(England) Derry John @·AIRCRAFTUBE

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  • de Havilland DH-115 Sea Vixen de Havilland DH-115 Sea Vixen
    de Havilland DH-115 Sea Vixen

John Derry

5 December 1921 – † 6 September 1952

John Derry was the first Briton to exceed the speed of sound flying a de Havilland DH.108 research aircraft in September 1948, only to be killed four years later (on the 6th September, 1952), when his DH.110 twin boom fighter broke up in the air at the Farnborough airshow.

In his short life he had become a brilliant test pilot for both Supermarine and de Havilland following his war service with No 182 Squadron flying Hawker Tempest.

He is widely believed to have exceeded the speed of sound on 6 September 1948, when he lost control of his de Havilland DH.108 aircraft and the Mach meter briefly showed supersonic speeds in a shallow dive from 12,200 m (or 40,000) ft to 9,100 m (or 30,000 ft), although recording apparatus was switched off.

Career

Joining the RAF as soon as possible, when he was eighteen, he initially served as a wireless operator/air gunner in Hudsons before the chance came to train as pilot, taking him on to Typhoons and Tempests.

In 1946 he joined the Central Fighter Establishment, becoming CO of the Tempest Squadron of the Day Fighter Leader School where he found and improved his ability as a demonstration pilot. Looking to the future he applied for a vacancy of test pilot with Supermarine but after only ten months he was approached by de Havilland who had lost Geoffrey de Havilland junior in one of the DH.108 crashes and thus needed a new strong member of their test team. His work included Vampire and Venom but more particularly the much more advanced aircraft DH.108 and DH.110.

It was at Hatfield that John Derry really entered the world of high speed flying, this in the days when the sound barrier was a mysterious problem to be overcome. It was a period of extremely high risk and many able test pilots were lost as the design teams and pilots struggled with the aerodynamic, stress and thus structure problems. To say nothing of control cable stretch problems which sounds extremely basic given the forces involved.

Farnborough crash

Like so many other prototypes and developmental aircraft in the 1950's, the DH.110 crash was the result of a combination of unanticipated aerodynamic loads from transonic flight on airframe structures designed for subsonic flight. In this case, the wing structure used for the Vampire and Venom proved to be incapable of sustaining the forces from a supersonic dive followed by a rolling pullout.

Derry had already completed a low-level supersonic pass of the 120,000 spectators at the 1952 SBAC air display, when he banked left to fly a wide circular turn. Heading toward the crowd at approximately 450 knots (or 833 km/h), he started to pull the DH.110 into a climb when the outer starboard wing, immediately followed by the outer port wing, broke off the aircraft. The dramatic change in the centre of gravity of the aircraft resulted in both engines being torn from the airframe.

With the public address announcer shouting "Look out!", one engine crashed harmlessly into some parked vehicles while the other broke into two sections and ploughed into Observation Hill, injuring and killing numerous spectators. The cockpit crashed into the runway and injured more members of the public. Derry and flight test observer Anthony Richards perished in the crash, along with 29 spectators.

The accident report was released on 8 April 1953. It stated that the combination of forces associated with both turning and straightening out had caused an instability in the airframe structure. The D-nose leading edge arrangement was found to be at fault; while successful in lighter de Havilland aircraft such as the Vampire, the structure was compromised under stress by the heavier DH.110. The aircraft was not flown again until June 1953, and then only after significant re-design. The DH.110 was eventually developed into the successful naval fighter, the Sea Vixen.

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