07/31/2009. The OY-51 was designed to an USAAC specification for a two-saet army co-operation and artillery observation aircraft with STOL capabilities, alike the Fieseler Fi-156 Storch. Ryan started development in 1938 and to achieve the STOL goals the aircraft was fitted full-span slots to the leading edge of the wings and Fowler flaps of very wide chord to the trailing edge.

Three aircraft were ordered by the USAAC from Ryan at San Diego, California, in 1939, s/n 40-703, 40-704, and 40-705. Powered by a 440 hp Pratt & Whitney R-985-21 Wasp Junior they were flown in 1940. Test results confirmed the calculated performance, however, the USAAC contract for series production went to the competing Stinson O-49. In October 1941 the three YO-51s were relegated to ground instructional airframes.

Span: 50 ft 0 in (15.24 m)
Length: 34 ft 6 in (10.49 m)
Max T/O weight: 4,206 lb (1,908 kg)
Max speed: 130 mph (209 kmh)
Cruise speed: 107 mph (172 kmh)