As a result the Air Ministry Specification 12/26 for a new light bomber required an improvement upon the performance of the Fox.
Hawker's submission for this requirement, which eventually became known as the Hart, was evolved in conjunction with Rolls-Royce, and when submitted in late 1926 proved sufficiently attractive for construction of a prototype to be authorised. Sidney Camm's design utilised what became known in later years as 'Hawker's patent metal construction system', a lightweight and robust structure with fabric covering. From Rolls-Royce came a new engine - known then as the F.XI, a development of the Falcon engine, which had weight-saving six-cylinder monoblocs instead of individual cylinders.
The airframe design was that of an uncluttered single-bay biplane, streamlined fuselage, a conventional Hawker tail unit, and fixed landing gear with tailskid. The biplane wings were of unequal span, the lower wing of constant chord and with a straight leading edge. The upper wing was slightly swept back and incorporated the ailerons and Handley Page leading-edge slots.
The prototype (J9052) was flown for the first time in late June 1928 by Flt Lt Bulman and was subsequently flown in competitive evaluation against the Avro Antelope and Fairey Fox II. With superior performance of the Hart confirmed, 15 pre-production aircraft were ordered initially for development and familiarisation, and the first 12 of these entered service with the RAF's No 33 (Bomber) Squadron in late 1929 or January 1930 and one was sent for trials in India.
In RAF service the Hart was to have a number of variants. These included the 1932 Hart Trainer (483 built, not including conversions of other models); Hart C communications aircraft; and tropicalised versions known as the Hart India and Hart Special. A version was built for the Royal Navy, serving both with wheeled and float landing gear, and this was designated Hawker Osprey. In addition Harts were built for overseas customers which included Estonia, Sweden (also licence-built 42 Pegasus-engined Harts) and Yugoslavia, while ex-RAF aircraft eventually went to South Africa, Egypt and Southern Rhodesia.
Hawker Hart I of the RAF
Harts remained in service with the RAF on the North-West Frontier in India until displaced by Bristol Blenheims in 1939. Some Royal Navy Ospreys were used for target towing and training until 1940, but so far as is known the last in operational service was a Hart used by the South African Air Force well into World War II. Most extensively built between-wars British military aircraft, a total of 952 had been constructed when production ended in 1937, with Armstrong Whitworth, Gloster and Vickers acting as sub-contractors.
Hawker records also refer to a civil-registered Hart, first flown on 15 September 1932 and known as the Hart II. This was powered in succession by a Kestrel IIS, Kestrel VI and Kestrel XVI, with the latter having an all-up weight of 2,109kg. It was used for demonstrations at air displays and for taking air-to-air photographs of Hawker aircraft, accumulating 627 flying hours in these roles from August 1933.
Powered by a single 525 hp Rolls-Royce Kestrel IB, the Hart had a maximum speed of 172 mph (276 km/h) at 10,000 ft (3,050 m).
The Hart was eventually displaced by a developed version known as the Hind.
Engine: 1 x Rolls-Royce Kestrel XDR, 380kW / 525 hp
Max take-off weight: 2066 kg / 4555 lb
Empty weight: 1148 kg / 2531 lb
Wing loading: 13.12 lb/sq.ft / 64.0 kg/sq.m
Wingspan: 11.35 m / 37 ft 3 in
Length: 8.94 m / 29 ft 4 in
Height: 3.17 m / 10 ft 5 in
Wing area: 32.33 sq.m / 348.00 sq ft
Max. speed: 160 kts / 296 km/h / 184 mph
Service Ceiling: 6510 m / 21350 ft
Range: 408 nm / 756 km / 470 miles
Armament: 2 x 7.7mm / .303 in machine-guns, 230kg of bombs