The 16th production Keystone LB-6 on the 1929 contract (29-026) was converted to the XLB-11 at Wright Field in March 1930. The XLB-11 differed from the LB-6 in being powered by by a pair of experimental 525 hp Wright R-1750-3 Cyclone radial engines. In April 1930, the XLB-11 became the XLB-11A when it was fitted with geared G1R-1750 Cyclones. The XLB-11/11A was purely experimental, and did not lead to a production order. After completion of testing in May 1932, the aircraft was converted back to an LB-6 before being sent to the 40th School Squadron at Kelly Field to finish its career as a ZLB-6.
Specification of the Keystone LB-11:
Two 525 hp Wright R-1750-3 Cyclone air-cooled radial engines. Maximum speed 115 mph at sea level Weight: 13,000 pounds gross. Wingspan 75 feet, length 49 feet 3 inches, height 15 feet 6 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.