DH 98 Mosquito Bomber – The Versatile Wooden Wonder
Some aircraft are created great such as the DH 98 Mosquito. As soon as they roll off the production lines they are welcomed into service and soon fit perfectly into the role for which they are designed. In other aircraft, greatness only becomes apparent over time and often in roles for which they may not have been originally designed.
The Mosquito was designed in the late 1930s in Britain as a light bomber. However, the RAF weren’t much interested. The new aircraft was to be constructed of wood as opposed to the all-metal warplanes then coming into service around the world.
It seemed like a throwback to an earlier era and it was only reluctantly accepted because it didn’t require the scarce metals needed to build other combat aircraft.
This was seen by many as a short-term, second-best, interim solution that would have to be tolerated only until resources were available for other new all-metal designs to be produced.
Instead, the DH 98 Mosquito bomber proved to be one of the best and most versatile designs of World War Two that, rather than being an antiquated wooden design, was actually a forerunner of entirely new approaches to aircraft design and construction.
During the 1930s, most military aircraft manufacturers in Britain and elsewhere were beginning to move away from the braced wooden structures used in earlier fighters and bombers and towards all-metal construction.
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The benefits were obvious – metal construction was stronger and more resistant to combat damage and avoided the need for drag-inducing external struts and bracing. But one British aviation company continued to explore the possibilities of wood construction: de Havilland.
In the early 1930s, de Havilland produced several very successful civilian biplanes including the DH 89 Dragon Rapide airliner and what would become the RAF primary trainer, the DH 82 Tiger Moth.
However, the company was also experimenting with the design of advanced monoplanes. The DH 88 Comet was a sleek, low-wing, twin-engine monoplane with retractable gear that was designed primarily to take part in air races.
Just five were built but this aircraft set new speed and distance records and in 1934, a DH 88 won the prestigious Victorian Centenary Air Race from Mildenhall in England to Melbourne in Australia.
Experience gained from the design and build of the DH 88 Comet led to the creation of the DH 91 Albatross Airliner/Mail Plane. This was another sleek, low-wing monoplane with twin tails (it looked rather like a scaled-down version of the later Lockheed Constellation airliner) designed for high speed and long range.
At a time when many airliners were biplanes or ungainly monoplanes with fixed undercarriage, the DH 91 looked futuristic and elegant, but just seven were built before World War Two began in September 1939.
What both the DH 88 Comet and DH 91 Albatross had in common was a unique form of construction. Both were built primarily of wood but used a quite different approach to the braced structures of earlier wooden aircraft.
The wings used spruce spars and outer skin and the fuselage was built from a unique sandwich of two skins of plywood around a core of balsa wood.
This approach allowed the creation of a much more streamlined design that featured more aerodynamically efficient curves than were possible using metal structures.
No fasteners were used in basic construction – all major components were glued. This created an immensely strong structure that avoided the need for external fasteners, reducing drag and improving streamlining.
At the time, the use of a wooden structure in an aircraft looked a little old-fashioned to many people. Now, we can see this as the forerunner of the composite structures used in most military aircraft.
Birth of the DH 98
In 1936, the British Air Ministry issued specification P.13/36 calling for designs for a new high-speed medium bomber. De Havilland responded in April 1938 with a design derived from the Albatross airliner, with a wooden structure and power provided by a pair of the then-new Rolls-Royce Merlin water-cooled engines but lacking any defensive armament.
Their proposal was rejected. The Air Ministry felt that de Havilland lacked experience in military aircraft design (they hadn’t created a new military aircraft since World War One) and they didn’t like the notion of an unarmed bomber – all the other British medium bomber designs of the period, including the Blenheim, Wellington and Hampden, featured defensive gun positions. But most of all, they disliked the proposed wooden structure.
Undeterred, de Havilland continued to refine the design of what was designated the DH 98 under the leadership of Chief Engineer Ronald E. Bishop. Leaving out heavy and drag-inducing gun turrets also meant that the crew could be reduced to just two: a pilot and Navigator/Bomb Aimer, making the aircraft even lighter.
De Havilland believed that it would be possible to create an aircraft capable of carrying a bomb load of 1,000lb over a range of 1,500 miles and with a startling top speed of over 400mph, making it faster than any fighter then in service.
The RAF remained unconvinced of the need for a fast light bomber, and the DH 98 project might have died on the drawing board but for one important fact: Britain was critically short of metals needed to create the aluminium alloys used in the construction of most metal military aircraft.
The wooden Mosquito bomber could be produced without the extensive use of strategic materials.
Despite this, many in the RAF were not at all happy with the notion of a wooden aircraft. Air Chief Marshall Sir Wilfrid Freeman (a personal friend of Geoffrey de Havilland), disagreed and an initial order for 50 DH 98 aircraft was placed in March 1940. To many in the RAF, the new aircraft became known as “Freeman’s Folly.”
Mosquito Bomber In Service
The construction of the DH 98 was truly unique. The wings were made from spruce spars and stringers covered in a double layer of birch plywood skin and finished with a layer of fabric.
The fuselage comprised seven bulkheads created from spruce blocks covered in layers of plywood and an outer skin formed of a sandwich of outer plywood around a balsa-wood core. This created a structure that was both immensely strong but also very light.
The DH 98 had an empty weight of around 14,000 lbs compared to, for example, the Wellington Bomber which had an empty weight of around 19,000 lbs.
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This construction approach not only saved on vital alloys, it saved on the creation of machine tools and even allowed firms with no previous experience in aircraft production to manufacture parts of the airframe – furniture and even piano manufacturers were able to become part of the expanded DH 98 manufacturing process.
The first prototype flew in May 1940 and it proved to be just as fast as de Havilland had promised, reaching a top speed of over 380 mph.
The aircraft was given the official name “Mosquito” and following the first delivery in the summer of 1941 a total of over 7,500 DH 98s would be manufactured in Britain, Canada and Australia in over twenty-five different variants that would see service with the RAF, the Royal Navy, the USAAF and the Red Air Force.
It didn’t take long for the derisive nickname “Freeman’s Folly” to be replaced by a new name given to the DH 98 by the men who flew it: the Wooden Wonder.
The last operational flight of an RAF DH 98 would not take place until 1963, not a bad service record for an aircraft that many in the RAF had not wanted at all!
The first 50 models of the DH 98 ordered by the Air Ministry in 1940 were all photo-reconnaissance (PR) versions. The PR.1, provided with a Perspex nose section for camera aiming and five camera ports, performed its first sorties in September 1941.
It proved so successful that a range of Mosquito PR versions followed culminating in the PR.32, used in the final months of World War Two and able to achieve a top speed of 430mph and a maximum altitude of 42,000 feet.
Although only unarmed PR versions were originally ordered, the design team at de Havilland had incorporated provisions for the fitment of armament in the design of the DH 98 from the beginning.
The second prototype, designated the F.II, was intended as a long-range fighter version and was armed with four .303-caliber Browning machine guns in the solid nose and four Hispano 20mm cannons in a ventral tray.
This gave the aircraft devastating firepower, but continuing night-time bombing raids by German aircraft meant that what the RAF particularly needed in 1941 was a night-fighter that could replace the effective but slow Bristol Beaufighter.
In the summer of 1941, an F.II was fitted with Mark IV (AI.IV) airborne intercept radar to create the first Night Fighter Mosquito, the NF.II. Several improved variants were produced culminating in the NF-30, introduced in August 1944 and fitted with more powerful engines and AI.IX radar in a nose radome.
The speed of the Mosquito made it an ideal night fighter and by the time that the war ended, NF versions of the Mosquito had accounted for the destruction of more than 600 enemy aircraft.
The bomber and fighter/bomber versions of the DH 98 also proved to be very effective indeed. The first Bomber Mark IV (B.IV) Series I incorporated the same Perspex nose used in the PR version, deleted all defensive armament and was able to carry up to 1,000 lbs of bombs.
Subsequent versions of the bomber version were able to carry up to 2,000 lbs of bombs and a few were even modified to carry the 4,000lb High Capacity (HC) Cookie bomb. The fighter/bomber (FB) version retained the machine gun and cannon armament and added a small bomb bay that could carry up to 1,000 lbs of bombs.
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Bomber variants took part in several low-level precision strike missions including an attack on the Gestapo prison at Amiens in occupied France that led to the escape of over 250 Allied prisoners.
In another low-level raid, DH 98 aircraft destroyed the main Berlin Broadcasting Station on the day that Herman Goering was planning to make a nationally broadcast speech. That led to an outburst in which the head of the Luftwaffe complained:
“It makes me furious when I see the Mosquito. I turn green and yellow with envy. The British, who can afford aluminium better than we can, knock together a beautiful wooden aircraft that every piano factory over there is building!”
There is probably no greater accolade that any combat aircraft can receive than to be singled out for envious comment by the head of the enemy air force!
The DH 98 excelled in every role in which it was used. It was an outstanding fighter and night fighter, a superb precision bomber, an effective fighter/bomber, a useful photo-reconnaissance aircraft and a great pathfinder for heavy bombing raids.
Yet this was an aircraft that many people in the RAF hadn’t wanted back in 1939. Then, its wooden construction was seen as a backward step, reluctantly accepted only because it saved the use of scarce alloys.
Only later would it become apparent that this was a design of genius, creating a lightweight, fast, reliable and versatile aircraft that became one of the best combat aircraft of World War Two.
Rather than simply being an interim design used until all-metal replacements were available, the DH 98 showed that the innovative use of composite materials could create sleek, fast, effective combat aircraft. De Havilland would go on to design some iconic post-war jet aircraft including the Vampire, Venom and Sea Vixen but none would achieve the impact or lasting appeal of the Wooden Wonder.
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- Crew: Two: pilot, bomb aimer/navigator
- Length: 44 ft 6 in (13.56 m)
- Wingspan: 54 ft 2 in (16.51 m)
- Height: 17 ft 5 in (5.31 m)
- Empty weight: 14,300 lb (6,486 kg)
- Max takeoff weight: 25,000 lb (11,340 kg)
- Powerplant: 1 × Rolls-Royce Merlin 76 V-12 liquid-cooled piston engine, 1,710 hp (1,280 kW) driving the left propeller
- Powerplant: 1 × Rolls-Royce Merlin 77 V-12 liquid-cooled piston engine, 1,710 hp (1,280 kW) fitted with a blower for cabin pressurisation, driving the right propeller
- Maximum speed: 415 mph (668 km/h, 361 kn) at 28,000 ft (8,500 m)
- Range: 1,300 mi (2,100 km, 1,100 nmi)
- Service ceiling: 37,000 ft (11,000 m)
- Rate of climb: 2,850 ft/min (14.5 m/s)