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)