A deadly Swallow

Even though World War II was still raging in 1944, Great Britain began looking ahead at the post war era of commercial transports, whose development had been at a standstill for many years. The Ministry of Aircraft Production formed a selection committee, the Brabazon Committee, to consider the issue, and in May 1944, the committee issued a specification for a jet transport with a range of 800 miles and a speed in excess of 450 mph.

The De Havilland Company, builder of the Mosquito and Tiger Moth trainer, had already flown its first jet fighter, the Vampire, and began design work on a futuristic, four-engine tailless transport with a heavily swept wing, the DH. 106, which eventually became the Comet. The design was based on the knowledge that swept wings delayed the onset of compressibility, thus allowing higher speeds for lower drag, but there was still much unknown about such a wing.

 To develop more data on the wing, the company built two prototype concept aircraft, the DH. 108, which were to be half scale models of the DH. 106. The first DH. 108 was strictly for low speed research, while the second was to be used for high speed research close to, or even exceeding, the speed of sound, appropriately known at that time as the “sound barrier.”

The DH. 108 concept design bore a striking resemblance to the Messerschmitt Me 163 Komet rocket fighter, so with the end of World War II in Europe De Havilland engineers rushed to interview Herr Waldemar Voigt, the chief designer and engineer of the Me 163. In the summer of 1945, the De Havilland engineers interviewed Voigt and, while they received invaluable data on swept wing research, the information they received about the tailless delta configuration was not encouraging.

Voigt told them that the tailless design had severe problems and that such aircraft were prone to violent and uncontrollable pitch changes, especially as they approached the speed of sound. Additionally, the design had a common flaw of swept-wing aircraft, “Dutch roll,” instability characterized by a combined rolling and yawing movement at lower speed ranges.

Not surprisingly, shortly thereafter de Havilland abandoned the tailless delta design for the DH. 106 airliner and returned to a conventional tail and rudder design. Nevertheless, the company decided to continue with the DH. 108, in what in retrospect seems to have been a fit of bloody-mindedness given what they had learned from Voigt.

The first prototype, intended for low speed tests, first flew on May 15, 1946, and was named the “Swallow.” The aircraft performed reasonably well and on Aug. 23, 1946, the second prototype, intended for high speed testing, made its maiden flight.

Serious testing showed the second Swallow was very fast and plans were quickly made for an attempt on the world closed circuit speed record. Then, on Sept. 27, 1946, the day before the attempt was to be made, the aircraft disintegrated in a high speed, low level practice run.

The preliminary finding was that the aircraft was hit by a freak wind gust that caused it to pitch down. Two months later, de Havilland began construction of a third DH. 108 for more high speed tests and another attempt at the world speed record.

On July 21, 1947, the third Swallow rolled out, and less than a year later, on April 12, 1948, it made a run at the speed record on the evening when the thermal currents suspected of causing the second prototype’s crash had dissipated. The run was successful and the record was broken by more than 40 mph. Then, on Sept. 9, 1948, the Swallow — in a sense — set an even more important record, becoming the first jet aircraft to break the sound barrier. The other aircraft that had broken the sound barrier had been rocket powered (Bell X-1) or mixed powered (Douglas D-558-2).

On that day, the Swallow was doing a series of dives intended to approach the sound barrier when, at about .97 Mach, the aircraft pitched violently up then quickly pitched down into a 75 degree nose down dive. Before the de Havilland test pilot could recover it had reached Mach 1.05, though the test data recorder had failed. The Swallow exceeded the speed of sound again on March 1, 1949, in a similar out of control situation, but this time it was recorded. Needless to say, there was considerable “discussion” on the other side of the Atlantic about whether one could claim the record in an out of control state.

The two Swallows were turned over to the Royal Air Force test establishment in October 1948 and had — perhaps not unexpectedly — an unhappy career.

The second high speed Swallow broke up after it entered a steep dive, probably because the pilot passed out because of an oxygen system malfunction.

The remaining DH.108, the slow speed test aircraft, underwent a series of low speed stall tests even though renowned test pilot Eric “Winkle” Brown had described the Sparrow as “A Killer. Nasty Stall. Vicious undamped longitudinal oscillation at speed.” Sadly, on May 1, 1950, an RAF test pilot was doing a stall series when the Sparrow went into an inverted spin. The pilot tried to eject but the seat failed and he was killed — the third test pilot killed by the three Sparrows.

(For questions or comments, contact Dr. Michel at marshall.michel@ramstein.af.mil.)