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History of the de Havilland Mosquito

Current Project | Past Restorations | Restorations | History of A52-600

The de Havilland Aircraft Company was noted for its light aircraft, such as the famous DH82 Tiger Moth, and some mixed construction transport planes. In 1936 de Havilland had built the DH91 Albatross airliner and mailplanes entirely in wood. In 1938 de Havilland proposed to the Air Ministry that they should build a bomber or reconnaissance aircraft that would be so fast it could be unarmed. The Air Ministry was generally hostile to the plan and turned de Havilland down. In October 1938 the Air Ministry informed de Havilland that de Havilland's contribution was best served by constructing mainplanes for one of the existing bomber aircraft programs.

De Havilland was not deterred and continued with the Mosquito project as a private venture. The proposal was based on reducing weight by removing the gun turrets and having a crew of two instead of six. The aircraft would be smaller and burn less fuel. With twin Merlins, an unarmed bomber could carry 1,000lb (454kg) of bombs for 1,500 miles (2400km) at a speed of almost 400mph (644km/h) which was almost twice that of current British bombers at the time.

With great foresight de Havilland proposed to build the aircraft predominantly of wood; another issue the Air Staff did not approve of. However, de Havilland had surmised that in time of war aluminium for aircraft would be a very scarce commodity, and so would the expertise of those personnel who were skilled in the metal construction. There would be, on the other hand, many experienced carpenters, piano, cabinet, and furniture makers available whose skills could be used.

Like the Comet and Albatross mainplanes, de Havilland constructed Mosquito mainplanes out of shaped pieces of wood and plywood cemented together with Casein glue. Approximately 30,000 small, brass wood screws also reinforced the glue joints inside a Mosquito mainplane (another 20,000 or so screws reinforced glue joints in the fuselage and empennage). The internal mainplane structure consisted of plywood box spars fore and aft. Plywood ribs and stringers braced the gaps between the spars with space left over for fuel tanks and engine and flight controls. Plywood ribs and skins also formed the mainplane leading edges and flaps but de Havilland framed-up the ailerons from aluminium alloy and covered them with fabric. Sheet metal skins enclosed the engines and metal doors closed over the main wheel wells when the pilot retracted the landing gear.

To cover the mainplane structure and add strength, de Havilland woodworkers built two top mainplane skins and one bottom skin using birch plywood. The top skins had to carry the heaviest load so the designers also beefed them up with birch or Douglas fir stringers cut into fine strips and glued and screwed between the two skins. The bottom skin was also reinforced with stringers. Together the top and bottom skins multiplied the strength of the internal spars and ribs. A Mosquito mainplane could withstand rigorous combat manoeuvring at high G-loads when the aircraft often carried thousands of additional pounds of fuel and weapons. To maintain strength, trim weight, and speed fabrication time, the entire mainplane and spar was finished as a single piece, wingtip to wingtip, with no break where the wing bisected the fuselage. A finished and painted mainplane was light and strong with a smooth surface unblemished by drag inducing nail or rivet heads.

De Havilland engineers and technicians used generally the same techniques to construct the Comet, Albatross, and Mosquito mainplanes out of wood and plywood. When they designed and built the fuselage, however, they copied the methods and materials employed to build the Albatross fuselage. This airliner was the product of the brilliant mind of Arthur E. Hagg, de Havilland's Chief Draftsman in 1937. He left the company that same year but his ideas lived on in the Mosquito. Hagg created a light, strong, very streamlined structure by sandwiching 9.5mm Ecuadorian balsa wood between Canadian birch plywood skins that varied in thickness from 4.5mm to 6mm. The plywood/balsa/plywood sandwich was formed inside concrete moulds of each fuselage half, and each mould held seven birch plywood formers reinforced with spruce blocks, plus bulkheads, floors, and other structural members. As the glue cured, metal clamps held the skin layers tight to the mould. Technicians finished the edge of each half of the fuselage with male and female wedge joints as fitters attached wiring and other equipment to the inner walls. Final fuselage assembly was reminiscent of a typical plastic model aircraft kit as the two halves were glued and screwed together. Fabricators completed the final step in building the fuselage when they covered it with Madapolam (fabric).

To build the empennage, workers framed the rudder and elevator out of aluminium and covered the structures with fabric but the vertical and horizontal stabilisers were constructed from wood. Although the materials are different, Hagg's composite sandwich construction material is similar to the foam and fibreglass composite sandwich developed by Burt Rutan during the 1970s. The hydraulic plain flaps were wood. The coolant radiators were in the mainplane leading edge between the engines and the fuselage. The landing gear was simple twin shock struts filled with rubber blocks. Engine mounts were welded steel tube. The total weight of castings and forgings used in the aircraft was a mere 280lbs (127kg).

On the 1 March 1940 an order was given to de Havilland for 50 aircraft against Air Ministry Specification B.1/40, but was cancelled again in the aftermath of Dunkirk. After many false starts it was eventually re-instated on the 25 November 1940. The prototype Mosquito (W4050), which had been secretly built at Salisbury Hall near Hatfield, was flown for the first time on the 25 November 1940. The aircraft was painted bright yellow so it would not be fired on by allied anti-aircraft guns or planes.

Original estimates were that, with twice the power of a Spitfire, twice the wetted area and over twice the weight, the Mosquito would still be 20mph (32km/h) faster than the Spitfire. The Air Ministry was very sceptical. When the prototype was officially tested at Boscombe Down in February 1941 they were proved wrong and it exceeded this estimate by achieving a top speed of 392mph (631km/h). It was the fastest aircraft in Bomber Command until May 1951.

Once it had proved itself, official attitudes towards the Mosquito changed and development commenced. The wingspan was increased from 52ft 6in (16m) to 54ft 2in (16.51m). It was fitted with a larger tailplane, improved exhaust system, and lengthened nacelles that improved stability. Even though it had been designed as an unarmed aircraft there was still room to fit a variety of .303inch (7.7mm) machineguns and 20mm and 57mm cannon in addition to the bomb load.

Forty nine of the original short-nacelle Mosquitoes entered service during the summer of 1941 either as photo-reconnaissance (PR) aircraft or converted to B IV series 1 bombers with a bomb load of 2,000lb (907kg). The first mission was a PR trip to Bordeaux and La Pallice on 17 September 1941 by W4055 of RAF No 1 Photographic Reconnaissance Unit. The first bomber mission was flown by four aircraft (including W4072) of RAF No 105 Squadron immediately after a "1,000 bomber raid" to Cologne on 30-31 May 1942.

Many other raids followed and some were designed more for effect than destruction. On 31 January 1943, RAF No 105 Squadron became the first Mosquito Unit to bomb Berlin. Hermann Goering, head of the Luftwaffe, was due to address a parade in the morning and the raid effectively disrupted it. Not content with this, aircraft from RAF No 139 Squadron went to Berlin in the afternoon and gave the parade being addressed by Dr. Goebels the same treatment. This action very effectively discredited Goering's boast that no enemy aircraft would fly unscathed over Berlin.

Some of the most famous roof top height raids were due to the precision bombing by the Mosquito. Among these were raids on the Gestapo Headquarters in Oslo, the Central Registry in The Hague, Shell House in Copenhagen, and Amiens Jail. They were expected to hit a single enemy building in the middle of a city with minimum harm to the civilians. In many cases they did not achieve all they set out to do but the effect on enemy morale was devastating.

The Mosquito was used effectively for photo-reconnaissance, a bomber, a fighter-bomber, a night-fighter, an intruder, a trainer, a pathfinder, a target marker, a torpedo-bomber, a U-boat killer, a day ranger, a minelayer, and a target tug. The aircraft could be fitted with varying bomb loads, including the Wallis spinning bomb, up to the 4000lb (1814kg) bomb or rocket projectiles for anti-tank and anti-transport use.

The Mosquito served in all theatres of the war and flew from all types of airfields. Some were aircraft carrier-based and a Mosquito was the first twin-engine aircraft to land on a carrier. They also flew countless missions in civilian garb throughout the war to neutral Sweden carrying despatches, returning with ball bearings and, sometimes, passengers.

More than 400 subcontractors built Mosquito components in England. The main factory at Hatfield and several other co-producers assembled these components into finished Mosquitoes. The aircraft was also produced in Canada and Australia and a United States production program was discussed but dropped when Canadian Mosquitoes began to fly.

In 1942, the Australian de Havilland factory at Bankstown commenced production of a fighter-bomber Mosquito, the DHA 98 FB Mk 40. Initial delays were caused by the unavailability of Canadian birchwood, and Australian coachwood had to be substituted.

The first Australian Mosquito was delivered on 23 July 1943, and accepted by the RAAF on 5 March 1944. The FB Mk 40 was equivalent to the RAF FB Mk VI and, although 212 were built at Bankstown (A52-1/212), only 209 served with the RAAF because A52-12, 18 and 24 crashed before acceptance. Six of the FB Mk 40s were converted for photo-reconnaissance as PR Mk 40s, and these aircraft operated so effectively that a further 28 FB Mk 40s were converted to PR Mk 41s. Previously, A52-90 had been re-engined with Packard Merlin 69s and became the sole FB Mk 42: however, this marque was superseded and A52-90 was used as the prototype for the PR Mk 41 and re-serialled A52-300.

On 28 January 1943, a RAF Mk II (DD664) became the first Mosquito to operate with the RAAF when, as A52-1001, it was used as the prototype for the local FB Mk 40. It was also the forerunner of 14 RAF T Mk IIIs (A52-1002/1015). Australian versions of these trainers were developed by converting 22 FB Mk 40s to T Mk 43s. In addition, a further 61 ex-RAF Mosquitoes were used by the RAAF as follows: 38 B Mk VIs (A52-500/537) and 23 PR Mk XVIs (A52-600/622). Thus, altogether 209 Australian Mosquitoes and 76 UK-built Mosquitoes served with the RAAF. These aircraft fitted with a variety of engines including the Merlin 31, Merlin 33 and Packard Merlin 69.

The RAAF Mosquitoes played a limited, but effective, part in the later years of the Pacific War and served with No 1 Photographic Reconnaissance Unit, Nos 87 and 94 Squadrons, No 78 Wing, No 1 Aircraft Performance Unit, Aircraft Research and Development Unit, Central Flying School, No 5 Operational Training Unit and Ferry/Survey Flights. Post-war, photo-reconnaissance Mosquitoes were used extensively between 1947–53 on survey flights throughout Australia. Mosquito flying ceased (mainly) in 1954, and the aircraft still on RAAF strength were passed to DAP for disposal, except for a few which were transferred to the Royal New Zealand Air Force.

After the war, Mosquitoes laden with cameras surveyed all of India, Cambodia, and Australia. The last Mosquito built, an NF 38 (VX916), rolled off the production line at Chester on 28 November 1950, and the last operational combat mission was on 21 December 1955 when a Mosquito PR 34A conducted a reconnaissance mission above suspected communist strongholds hidden in the jungles of Malaya.

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