The Keystone LB-6 and LB-7 were 1920s American light bombers, built by the Keystone Aircraft company for the United States Army Air Corps, called Panther by the company, but adoption of the name was rejected by the U.S. Army.
The LB-6 was in competition with the Curtiss XB-2 for production in early 1928 and although the Curtiss aircraft was clearly the better of the two, the conservative Army Air Corps leadership chose the Wright-powered LB-6 and the Pratt & Whitney-powered LB-7, ordering 35 aircraft.
The LB-6/LB-7 was the first operational service model of a 13,000 lb (5,897 kg) twin-tail biplane bomber of a series produced by Keystone. 35 served operationally between 1929 and 1934. A number of variants were built for test and evaluation purposes but never placed into production or service. The LB-10 variant became the basis for the B-3 to B-6 series of similar bombers that were the last biplane bombers ordered by the Air Corps.
The Keystone XLB-6 prototype was created by refitting the final triple-tailed Keystone LB-5 (serial number 27-344) with an LB-5A tail unit; longer (75 foot) straight-chord, untapered and noticeably swept-back wings; and 525 hp (391 kW) Wright Cyclone R-1750-1 radial engines suspended on struts between the wings rather than mounted on the lower wing. This produced a bomber with twice the rate of climb as the LB-5 and slightly faster cruise speed. Production LB-6s featured a five-foot longer fuselage.
The LB-7 used the same extended-span LB-6 airframe powered by Pratt & Whitney Hornet engines.
The remaining variants were ordered before the 1930 change of designators by the United States Army Air Corps from "LB-" (Light bomber) to "B-", but were delivered after the change. Although delivered as bombers, they saw service as cargo and observation aircraft. The LB-10 variant became the basis of the B-3 through B-6 bombers, all of which used the original LB-6 design, and which served as the primary bombardment force of the Army Air Corps prior to the advent of the monoplane bomber.
According to an article in the Baltimore Sun the XLB-12 Prototype was used on a refueling and bombing trial in April 1929.[1]
Big Bomber to be Refueled during Flight
"The huge twin-motored army bomber (sic) which will take off from Dayton, O., fly to New York City and be refueled while in midair, after which she will drop bomb flares on the city and make a return flight to the Dayton army field. The flight is to be a practicable demonstration by the Army Air Corp of the value of refueling airplanes in the air when engaged in bombing expeditions over a long distance". The aircraft was wrecked in August the same year.[2]
Beginning in March 1931 the surviving bombers in the Continental United States were taken out of front-line service, re-designated the ZLB-6 and ZLB-7, and sent to the 40th School Squadron at Kelly Field, Texas, where all were scrapped or surveyed by April 1935. The Hawaiian LB-6s served until 1934, when they too were surveyed in-situ.
Production version of the XLB-10, 63 built, all redesignated B-3A prior to delivery. 36 built as B-3A with Pratt & Whitney engines; the remaining 27 became B-5s with Wright engines.
LB-11
One LB-6 re-engined with 525 hp (391 kW) R-1750-3s for evaluation.
LB-11A
LB-11 re-engined with 525 hp (391 kW) GR-1750s for evaluation.
(X)LB-12
Similar to the LB-7, with 575 hp (429 kW) R-1860-1 Hornet B engines for evaluation.
LB-13
Proposed version with 525 hp (391 kW) GR-1690 Hornet A engines; seven ordered, but re-engined and re-designated before production. Five delivered as the Y1B-4, two as the Y1B-6.
Proposed version with 575 hp (429 kW) GR-1860 Hornet B engines; three ordered, but re-engined and re-designated before production. Delivered as the Y1B-5.
ZLB-6
1931 designation of two LB-6 and the LB-11 (in 1933) as training aircraft.
ZLB-7
1931 designation of ten LB-7 as training aircraft.
United States
