Prototypes and test flights On 3 November 1940, the aircraft, still coded E0234, was transported by road to Hatfield, and placed in a small blast-proof assembly building, where successful engine runs were made on 19 November. Two Merlin 21 two-speed single-stage supercharged engines were installed driving three-bladed de Havilland Hydromatic constant-speed, controllable-pitch propellers. E0234 had a wingspan of 52 ft 2 in (15.90 m) and was the only Mosquito to be built with Handley Page slats on the outer leading edges of the wings. Test flights showed that these were not needed and they were disconnected and faired over with doped fabric (these slats can still be seen on W4050). On 24 November 1940, taxiing trials were carried out by Geoffrey de Havilland, Jr., who was the companys chief test pilot and responsible for maiden flights. The tests were successful and the prototype was subsequently readied for flight testing, making its first flight piloted by Geoffrey de Havilland, on 25 November. The flight was made 11 months after the start of detailed design work, a remarkable achievement considering the conditions of the time. For this maiden flight, E0234, weighing 14,150 pounds (6,420 kg), took off from a 450-foot (140 m) field beside the shed it was built in. John E. Walker, Chief Engine Installation designer, accompanied de Havilland. The takeoff was straight forward and easy and the undercarriage was not retracted until a considerable height was attained. The aircraft reached 220 mph (350 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 E0234 also had a tendency to drag to port slightly, so a rigging adjustment was carried out before further flights. On 5 December 1940, the prototype experienced tail buffeting at speeds between 240 miles per hour (390 km/h) and 255 miles per hour (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 rear section of the inner engine nacelles was disturbed, leading to a localised stall and the disturbed airflow was striking the tailplane, causing buffeting. In an attempt to smooth the air flow and deflect it from forcefully striking the tailplane, non-retractable slots fitted to the inner engine nacelles and to the leading edge of the tailplane were experimented with. 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 wings trailing edge: this meant the flaps had to be divided into inboard and outboard sections. By January 1941, the prototype was carrying the military serial number W4050. 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 would be a perfect replacement for the Bristol Beaufighter. 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 miles per hour (32 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 miles per hour (631 km/h) at 22,000 feet (6,700 m) altitude, compared to a top speed of 360 miles per hour (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 (A&AEE) based at Boscombe Down, although de Havillands 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: this was replaced by the fuselage of the Photo-Reconnaissance prototype W4051 in early March. In spite of this setback, the Initial Handling Report 767 issued by the A&AEE stated The aeroplane is pleasant to fly ... Aileron control light and effective ... The maximum speed reached was 388 mph (624 km/h) at 22,000 ft (6,700 m), with an estimated maximum ceiling of 33,900 ft (10,300 m) and a maximum rate of climb of 2,880 ft/min (880 m/min) at 11,400 ft (3,500 m). W4050 continued to be used for various test programs, essentially as the experimental workhorse for the Mosquito family. In late October 1941, it returned to the factory to be fitted with Merlin 61s, the first production Merlins fitted with a two-speed, two-stage supercharger. The first flight with the new engines was on 20 June 1942. W4050 recorded a maximum speed of 428 mph (689 km/h) at 28,500 ft (8,700 m) (fitted with straight-through air intakes with snowguards, engines in F.S. gear) and 437 mph (703 km/h) at 29,200 ft (8,900 m) without snowguards. In October 1942, in connection with development work on the NF Mk XV, W4050 was fitted with extended wingtips increasing the span to 59 ft 2 in (18.03 m), first flying in this configuration on 8 December. Finally, fitted with high-altitude rated two-stage, two-speed Merlin 77s, it reached 439 miles per hour (707 km/h) in December 1943. Soon after these flights,W4050 was grounded and was scheduled to be scrapped, but instead served as an instructional airframe at Hatfield. In September 1958, W4050 was returned to the Salisbury Hall hangar in which it had been built, restored to its original configuration, and became one of the primary exhibits of the de Havilland Aircraft Heritage Centre. W4051, which was designed from the outset to be the prototype for the photo-reconnaissance versions of the Mosquito, was slated to make its first flight in early 1941. However, the fuselage fracture in W4050 meant that W4051s fuselage was used as a replacement; W4051 was then rebuilt using a production standard fuselage and first flew on 10 June 1941. This prototype continued to use the short engine nacelles, single-piece trailing edge flaps and the 19 ft 5.5 in (5.931 m) No. 1 tailplane used by W4050, but had production standard 54 ft 2 in (16.51 m) wings and, thus configured, became the only Mosquito prototype to fly operationally. Construction of the fighter prototype, W4052 was also carried out at the secret Salisbury Hall facility. The new prototype differed from its bomber brethren in a number of ways. It was powered by 1,460 hp (1,090 kW) Merlin 21s and had an altered canopy structure with a flat bullet-proof windscreen. Four 20 mm (.79 in) Hispano Mk II cannon were housed in a compartment under the cockpit floor, with the breeches projecting into the bomb bay. The bomb bay doors were replaced by manually operated bay doors which incorporated cartridge ejector chutes. The solid nose mounted four .303 in (7.7 mm) Browning machine guns and their ammunition boxes which were accessed by a single large, sideways hinged panel. In accordance with its role as a day/night fighter prototype W4052 was equipped with AI Mk.IV equipment, complete with an arrowhead-shaped transmission aerial mounted between the central Brownings, and receiving aerials through each outer wingtip, and it was painted in overall black RDM2a Special Night finish. It was also the first prototype constructed with the extended engine nacelles. W4052 was later tested with other modifications including bomb racks, drop tanks, barrage balloon cable cutters in the leading edge of the wings, Hamilton airscrews and braking propellers, as well as drooping aileron systems which enabled steep approaches, and a larger rudder tab. The prototype continued to serve as a test machine until it was scrapped on 28 January 1946. W4055 flew the first operational Mosquito flight on 17 September 1941. During flight testing, the Mosquito prototypes were modified to test a number of experimental configurations. W4050 was fitted with a turret behind the cockpit for drag tests, after which the idea was abandoned in July 1941. W4052 had the first version of the Youngman Frill airbrake fitted to the fighter prototype. The frill was opened by bellows and venturi effect to provide rapid deceleration during interceptions and was tested between January - August 1942, but was also abandoned when it was discovered that lowering the undercarriage had the same effect with less buffeting. Production plans and American interest The Air Ministry had authorised mass production plans to be drawn up on 21 June 1941, by which time the Mosquito had become one of the worlds fastest operational aircraft. The Air Ministry ordered 19 photo-reconnaissance (PR) models and 176 fighters. A further 50 were unspecified; in July 1941, the Air Ministry confirmed these would be unarmed fast bombers. By the end of January 1942, contracts had been awarded for 1,378 Mosquitos of all variants, including 20 T.III trainers and 334 FB.VI bombers. Another 400 were to be built by de Havilland Canada. On 20 April 1941, W4050 was demonstrated to Lord Beaverbrook, the Minister of Aircraft Production. The Mosquito made a series of flights, including one rolling climb on one engine. Also present were US General Henry H. Arnold and his aide Major Elwood Quesada, who wrote I ... recall the first time I saw the Mosquito as being impressed by its performance, which we were aware of. We were impressed by the appearance of the airplane that looks fast usually is fast, and the Mosquito was, by the standards of the time, an extremely well streamlined airplane, and it was highly regarded, highly respected. The trials set up future production plans between Britain, Australia and Canada. The Americans did not pursue their interest. It was thought the Lockheed P-38 Lightning could handle the same duties just as easily. Arnold felt the design was being overlooked, and urged the strategic personalities in the United States Army Air Forces to learn from the design if they chose not to adopt it. Several days after the attack on Pearl Harbor, the USAAF then requested one airframe to evaluate on 12 December 1941, signifying that the USAAF realised that they had entered the war without a fast dual-purpose reconnaissance aircraft. r/max
Posted on: Sat, 20 Dec 2014 19:00:02 +0000
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