Keystone LB-6

The Keystone LB-6 was a modified version of the LB-5 twin-engined biplane light bomber, with larger wings, a longer fuselage and new engines. The XLB-6 of 1927 had a wingspan of 74ft 9in, 7ft 9in wider than those of the LB-5, and was powered by 525hp Wright R-1750 radials. These more powerful engines made it 9mph faster than the LB-5, but they also gave it a service ceiling of 14,770ft, a big improvement on the 8,000ft ceiling of the LB-5.

In early 1928 the XLB-6 competed against the Curtiss XB-2 for a production order. The XB-2 had a top speed of 130mph, a service ceiling of 16,140ft and could carry 2,500lb of bombs, and outclassed the XLB-6 in every way, but despite this the Keystone bomber still won the contest. The XB-2 had a wingspan of 90ft, and was felt to be rather too big.

In the end both aircraft would enter production – Keystone received an order for 17 LB-6s, Curtiss an order for 12 B-2s. Even after demonstrating its superior performance in service, the Curtiss still failed to receive any further orders, while the Keystone bomber was ordered as the B-3A, B-4A, B-5A and B-6A.

The Keystone LB-6 was similar to every other Keystone bomber. It was a conventional biplane. Unlike on the LB-5 the engines were carried in pods positioned between the wings, close to the fuselage. It was armed with five machine guns, two in a nose position, two in the rear cockpit and one firing down through a fuselage tunnel. The 17 production LB-6s had a longer fuselage than the XLB-6 (49ft 3in compared to 43ft 6in) and a modified tail structure, although still with two vertical control surfaces. These changes combined to reduce the ceiling but increase the range of the aircraft.

The LB-6 was preceded into service by the LB-7, which had the same physical dimensions as the LB-6 but was powered by two Pratt & Whitney R-1690-3 radial engines. The LB-7s were given late 1928 serials and the first ten serial numbers of 1929, while the LB-6s were given the serial numbers 29-11 to 29-27.





Wright R-1750


525hp each




74ft 6in



43ft 6in

49ft 3in


18ft 1in

18ft 1in

Empty Weight



Gross Weight



Maximum Speed

116mph at sea level


Cruising Speed



Climb rate






Range with full bomb load

440 miles

632 miles


Five 0.30in machine guns

Bomb load


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How to cite this article: Rickard, J (8 October 2008), Keystone LB-6 ,

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