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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.
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XLB-6 |
LB-6 |
Engine |
Wright R-1750 |
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Power |
525hp each |
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Crew |
5 |
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Span |
74ft 6in |
75ft |
Length |
43ft 6in |
49ft 3in |
Height |
18ft 1in |
18ft 1in |
Empty Weight |
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Gross Weight |
13,018lb |
13,440lb |
Maximum Speed |
116mph at sea level |
114mph |
Cruising Speed |
93mph |
95mph |
Climb rate |
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Ceiling |
14,770ft |
11,650 |
Range with full bomb load |
440 miles |
632 miles |
Guns |
Five 0.30in machine guns |
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Bomb load |
2,000lb |
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