page_title: De Havilland Mosquito
section_title: Prototypes and test flights
hierarchical_section_title: De Havilland Mosquito / Development / Prototypes and test flights
caption_attribution_description: The first prototype to fly (E-0234 later W4050) being restored at the de Havillard Aircraft Heritage Centre near St Albans.
context_page_description: The de Havilland DH.98 Mosquito is a British twin-engined, shoulder-winged multirole combat aircraft, introduced during the Second World War. Unusual in that its frame was constructed mostly of wood, it was nicknamed the "Wooden Wonder", or "Mossie". Lord Beaverbrook, Minister of Aircraft Production, nicknamed it "Freeman's Folly", alluding to Air Chief Marshal Sir Wilfrid Freeman, who defended Geoffrey de Havilland and his design concept against orders to scrap the project. In 1941, it was one of the fastest operational aircraft in the world.
  Originally conceived as an unarmed fast bomber, the Mosquito's use evolved during the war into many roles, including low- to medium-altitude daytime tactical bomber, high-altitude night bomber, pathfinder, day or night fighter, fighter-bomber, intruder, maritime strike, and photo-reconnaissance aircraft. It was also used by the British Overseas Airways Corporation as a fast transport to carry small, high-value cargo to and from neutral countries through enemy-controlled airspace. The crew of two, pilot and navigator, sat side by side. A single passenger could ride in the aircraft's bomb bay when necessary.
context_section_description: On 3 November 1940, the prototype aircraft, painted in "prototype yellow" and still coded E-0234, was dismantled, transported by road to Hatfield and placed in a small, blast-proof assembly building. Two Merlin 21 two-speed, single-stage supercharged engines were installed, driving three-bladed de Havilland Hydromatic constant-speed controllable-pitch propellers. Engine runs were made on 19 November. On 24 November, taxiing trials were carried out by Geoffrey de Havilland Jr., the de Havilland test pilot. On 25 November, the aircraft made its first flight, piloted by de Havilland Jr., accompanied by John E. Walker, the chief engine installation designer.
  For this maiden flight, E-0234, weighing 14,150 pounds (6,420 kg), took off from the grass airstrip at the Hatfield site. The takeoff was reported as "straightforward and easy" and the undercarriage was not retracted until a considerable altitude was attained. The aircraft reached 220 mph (355 km/h), with the only problem being the undercarriage doors – which were operated by bungee cords attached to the main undercarriage legs – that remained open by some 12 inches (300 mm) at that speed. This problem persisted for some time. The left wing of E-0234 also had a tendency to drag to port slightly, so a rigging adjustment, i.e., a slight change in the angle of the wing, was carried out before further flights.
  On 5 December 1940, the prototype, with the military serial number W4050, experienced tail buffeting at speeds between 240 and 255 mph (385 and 410 km/h). The pilot noticed this most in the control column, with handling becoming more difficult. During testing on 10 December, wool tufts were attached to suspect areas to investigate the direction of airflow. The conclusion was that the airflow separating from the rear section of the inner engine nacelles was disturbed, leading to a localised stall and the disturbed airflow was striking the tailplane, causing buffeting. To smooth the air flow and deflect it from forcefully striking the tailplane, nonretractable slots fitted to the inner engine nacelles and to the leading edge of the tailplane were tested. These slots and wing-root fairings fitted to the forward fuselage and leading edge of the radiator intakes, stopped some of the vibration experienced, but did not cure the tailplane buffeting.
  In February 1941, buffeting was eliminated by incorporating triangular fillets on the trailing edge of the wings and lengthening the nacelles, the trailing edge of which curved up to fair into the fillet some 10 in (250 mm) behind the wing's trailing edge; this meant the flaps had to be divided into inboard and outboard sections. With the buffeting problems largely resolved, John Cunningham flew W4050 on 9 February 1941. He was greatly impressed by the "lightness of the controls and generally pleasant handling characteristics". Cunningham concluded that when the type was fitted with AI equipment, it might replace the Bristol Beaufighter night fighter.
  During its trials on 16 January 1941, W4050 outpaced a Spitfire at 6,000 ft (1,800 m). The original estimates were that as the Mosquito prototype had twice the surface area and over twice the weight of the Spitfire Mk II, but also with twice its power, the Mosquito would end up being 20 mph (30 km/h) faster. Over the next few months, W4050 surpassed this estimate, easily beating the Spitfire Mk II in testing at RAF Boscombe Down in February 1941, reaching a top speed of 392 mph (631 km/h) at 22,000 feet (6,700 m) altitude, compared to a top speed of 360 mph (580 km/h) at 19,500 feet (5,900 m) for the Spitfire.
  On 19 February, official trials began at the Aeroplane and Armament Experimental Establishment (AAEE) based at Boscombe Down, although the de Havilland representative was surprised by a delay in starting the tests. On 24 February, as W4050 taxied across the rough airfield, the tailwheel jammed leading to the fuselage fracturing. Repairs were made by early March, using part of the fuselage of the photo-reconnaissance prototype W4051. In spite of this setback, the Initial Handling
caption: W4050 being restored at the de Havilland Aircraft Heritage Centre near St Albans
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