In 1924, Air Ministry Specification 7/24 was issued to Hawker for a 'High-Powered Single-Seater Fighter Landplane'. The resulting aircraft was an advanced experimental design from W.G. Carter which combined the lightest and smallest airframe possible, with the most powerful suitable engine available at the time.
The engine was the 600+ hp Rolls-Royce Condor III V12, a liquid-cooled piston engine which was thought could deliver a top speed of more than 200 mph (320km/h) if mated to an optimised airframe.
Carter’s resulting Hornbill was a single-bay, slightly staggered biplane of equal span and constant chord and of composite wooden and metal construction.
The streamlined front fuselage was fabricated from steel tubing and skinned with duralumin sheet to a point aft of the cockpit. The empennage was constructed from wood with fabric covering with the engine extremely closely cowled and the interplane struts carefully designed for minimum drag.
The prototype (J7782) made its first flight in the hands of test pilot F.P. Raynham at Brooklands on 1st July 1925.
Initially configured with twin underwing radiators, the Hornbill was tested with both wooden and metal propellers and spent the remainder of 1925 being evaluated at the Royal Aircraft Establishment (RAE) Farnborough by Air Staff pilots and at the Aeroplane & Armament Experimental Establishment (A & AEE) at Martlesham Heath.
Reports by Hawker test pilot P.W.S. Bulman and Service test pilots revealed that there were issues of directional stability and control at speeds over 150 mph and with the handling in steep turns. A larger rudder was fitted to address these problems.
The Condor engine was also liable to overcooling and the aircraft’s performance was surprisingly disappointing, so the machine was returned to Brooklands for modification in May 1926.
Accordingly, a more powerful 698 hp Condor IV engine was fitted, the longer crankcase of which necessitated a re-profiled cowling and a single semi-circular radiator was located between the undercarriage struts. Much of this modification work was overseen by designer Sydney Camm.
Subsequent test flights saw the Hornbill reach speeds just short of 200 mph although its climb performance above 16,000ft (4,877m) deteriorated alarmingly.
The Hornbill made its public debut at the 1926 RAF Display at Hendon that July, after which it went back to the A & AEE for performance and wingtip-research trials. As part of these trials, the Hornbill was flown against the RAF’s contemporary frontline fighter, the Armstrong Whitworth Siskin IIIA.
Whilst the Hornbill was found to be considerably faster up to around 20,000ft (6,096m), the Siskin had much better performance at higher altitudes. This largely doomed the aircraft in terms of garnering an RAF order for production.
The Hornbill also suffered from engine overheating and directional stability problems, along with some structural problems with the empennage. The most severe criticism of the Hornbill however, was saved for its extremely cramped cockpit, the result of the blending of the finely contoured engine cowling and the lines of the forward fuselage.
As a result, no orders were forthcoming and the sole Hornbill was used for extensive trials by the manufacturer and by the Royal Aircraft Establishment at Farnborough. These were mainly for research into low-speed flying as the aircraft had demonstrated outstanding qualities at low speeds.
The Hornbill made its last flight in May 1933, having amassed some 1,080 flying hours. As an experimental machine, the aircraft had yielded much invaluable data, but its use as an operational RAF fighter was precluded by its significant shortcomings, both in performance terms and, importantly, its accommodation.
Hawker test pilot P.W.S. Bulman summed up the Hornbill as being 'too clever by half, and the designer almost forgot that the pilot is an important part of the design'.
Variants & Numbers
|Powerplant||1 x 600 hp Rolls-Royce Condor IIIA V12 liquid-cooled piston engine driving Watts two-bladed wooden propeller or Fairey-Reed metal propeller; later 1 x 698 hp Rolls-Royce Condor IV.|
|Maximum weight||With Condor IV: 3,769lb|
|Capacity and Armament||Single pilot; One fixed forward-firing Vickers Mk 2 machine-gun with 1,000 rounds|
|Maximum speed||With Condor IV: 187 mph at sea level|