The Short and Deadly Career of the De Havilland Swallow

Evolution of the Comet from mailplane to jetliner

The Allies reaped a technological windfall with the unconditional surrender of Nazi Germany in May 1945. Both the United States and Great Britain in particular found that their wartime studies of future jet aircraft experienced quantum leaps in performance with the incorporation of the aeronautical knowledge of the personnel technical documents, and aircraft of the Third Reich. During the final half of the Second World War, Britain grappled with the future of passenger flight with the Brabazon Committee's deliberations on the future of commercial aviation. Of the five designs put forth by the Committee, the most advanced was the Type IV design for a jet-powered 100-passenger design. This aircraft would become the De Havilland DH.106 Comet- but the DH.106 started out as a very small, modest adaptation of the Vampire jet fighter as jet-powered mailplane with a six-seat passenger compartment. But with the input of the Brabazon Committee, the DH.106 evolved into a substantially larger aircraft that at one point was a tailless design before taking on the shape now familiar as the Comet. 

TG283, the low-speed DH.108 aircraft

The British were particularly interested in the Messerschmitt Me 163 Komet rocket-powered point interceptor- it was fast, had modestly swept wings, was tailless and was known to have good flying characteristics. As a result of their evaluation of the Komet, the government issued the E.18/45 requirement which was awarded to De Havilland for the construction of two small jet-powered research aircraft to study swept wings and the tailless configuration. Designed by De Havilland engineer Ronald Bishop, what was designated the DH.108 used the fuselage of the De Havilland Vampire jet fighter which was stretched and streamlined combined with a new swept vertical fin and new swept wings. This served to save time and effort and like the Vampire jet fighter, the DH.108 had wing root intakes. Unofficially named "Swallow", the two prototypes received the RAF serials TG283 and TG306. TG283 had a 43-degree swept wing and was intended for low speed testing while TG306 had a 45-degree wing and was assigned to high-speed transonic testing. Initial wind tunnel studies suggested that the Swallow would have lousy stall characteristics, so the first of the two to fly, the low-speed assigned TG283, had fixed wing slats and anti-spin parachutes in fairings on the wingtips. It made its first flight on 15 May 1946 and TG306, the high-speed Swallow, made its first flight a month later and had automatic wing slats but no anti-spin parachutes.

VW120, the third DH.108 Swallow that broke the sound barrier in 1948

The test pilot for the DH.108 was the chief test pilot for the company, Geoffrey De Havilland, Jr, the son of the company's founder. After several problem-free test flights it was found that both aircraft lacked the predicted poor stall characteristics and the high speed aircraft, TG306, joined the formal research program on 23 August 1946. By the time De Havilland had safely taken it to 630 mph at altitude with no problems, it was decided he would take TG306 to break the world speed record. On a practice run over the Thames Estuary on 27 September 1946, the aircraft exceeded its structural limits at high speed and broke up, killing Geoffrey De Havilland, Jr, as the aircraft had no ejection seat. John Cunningham succeeded De Havilland as chief test pilot and took over flying the DH.108. To replace the lost aircraft, a third DH.108 was ordered and received the RAF serial VW120. It featured a more pointed nose, revised canopy and cockpit including a Martin-Baker ejection seat, and a higher thrust Goblin engine than what had powered the first two aircraft. Cunningham took VW120 up on its maiden flight  on 24 July 1947. With Cunningham and fellow test pilot John Derry flying VW120, a series of new speed records were set in 1948 and on 9 September of that year, Derry took VW120 past Mach 1 in a dive from 40,000 feet, making the DH.108 Swallow the first British aircraft to break the sound barrier- though it must be pointed out that Derry had for the most part lost control of VW120 during the supersonic portion of the flight but had safely recovered and landed. 

After flying demonstrations at the 1948 Farnborough SBAC air show, VW120 was handed over to the Royal Aircraft Establishment to join TG283 (the first Swallow) in the research program. On 15 February 1950 RAE test pilot Stuart Muller-Rowland was killed when VW120 broke up due to structural failure during a high speed test run. Three months later TG283 was lost and killed its test pilot, RAF Squadron Leader G.E. Genders, when it stalled at low speed and low altitude. 

Despite the loss of all three DH.108s with the loss of life, the data from the Swallow flight test program and the research program at the Royal Aircraft Establishment benefited not just the design of the DH.106 Comet jetliner, but also that of the DH.110 Sea Vixen naval fighter as well.

Source: Military Aircraft Monthly International, Volume 9, Issue 12. "A Deadly Swallow: The short sharp story of De Havilland's DH.108" by Nico Braas, p28-32.

The Barnes Wallis Swallow

As the Second World War began to wind down, renowed British aircraft designer Barnes Wallis started investigating the challenges of supersonic flight and concluded early on that a variable geometry swing wing was the best way to accommodate the center of gravity changes in moving between the subsonic and supersonic regimes. In 1946 he wrote an engineering paper entitled "The Application of the Aerodynamic Properties to the Stabilisation and Control of Aerodynes" (quite a mouthful) in which he combined his ideas on swing wings with laminar flow studies. Starting out with small hand launched models, Barnes Wallis gradually moved up to larger versions that were launched for a catapult at 100mph. His models had slender, ovoid fuselages with swing wings mounted far to the aft and a single highly swept fin. With the end of the war, the British government was eager to regain research ground lost to the Americans and Vickers was awarded a contract of a half-million pounds to study supersonic flight. With the cancellation of the Miles M.52 supersonic research aircraft, some of Vickers' money was reallocated to Barnes Wallis' project which was given the code name Wild Goose.

The Wild Goose project ran to 1954 and it used progressively larger radio controlled models based on Barnes Wallis' designs. The later models had provisions for rocket engines in the fuselage and the RAF took notice, considering the Wild Goose design as the basis of a long range surface-to-air missile to intercept Soviet bombers before they reached UK airspace. Wild Goose ended in 1954 but the research data acquired went over to a classified project known as Green Lizard. This project called for a compact missile fired from a storable tube with flip out wings for which Barnes Wallis supersonic design work was applicable. Green Lizard was envisioned as both a surface-to-surface missile that could dispense submunitions or a surface-to-air missile powered by turbojet engines for the long range interception of Soviet bombers. It's not known exactly when the Green Lizard project was terminated, but it may have run in parallel to the Wild Goose project.

As the database on his designs grew, Barnes Wallis then moved into a manned aircraft applications of his swing-wing designs. Small aircraft builder Heston Aircraft was a subcontractor on the Wild Goose project and Wallis worked with Heston to build a small flying demonstrator designated JC.9. With a single seat, retractable tricycle undercarriage and 46 feet in length, the JC.9 was planned to fly first as a glider, then have an turbojet engine installed for powered trials. The JC.9 was then shipped in sections to the Vickers Weybridge facility for final assembly, but for reasons unknown, it remained disassembled until scrapped.

By 1954 Barnes Wallis began thinking even bigger, adapting his unique swing wing design to a supersonic intercontinental range aircraft. The RAF had issued OR.330 (Operational Requirement 330) that called for high flying supersonic bomber/reconnaissance aircraft. Although not responsible for Vickers' submission for OR.330, Wallis adapted his design to meet the stringent requirements, coming up with a sleek arrowhead shaped tailless aircraft with slender swing wings pivoted at the aft end of the fuselage. Pod-mounted engines pivoted on the tips of the swing wings and also provided some directional control. Calling his revolutionary design the Swallow, small scale models were tested in Vickers' wind tunnels with encouraging results. Scale flying models of the Swallow powered by rocket engines easily attained Mach 2.5 in flight tests. While the Swallow wasn't selected for OR.330, the RAF was sufficiently interested to continue funding Wallis' work towards a scaled-down flying demonstrator called the Research Swallow that could be readily adapted for military roles. Versions of the Research Swallow were submitted to the RAF and Royal Navy as a supersonic strike fighter.

The most impressive would have been the bomber version of the Swallow and a supersonic military transport. The Swallow bomber would have been approximately the size of the B-1 bomber with 4-5 crew, a cruising speed of Mach 2 and a range of 5,000 miles carrying a single Red Beard nuclear bomb. The military transport was even larger with a civilian airliner version that could have carried 60 passengers between the UK and Australia nonstop. Development work on the bomber and transport versions of the Swallow was estimated at 10 years, but the infamous 1957 Defence White Paper of Duncan Sandys that stated the era of manned military aircraft was being eclipsed by missiles ended funding for the Swallow.

As consolation, Barnes Wallis was allowed to meet with the American Mutual Weapons Development Program to see if the United States was interested in his extensive work. Exchange visits were conducted between Wallis' facility at Vickers and Wallis himself led several teams to the United States to meet with NASA's Langley research facility. A six month joint UK-US development program was conducted at NASA Langley to further refine Wallis' work. By June 1959, NASA's extensive testing uncovered pitch up problems in certain flight regimes as well as higher than expected drag. This effectively killed off the Swallow as an aircraft design, but NASA found the body of work still applicable to a more conventional tailed swing design. This design would eventually evolve into the world's first production swing-wing combat aircraft, the General Dynamics F-111 Aardvark.

Source: Secret Projects: Flying Wings and Tailless Aircraft by Bill Rose. Midland Publishing/Ian Allan, 2010, p27-31.