Boeing YB-9 The YB-9 was originally owned, developed and tested by Boeing as the XB-901 (NX10633). The plane was based on the Model 200 commercial transport but was enlarged and adapted to the bomber role. The YB-9 was powered by two Pratt & Whitney R-1860 radial engines which gave it a top speed of 163 mph. Later in its service life, the YB-9 was fitted with the same engines powering the Y1B-9A service test aircraft bringing its top speed to 188 mph; as fast as the U.S. Army pursuit planes of the time. A total of seven aircraft were built: the prototype YB-9, a liquid-cooled engine Y1B-9, and five service test Y1B-9As. The aircraft never entered production mainly because there were even better aircraft being designed which would change the course of U.S. bomber development. Type Number built/ converted Remarks YB-9 1 Boeing XB-901 TECHNICAL NOTES: Armament: Two .30-cal. machine guns and 2,200 lbs. of bombs Engines: Two Pratt & Whitney R-1860 radials of 575 hp each Top speed: 163 mph at sea level Cruising speed: 137 mph Service ceiling: 19,400 ft. Range: Approx. 500 miles with a full normal bomb load Span: 76 ft. 9 in. Length: 51 ft. 6 in. Height: 12 ft. 8 in. Weight: 12,663 lbs. gross Crew: Four Serial numbers: 32-301 (originally Boeing-owned NX10633, XB-901 Model 215) Click here to return to the Bomber Aircraft index.