In order to test experimental engine installations, the next-to-last Keystone LB-7 on the 1929 contract (29-009) was fitted in December of 1929 at Wright Field with a pair of geared 550 hp Pratt & Whitney R-1860-3 radial engines in place of the ungeared R-1690 Hornets. The gearing ratio of these engines was 2:1. The re-engined aircraft was redesignated XLB-8. It was common practice during the 1920s and 1930s to assign different designations to versions of the same aircraft which differed from each other only in the type of engine that powered them.
Only one of these R-1860-powered aircraft was built. The plane burned on 3/18/31.
Specification of the Keystone LB-8:
Two 550 hp Pratt & Whitney R-1860-3 alr-cooled radial engines. Maximum speed 112 mph at sea level. Weight: 13,250 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.