De Havilland Hornet - Design and Development

Design and Development

Designed as a private venture for a long-range fighter destined for the Pacific Theatre in the war against Japan, Specification F.12/43 was written around the type. From an early stage it was also envisaged that the Hornet could be adapted for naval use, operating from aircraft carriers. As a result priority was given to ease of control, especially at low speeds, and good pilot visibility. Construction was of mixed balsa/plywood similar to the Mosquito, but the Hornet differed in incorporating stressed Alclad lower-wing skins bonded to the wooden upper wing structure using the then-new adhesive Redux. The two wing spars were redesigned to withstand a higher safety factor of 10 versus 8.

Apart from the revised structure, the Hornet's wings were a synthesis of aerodynamic knowledge that had been gathered since the Mosquito's design process, being much thinner in cross section, with de Havilland designers adopting a laminar flow profile similar to the P-51 Mustang and Hawker Tempest. The control surfaces consisted of hydraulically operated split flaps extending from the wing root to outboard of the engine nacelles; as in the Mosquito, the rear of the nacelle was part of the flap structure. Outboard, the Alclad-covered ailerons extended close to the clipped wing tips and gave excellent roll control.

The Hornet used "slimline" Rolls-Royce Merlin engines with engine ancillaries repositioned to minimise frontal area and drag. It was unusual for a British design in having propellers that rotated in opposite directions; the two engine crankshafts rotated the same direction, but the Merlin 131 added an idler gear to reverse its propellor's rotation (to clockwise, viewed from the front). This cancelled the torque effect of two propellers turning in the same direction that had affected earlier designs (such as the Mosquito). It also reduced adverse yaw caused by aileron trim corrections and generally provided more stable and predictable behaviour in flight. De Havilland tried props that rotated outward at the tops of their arcs (as in the P-38 Lightning), but this configuration blanketed the fin and reduced rudder effectiveness at low speeds, compromising ground handling; on production Hornets the conventionally rotating Merlin 130 was on the port wing with the Merlin 131 on the starboard.

Because of the revised induction arrangements of the Merlin 130 series, the supercharger and carburettor air intakes could be placed in the leading edges of the wings, outboard of the nacelles. Other versions of the Merlin, which used "updraft" induction arrangements, required that the intakes be placed in a duct below the main engine cowling. The main radiators were also mounted in the inboard leading edges of the wings. Internal fuel, to a maximum capacity of 432 Imp gal (1,964 l) (F 3) was stored in four self-sealing wing tanks which were accessed through detachable panels forming part of the lower wing surfaces.

To assist airflow over the wing, the engine nacelles were mounted low, which meant that the undercarriage legs were reasonably short and the pilot's field of view was improved. The single-legged undercarriage units were simpler and cleaner than those of the Mosquito, using the same de Havilland-developed, rubber-in-compression energy absorption system. The main wheels were also smaller and lighter.

To further aid the pilot's field of view the unpressurised cockpit was mounted well forward in the fuselage and was housed under an aft sliding, perspex blister canopy. The three-panel windscreen was designed so that refraction through the panels meant that there were no obvious blind spots caused by the corner tie-rods; all three panels were bullet-proof laminated glass. An armour-plated bulkhead (hinged near the top to provide access to the back of the instrument panel and the rudder pedals), was part of the nose structure, with the pilot's back and head being protected by another armoured bulkhead built into the cockpit. Below and behind the cockpit floor was a bay housing the built-in armament of four short-barrelled 20 mm (.79 in) Hispano V cannon, with 190 rpg, firing through short blast tubes.

Fuselage construction was identical to the earlier Mosquito; a balsa wood "pith" sandwiched between plywood sheets which were laid in diagonal panels. Formaldehyde cement was the bonding agent. The fuselage halves were built on large concrete or wood patterns, equipment was fitted in each half and they were then joined along the top and bottom centre lines using wooden reinforcing strips. The entire fuselage was then tightly wrapped in fine aviation fabric which was doped in place. The tailfin which had the trademark, gracefully curved de Havilland shape, was an integral part of the rear fuselage. On Late Mk Is and future production aircraft, a fin fillet was added to the base of the unit.

The horizontal tail unit was an all-metal structure, again featuring the distinctive de Havilland shape later repeated on the Chipmunk.