The Keystone LB-7 was the highest numbered entry in the US Army Air Corps Light Bomber series to enter production, although the 18 aircraft ordered were actually built before the similar LB-6.
The prototype XLB-6 of 1927 had been given longer wings than the standard LB-5. Both the production LB-6 and the LB-7 retained the new wings, and were given a longer fuselage and redesigned twin-rudder tail unit. The first of the eighteen aircraft ordered was used as the XLB-7 for prototype testing, before joining the rest of the production aircraft as a standard LB-7.
The only difference between the LB-6 and the LB-7 was the engines. The LB-6 used Wright R-1750 engines, while the LB-7 used Pratt & Whitney R-1690-3 Hornet Bs.
According to the performance figures given by the National Museum of the USAF the LB-6 and LB-7 had exactly the same performance figures. This should not really surprise, as the two aircraft were of identical design, and were both powered by 525hp radial engines.
The LB-7 was used as the basis for a number of experiments with new engines. One became the single LB-8 when it was given geared Pratt & Whitney R-1860-3 radials. Another became the single LB-9 after receiving geared Wright Cyclone engines, and a third became the XLB-12 and was used to test the Pratt & Whitney R-1690-3 engine.
The LB-7 was the last entry in the Light Bomber series to enter production. An order was placed for 63 LB-10s, but these were all produced as either the B-3 Panther or B-5 Panther.
On 5 August 1929 nine LB-7s, each with 11-12 hours of gasoline onboard, left Langley Field heading for Rockwell Field California, to take part in the national air races. In 1928 the outward journey had taken six days, but in 1929 the LB-7s reached Rockwell in 40 hours, arriving on the evening of 6 August. Three off them then immediately carried out a practise mission of Point Loma. One was used in the 1930 exercises as a transport aircraft, and despite claims that all LB aircraft were give B designations in 1930, four LB-7s, with their original designation, were used in the 1931 Air Corps exercises.
Engine: Pratt & Whitney R-1690-3 radials
Power: 525hp each
Span: 75ft 0in
Length: 49ft 3in
Height: 18ft 1in
Gross Weight: 13,070lb
Maximum Speed: 114mph at sea level
Cruising Speed: 95mph
Range: 632 miles with full bomb load
Guns: Five 0.30in machine guns
Bomb load: 2,000lb