set high on the vertical stabiliser encountering low pressure and low downwash and if set low on the rear fuselage directly in the region of high pressure and high downwash. The solution was unheard of: place the tail directly in the same plane as the wing and avoid the extremes of either. Republic Aviation bid to build the X-15 with a pronounced vertical tail and conformal cockpit canopy. NASA

Complete with air data probe for early tests to validate the design concept in flight, the X-15 was the first rocketplane designed on the basis of a comprehensive set of data from supersonic research with the X-1, X-2 and Skyrockets. NASA

Langley laboratory probably contributed much of what would become the X-15 design, producing advanced but theoretical analysis extrapolated from accumulating data with the X-1 series and the Skyrocket. Several alternative flight trajectories were constructed and analysed to see what impact they had on alternative configurations. The kind of research the aircraft was conceived to accomplish was instrumental in directing the configuration of the design. Skin temperature was a critical consideration when evaluating the flight regime and a limit of 1200ºF had been set as the maximum permissible due to the limitation of existing materials, until it was accepted that this threshold would have to be reset at 2000ºF as the equilibrium temperature for the underside of the wing. Attention to the thermal effect on materials and structures occupied a large part of the year, with considerable theoretical and test activity focusing on the way a wing structure could be built to accept some form of thermal flow while allowing a limited degree of wing distortion to accommodate unequal structural expansion.

As studies progressed this would be resolved around a temperature threshold of 1200ºF without inhibiting the performance of the aircraft or limiting the flight envelope. Nevertheless, the heating effects of reentering the denser layers of the atmosphere led engineers to calculate that a maximum altitude of 500,000ft was about the limit for the materials of the day. The science of thermodynamics was a totally new world for engineers, who had only the wind tunnel studies to go on and for which there was virtually no information at all on the strange world at the edge of the heart barrier – the place where speed and air meet at the limits of materials technology defined by mechanics and kinetic energy. But this was what the X-15 was all about, trying to find answers to questions which could only be asked when the hypersonic aircraft began flying. Similar problems had been encountered by rocket scientists trying to find a way to keep warheads intact across intercontinental distances. In 1954 there was a surge in the development of ballistic missiles which would be capable of hurling thermonuclear weapons ➤ NAA’s X-15 was half aircraft/half spacecraft, with attitude control thrusters and a rocket motor more powerful than the V-2. NAA

ROCKETPLANES 115

The ergonomic design of the cockpit owed much to the work of test pilot Scott Crossfield, the first man through Mach 2. NASA

Joe Walker moved from the X-2 to the X-15 for early research flights. NASA

halfway round the world and although it would be 1960 before they became operational, the environment into which the X15 would be delivered was not dissimilar in the challenges it faced to those confronting missile engineers in the second half of the 1950s. But more important for aviation, it would help define the limits to which very high speed combat aircraft could operate and it was that which attracted the air force.

a ticket to riDe

In July 1954 the NACA had reached its conclusions about prospects for a completely new aircraft. On the 9th it held a conference attended by the air force, the navy, the Wright Air Development Center, the Air Research and Development Command and the Scientific Advisory Board to outline its idea for a hypersonic research aircraft. Unlike the start made on the X-1 and the X-2, they were beginning with a calculated idea of prospects for achieving their goal based on measurements and test results from a decade of supersonic research; an effort which involved 10 rocket-powered research aircraft, consisting of three X-1s, three X-1As, two X-2s and two Skyrockets. During the conference the navy said that it had asked Douglas to look at whether it could build a rocket plane which could reach an altitude of 190 miles and of course it could – 116 ROCKETPLANES

“During the conference the navy saiD that it haD askeD Douglas to look at whether it coulD builD a rocket plane which coulD reach an altituDe of 190 miles anD of course it coulD – but it woulD burn up on re-entry” but it would burn up on re-entry because no materials to hand could protect it from the heat generated through friction with the atmosphere at the re-entry speeds thus incurred. But one highly productive outcome of the July 9 meeting was that numerous aircraft manufacturers sent their representatives to Langley to find out more about the hypersonic project. All these factors came together on October 5, 1954, when in an historic meeting the committee gave approval for the programme to proceed and NACA director Hugh L Dryden began discussions with the air force and the navy about compiling a technical specification from which contractors could bid with proposals. That specification stipulated a design maximum speed of 6600ft per second (4500mph) and a peak altitude of 250,000ft (47.35 miles), both values slightly lower than earlier recommendations had provided as concept targets. On December 14 the package was

examined by the Department of Defense Air Technical Advisory Panel, which endorsed the programme as a NACA project but with its oversight. The day before New Year’s Eve, the US Air Force Air Materiel Command began the process to set out a design competition whereby industry bidders would provide their own unique solutions to the technical requirements. This was a very different way of doing business than the way in which, a decade earlier, Bell Aircraft had received contracts to build first the X-1 series and then the X-2. With the New Year came rapid progress. On January 17, 1955, personnel at the WrightPatterson Air Force Base provided the NACA with the project designations and the formal agreement to assign the new aircraft as Project 1226 and the programme as the X-15. The next day a bidders’ conference was held and representatives from Bell, Boeing, Chance Vought, Convair, McDonnell Douglas, North American Aviation, Northrop and Republic Aviation came to see what was

required. On February 4, a further conference was held for the candidate engine builders, attracting attendance from Aerojet, General Electric, North American and Reaction Motors. The deadline for bids was May 9 and it was made clear that more than one proposal could be entered by each company, the possibility of a two-seat design being laid open for an observer instead of instrumentation. Because the aircraft would have to be matched with an appropriate engine, airframe bidders were asked to consider four potential rocket motors: the Bell XLR-81, the Aerojet XLR-73, the Reaction Motors XLR-10 or XLR-30 or the North American NA5400. Each manufacturer had gone away and looked carefully at what was required from the specification and by May only four contenders remained in the game. In the interval, the NACA had shared with each contender results from the 10 x 14in wind tunnel at Ames and the Mach 4 blowdown jet tunnel at Langley. These laboratory assets were crucial to giving the candidate manufacturers the detailed results from the aerodynamic and aerothermal analyses of information returned by the numerous supersonic flights of the preceding decade. The chairman of the NACA group was Hartley Soulé and it was he who coordinated

all the various proposals and examined the development options available; but as the decision neared as to who should build the X15 it became apparent that the optional rocket motors were in no fit state for selection. The power required to propel the aircraft to Mach 6+ and unprecedented altitudes called for a motor with much greater thrust than anything attached to a winged vehicle before. Walt William suggested that an interim propulsion system should be adopted until the definitive motor was decided upon. There was really only one choice. The XLR-11 motor which had been the powerplant for all X-1 and rocket-powered Skyrocket vehicles would be a valued substitute to get flights under way prior to selecting and installing the much more powerful motor. But the XLR-11 would be unable to give the X-15 even a reasonable performance to get the aircraft qualified for research flights so a double-pack comprising two motors stacked one above the other was proposed. By the end of June 1955, the bids had been evaluated and the evaluations rated the lead contender as North American Aviation, followed in order of preference by Douglas, Bell and Republic. NAA had produced an outstanding proposal brochure and impressed the review committee with its selection of Inconel X as the primary material for the wing structure.

This material has great strength at high temperatures and had been developed specifically by the company for such applications. The engineers on the selection teams were so taken with this material that they applied a universal rule that if for some reason the decision should go in favour of another proposer, constructor would have to use Inconel X in fabricating the wing and other hot structures. Over the next several months numerous teams and bodies involved in Project 1226 were consulted about the proposals and over the points system used to grade each design. Some felt that the decision to use Inconel X disadvantaged others while a small number thought it was an insidious way of locking in North American despite the outcome, since it would produce the Inconel X anyway. Despite misgivings and lengthy deliberations, NAA’s proposal kept coming back in favour – until the company suddenly withdrew its bid. In an unexpected shift, the company believed that it would be unable to meet all its existing commitments and fulfil the schedule required by the customer for this highly advanced hypersonic research aircraft. But on learning that it was hot favourite, vice-president and chief engineer Raymond H Rice wrote to the NACA and proposed either a stretch of the schedule by eight months or a total withdrawal, leaving the design proposal ➤

Designed at the insistence of Scott Crossfield, the ground simulator gave X-15 pilots an essential learning tool. NAA

jet engines; the Boeing B-50, a development of the B-29 which was much heavier and had several refinements and the Convair B-58 Hustler, a Mach 3 bomber, but it would not fly until 1956 and the NACA needed a proven and reliable carrier-plane. Given the need for a reliable, proven, launch platform, the only logical choice was the Boeing B-52 Superfortress which had made its first flight on October 2, 1952, and which by 1954 was in production for Strategic Air Command. The initial production version, the B-52A, was almost in parallel development with the X-15 and while this would not enter operational service before November 1957 it was clearly a winner. But instead of carrying the rocket-plane in a modified fuselage bomb bay, it was to be hung under a shoe pylon on the starboard wing inboard of the inner engine pair. In fact it was one of the three B-52A models which was modified for use and redesignated NB-52A. The design of the X-15 was a simple wingbody structure to simplify the transonic and low supersonic regimes while retaining its suitability for hypersonic research. Several design aspects were logical and had emerged before the contract was signed, such as the wedge-shaped tail described earlier. A conventional forward-facing windscreen, rear hinged canopy hatch and blended aerofoil surfaces defined the requirements placed upon the design team. Overall, the aircraft shape appeared simple and economic, conventional in outline and with side-chines blending the circular crosssection fuselage with the thin wings. Beyond those conservative design choices, the aircraft was anything but conventional. NAA’s chief structures engineer calculated that the aircraft would experience 800-1200ºF over much of its external surface (the ‘wetted’ area) during flight and the choice of materials

came down to corrosion-resistant steels, titanium and nickel alloys for the structural shape of the vehicle. Because these materials were limited to no more than 800ºF, Inconel X would cover the entire external surface of the aircraft. High-strength aluminium was the original material of choice for the pressure shell of the cockpit and for the equipment bay where sensitive operational systems would be housed. At first, high-strength titanium alloys were selected for much of the internal structure of the fuselage, the wings and the tailplane, while others which had less attractive thermal properties but were easy to weld were selected for other sections. This compromise was expensive and posed challenges. NAA eventually selected 6A1-4V, a highly desirable alloy with good thermal properties and which could be welded. In the aft fuselage where loads incurred by the rocket motor were prevalent, titanium frames were incorporated, but welding became a fine art blending materials together which were then inspected by radiographic instruments. The most common form was fusion welding in most areas of the structure, but resistance welding was also used whereby a force was applied with an electrical current flowing through contact electrodes on the parts to be welded. The resulting nugget fuses the two materials together with no flux needed and only a low voltage current applied, safe and economical on time and materials. Much of

the technology applied to the X-15 was to prove useful in high-performance aircraft and to the newly emergent space programme of the 1960s, materials science being one. Simplified, the interior of the X-15 carried a rocket motor in the rear fuselage, a cockpit section in the nose, while the main body of the aircraft contained propellant tanks. The aft and forward sections were semi-monocoque while the centrebody with the propellant tanks was monocoque. Positioning the tanks and achieving control over the centre of gravity was one of the big headaches of the design phase. At maximum throttle, the rocket motor would consume nine tons of propellant in just 86 seconds, burning off 59% of the weight of the aircraft at ignition. With such a prolific consumption there would be no time to trim the centre of gravity with balanced propellant consumption over time. To ease the problem, the forward liquid oxygen tank had an annular shape with toroidal end domes, divided into three compartments and containing a total of 10,400lb of oxidiser. In the centre of the annular ring was buried the helium tank for pressurisation. Aft of the LOX tank and the centre of gravity, the anhydrous ammonia tank carried 8400lb of fuel and was of a similar annular shape. Because it was located forward of the fuel tank, the liquid oxygen was transferred aft to the rocket motor by a pipe running outside the fuel tank and inside the port-side chine running down the side of the fuselage to the ➤

“At mAximum throttle,the rocket motor would consume nine tons of propellAnt in just 86 seconds, burning off 59% of the weight of the AircrAft At ignition. with such A prolific consumption there would be no time to trim the centre of grAvity” Left, top: Tests with the XLR11 installed in the X-24A. NASA Left, bottom: The XLR-99 was a throttleable rocket. USAF Right: Initially, the X-15 was equipped with vertically paired XLR11 motors. USAF

ROCKETPLANES 119

Suspended under the starboard wing of a purpose-built pylon, with a loaded weight of 34,000lb, only the B-52 could lift the X-15 into the air. NASA

Three X-15 rocketplanes (right) plus three lifting-body research aircraft (left) comprising (from the front) the HL-10, M2-F1 and M2-F2. NASA

Accompanied by an F-104A chase plane, the X-15 flares for touchdown which, at 200mph, was always going to be a critical test of skill. NASA

120 ROCKETPLANES

“EightthrustErs wErE locatEd in four pairs inthE nosE, Each pair at 90º to thE othEr,with two thrustErs on Each outEr wing surfacE.with hydrogEn pEroxidE as propEllant,thE pitch and yaw jEts Each dElivErEd a thrust of 113lb whilE thE jEts for roll control Each had a thrust of 50lb” aft section of the fuselage. Fuel from the aft tank was fed directly to the engine by an internal delivery pipe. Pressurisation of the fuel and oxidiser tanks was with helium, propellants being driven into the motor by a turbopump driven by a hydrogen peroxide gas generator powering two separate pumps, one each for fuel and oxidiser. In the 1950s this was a standard layout for rocket motors of many kinds and sizes. Some of the hydrogen peroxide was bled off to the attitude control system which would be used to stabilise the aircraft in the rarefied altitudes to which the X-15 was flown. Eight thrusters were located in four pairs of two in the nose, each pair at 90º to the other, with two thrusters (up and down) on each outer wing surface. With hydrogen peroxide as propellant, the pitch and yaw jets each delivered a thrust of 113lb while the jets for roll control each had a thrust of 50lb. Early flights with the X-15 would use a pair of Reaction Motors XLR-11 rocket motors which delivered a combined thrust of 12,000lb

when all eight combustion chambers were lit up. As readers will recall from earlier descriptions of its application to the X-1 series, this rocket motor had four chambers with each lit separately. The first two X-15s were initially fitted with the dual XLR-11. The definitive Reaction Motors XLR-99 engine was altogether different and would take longer to develop than the time required to get the X-15 flying. It had a single combustion chamber with a maximum thrust of 57,850lb at 100,000ft and in its initial configuration this engine could be throttled from 50-100% of total rated thrust. Later improvements allowed it to be throttled down as low as 30% while remaining stable. The XLR-11 had been a standard, fixedthrust rocket motor with basic technology and no innovative and advanced engineering such as that applied to the XLR-99. Located on the left side of the pilot, initially the throttle had three positions: Off, 50% and 100%. It would be modified later as the additional throttle gradient was added. With very little space and volume in the aft

Carried to an altitude of more than 30,000ft, the X-15 was almost entirely dependent on the B-52 for power and communications prior to release. NASA

fuselage in which to pack the engine, it was a complex and daunting piece of engineering, the first throttleable, man-rated rocket motor built. Man-rating was a phrase used at the time to indicate a level of unprecedented reliability and safety, a categorisation of failsafe engineering that would greatly lower the risk to the pilot’s life. Later, it would be a classification of reliability for space rockets carrying astronauts and this rating was applied when conventional missiles were used for manned space flights. Flying the X-15 would be unlike anything else yet put in the air. With aerodynamic control surfaces for biting the air and jet thrusters when there was no air to bite, control between the atmosphere and the nearvacuum of extreme altitude would pioneer the way later vehicles would fly into space. The pilot had three controls: a central control stick much like a conventional aeroplane; a left-hand side-stick for operating the thruster jets and a right-hand side-stick for blending aerodynamic controls with the thrusters as the vehicle went out of and then back into the denser atmosphere on altitude runs.

‘Go’ for fliGht

Following highly detailed analysis of the final design from North American, the company got the formal go-ahead to start building the three aircraft on June 11, 1956. Within months the NACA and the air force would be left without a rocket-powered research aircraft until the first X-15 was ready for flight. It took a little over two years to build the first one (56-6670) which was ceremoniously rolled out of the Los Angeles factory on October 15, 1958. This was a great time for American rocketry and space travel too, little more than two weeks after the NACA had become the National Aeronautics and Space Administration.

An early drop test has the X-15 falling and banking to starboard for a descent to the lake bed, a critical requirement for landing being to jettison the lower half of the ventral tail. NASA

Within a few days 56-6670 had arrived at Edwards Air Force Base, California, and preparations for flight tests began. That would take several months and in the meantime engineers completed modifications to two eight-engine B-52s which were being converted into motherplanes for the X-15 programme. One B-51A (52-003) was designated NB52A and this ship had been at North American’s Palmdale facility for conversion work since February but arrived back at Edwards in November. The second aircraft, a B-52B (52-008), was designated NB-52B and was on the flight line by mid-1959. In addition to the motherships, chase planes were selected and assigned, their pilots receiving orientation and familiarisation briefings on how they would be accompanying this hot rocket ship. They would be assigned specific locations along the flight path to report visually and take photographs of key

stages in the flight, each one different according to the requirements of the specific objectives. Throughout the X-15 programme, chase aircraft would include the North American F100 Super Sabre, Lockheed F-104 Starfighter, Lockheed T-38 Talon, Northrop F-5 Tiger and McDonnell F-4 Phantom II. In all, chase pilots would fly 741 sorties in support of the X-15. The first flight test had Scott Crossfield in the cockpit of the X-15 for a captive flight on March 10, 1959. Unlike the previous supersonic rocket planes, the pilot would ingress the cockpit with the aircraft on the apron. There was no way he could move from the B-52 to the X-15 in flight. Three more captiveactive flights were conducted in April and May prior to the first release for a glide back down to the lakebed on June 8 from an altitude of 37,550ft. This was the only glide flight scheduled for the X-15 but when the pitch ➤ ROCKETPLANES 121

Neil Armstrong made his first flight in the No 1 X-15 on November 30, 1960 and gives his feedback. Only seven of the eight rocket chambers ignited. NASA

damper failed, the fully fuelled aircraft began bucking motions which were compounded by pilot-induced-oscillations (PIO) from which Crossfield quickly recovered and touched down after a free flight lasting four minutes 57 seconds. The first powered flight was made on September 17, 1959, with the second X-15 (566671) carrying the XLR-11 twin-pack. After dropping away from the carrier-plane, all eight chambers on the rocket motors were lit up in turn and burned for a total of three minutes 44 seconds. In an incredible burst of power and performance, it accelerated to a speed of Mach 2.11 (1393mph) in a flight lasting nine minutes 11 seconds from drop to landing. There were a few minor problems including a failure in the turbopump case and the roll damper but it had demonstrated outstanding performance and vindicated the claims of design engineers confident that they had solved problems unimaginably complex only a few years earlier. A repeat flight was flown on October 17, nudging up to 61,781ft and slightly higher than the previous flight, but apart from a minor fire in the hydrogen peroxide compartment and in the engine compartment and ventral tail section, an oil damper failure and nose gear door mishap, it had gone well. But the problems were not show-stoppers. Encounters with failure were all in a rocket pilot’s day! The third powered flight, and the second with the No. 2 X-15, began as usual on November 5 but quickly escalated into a potential catastrophe when an explosion ripped through the lower XLR-11 just 14 122 ROCKETPLANES

seconds after ignition and going supersonic. Chase pilot Bob White called out over the radio: “Looks like you had an explosion in the rocket motor.” And then, a few seconds later and with greater urgency: “You have a fire! Please shut down.” Rapidly shutting down the power, Crossfield began a propellant dump which lasted one minute 54 seconds as he brought the X-15 around for an emergency landing. Rogers Dry Lake was too far so he headed for Rosamond Dry Lake and touched down just five minutes 28 seconds after the drop. As he brought the rocket plane in, it still had some fuel on board and as the nose slammed down, the leg broke and the back of the X-15 snapped in two just forward of the LOX tank and immediately behind the cockpit. Fire trucks always on standby at prime and secondary landing sites raced to the scene, dowsing the aircraft with fire-suppressant. Crossfield had been lucky and while affirming afterwards that it never crossed his mind to eject after the explosion, there were several examples of X-planes catching fire and being dumped on the desert floor. Despite the additional weight of residual fuel, the engineers were determined to discover the real reason why the nose leg failed and eventually discovered that the leg was not sufficiently responsive to the loading which occurred as weight was transferred from the skids to the nose. It was simply too stiff and required additional damping. The damage to 56-6671 was quickly made good, a splice plate being added at top and bottom and extra fasteners being attached, modifications which would eventually be

carried out on the other two aircraft when they recycled back into the maintenance shops. Meanwhile, the first aircraft, 56-6670, received a double XLR-11 rocket motor package and arrived back at Edwards ready to make its first powered flight on January 23, 1960, another run to Mach 2 for Scott Crossfield. This was the first time the NB052B was used in its modified motherplane role and the first flight of a stable guidance platform on the aircraft. Over the next several weeks more flights were made, with increasing success despite the odd gremlin appearing to mar a clean fault sheet, and Joe Walker, NASA’s official X-15 test pilot, flew the aircraft for the first time on March 25 when he too reached Mach 2. By this time NASA had assigned Neil Armstrong and John McKay while the air force named Cpt Robert White and Maj Robert Rushworth and the navy selected Cdr Forest Peterson to fly the X-15. Later, NASA would also assign Milton Thompson and William Dana and the air force would add Cpt Joe Engle, Cpt William Knight and Maj Michael Adams to the flight roster. As the flight rate picked up pace, a number of milestones were reached. On May 6, 1960, Cpt White flew the first mission with physiological measurements recorded on board from biosensors attached to the pilot’s body, a technique which would be a characteristic feature of all space flights. His flight was not without its drama, however, when the lower section of the ventral tail failed to jettison as required, an emergency procedure ensuring that it did on landing gear deployment.

On May 12, 1960, Walker flew the first X-15 flight through Mach 3, achieving a maximum speed of 2111mph and an altitude of 77,882ft. During another flight on August 4 he reached Mach 3.31 (2196mph), the fastest achieved in an X-15 powered by twin XLR-11 rocket motors. While these flight activities were logging performance data for the first two aircraft, the third X-15 (56-6672) received the first flightready XLR-99, delivered to Edwards Flight Test Center on March 28, 1960, and installed over the next several weeks. The development had taken longer than hoped but it had been prudent to get the aircraft flying on the interim powerplant. Now only a few static tests on the No. 3 aircraft stood in the way of a significant performance improvement. On June 8, Crossfield was in the cockpit for a routine test, not considered hazardous and so low-key that he was wearing a conventional suit and tie. Just there to throw appropriate switches and to monitor an engine restart procedure, he cycled the engine through its first run. Then, while proceeding through the restart cycle, a terrific explosion blew the nose off the aircraft and hurled it forward 100ft, imposing an estimated 45G on Crossfield, who testified to it being the loudest noise he had ever heard in his life and creating a light brighter than the sun. The No. 3 X-15 was returned to North American on June 17 for substantial rebuild while the second Thiokol XLR-99 was delivered to Edwards and installed in the No. 2 aircraft. Again, a comprehensive ground test programme thoroughly checked out the integrated rocket motor and airframe and this

time the relief valve and pressurising gas regulator which had failed on the first engine did not repeat the occurrence. Crossfield flew this aircraft with its potent rocket motor for the first time on November 15, 1960, the 26th flight of the X-15, and achieved a speed of Mach 2.97 (1960mph), the highest speed he would ever achieve. Only minor glitches marred a successful flight, a loss of pneumatic pressure being one. Crossfield’s role as contractor test pilot was coming to an end, all the requirements of the manufacturer were being met and it would soon be time to hand the X-15 over to NASA, the customer. Another flight on November 22 to check out the restart capability of the XLR-99 went perfectly, with modified throttle settings selected to operate sequentially at 50%, 75% and 100% of rated thrust. Crossfield’s final flight was on December 6, his 14th on the rocket plane and the 30th for the X-15. Under the contractual agreement, North American would restrict its flight tests to altitudes below 100,000ft and speeds around Mach 2. Now it was an all-NASA/Air Force/Navy operation but the first X-15 was returned to North American for installation of its XLR-99, departing Edwards on February 8, 1961, and returning on June 10 to join the No. 2 aircraft on the flight line.

hypersonic flighT

As the test pilots picked up pace the engineers developed increasingly sophisticated flight plans, probing many aspects of the aerodynamic and thermodynamic environment which the aircraft was designed to explore.

The robust nature of the programme was a far cry from the primitive days with the X-1 and the Skyrocket. Even the relative ambitious operations with the X-2 paled in significance to the outstanding capabilities of this new-generation rocket plane. Ever since Chuck Yeager had flown through the sound barrier in October 1947, it had been assumed that the pilots who first flew into space would do so on wings with which they could control a safe return to Earth to a conventional landing strip. It had not turned out that way. Almost exactly 10 years after Yeager’s flight the Russians had launched the world’s first artificial satellite, Sputnik 1. The reaction in America and around the world had been profound, stimulating the formation of NASA from the NACA and pitching the new civilian space agency into a race to be the first to put a man in orbit. Not with a winged rocket plane but in a capsule on top of a converted ballistic missile. To the test pilots who had flown through Mach 1 and Mach 2, planned for Mach 3 and seen the construction of a rocket plane capable of taking them to the fringe of space, it had been a bitter disappointment. Not least because the plan for America’s man-in-space programme had been lifted from the air force and renamed Project Mercury, snatched from an air force to which many test pilots had pledged loyalty and in whom they had placed trust that one day machines with wings would carry them into space. Even as North American was handing over the three X-15 aircraft to the customers who would not take the rocket plane and explore ➤

“The reacTion in america and around The world had been profound, sTimulaTing The formaTion of nasa from The naca and piTching The civilian space agency inTo a race To be The firsT To puT a man in orbiT. noT wiTh a winged plane buT in a capsule on Top of a converTed ballisTic missile.” Left, top: The X-15 was hazardous until all toxic propellants and fluids had been removed. Left, bottom: Neil Armstrong displays the ball-nose aerodata sensors. Below: Structural failure on landing after the third drop test of the No 2 X-15 on October 5, 1959. NASA

ROCKETPLANES 123

Parked outside a hangar at the renamed Dryden Flight Research Center, the second X-15 shares ramp space with the HL-10, developed to investigate the handling qualities of a lifting-body concept. NASA

new areas of the flight envelope, other military test pilots had been selected to fly the manned Mercury missions. The first of these, Alan Shepard, made a suborbital hop into space on May 5, 1961, a mission lasting 15 minutes from Cape Canaveral and ending in a splashdown off the coast of Florida. It came less than a month after Yuri Gagarin had made Russia the first country to put a man in space. For NASA, the air force and the navy, there were new frontiers to pursue but the X-15 would not be the vehicle to carry them into space until more speed and altitude flights had taken place. Yet, in addition to the Mercury flight, the X-15 created a double celebration for Americans by being the first aircraft to exceed Mach 4. Piloted by Robert White on his flight X-15 flight, the No. 2 aircraft achieved Mach 4.43 (2905mph) on March 7, 1961. Yet even as these flights progressed, the contribution being made by the X-15 programme to space flight was significant. Piloted by Joe Walker, on March 30, 1961, the second X-15 was flown to a height of 169,700ft, setting a new record. He was wearing the new A/P22S-2 full-pressure suit of the type which had been the base design for the Mercury astronaut suit. This suit would form the template for the suits worn by Gemini and Apollo astronauts and by U-2 and SR-71 flights. But the records for the X-15 itself were tumbling fast. On April 21, 1961, Robert White made the first flight faster than 3000mph when he flew the No. 2 aircraft to Mach 4.62 (3074mph). 124 ROCKETPLANES

Six of the 12 pilots who would fly the X-15: (from left) Joe Engle, Robert Rushworth, John McKay, William ‘Pete’ Knight, Milton Thompson, and William Dana. NASA

Just over two months later, on June 23 he became the first man to fly a winged aircraft faster than Mach 5, achieving a speed of 3603mph (Mach 5.27) and an altitude of 107,700ft. This flight also inadvertently demonstrated the effectiveness of the pressure suit when it was required to automatically pressurise and protect the pilot when the cabin atmosphere dropped to a level equivalent to an altitude of 56,000ft – far too low to sustain life. On these speed and altitude flights the effects of heat and stress were making visible signs too, with skin buckling and discolouration. But this was the purpose of the aircraft and in that regard it was doing its job. Technology development was a

fundamental part of the aircraft’s flight objectives and one such example was the introduced of the Honeywell MH-96 adaptive flight control system. The purpose of this was to integrate signals from sensors in the aircraft’s platform to adjust the balance between the aerodynamic controls and the thruster jets, one phasing in as the other phased out. An engineering test pilot by profession, Neil Armstrong had worked on the development of this system and it was first flown by him on the first flight of the No. 3 X15 after it returned to Edwards following repair after the ground explosion on June 8, 1960. That flight took place on December 20, 1961, and although the MH-96 system

dropped out as the aircraft was released from the motherplane, it re-engaged after the engine was ignited. Nevertheless, there were some erroneous inputs during the flight but it successfully demonstrated the adaptive flight control system which would be developed into a widely used application. The No. 1 X-15 had made its first flight with the XLR-99 on August 10, 1961, and all three aircraft were now engaged in flight tests. The MH-96 adaptive control system was fine-tuned to the excellent hypersonic handling qualities of the X-15 and was routinely handling the transfer between flight control systems to the point it was becoming apparent that it was capable of handling flight adaptations without the pilot intervening. This was all the more noticeable on altitude flights which were becoming increasingly more capable throughout the second half of 1961. On October 11, 1961, White had piloted the No. 2 X-15 to an altitude of 217,000ft and on April 30, 1962, Walker reached 246,700ft with the No. 1 aircraft, thus achieving the design height. But there was more to come. On July 17, White eclipsed that by flying the No. 3 aircraft to a height of 314,750ft which qualified him for US Air Force astronaut wings, thus becoming the fifth American to reach space, preceded by Alan Shepard and Virgil ‘Gus’ Grissom on suborbital ballistic flights and John Glenn and Scott Carpenter on orbital flights. But few today recognise this achievement and even NASA will not include Bob White in the astronaut league of space and women because they adopted a notional height of 62 nautical miles (375,720ft) as the qualifying altitude. In reality, an altitude of 400,000ft (75.75 miles) makes the most sense since that is the altitude at which there is sufficient air to exert a retarding influence of 0.05G on an object returning from space. NASA uses that retardation measurement to define ‘entry interface’. That is the altitude at which NASA places the division between earth and space, the altitude at which the planet exerts a measurable influence on a free body in motion.

Released for flight and under power, the X-15A-2 achieved speed and altitude potential of its design... but carried the airframe to the limit of its ability. NASA

Extended in length and carrying two jettisonable drop tanks to increase burn duration of the rocket, the X-15A-2 was the definitive version of this plane. NASA

As the X-15 flights progressed and more records toppled, the achievements of the winged rocket plane were eclipsed in the public eye by dramatic and breath-taking achievements from NASA’s manned space programme. In 1965 and 1966 NASA’s Gemini programme would conduct 10 flights involving space walking, 14 day missions and rendezvous and docking as prelude to the manned Apollo flights which would commence in October 1968. But not everyone accepted that the X-15 pilots had reached space, which was after all an arbitrary line above Earth where the atmosphere ended and the vacuum that is space began. The Federation Aeronautique Internationale (FAI) is the international body which sets the agreed parameters for aviation records and they determined that an altitude of 100km was that arbitrary line where space begins, or 328,100ft. Everyone reaching that attitude would qualify under international rules. The record set by White was less than that, measuring only 95.9km. But the air force judged an altitude of 50 miles, or 80.45km, to

be the arbitrary line, an altitude of 264,000ft. Nevertheless, two flights, both by the same pilot, did accommodate the FAI requirement. On July 19 and again on August 22, 1963, Joe Walker reached altitudes of 347,800ft and 354,200ft respectively in the No. 3 aircraft. On the latter flight the X-15’s XLR-99 engine had been fired for 85.8 seconds and the flight lasted a total of 11 minutes 8.6 seconds from release to landing. The X-15 had been equipped with a towed balloon deployed at attitude in an attempt to measure the density of the Earth’s atmosphere. It failed, as did a similar experiment on a Mercury spacecraft trailing a similar balloon from orbital altitude. That year the X-15 No. 1 became the first piloted aircraft to exceed Mach 6, achieving a speed of 4018mph (Mach 6.06) and a remarkable achievement for the unmodified aircraft. The pilot was Maj Robert Rushworth and the XLR-99 had fired for 81.2 seconds in a flight that lasted a total of nine minutes 24 seconds. Flights to higher speeds were sought through modifications to the second X-15 following a landing accident which occurred to John McKay on November 9, 1962, in which an aborted flight resulted in a heavy landing causing the left skid to fail and the part wing and stabiliser to dig in and roll the aircraft inverted on the ground. McKay suffered a crushed vertebrae but returned to flight five months later. While the No. 2 aircraft was being rebuilt, a substantial re-engineering of the aircraft equipped it for very much higher speeds and for this it was re-designated X-15A-2 and equipped with two external drop-tanks. With these, the engine burn time would be increased by 70%, each tank being 23.5ft long and 3ft 2in in diameter. The port side tank held liquid oxygen and three helium pressurisation bottles. The starboard side tank held the extra anhydrous ammonia fuel and together the two tanks added 13,500lb weight to the aircraft, the port tank being 2000lb heavier than the other. The tanks were costly and an effort was made to reuse them. ➤ ROCKETPLANES 125

Escorted by a T-38 chase plane, the X-15 prepares for a research flight, one of 199 between 1959 and 1968. NASA

An additional modification to the X-15A-2 was a 29in extension in the length of the fuselage between the two propellant tanks for 48lb of liquid hydrogen for a scramjet engine which was to be located beneath the fuselage and forward of the ventral tail. It also had a longer landing gear with modifications to the thermal protection which comprised a sprayon ablator that would burn off at extreme temperature and protect the underlying structure. The left cockpit window was changed to an elliptical shape with an eyelid that could be closed for high speed runs and opened by the pilot for landing. The aircraft returned to operations on June 25, 1964, with a checkout run by Rushworth to Mach 4.59. Several more flights followed as required for working up the flight capability to test thermal properties as well as the engineering of the newly modified aircraft. On November 18, 1966, piloted by William Knight, the A-2 clocked Mach 6.33 (4250mph) following an engine burn lasting two minutes 16.4 seconds, a historic achievement but one in which the programme demonstrated its flexibility and operational effectiveness. Earlier that day an attempted flight by the No. 3 aircraft had been aborted due to a minor technical problem. Such simultaneous operation with two X-aircraft on the same day was a sure indication that NASA had entered a new era with hypersonic flight activity. The speed flight boosted confidence in a very special, very high speed run, using the same MA-25S ablative compound which had worked well under real conditions. Piloted by McKnight, the flight began during the early afternoon of October 3, 1967, with the drop coming one hour into the flight. The engine was lit and special care and attention to this specific flight paid dividends. The aircraft reached a maximum altitude of 126 ROCKETPLANES

102,100ft and levelled off for the speed run. The motor ran for two minutes 21 seconds and pushed the X-15A-2 to a world shattering record of Mach 6.7 (4520mph), the fastest and winged vehicle would fly until the Shuttle was returned to Earth on April 14, 1981, two days after launch on its first flight. A world record which stands to this day for a winged aeroplane. The X-15 landed after a free flight time of eight minutes 17 seconds. During the flight, shock waves had burned through the leading edge of the ventral tail starting a small fire in the lower engine bay, the attached dummy scramjet was jettisoned when heat ignited the separation charges, the external tank jettison system was compromised. But it had been a total success in providing data and even in its fatigued state providing engineers with a fascinating forensic insight into hypersonic flight within the atmosphere. This was the last flight for the A-2 variant and a total vindication of the original design eked out over long nights and hot coffee. Just over a month after the record altitude flight, on November 15, 1967, the No. 3 aircraft began a high speed run piloted by Michael Adams. The flight began with the B52 taking off around 9.15am and release of the X-15 at 10.30am. The rocket motor ran for its anticipated 82 seconds and the aircraft achieved an altitude of 266,000ft and a maximum speed of Mach 5. On re-entering the denser layers of the atmosphere the aircraft began to yaw wildly and although Adams regained control from a spin, the pilot appeared to chase the automatic inputs from the MH-96 stability augmentation system. The aircraft entered an uncontrollable oscillation and disintegrated, killing the pilot. The sole remaining X-15, aircraft No. 1, did not fly for four months and there was never a satisfactory judgement as to whether the

accident to No. 3 was caused by pilot error or some insidious combination of conflicting control commands and inputs that overwhelmed the skills of a competent astronaut. For that was what he was, having flown to an altitude fractionally above that considered by the air force as a qualifying flight. The effect was heavy on a team which had by this time conducted 190 successful and safe flights with the loss of one aircraft and its pilot. The programme was running to a natural end, notwithstanding the extraordinary quantity of data returned by the three aircraft – the world’s first and only hypersonic aircraft. A few more research flights were made, the last on October 24, 1968, when Bill Dana flew a free flight lasting 11 min 28 sec to a maximum speed of Mach 5.38 (3716mph) and a top altitude of 255,000ft. There was an attempt to fly the aircraft one last time to complete a record 200 drops in nine years but in eight attempts between November 25 and December 20, 1968, one gremlin after another crept in to prevent that happening. Pete Knight was in the aircraft ready to fly on that last attempt, five days before Christmas, but a snowstorm hit Edwards and a voice came over Pete’s intercom, “Someone is trying to tell us something. It’s time to wrap up the programme.” After the No. 1 aircraft had been lowered from the NB-52A it was placed in storage and then moved to its final resting place, the National Air and Space Museum in Washington DC, where it remains under the same roof as the Bell X-1, which first took a pilot through the speed of sound. The X-15A-2, the No. 2 aircraft, is at the National Museum of the US Air Force, WrightPatterson Air Force Base, Dayton, Ohio. ■

THE FINAL

FRONTIER Rocketplanes took a back seat a affter t the X-15 while test pilots and astronauts went to the moon and rode a winged wii spacecraf aft ft called Shuttle to build a giant space stati tion i – unti til i a group of entr trepreneurs r and billionaires revived the concept.

T

he motivation for a lot of rocket pilots was the desire to fly into space and aft fter t it became possible to design aircraft ftt for hypersonic flight above Mach 5 that possibility tyy became a plausible option. But it was not one taken up and utilised aft fter t the Space Race began in the late 1950s. In October 1957, two tw w years before the X-15 began its first drop tests, Russia launched Sputnik 1 and a race started to put the first man in space. Speed of a different kind was essential as time became the criteria for choosing the way to do that. Instead of the steady and logical progression toward winged rocketplanes capable of reaching orbit, converted ballistic missiles were fast-tracked to launch capsules designed using the physics of survivable reentry warheads. That challenge had been cracked by the mid-1950s, opening the way for a simpler and quicker method of putting humans in space. It had not always been that way. Before Sputnik 1, the next progressive step beyond the X-15 would have been Dyna-Soar, an amalgam of ‘dynamic soaring’, a concept in which a winged rocketplane would be fired into space by a converted missile on a ballistic flight carrying it half way round the world, or directly into orbit where it would

remain for several days. It grew out of the air force’s interest in commanding the highground of the future battlefield – space itself. Th The h NACA saw it in some respects as a continuation of the hypersonic research programme, albeit as an ‘operational’ US Air Aii Force programme. Dyna-Soar would blend the research work of the X-series and the Sky kyrocket y programme into a winged re-entry vehicle capable of dissipating heat generated by the kinetic energy gyy of returning through the atmosphere at Mach 25. Launched Laa by a ballistic missile and recovered like a spaceplane it never was truly in the category of a rocketplane: defined as a vehicle carried into the air by wings, powered to higher performance by an integral rocket motor, returning to Earth for a conventional landing. Dyna-Soar was approved in 1957 and on June 16, 1958, the air force announced that Boeing had been selected to build it while the Martin company would manage the Titan missile to launch it. Dyna-Soar was envisaged as a multi-stage programme, transitioning from suborbital hypersonic tests to flights around the world and finally to orbital missions, some of which were envisaged as satellite intercept and destroy roles. Exactly one month after Boeing got the contract the National Aeronautics and Space Act was signed pledging a new civilian space

agency formed out of the old NACA – the National Aeronautics and Space Administration (NASA). The writing was on the wall. Major space adventures would be under the control of the civilian agency, not the military. Despite vigorous objections, the air force was gradually levered out of the space role, its Man-In-SpaceSoonest (MISS) programme for an orbiting capsule launched by ballistic missile being transferred to the new space agency where it was immediately re-born as Project Mercury. Th The h air force had never seen MISS as the successor to the X-series rocket-ships but now Dyna-Soar was threatened by another programme, way above Top Secret, which had been under way at the CIA (Central Intelligence Agency) for some time. The classified programme was given a variety tyy of coded names and designations but it is remembered today as Corona, an unmanned spy satellite born long before anyone had put anything in orbit. It was only a matter of time before the potential of a cheap automated spy satellite killed off the idea of an expensive orbiting manned spyplane. In 1961, Defence Secretary Robert McNamara relegated Dyna-Soar to an experimental role for research purposes when it became the X-20. Two years later it was cancelled outright. ➤

Boeing’s Dyna-Soar, a rocket-powered military spaceplane, was cancelled in 1963 despite years of development work.

A new stArt

For 30 years after the cancellation of the X-20, thoughts of a new rocketplane were preserved only in the dreams of aviation pioneers and a few engineers. As the space programme evolved and men went to the moon, NASA developed a winged spacecraft – the Shuttle – and between 1981 and 2011 flew 133 orbital flights during which it was used as a truck for lifting pieces of the International Space Station into orbit. But in 1993 the seeds of a new project had begun to grow. Not in any government agency or military research department but in the

Dyna-Soar vehicle atop its Titan I booster.

128 ROCKETPLANES

speculative imagination of a few way-out dreamers who thought that technology and a renewed learning curve off the back of the Shuttle, made it plausible to reopen the possibility of a rocketplane to space. Not as a research project or for scientific purposes but as a rocket powered aircraft capable of reaching an altitude of at least 100km and thereby qualifying as a space flight, before descending for a controlled landing. Because of its similarity in purpose to the popular light aircraft used for fun and pleasure, it was named as the ‘Piper Cub’ of space. That quickly became SpaceCub and the idea was taken to the May 1995 International Space Development Conference organised by the US National Space Society where it was received with rapturous enthusiasm. The very idea of ordinary people flying into space was so radical a departure from the heavy hand of government-controlled space flight that its sheer audacity appealed to Americans across the country. To reach beyond the edge of the atmosphere is easy, requiring a speed of only 5600mph and a mass ratio (structural weight to gross weight) of 0.5. Reaching orbit is a completely different matter and requires a speed of 17,500mph – Mach 25. A major problem is the ability to create a small rocketplane capable of supporting several people for a weightless experience of about five minutes followed by re-entry and a survivable thermal protection system. A personalised rocketplane was an idea that would catch on big. Within a few hours of hearing about this idea, qualified medical physician and aerospace engineer Peter Diamandis

announced the X-Prize, named after the Xseries of rocket research aircraft as well as the many other experimental flying types developed under this designation. Peter Diamandis was only just 34 years of age but fired with the enthusiasm of an entirely new group of rocket entrepreneurs, and the promise of opening up space to the ordinary citizen. The die was cast. The X-Prize needed funds and a series of backers provided sufficient money to offer a prize of $10 million, which was appropriate as X is the Roman letter for ‘10’. The idea was inspired in no small part by the series of prizes which had inspired pioneer aviators after the First World War, most notable among which was the Orteig Prize of 1919, offered to the first pilot to make a solo flight across the Atlantic, which prompted Charles Lindbergh to make the flight and claim the prize in 1927. That challenge, and Lindbergh’s flight, had inspired a new generation of pioneers making flights which opened up the world for aviation. The XPrize founders wanted to do just the same thing for opening up rocketplane travel to space for everyone. Some 26 teams competed for the prize, ranging from very small companies to major organisations and from hobbyists to wealthy benefactors employing rocket engineers and planemakers. The project gathered momentum but success was not quick. In May 2004 it was renamed the Ansari X Prize when billionaire entrepreneurs Anousheh and Amir Ansari donated several million dollars to this and other technology development programmes. It came only a few months before the winning team claimed their reward.

Scaled Composites SpaceShipOne on June 21, 2004, after it made the world’s first privately funded flight into space.

SpaceShipOne

A lead contender for the Ansari X Prize, Burt Rutan had made his name in the field of composites applied to novel aircraft design and engineering challenges, creating a generation of functional but highly aesthetic aircraft designs which were field-leaders in efficiency and refined aerodynamics. Supported by the wealth of Paul Allen, the co-founder of Microsoft, Rutan recruited specialised teams and talented individuals experienced in the fields of rocket science and propulsion engineering. Rutan had achieved global recognition for his Voyager aircraft which made an unrefuelled nonstop flight around the world in nine days during December 1986. The prize required two flights to an altitude in excess of 100km within two weeks using the same vehicle. Known as Tier One, the Rutan bid achieved its first flight to an altitude of 102.9km on September 29, 2004, piloted by Mike Melville and flew again, to an altitude of 112km, on October 4, piloted by Brian Binnie. Their rocketplane was named SpaceShipOne and it would inspire a new type of entrepreneur

SpaceShipOne now resides in a museum.

Virgin Galactic’s SpaceShipTwo, with black underside, attached to its WhiteKnightTwo launch vehicle during glide test flights.

and a new generation of rocketplane designs, all of which, now that it was proved to be possible, had their sights set on making money from what was the world’s first non-government space flights. SpaceShipOne was able to carry a total of three people including the pilot. It had a length of 28ft, a wingspan of 16ft 5in and a total loaded weight of 7,900lb. It was powered by a hybrid rocket motor delivering a thrust of 16,500lb and had a rate of climb of 82,000ft per minute. But the idea behind the prize was not to achieve records but to attract a new generation of pioneers to fully commercialise flight to the edge of space. It certainly caught the attention of British entrepreneur Richard Branson. Fired by the excitement of carrying people into space on a routine basis, in 2005 Branson set up The Spaceship Company with Burt Rutan, at first jointly owned and then solely by Virgin Galactic from 2012. The idea of sending thrill-seekers to the edge of the atmosphere required a larger rocketplane and that was designed with a

capacity to carry six people including two pilots. Named SpaceShipTwo, it has a length of 60ft, a span of 27ft and a gross weight of 21,400lb. Theoretically, it has a maximum speed of 2500mph and a peak altitude of 361,000ft (110km). At first SS2 was to have been powered by a hybrid liquid/solid rocket motor manufactured by the Sierra Nevada Corporation but this was changed in May 2014 to a similar type of propulsion system but with a change in the type of solid fuel employed. There had been major problems developing SS2 and in tests with its engine. In July 2007 three technicians were killed and one seriously injured when an explosion occurred. The motor had been a serious problem for several years and the change in 2014 placed development of RocketMotorTwo in with Virgin Galactic. The new solid fuel is a thermoplastic polyamide and several test runs of more than 60 seconds had been carried out but modifications were necessary to the wing structure of SS2 for it to hold methane and helium for controlled start-up and shutdown. ➤

Concept art for Virgin Galactic’s base, Spaceport America, which has now been built near El Paso in New Mexico, USA.

SpaceShipTwo

By October 2014, SS2 had completed 54 glide flights from its White Knight 2 mother-plane demonstrating aerodynamic performance and the feathering concept of its twin boom and tail assembly. This is a key element in the successful descent of SS2, whereby the two booms are rotated so as to reduce the speed as well as the descent rate in a concept described as a shuttlecock manoeuvre to prevent excessive speed build-up and thermal stress on the vehicle. This is only possible because of the relatively low speed compared to a vehicle reentering the atmosphere from orbit. Marketed as an opportunity for ordinary people to reach space, SS2 had nevertheless been delayed far beyond its original schedule, when it was expected to have begun commercial fee-paying flights for passengers by 2010 at the latest. Powered tests with SS2 began with a supersonic flight on April 29, 2013, followed by a second run on September 5. The third flight on January 10, 2014, carried SS2 to an altitude of 71,000ft and a speed of Mach 1.4 but delays followed and the pace of the programme was plagued by minor technical difficulties. The fourth powered flight was made on October 31, 2014, from the Mojave Air and Space Port in California where considerable State and local business investment had created a preparation ground for space tourism by rocketplane. This flight was the first powered attempt in nine months but only 11 seconds after ignition of the rocket motor the SS2 broke up and was destroyed, killing its

130 ROCKETPLANES

The second SpaceShipTwo vehicle under construction in Mojave, California.

co-pilot Michael Alsbury and seriously injuring the pilot Peter Siebold. Wreckage of SS2, named Enterprise, was scattered over a 35 mile wide area of the desert. Virgin Galactic has ordered five SpaceShipTwo rocketplanes, the second named Voyager being due for completion late in 2015. The investigation into the crash has focused on premature activation of the rotatable twin-boom assembly which appears to have caused the break-up of the rocketplane.

Richard Branson is determined to press ahead with plans for the future operation of Virgin Galactic and its pioneering role in bringing rocketplane flight to everyone, although there is no firm date when that can be realised. The challenges faced by that determination are great and the loss of Enterprise and its co-pilot bears grim testimony to the price paid, across the decades since the tiny X-1 first broke the sound barrier in October 1947, by so many pilots whose dreams lie shattered across the desert floor. ■

Today, modern high performance combat aircraft can easily exceed Mach 2... and some highly refined designs have exceeded Mach 3. Yet there was a time when even the speed of sound was a barrier to fast aircraft. Even as the jet engine was becoming accepted, just after the end of the Second World War, the development of high-speed flight was in its infancy. Turning to rocket propulsion, an intrepid band of test pilots pitted skill against danger and deliberately flew into harm’s way to test the limits and burst through the so-called sound barrier. From Chuck Yeager’s recordbreaking flight in October 1947 – when he became the first pilot to exceed Mach 1 – to routine flights to Mach 6 with the X-15 more than 15 years later, this publication tells the stor y of the rocketplanes that paved the way for the supersonic aircraft of today. But that was not an end, merely a beginning. Beyond the present, taking the rocketplanes stor y into the future, Virgin Galactic promises to make ever yone a rocketplane passenger and achieve the ultimate thrill of flying in a winged aircraft powered by a rocket motor – beyond the atmosphere to the edge of space itself. From the publisher of:

BY DAVID BAKER ISBN :978-1-909128-72-9 £6.99