The Keystone LB-9 was the designation given to the last LB-7 after it was re-engined with geared Wright Cyclone engines. In theory these were more efficient than the direct drive engines used on the LB-7, but the performance of the LB-9 was very similar to that of the LB-7, and worse than that of the LB-8, also built to test geared engines. The LB-9 had more powerful engines, but geared at a ratio of 1.58:1, while the Pratt & Whitney engines of the LB-8 were geared at 2:1. Neither the LB-8 or LB-9 was ordered into production.
One of the LB-6s may have been used to produce the LB-9, although it is more likely that the last of the LB-7s was actually used. The confusion is caused by the unusual order of the serial numbers of the LB-6 and LB-7. Despite the higher sequence number, the LB-7s were given a mix of late 1928 and the first ten 1929 serial numbers (29-1 to 29-10), while the LB-6s were given the serial numbers 29-11 to 29-27. Given that the only difference between the LB-6 and LB-7 was the engine used, it doesn’t actually make any difference which version supplied the airframe for the LB-9, itself an engine test-bed.
Engine: Two Wright GR-1750B Cyclones radial engines
Span: 75ft 0in
Length: 49ft 3in
Height: 18ft 1in
Gross Weight: 13,100lb
Maximum Speed: 118mph at sea level
Cruising Speed: 95mph
Guns: Five 0.30in calibre machine guns
Bomb load: 2,000lb