The Hawker Harrier was one of a number of aircraft designed to replace the Hawker Horsley bomber, but after an expansion of the specification to include a role as a torpedo bomber it proved to be badly underpowered and never entered production. The Horsley had been designed in response to Air Ministry specification 26/23, but didn't make its maiden flight until March 1925. By this time the Air Ministry had decided that the bomb load called for in the earlier specification was too low, and during 1925 issued a new bomber specification, 23/25. Eventually the Horsley turned out to be robust enough to carry the higher bomb load called for in this new specification (the second prototype was built with 23/25 in mind) - it could carry a single 1,500lb bomb, while the Harrier as originally designed could only carry 1,000lb of bombs - but this was not clear when work on the Harrier began.
Four aircraft were produced in response to 23/25 - the Hawker Harrier, Gloster Goring, Westland Witch and Handley Page Hare. It had been issued alongside a second specification, for a coastal defence torpedo bomber capable of carrying a 2,800lb torpedo, specification 24/25. This produced the Blackburn Beagle and Vickers Vildebeest. When these designs was compared by the Air Ministry it became clear than any aircraft produced to satisfy 24/25 would also satisfy 23/25, and so the two contests were merged. Comparative tests were to begin in January 1929.
The Harrier was designed from the start to use an all-metal framework. The wing spars used Hawker's new dumb-bell spars which had two rolled hexagonal steel booms joined by a steel web (patented jointly by Fred Sigrist and Sydney Camm's deputy Roy Chaplin). This system produced strong but light spars. The main framework was built using tubular steel. The aircraft was a single-bay biplane, with a larger upper wing. Both wings were slightly swept back and had a slight dihedral. The aircraft could carry two 500lb bombs under the fuselage or four 250lb bombs under the wings.
In November 1927 the Harrier was sent to Martlesham Heath for evaluation. It just about met the 23/25 specification, but the A&AEE pointed out that it carried a lower bomb load than the final version of the Horsley, and warned Hawkers that it was unlikely that the Air Ministry would continue with specification 23/25. The aircraft was returned to Hawkers, where it was modified to take part in the new combined competition. This involved re-stressing the fuselage so it could carry a 2,800lb torpedo. Although the engine power was also increased the new aircraft was badly underpowered. When it returned to Martlesham Heath in January 1929 it was discovered that it couldn't take off when carrying the torpedo, the gunner and a full fuel load. Trials had to be carried out without the gunner and with a half fuel load, and even then the pilot sometimes needed to use emergency power at take-off. Unsurprisingly the Harrier didn't make it through to the next round of the contest, which would be between re-engined versions of the Vildebeest, Beagle and Hare.
The Harrier was briefly considered as a possible parachute test aircraft, before being assigned to the Bristol Engine Company at Filton, where it was used as an engine test bed. It was used to test the Bristol Orion radial engine and the 870hp Bristol Hydra 'double octagon' 16-cylinder twin-row radial engine, an experimental engine built at the same time as their more successful 'sleeve valve' engines which saw a great deal of service during the Second World War.
Engine: Bristol Jupiter VIII geared radial engine
Wing span: 46ft 3in
Length: 29ft 7in
Height: 13ft 4in
Empty Weight: 3,278lb
Loaded (bombs): 5,656lb
Loaded (torpedo): 7,179lb
Max Speed (bombs): 135.5mph at 5,000ft
Max Speed (torpedo): 127mph at 5,000ft
Climb (bombs): 18 min 30 sec to 10,000ft
Climb (torpedo): 29 min 15 sec to 10,000ft
Service Ceiling (bombs): 13,800ft
Service Ceiling (torpedo): 10,500ft
Armament: One fixed forward firing Vickers gun and one flexibly mounted Lewis gun on Scarff ring
Bomb-load: Four 250lb or eight 112lb bombs or one Admiralty Type VIII 2,844lb torpedo
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