De Havilland DH 108 - Testing

Testing

The first DH 108 prototype, serial number TG283, utilising the Vampire fuselage and a 43° swept wing, flew on 15 May 1946. Designed to investigate low-speed handling, it was capable of only 280 mph (451 km/h). The de Havilland Chief Test Pilot Geoffrey de Havilland Jr., son of de Havilland company owner-designer Geoffrey de Havilland, gave a display flight in the DH 108 during the 1946 Society of British Aircraft Constructors (SBAC) airshow at Radlett. In later low-speed testing designed to clear the rear fuselage at high angles of attack, the first prototype was fitted with longer Sea Vampire landing gear.

The second, high-speed prototype, TG306, with a 45° swept wing incorporating automatic leading-edge Handley Page slats and powered by a de Havilland Goblin 3 turbojet, flew soon after in June 1946. Modifications to the design included a more streamlined, longer nose and a smaller canopy (framed by a strengthened metal fairing) facilitated by lowering the pilot's seat. While being used to evaluate handling characteristics at high-speed, on 27 September 1946 TG306 suffered a catastrophic structural failure that occurred in a dive from 10,000 ft (3,050 m) at Mach 0.9 and crashed in the Thames Estuary. The pilot, Geoffrey de Havilland Jr., was killed in the accident. Early wind tunnel testing had pointed to potentially dangerous flight behaviours, but pitch oscillation at high-speed had been unexpected. The subsequent accident investigation centred on a structural failure that occurred as air built up at Mach 0.9, pitching the aircraft into a shock stall that placed tremendous loads on the fuselage and wings. The main spar cracked at the roots with the wings immediately folding backwards.

After the loss of the second prototype, VW120 became the third and final prototype based on the newer Vampire F.5 fighter built at Hatfield. It differed from the first test aircraft in that it featured an even more streamlined pointed nose and smaller reinforced canopy (lowering the pilot's seat allowed for a more aerodynamic canopy shape to be employed). Power-boosted elevators had been specified as a means to control the pitch oscillations at the root of the earlier disaster. A more powerful Goblin 4 of 3,738 lbf (16.67 kN) thrust had the potential to push the DH 108 into the supersonic range. VW120 first flew on 24 July 1947 flown by John Cunningham, the wartime nightfighter ace.

Considered an important testbed for high-speed flight, VW120 was readied for an attempt at the World Speed Record then held by a Gloster Meteor at 616 mph (991 km/h). The second prototype, TG306, was a "back up" for the attempt before it fatally crashed. On 12 April 1948, VW120 established a new World Air Speed Record of 604.98 mph (974.02 km/h) on a 62 mile (100 km) circuit. Then, on 6 September 1948, John Derry is thought to have probably exceeded the speed of sound in a shallow dive from 40,000 ft (12,195 m) to 30,000 ft (9,145 m).

In 1949, VW120 put on an aerial display at Farnborough and scored third place in the Society of British Aircraft Constructors Challenge Trophy Air Race before being turned over to the Ministry of Supply and test flown at RAE Farnborough. It was destroyed on 15 February 1950 in a fatal crash near Brickhill, Buckinghamshire, killing its test pilot, Squadron Leader Stuart Muller-Rowland. Accident investigation pointed to a faulty oxygen system that incapacitated the pilot. A later coroners report published in the local newspaper one month later confirmed that the pilot died from a broken neck. As a direct result in the failure of the left wing in the dive just above the garage at brickhill. This failure is probably what caused the "bang" as described by witnesses at brickhill. The swishing sounds were from the aircraft spinning at a high rate though only having one wing. It came down in the woods after glancing off an oak tree, the traces of the impact were still visible 50 years later. The airframe and right wing were dismantled by the military, and removed very quickly. The left wing was also recovered from the fields just north of brickhill. A German field worker in a nearby field ran over to the crash site and was met by the garage mechanic from brickhill garage that had jumped in his car and also rushed to the crash site to offer assistance. The pilot was already dead. A search for the crash site in 2001 by a local metal detectorist was successful, by finding some of the mounting bolts "cone shaped" that were removed when the remains were dismantled on site. The very tree that the plane had hit was also found and the trace still visible. The earlier theory that a faulty oxygen system was the cause was ruled out by the coroner in his later report. The structural failure of the left wing in the high speed dive was the cause of the crash. info C.P.Martin

Finally, on 1 May 1950 during low-speed sideslip and stall tests the first prototype, TG283, was lost in a crash at Hartley Wintney killing the pilot Sqn Ldr George E.C. Genders AFC DFM, when, after abandoning the aircraft at low altitude in an inverted spin, his parachute failed to open in time. In all, 480 flights had been made by the three Swallows.