Hawker Hornbill

The Hawker Hornbill was the last Hawker military aircraft designed under the direction of George Carter. The design was started in 1925 and the first flight took place in July 1925. The Hornbill did not achieve service in the Royal Air Force due to problems in its power plant and radiator. Only one aircraft was built.

Development and design
In 1924, H.G. Hawker Engineering made a proposal to the British Air Ministry to build a new single-seat fighter powered by the Rolls-Royce Condor engine. As a result, the Air Ministry placed an order for a single prototype, drawing up Specification 7/24 to cover the aircraft. Many of the normal requirements included in fighter specifications were omitted with the hope of resulting in an aircraft with higher performance. The specification required a speed of 208 mph at sea level and a service ceiling of 29000 ft, with an armament of a single machine gun. The new design, named the Hawker Hornbill, was produced under the supervision of Hawker's Chief Designer W. G. Carter, shortly before he resigned and was replaced in his role by Sydney Camm.

The Hornbill was a single-bay biplane of mixed metal and wood construction. The front fuselage structure and engine mount was made of steel tube, and was covered with duralumin cladding, while the fuselage from the cockpit rearwards had a wooden structure with fabric covering. The wings had spruce spars and ribs and were also covered in fabric. The water-cooled Rolls-Royce Condor engine was tightly coweled to minimise drag, and drove a two bladed propeller (initially a fine-pitch Watts). The engine was cooled by a pair of semi-circular radiators beneath the lower wings. The pilot sat in an open cockpit behind the engine and fuel and oil tanks, with a cut-out in the upper wing trailing edge to improve his view. A single Vickers machine gun could be mounted low on the port side of the fuselage.

Testing
The prototype, powered by a 650 hp Condor III engine, made its first flight in the summer of 1925 with F. P. Raynham at the controls, probably early in July that year. The Condor III engine was not compatible with Synchronization gear so the gun was not fitted. Test pilot duties soon passed to George Bulman, who reported that performance was disappointing. As a result, the propeller was replaced by a coarser-pitch metal Fairey-Reed propeller, but this had little effect. Another problem was that the engine suffered from over-cooling, with part of the radiators blanked off as a result.

In February 1926, the Hornbill was returned to Hawker's works at Kingston-on-Thames for modifications to be made. The engine was replaced by a 698 hp Condor IV fitted under a modified, longer, cowling, while the two radiators were replaced by a single semicircular radiator under the fuselage, and the fin and rudder were modified, giving a slightly larger area. The modified prototype returned to flight in May 1926, and was displayed at the RAF Display at Hendon Aerodrome in July that year. The aircraft was then sent to RAF Martlesham Heath for testing and service trials. While the aircraft was much faster than the contemporary Armstrong-Whitworth Siskin at low altitudes, performance dropped off above 15000 ft and the aircraft's ceiling was well below the 29000 ft required by the specification. Handling at high speeds was poor, with the aircraft lacking stability. At 150 mph or above, steep turns could not be made without applying full rudder. Engine overheating occurred during flight tests, which may have been a result of using normal service fuel for extended high power runs. The cockpit was extremely cramped, with it not being possible for the pilot to reach the machine gun's cocking handle or the aircraft's compass or map case, while escape from the cockpit by parachute was considered to be difficult. The type was considered to be unsuitable for use as an interceptor, with Hugh Trenchard, the Chief of the Air Staff claiming that "...for war it would be practically useless".

The Air Ministry transferred the prototype Hornbill to the Royal Aircraft Establishment, where it was used as a testbed, being fitted with leading-edge slats on the upper wing, and undergoing extensive evaluation of its stability at and below the aircraft's stall speed. The aircraft completed its final trials in November 1932, and flew for the last time on 18 May 1933.