The last Keystone LB-7 on the 1929 contract (29-010) was converted with a pair of geared 575 hp Wright R-1750 Cyclone radial engines in place of its original Pratt and Whitney Hornets. The gearing ratio was 1.58:1. Convertion work was done at Wright Field in March 1931, and the aircraft was redesignated XLB-9. The purpose of this engine installation was purely experimental, and only one of these R-1750-powered XLB-9 aircraft was built. When testing was completed in December 1931, the aircraft was converted to an LB-6 and sent to the 40th School Squadron at Kelly Field.
Specification of the Keystone LB-9:
Two 575 hp Wright R-1750 Cyclone air-cooled radial engines. Maximum speed 118 mph at sea level. Weight: 13,100 pounds gross. Wingspan 75 feet, length 43 feet 5 inches, height 18 feet 1 inches, wing area 1148 square feet. Two Lewis machine guns in an open gunner's position in the nose, two Lewis machine guns in an open dorsal gunner's position, one Lewis gun firing downward through an opening in the lower fuselage.