The 17th production Keystone LB-6 on the 1929 contract (29-027) had been completed as the LB-10. The LB-10 differed from the LB-6 in being powered by a pair of experimental 525 hp Wright R-1750-1 Cyclone radial engines, plus it had a single rudder in place of the twin rudders which Keystone had standardized on the LB-5A.
The single-rudder adaptation introduced by the LB-10 had impressed the USAAC, and 63 examples were ordered under the designation LB-10A. Serials were 30-281/343. The LB-10A differed from the LB-10 in being powered by a pair of Pratt & Whitney R-1690-3 radials, as well as in having a slightly smaller wingspan and a slightly shorter fuselage.
However, before the first LB-10A could be delivered, the USAAC had dropped the LB designation and was listing a ll of its bombers under the B series. The LB-10A was redesignated B-3A.
The first B-3A was delivered in October of 1930. The B-3A carried a crew of five--pilot, copilot, bombardier, front and rear gunners. The sixty-three B-3A bombers ended up serving with the 6th Composite Group based in the Canal Zone and the 4th Composite Group based in the Philippines. In addition, the 19th Bomb Group was activated in June 1932 with nine B-3As. The Keystone B-3A of the early 1930s was not very much faster than the biplane bombers that flew during the First World War. It would seem at first sight, then, that the state of the art had not advanced very far in the past fifteen years. However, performance was not the entire story--the Keystone bombers were far more safe and much more reliable than the Handley Page, Gotha, or Friedrichshafen bombers of World War 1. In May of 1932, a group of B-3A biplane bombers flew down the Hudson River to parade above New York City in a display of America's aerial strength. At that time, this parade of lumbering Keystone bombers represented virtually the entire bomber strength of the Army Air Corps.
30-281/343 Keystone B-3A
Specification of the Keystone B-3A:
Two 525 hp Pratt & Whitney R-1690-3 Hornet air-cooled radial engines. Maximum speed 114 mph at sea level, 109.5 mph at 5000 feet. Cruising speed 98 mph. Landing speed 56 mph. Service ceiling 12,700 feet. Initial climb rate 650 feet per minute. An altitude of 5000 feet could be attained in 9.4 minutes. Range was 860 miles. Weight: 7705 pounds empty, 12,952 pounds gross. Wingspan 74 feet 8 inches, length 48 feet 10 inches, height 15 feet 9 inches, wing area 1145 square feet. Armed with three Browning machine guns, one in each of nose, dorsal, and ventral positions. A bomb load of 2500 pounds could be carried.