This November 25th marks the 75th anniversary of the first flight of the de Havilland Mosquito. To celebrate this event and mark the anniversary, we take a brief look at how we got where we are today.
The Birth of the Mosquito – the First True Multi-Role Combat Aircraft
It was in the late 1930s that Geoffrey de Havilland began to think about a wooden warplane. Despite the fact that wooden aircraft were seen as being out-moded by almost everyone in the Royal Air Force, de Havilland’s had produced two wooden types which had high performance in their class. One, the DH.88 Comet had won the U.K. to Australia air race, and the other the four-engined DH.91 Albatross had proved itself to be a popular high-performance airliner. Indeed, when asked to tender for a new medium bomber, de Havilland’s first studies had been of a developed version of the Albatross. More thought gave rise to the radical idea of eliminating the drag and weight of the gun turrets (and guns and their ammunition, and their gunners), and designing the smallest possible airframe that could carry 1,000lbs of bombs whilst being powered by two of the newly-developed Rolls-Royce PV.12 engines (soon to be called the Merlin).
The troubles that Geoffrey de Havilland, Snr and his design team had in persuading the Directorate of Technical Development of the Air Ministry to accept an unarmed, wooden bomber/reconnaissance aircraft are well-known. The battle that was fought at the highest levels inside the Air Ministry on behalf of the Mosquito by Air Marshal Wilfrid Freeman, the Air Council’s Member for Research and Development, led to the aircraft being called ‘Freeman’s Folly’; Freeman was convinced, unlike many other senior officers, of the rightness of the design, and under the powers assigned to him ordered one prototype to Specification B.1/40/dh. The initial production contract for a total of 50 aircraft followed later, on Friday, 1st March, 1940.
To achieve the projected performance, the Mosquito would have to be built in a radical manner. Very thin sheets of flexible 3-ply plywood were laid over a mahogany mould (some later moulds were concrete) representing one half of a fuselage. Six plywood and spruce bulkheads (the last, Bulkhead ‘G’ at the tail was installed later) would have been already slotted into gaps in the mould and various spruce sections laid in place where strength was needed; shaped pieces of balsa would then be used to fill in the gaps in between. Other sheets of thin, flexible plywood completed the basic shell, whilst the whole ‘sandwich’ would be saturated with casein wood glue, then held to the form with strong spring steel straps, and the adhesive ‘cured off’.
Pairs of fuselage halves were built at the same time, so that they were subjected to the same temperature and humidity. The major electrical, pneumatic and hydraulic systems and flying controls would then be installed in the two halves, and mated together, by means of a ‘V/notch’ joint and thin strips of plywood secured with more adhesive and brass screws – a person of small stature was usually selected to work in the tight confines of the tail section. A group of six men and women could finish this process in just one week. Casein is a phosphoprotein found in milk, and a glue is formed when it is mixed with slaked lime, water and sodium hydroxide. This white casein glue was adequate to the task at the time, but later urea-formaldehyde gap-filling adhesives such as Aerolite 303 were used; this gave a stronger bond and was resistant to biological attack by fungus and insects as well as high humidity. It is said that an Aerolite bond was actually three times stronger than spruce itself. The whole process was eminently suitable for industrialised mass production.
The Wooden Wonder
The Mosquito was referred to as ‘The Wooden Wonder’, in that approximately 60% by weight of the aircraft was wood of one species or other. Canadian yellow spruce for the laminated wing spars from British Columbia, balsa from Ecuador (which despite its lack of strength is technically a hardwood), and birch – for the plywood – from Wisconsin and the British Isles; all of these played their part, along with other woods such as Douglas fir. The spruce, vital for the wing spars and other components, had to come from old-growth forests, be perfectly straight and close-ringed, and have an ultimate strength of approximately 60N/mm2 (in today’s values); this was equal to some light alloys. The Air Ministry publication DTD36B, which contained the specification for spruce to be used in aircraft construction, was quite a strict one, laying down values for density, moisture content, straightness of grain and other criteria. Only one in ten trees felled passed the necessary tests for wood to be used in Mosquito wing spars. Certain areas of the airframe used ash for its hard-wearing qualities, and the wing-root pick-up structures were made from walnut, chosen for its great strength.
Designed and built in secrecy at Salisbury Hall, close to Hatfield, the prototype was given the Class B registration E0234 by the company. It was painted all-over Trainer Yellow, with black spinners, then dis-assembled and transported by road to Hatfield on the 3rd November, 1940. Careful re-assembly was followed by ground runs of the two Merlins, then a series of taxi tests, starting on 24th November. Geoffrey de Havilland, Jnr, the company’s Chief Test Pilot, made these faster and faster, until the machine left the muddy surface of Hatfield – briefly – on the last one. The following morning, 25th November, E0234 was prepared for the first flight; its all-up weight being 14,150lbs. Geoffrey de Havilland Jnr was accompanied by J.E. Walker, the Engine Installation Designer, as the Flight Test Observer. The Mosquito lifted off cleanly at 3.45pm. A short test flight of just 30 minutes followed, the only trouble encountered being some tail buffeting, caused by uneven airflow over the rear part of the short engine nacelles. (Note, this was eventually to be solved by lengthening these items). A lengthy flight test career lay ahead for W4050 (the official serial she had been assigned); on some of these flights she carried Richard (Dick) Whittingham, the Experimental Flight Inspector, whose diaries of the time you can read here.
The first Mosquito, W4050, was highly maneouverable and exhibited blazing speed – over 25 mph faster than the current Mark of Spitfire. This was achieved in part by having a smooth, fabric-covered plywood surface, and also the positioning of the Mosquito’s wing close to its nose (this helped limit viscous drag). Bomber (B. Mk.IV), fighter (F.Mk.II), and photo-reconnaissance prototypes (P.R. Mk.I) swiftly followed, along with a dual-control trainer (the T. Mk. III). After masterful demonstrations of the Mosquito by Geoffrey de Havilland, Jnr. in front of delegations of high-ranking officers (including U.S. General H. ‘Hap’ Arnold) the view of the aircraft went from, ‘Do we really want the Mosquito?’ to ‘How many can we have, and how soon?’
Thus was the world’s first true ‘multi-role combat aircraft’ born.
A dedicated group of volunteers at the De Havilland Aircraft Museum at Salisbury Hall, London Colney, have spent four years restoring W4050 – four years that have seen the prototype “Wooden Wonder” totally dismantled and restored to its wartime configuration. W4050 is the only extant wartime piston-engined prototype in the world. The aircraft will be on display for the commemoration of the 75th anniversary of her maiden flight at special openings of the museum from 27th – 29th November. Further details and opening times are available on their website.
At one time – not long ago – the future of the Mosquito looked bleak. It was the forgotten hero of the Second World War and looked set to remain so. But thanks to the work of Glyn Powell and his team in New Zealand the future is very bright for the Mossie. Glyn and the team at AvSpecs have brought the Mosquito back to life, and Glyn could rightly be called The Man Who Saved The Mosquito.
The good news is that there are now two flightworthy Mosquitoes – one in the U.S. and one in Canada and, at time of writing, four known projects ongoing to return Mosquitoes to flight. Two are on or awaiting the production line in New Zealand – both for private individuals in the U.S. and two are proposed for the U.K.: one is a private venture and the other is yours truly – The People’s Mosquito, which is publicly funded and operating as a charitable project.
So it can now be said of the Mosquito: the future is bright, the future is flight!
To see The People’s Mosquito take to the air will require public money and we are relying on donations from individuals and corporate sponsors. To help support us in this venture please donate what you can by visiting our Donate page. Or visit our online store – the TPM shop – where you can show your support by buying one of our t-shirts or sweat-shirts. Our profits from sales go directly towards returning a Mosquito to British skies.
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