Supermarine Type 224
Supermarine's single-prototype fighter to Air Ministry Specification F.7/30, designed by R. J. Mitchell and first flown in February 1934. The evaporative cooling of its Rolls-Royce Goshawk engine proved troublesome and its speed and climb fell well short of prediction, so the Air Ministry rejected it and the production order that followed went to the Gloster Gladiator. Mitchell set the design aside and started again; the lessons he drew from the Type 224 fed the complete redesign that became the Spitfire. The prototype ended its career as a target in 1937.
Why It Mattered
The Type 224 was Supermarine's answer to Air Ministry Specification F.7/30, the 1931 requirement for a modern fighter to succeed the Gloster Gauntlet. R. J. Mitchell came to the design fresh from Supermarine's Schneider Trophy racing successes, confident that his high-speed experience would produce a fast fighter. The aeroplane flew in February 1934, but its speed and climb fell far below prediction, and the Air Ministry rejected it. Its importance lies in what Mitchell took from the failure: he set the design aside and produced a complete redesign, with straight wings and a thinner section. In January 1935 the Air Ministry wrote Specification F.37/34 around that new design, the line that led on to the Spitfire.
Design Notes
Mitchell chose an inverted gull wing, a shape adopted to shorten the fixed undercarriage legs and so reduce drag. The undercarriage was fixed and enclosed in large fairings, and the wing was built around a single main spar. That spar's leading edge served as the condensers of the engine cooling system, forming a stiff 'D-box' structure. The engine was a 600-horsepower Rolls-Royce Goshawk II, evaporatively cooled: its water was allowed to boil off as steam, then condensed and recirculated. The system's collector tanks sat in the undercarriage fairings, where the near-boiling water could flash back to steam at a slight change of pressure and stall the pumps. Armament was four 0.303 in Vickers machine guns, and Mitchell chose a thick wing section, in contrast to the thin sections of his racing seaplanes.
Operational History
The Type 224, serial K2890, was one of three prototypes the Air Ministry officially selected under F.7/30, the others coming from Blackburn and Westland. It first flew on 19 February 1934, piloted by Joseph 'Mutt' Summers. Testing showed a wide gap between prediction and result: a maximum speed of 228 mph and a climb to 15,000 feet in nine and a half minutes, against 245 mph and six and a half minutes predicted. The wing also brought lateral-stability problems, addressed with further wind-tunnel testing and an enlarged fin. Mitchell discussed improvements — a new wing, tailplane and engine arrangement promising 265 mph — but the Air Ministry judged that a new aircraft, not a modified 224, was needed. In January 1935 further construction was cancelled; only the one prototype was built, and the type never entered service. The production order arising from F.7/30 went instead to Gloster, whose private-venture SS.37 was ordered in mid-1935 as the Gladiator.
Afterlife
The prototype was transferred to the Aeroplane and Armament Experimental Establishment at RAF Martlesham Heath on 25 May 1937. It ended its career that summer, used for target practice at Orford Ness in Suffolk, and was destroyed. Supermarine had asked the Air Ministry to reserve the name Spitfire for the Type 224, but its use for the 224 was later dropped and the name passed to the new design. That design, the Spitfire prototype K5054, first flew from Eastleigh on 5 March 1936, two years after the 224.