Issue 9 - North American F-86 Sabre: Swept wing technology

Published: 02:54PM Mar 24th, 2011
By: Web Editor

It was mainly German aeronautical engineers who pioneered the swept wing for aircraft, says François Prins.

Issue 9 - North American F-86 Sabre: Swept wing technology

We tend to think that the swept wing is something that only came about with the advent of jet aeroplanes, but in reality it was being experimented with by several aircraft designers from the earliest days of manned flight.

While powered aircraft kept to a simple design of fairly square wings with little or no sweep, glider enthusiasts were going further and adding sweep to the wings of their craft as the searched for better flight characteristics that suited a machine dependent on the wind.

In Britain, José Weiss experimented with hundreds of model gliders before making a full-size tail-less glider with swept wings. It flew successfully in 1908, so he built another but this time powered by 12-hp Anzani engine driving two propellers. During the winter of 1908-09 it was tested at an airfield in Essex but, until some modifications were carried out, refused to leave the ground.

Another pioneer of the swept wing theory was John William Dunne; he experimented with models before building a full-size tail-less glider with sharply swept back wings in late 1905. Encouraged by the success of the glider, Dunne built a powered aircraft which, after some initial problems, made several successful flights. Dunne built variants of the aircraft and one crossed the English Channel in 1913 to be demonstrated in France.

With the coming of war Dunne ceased work on his series of tail-less aircraft. However, many of his ideas and designs were adapted by others including Westland Aircraft. They built a series of tail-less gliders and powered aircraft which culminated with the successful Pterodactyl IV of 1931. It was not put into production and the swept wing theory was not taken up in Britain by any of the leading aircraft designers and manufacturers of the day.

German Experiments

The Versailles Treaty of 1919 forbade Germany to design and produce military aircraft. However, there was no mention of gliders and light sporting types, so the engineers who had worked on aircraft during World War One turned their talents to powerless flight. Gliding became a fast-growing sport and competitions held in Germany attracted participants from all over the world; it was seen as harmless and fun, but the data gathered from gliders could be used by the designers for other aeronautical applications.

One of the many glider designers was Alexander Lippisch; he had worked with Dornier in the latter stages of World War One and was one of many men who found themselves unemployed after 1918. Lippisch applied for a post as an aeronautical engineer with Fritz Schweizer who wanted to enter a glider for the 1921 Rhön competition. Lippisch built the glider and soon afterwards joined forces with another glider builder, Gottlob Espenlaub. They continued their experiments with tail-less craft and in 1927 Lippisch produced the first of his Stoch gliders, which would later be developed to take power units. These were developed into his Delta design series, which would eventually lead him towards the Messerschmitt Me 163 concept.

While Lippisch was experimenting with the Delta aircraft, the Horten brothers – Walter and Reimar – were building small glider models based on the Lippisch’s Delta tail-less design, but taking it further as a flying wing with the pilot and equipment housed almost entirely in the wing. They built and test flew large models that soon attracted the notice of the Deutsche Versuchsanstalt fur Luftfahrt (DVL) – the official German aircraft test organisation – who invited the Horten brothers to demonstrate a glider at an air show in Hangelar in June 1934. The DVL agreed to pay all expenses and the aircraft was shown to a large audience that included many influential members of the ruling Nazi party and the new Luftwaffe.

When Reimar returned home to Bonn he started work on a second aircraft; this was for a glider, but he also had plans to build a powered version. Both Lippisch and the Horten brothers continued their experiments with tail-less and/or flying wings throughout the 1930s. The Deutsches Forschunginstitut fur Segelflug (DFS), the German Research Institute for gliders, but also covertly for powered aircraft, gave Lippisch the opportunity to build a glider that could be easily converted to take an engine.

In 1938, Lippisch joined Messerschmitt AG at Augsburg; he now had the opportunity to develop his tail-less aircraft for one of the largest aircraft manufacturers in Europe. Some of his former colleagues from the DFS joined him at Messerschmitt and brought all his drawings and calculations for the rocket fighter that he had been working on before joining Messerschmitt.

The glider prototypes – DFS194 V1 and V2 – that Lippisch had built were also transferred to Augsburg and the proposed powered aircraft was designated Me163 in the Messerschmitt catalogue.

Early in 1939, in order to gain first hand knowledge of the Walter rocket motor that was scheduled to power the Me163, the DFS194 V1 was quickly modified so that the engine could be fitted. The aircraft was flown as a glider from Augsburg before being taken to the test centre at Peenemunde for powered trials. However, the outbreak of war halted work and the first powered flight was delayed until the summer of 1940. Trials with the light and very fast DFS194 encouraged the Luftwaffe high command and work proceeded on the first prototype Me163; this was flown from Peenemunde on 13 August 1941 for the first time and during trials it reached a top speed of 515mph (830kph).

Meanwhile, the Horten brothers had joined the Luftwaffe and the special organisation known as Sonderkommando 9, where they were allocated the task of developing their flying wing concept. Work proceeded and was developed by the Gothaer Waggonfabrik AG – better known as Gotha aircraft – during the early 1940s. By 1942 work had commenced on the Horten Ho IX V1 prototype to be powered by two BMW 003A-1 axial flow turbojets. However, problems were encountered by the build-team at Gottingen when they found that the BMW engines were larger in diameter than originally planned. The first prototype was thus finished and flown as a glider in the summer of 1944.

Rocket and Jet Power

By this time the Messerschmitt Me262 jet fighter and the Me163 rocket interceptor had both entered Luftwaffe service. When the first powered Ho IX flew, now powered by Jumo 004B-1 turbojets, it was behind schedule. The test started well but two hours into the flight one of the Jumo engines caught fire and the pilot had to make an emergency single-engine landing. Unfortunately, the Ho IX V2 was destroyed in the fire.

However, the aircraft showed promise and was ordered into production as Gotha Go229; the first pre-production example Go229 V3 was being made ready for flight when the Gotha plant at Friedrichsroda was captured and occupied by the advancing American army. Naturally, the Go229s that had been completed and those in-build were seized, as were other German advanced concepts at other locations.

What the Allies discovered was amazing, they knew that the Germans had been working on rocket and jet propulsion but they had not expected the sheer diversity of aircraft designs and concepts. One of the Messerschmitt aircraft they captured was powered by a single turbojet with a nose intake, sharply swept back wings, a high tail and cannon armament in the nose. Designated P.1101, the aircraft had wing sweep back that could be varied in flight from 20 degrees to 60 degrees. The P.1101 had been selected as the future fighter for the Luftwaffe.

Also discovered by the advancing troops was a similar design to the P.1101, which had been worked on quite independently by Kurt Tank of Focke-Wulf. Tank was not only an accomplished aeronautical engineer but also a fine test pilot; he insisted on flying any design he had been involved in. Tank’s Ta183 had been ordered early in 1945 for flight in May or June that year. Work was well-advanced when British troops captured Focke-Wulf at Bad Eilsen where Tank and his team were based. The Ta183 had not been built, unlike the P.1101 and all that could be seen were some scale models and hundreds of drawings. Tank was interrogated but did not give much away to those who were questioning him and he made no mention of the Ta183.

This aircraft was to have its wings swept back 40 degrees and mounted mid-fuselage; the tail-fin was raked back 60 degrees and the swept back tailplane was mounted on the top of the fin. Tank’s calculations showed that the Ta183, powered by a Heinkel-Hirth HeS 011 turbojet, could exceed 600mph (965kph) and in combat could cause havoc with the high-flying USAF bombers which were eluding
the Me 262s. Further, the Ta183 was to be armed with four 30mm MK108 cannons which would be more than a match for the guns carried by any allied aircraft of the time. Tank had other variations of the Ta183 planned and each was more advanced than the preceding example.

The British and the Americans were excited by what they found as they advanced through Germany; the sheer scale of jet and rocket technology was far beyond what they expected and even further removed from their own researches. In the UK and the US jet aircraft were being designed and built but none were as advanced as the Ta183 and P.1101 or the Me163 variants. The partially complete P.1101 was taken back to the US and handed over to the Bell Aircraft Corporation. They used the basis of the design for the X-5 which first flew in June 1951. There are striking similarities between the two aircraft but in essence the Bell X-5 was a totally new aeroplane.

Postwar Boost

The Soviets had lagged behind in jet technology until they were given a boost by the new Labour government of Britain with an outright gift of several Rolls-Royce Nene turbojets as well as information and drawings. Their own spy network had also gathered allied technology that went towards developing advanced aircraft within the Soviet Union. Their advancing armies captured various German design and test facilities along with the engineers and scientists working at the locations.

Tank’s Ta183 may have been gathered up by the British but the Russians found a full set of plans of the aircraft, along with several other advanced aircraft designs, at the Air Ministry building in Berlin. They now had the technology for a high-performance jet interceptor fighter. These microfilm plans were rushed to Moscow and pored over by Russian aeronautical engineers. There is little doubt that the Mikoyan-Gurevich (MiG) design bureau benefited from the plans.

Some sources state that MiG built and flew copies of the Ta183 design, which were developed and adapted as required. Certainly the resulting MiG-15 owes a debt to the Ta183 as does the North American F-86 Sabre which had started life with straight wings but soon gained a distinctive and more efficient swept wing that was firmly based on the captured German technology that found its way to the States.

Sweden went one better and built the Saab J29, which looks more like the Ta183 than either the MiG-15 or F-86.

Tank himself went on to other things including the building of the Pulqui jet fighter for General Peron in Argentina. Although the aircraft flew it did not enter production, but it bears a remarkable resemblance to one of the proposed variations of Ta183. Britain, America and Russia all benefited from the captured German swept-wing information which enabled the allies to make rapid strides which otherwise may have taken several years.

Words: Francois Prins

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