Curtiss XP-22

In 1931, the third production P-6 (which had been converted to P-6A standard) was withdrawn from service and returned to Curtiss for extensive modification as the XP-22. Retaining the V-1570-23 engine, the XP-22 was cleaned up aerodynamically and featured cantilever main undercarriage legs and wheel spats, plus a redesigned engine cowling with, initially, an annular radiator. The radiator was subsequently returned to a position beneath the rear of the engine. On 30 June 1931, the XP-22 demonstrated a level speed of 326km/h and on 10 July a USAAC contract was placed for 45 Y1P-22s. These were subsequently redesignated as P-6Cs, but prior to the start of production deliveries the designation was changed once more to P-6E. By this time, the engine of the XP-22, complete with cowling and three-blade propeller, plus the main undercarriage members, had been grafted on to the YP-20, which had thus become the XP-6E, while the XP-22 was returned to P-6A configuration.