Flying wings

The flowering of innovation in the development of German secret weapons during the war years was especially pronounced in the field of revolutionary aeronautics. Britain was consumed with finding responses to the German onslaught, but the German High Command became fanatical about the domination of the Western world. The engineers and visionaries came up with startling, stunning concepts, and the rate at which they progressed was astonishing. Some of the ideas could never reach fulfilment. One was for the 3 x 1,000 project, intended to bomb English cities. This was the aim of Reichsmarschall Hermann Göring, and would have involved a bomber carrying 1,000kg of explosives for 1,000km at 1,000km/h, equivalent to 2,200lb of bombs for 625 miles at 625mph.

The birth of the ‘flying wing’ had been in the USA where Jack Northrop had experimented with delta-wing designs in the late 1920s. Little came of it, however, until the pressures of World War II led to new calls for revolutionary aircraft designs. Both the United States and Germany began development, but research took longer than expected. In Germany, two brilliant brothers, Walter and Reimar Horten, revived the concept during war and planned to take it to unprecedented heights. Both were members of the Hitler Youth and later of the Nazi Party. They first designed an unpowered delta-wing glider, the Ho-229, for flight testing, and its initial flight was in March 1944. After this successful test, the development was taken over by the Gothaer Waggonfabrik Company. They installed an ejector seat for the pilot, and added systems to carry air to the jet engine with which it was proposed to power the plane. Even before the aircraft had flown under jet power, Göring had an order placed for 40 of these aircraft with the designation Ho-229. Further test flights showed that the plane had superb handling qualities, though there were some tragic accidents during the test flights of prototypes. The Germans were building a twin-engined Ho-229 V3 when the Americans arrived during the liberation of Europe at the end of the war.

During the final stages of the conflict, the United States military initiated Operation Paperclip, a top-secret initiative by the United States intelligence agencies to capture advanced German weapons research, and keep it out of the hands of advancing Soviet troops. A Horten test glider, and the partly built Ho-229 V3, were packed up and shipped to the United States, and the Hortens – for all their active Nazi participation – were secretly taken to America and given sanctuary. Their hardware was sent to Jack Northrop.

The first of Jack Northrop’s new generation of planes, the N-1M, had taken to the air in July 1941 at Baker Dry Lake, California. These pioneering test flights showed that the design clearly had a future, though the plane’s twin 65hp (48kW) Lycoming 0-145 four-cylinder engines left it low on power and the construction was too heavy. The power-plants were replaced with 120hp (88kW) six-cylinder air-cooled Franklin engines and the design was modified though, in spite of it all, the plane never went into production.

Engineering design of the first American delta-winged planes started in 1942. The aircraft would be constructed of the latest light-alloy sheet. There would be a cabin embedded in the delta wing with bunk beds for crew to sleep on during prolonged flights. Bomb bays would be fitted in each wing with seven gun turrets carrying machine guns. Yet progress was slow and the XB-35 did not make her first successful flight until June 1946 when she flew from Hawthorne, California, to Muroc Dry Lake. By May 1948 the plane was ready to start production, but the planes – powered by propeller engines – were rendered obsolete by the advent of the jet bomber. Jet engines were fitted to a few but they were not successful, though one plane, designated the YRB-49A, was tested as a reconnaissance aircraft. Although the United States Air Force had originally ordered 200 of the original B-35 planes, they proved unsatisfactory and not worth converting to jet propulsion so the entire project was peremptorily cancelled. It was a controversial decision, and Jack Northrop later stated that it was due to his refusal to accede to the wishes of Secretary of the Air Force Stuart Symington, who wanted Northrop to merge with the Convair Company. Jack Northrop insisted that unfair terms were being imposed on him, and that it was Symington who suddenly cancelled the flying wing. Northrop may have been right; Symington subsequently became President of the Convair Company when he resigned from government service shortly afterwards.

The final legacy of the Horten brothers’ original design lives on, however. Their aircraft were intended not only to be aerodynamically efficient, but also to reduce the radar signature. As the British began to develop and improve radar technology, the Germans were increasingly aware of the need to defeat its penetrating gaze. The Hortens used a unique glue in their planes, rather than metal nails or rivets; the glue – a carbon composite – and the low profile meant that the aircraft were far harder to see on radar. In 2009, a full-size reproduction of the Ho-229 V3 was constructed for a television documentary. It cost $250,000 (£160,000) and took 2,500 hours to build, but its radar profile was found to be less than 40 per cent of a World War II fighter (such as the Messerschmitt Bf-109). Not only was this a revolution in design, but the plane, had it gone into production, would have been the world’s first stealth bomber.

An Olympic vision – the Adolphine

An aircraft with a greatly extended range had begun as an idea before the war and by the war’s end it was envisaged as a plane that could span the world from high altitude. It is a remarkable story of both brilliance and foolhardy adventurism that far out-reached itself.

This story had its roots in 1936 in Berlin, site of the XI Olympiad. The city selected to host the next Olympics was Tokyo, Japan, and Hitler had a vision that the German team would fly direct from Germany to Japan in a record-breaking non-stop flight aboard a futuristic aircraft designed especially for the event. As it happens, plans for the Olympics were agreed at the Cairo Conference of the International Olympic Committee held in 1938 but Japan renounced the conference because of the Second Sino-Japanese War. Japan was thus stripped of her right to hold the games, which were rescheduled to be held in Helsinki, Finland. By this time, the Germans were already developing the super-plane Hitler had envisaged: work had started in 1937, when the Messerschmitt Company launched Projekt P-1064. It was viewed as a development of the Messerschmitt Bf-110 twin-engined heavy fighter into a reconnaissance plane that had unprecedented range. Conceived with a slender fuselage and with two engines, this was the Messerschmitt Me-261 and it was seen as spearheading German superiority in long-range flight. The Luftwaffe designated it the 8-261. Since it had the backing of the Führer, the projected aircraft was named Adolphine.

For its time, the plane was remarkably futuristic. The all-metal wings were deep and served as fuel tanks, and were fixed to a fuselage with a rectangular cross-section which had room for five crew, with pilot and co-pilot seated in the cockpit alongside the radio operator, and a navigational officer and engineer at the rear. The four Daimler-Benz DB-601 engines were coupled in pairs through a shared gearbox. Work was under way in 1939 and was supported from the highest levels of the Nazi power structure – but with the outbreak of World War II the 1940 Olympics were cancelled, and the project lost both urgency and direction. By August 1939, work had come to a standstill. Within a year, however, it was plain that the war would be no walkover for Germany, and the Luftwaffe began once again to involve long-distance bombers in their strategy. The Adolphine suddenly had a part in these plans, so work was resumed under conditions of urgency and the first prototype flew in December 1940.

It seemed highly promising and, with the DB-606 engines, the range was predicted to be as much as 12,000 miles (20,000km) for the production aircraft. The engines were in short supply, however. They were being produced as fast as possible, but all were needed for established, successful planes like the Heinkel He-177. The second version was flown in 1941, but Messerschmitt realized that the fuel-carrying wings posed a radical problem: there was no room in the wing structure for weapons. There was a plan for the aircraft to fly over New York, dropping propaganda leaflets, but this public relations scheme was abandoned when Allied bombing destroyed both prototypes. There was a third prototype, fitted with two DB-610 engines and with space for two further crew members. It first flew in early 1943 and in April 1943, the Me-261 V3 flew for 10 hours over 2,790 miles (4,500km), the distance from Europe to America across the Atlantic. It was an unprecedented achievement. Three months later the prototype crash-landed, damaging the undercarriage. The plane was used for several long-distance reconnaissance missions but the need for an aircraft to catch the public attention no longer existed, and the project was finally scrapped in 1944.

The idea of a plane that could cross the Atlantic had remained a continuing preoccupation of the German High Command throughout the war. The Commander-in-Chief of the Luftwaffe, Hermann Göring, often spoke of his wish to have a bomber that could curtail the ‘arrogance of the Americans’. One scheme had been to use the mid-Atlantic Portuguese islands of the Azores as a stop for fuel. The Portuguese dictator António de Oliveira Salazar had allowed the Germans to obtain fuel for their U-boats and Navy vessels from São Miguel in the Azores, but in 1943 he signed leases with the British, allowing them to use the islands as a base from which to patrol the North Atlantic by air.

The other designs were all for high-specification aircraft that could fly across the Atlantic and back without touching down. Those that were hurriedly prepared were the all-new Messerschmitt Me-264, upgraded versions of the existing Focke Wulf Fw-200 known as the Fw-300 and the Ta-400, an improved version of the Junkers Ju-290 (the Ju-390) and the Heinkel He-277. Messerschmitt were quick to produce a prototype of the projected Me-264, though in the event it was the Ju-390 which was chosen to go into production. In early 1944, the second prototype Ju-390 reportedly made a trans-Atlantic flight and came within 12 miles (20km) of the coastline of the United States. Another Ju-390 is also claimed to have flown from Germany to south-west Africa (present-day Namibia) early in 1944. These reports are all post-war, however, and are impossible to substantiate.

Many German aircraft companies investigated the problem of bombing the United States of whom Junkers, Messerschmitt, Heinkel and Focke-Wulf were the principal players. Long-distance aircraft were generally seen as impossible to construct in the time-frame, so the plans involved the capture of facilities on the Azores and the use of these strategic islands as a stopping-off point in the middle of the ocean. Bombers including the Ju-290, He-277 and Me-264 would then be within reach of United States targets with a bomb payload of up to 6.5 tons. Targets were listed in detail, and included American producers of light alloys, aircraft engines and optical equipment. Other targets were Canada and an Allied base in Greenland. It was calculated that attacks on American soil would cause the United States to devote her priorities to defending herself, rather than protecting Britain. In this way, the Germans would have less resistance from the British forces and the occupation of the United Kingdom would be easier to attain. However, these detailed plans failed to bear fruit.

Flying triangles

The DM-series of delta-winged planes was a joint project of the Darmstadt and Munich Akafliegs (Akademische Fliegergruppen, academic flight research teams). During planning all limits were set aside and what may seem impossible today was seriously considered, such as the DM-4 with a planned wing area of 753ft2 (70m2) that was calculated to reach speeds of 1,000mph (1,600km/h), well above the speed of sound.

These aircraft were not the only delta-shaped planes envisaged in Germany during the war. Alexander Lippisch, the distinguished Munich-born engineer, proposed to develop a ramjet defence fighter powered by a new and highly efficient form of propulsion unit. Rather than relying on air compressed by a spinning turbine, this new design – the ramjet – used the plane’s forward motion to collect and compress the air. Ramjets could operate at very high efficiency, but – because the plane must already be moving to compress the incoming air – they could not be used to propel the plane from a standing start. The ramjet only took over when the plane was already moving at speed. Lippisch named his design Projekt P-13a.

He persuaded the Darmstadt Akaflieg to build a full-scale flying prototype, which the company designated the Darmstadt D-33. Work was proceeding when the Akaflieg Darmstadt workshop was hit during an Allied bombing raid in September 1944, so the D-33 project was transferred to the Munich Akaflieg where the work was completed. They renamed the D-33 the Akaflieg Darmstadt/Akaflieg München DM-1. It was designed as a single-seat glider made from steel tubing and plywood that was impregnated with Bakelite, at the time a highly innovative process. The glider was discovered by United States soldiers when they arrived on site in May 1945, and the prototype was then inspected by Charles Lindbergh who arranged for it to be shipped back to the United States. The prototype was wind-tunnel tested and examined by scientists from the National Advisory Committee for Aeronautics (which later gave rise to today’s NASA – National Air and Space Administration). Among the planes inspired by this German design, as by the Hortens’ flying wing, were the Convair XP-92, America’s first delta-wing fighter, and Convair’s F-102 Delta Dagger which flew in Vietnam. Of a similar, uncompromising delta design was the Convair F-2Y Sea Dart which was a seaplane fighter that took off on buoyant skis from the surface of a body of water.

In Britain, research into the delta-wing concept gave rise to the Handley Page HP-115 and the Fairey Delta 2 or FD2 – the first plane to fly faster than 1,000mph (1,609km/h) – and then the great Avro Vulcan bomber. These are the planes that gave much of the technical data needed in the development of Concorde, the successful supersonic passenger aircraft. Once, when flying aboard Concorde to New York, I was told by a captain that it was not useful to think of Concorde as a supersonic airliner. That didn’t make sense to him – his advice was to envisage it instead as a huge supersonic jet fighter that carried passengers instead of weapons. He was right: that made far more sense.

Two aircraft in one

One novel method of reaching the United States from Germany was the proposal for a hybrid of two planes. A Heinkel He-177 would be used to transport a Dornier Do-217 bomber equipped with an extra Lorin-Staustrahltriebwerk ramjet engine until the planes were sufficiently close to the United States for the Do-217 to be released and fly on towards the target. The plane would deliver its bomb to United States territory and then be ditched in the Western Atlantic, where the pilot would be recovered by a German submarine. The design could not be realized as the distances proved to be insurmountable, so the idea was soon abandoned.

This was not the novel idea it might seem. The first planes to be carried as ‘parasites’ were small planes that could be released from giant airships in the 1920s. During the 1930s the Soviets experimented with the idea of carrying fighters aboard larger aircraft. The Zveno series became increasingly complex, until a Tupolev TB-3 carried three Polikarpov I-5 fighters: one mounted on each wing, and a third above the cockpit. By 1935 the Aviamatka had been flown, a TB-3/AM-34 which carried five small fighters. Some were deployed just once during the war years; in mid-1941, a Zveno flight from the Black Sea was dispatched to attack the Negru Voda bridge in Romania.

The idea of carrying a plane aboard a larger transporter also re-emerged elsewhere in Germany during World War II. The principle was nicknamed Mistel (Mistletoe) because of the way that a small plane could be carried, like the parasitic plant, safely attached to a larger one. The concept was that the ‘parent’ plane could carry the attack aircraft towards the target, so that the smaller aircraft could carry out its attack and still have a full fuel tank with which to return to base. The first of these trials earned the nickname Huckepack (Pick-a-Back, or Father-and-Son). The attack aircraft was to be a Focke-Wulfe Fw-190 Würger (Strangle) fighter that had been designed by Kurt Tank in 1938. As a fighter, this small plane became well known as a routine strike aircraft and a ground-attack plane. It would be carried aloft mounted above a Ju-88 Mark 4, a bomber based on the design of the successful Ju-88 but with more powerful engines. It flew for the first time in early 1940. The Mark 4 of the Ju-88 had a wingspan of 70ft (20m) compared to the 65ft 10.5in (18m) of the previous models, with improved streamlining and a somewhat larger cockpit offering improved visibility.

The first five of these combined Mistel aircraft were ready early in 1944 and training began in Nordhausen. Both upper and lower aircraft were initially crewed, but it was envisaged that the Ju-88 could eventually be controlled from the smaller fighter and released as an unmanned ‘flying bomb’. Once the Allied invasion of the Normandy coast began, the unit moved from Nordhausen to St Dizier with a squadron of 12 of the combined aircraft. They were used with some effect; the crashing of an unmanned fully laden Ju-88 was extremely unnerving for the British, and this curious combined aircraft went on to fly further successful missions.

The ultimate aircraft

For extreme long-distance raids, there remained one top-secret German proposal of immense potential. It was for the ‘antipodal bomber’, a stratospheric aircraft that could span the world. It was the brainchild of one of the greatest German visionaries, yet also one of the least well known. This was Eugen Sänger, born in Pressnitz, now in the Czech Republic, who had studied civil engineering at the Technical Universities of Graz and Vienna. As a student, Sänger had been captivated by Hermann Oberth’s book Die Rakete zu den Planetenräumen (The Rocket into Planetary Space) and indeed we will come across both Oberth and Sänger again later in this book when we look more specifically at rocket-powered weapons. It was Oberth’s book that inspired Sänger to change from studying civil engineering to a career in aeronautics and as a first step he joined the Society for Space Travel in order to learn more from Oberth. The subject of Sänger’s thesis was originally intended to be rocket-powered flight, but this was rejected by the university as being unrealistic. Instead he was instructed to submit a relatively mundane report on the statics of wing trusses. His original work was not lost, however; and Sänger went on to publish it under the title Raketenflugtechnik (Rocket Flight Technology) in 1933, and followed this with several magazine articles on rocket-powered flight. They appeared in an Austrian magazine Flug (Flight) and soon came to the attention of the German Air Ministry, who could envisage Sänger’s ideas as one way to build a bomber that could attack the United States from an airfield in Germany.

One of Sänger’s dreams was for his great antipodal bomber – a long-range sub-orbital aircraft, launched by rockets, that could travel around the world through the stratosphere and deliver a payload to the opposite ends of the earth. Sänger called his craft the Silbervogel (Silver Bird) and worked on the design with a brilliant young mathematician named Irene Bredt, of Vienna, Austria, whom he later married. Sänger also designed the rockets so they could generate a thrust of 225,000lb-ft (0.3 meganewton metres). The silver bird was known as the RaBo (Raketenbomber or Rocket Bomber) and it would be launched by rocket sled from a 2-mile (3km) launch-track at about 1,200mph (2,000km/h). It would then fire its own onboard rocket motors and climb to an altitude of 90 miles (145km) reaching a velocity of 13,700mph (22,100km/h). The craft would then slowly descend in a sub-orbital trajectory until it entered the upper atmosphere and, as its wings and body generated lift, it would bounce back into space before slowly descending again. After several ‘hops’, it would be at the opposite pole of the earth. It was calculated to be able to deliver a 8,800lb (4,000kg) bomb to the United States and then fly on to land in the Pacific where the Japanese would ensure it was recovered for the Germans. The complete flight would be 12–15,000 miles (19–24,000km) in length.

It was an adventurous and futuristic scheme – too futuristic for the Luftwaffe, who brought development to a halt as early as 1942. As we have seen, they preferred to invest in proven aircraft technology. Sänger was assigned to carry on research at the German Gliding Research Institute (Deutsche Forschungsanstalt für Segelflug) where he made important developments in ramjet design. He remained an authority on rockets, and came to prominence again when German rocketry was reaching its height.

The end of the project was not the end of the idea. After the war, calculations proved that the antipodal bomber would not have worked – the heat generated by the ‘hops’ into the upper atmosphere would have caused far greater heating than the Germans had realized, destroying the craft. Even so, the Soviets tried to tempt Sänger to move to Russia and continue his research there, but he declined the offer and instead continued his research in France, where he founded the French Astronautical Federation (Fédération Astronautique) in 1949. He spent his later years back in Germany, working on a ramjet-powered spacecraft that was never realized. He also pioneered the idea of using photons from the sun for long-distance space propulsion, and introduced the still-popular concept of the solar sail.

But the importance of the lifting properties of a body that is descending into the upper atmosphere still stands today. Sänger’s work and his wife’s calculations proved significant in the design of the North American X-15 rocket plane, the X-20 Dyna-Soar and eventually in the design of the Space Shuttle. In October 1985 the Messerschmitt-Bölkow-Blohm (MBB) Organization renewed studies of the Sänger system as the core of a two-stage spacecraft with horizontal take-off. The first stage would propel the plane to high speed and would then be jettisoned, allowing the second stage to fire and carry it further towards space. Launching the rocket on wheels, running on a ramp that later curves upwards to launch the rocket aloft, is a clear design advantage; for then it is the track which supports the weight, rather than the rocket thrust. It would be possible for the rocket to achieve high launch speeds by running horizontally before its path turned upwards, conserving onboard fuel for the entry into space. Who knows? Those secret ideas from World War II may yet find realization.

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