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Keystone LB-6
Role Light biplane bomber
Manufacturer Keystone Aircraft
First flight 1927
Primary user United States Army Air Corps
Number built 18 (LB-6)
18 (LB-7)

The Keystone LB-6 was an 1920s American light bomber built by the Keystone Aircraft company for the United States Army Air Corps. It was called the Panther by the company but adoption of the name was rejected by the U.S. Army.

The LB-6 was the first operational service model of a 13,000 lb (5,897 kg) twin-tail biplane bomber of a series produced by Keystone that included the follow-on LB-7 bomber. A number of variants were built for test and evaluation purposes but never placed into production or service.



The LB-6 was an upgrade of the earlier triple-tailed Keystone LB-5 with revised extended-span wings and powered by two 525 hp (391 kW) Pratt & Whitney R-1690-3 Hornet engines strut-mounted between the wings. Other variants were built with differing engines.

The final two 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.

XLB-12 protoype
XLB-12 port-side view


One LB-5 modified for evaluation.
Production version, 17 built.
LB-6 with 525 hp (391 kW) Pratt & Whitney R-1690 engines, 18 built.
One LB-7 re-engined with 550 hp (410 kW) Pratt & Whitney R-1830 engines for evaluation.
One LB-7 re-engined with 575 hp (429 kW) Wright GR-1750 engines for evaluation.
One LB-6 re-engined with 525 hp (391 kW) R-1690-3 engines.
Production version of the XLB-10, 63 built, all redesignated B-3A prior to delivery. 36 built as B-3A with Pratt & Whitney engines; remaining 27 became B-5 with Wright engines.
One LB-6 re-engined with 525 hp (391 kW) R-1750-3s for evaluation.
LB-11 re-engined with 525 hp (391 kW) GR-1750s for evaluation.
Similar to the LB-7, with 575 hp (429 kW) R-1830-1s for evaluation.
Seven aircraft delivered as the Y1B4-1 (5) and Y1B6-1 (2).
Production version with 575 hp (429 kW) GR-1830 engines, three delivered as the Y1B5-1.


 United States

Specifications (B-4A)

Data from The Illustrated Encyclopedia of Aircraft (Part Work 1982-1985), 1985, Orbis Publishing, Page 2255

General characteristics

  • Crew: Five
  • Length: 48 ft 10 in (14.88 m)
  • Wingspan: 74 ft 8 in (22.76 m)
  • Height: 15 ft 9 in (4.8 m)
  • Wing area: 1,145 ft² (106.37 m²)
  • Empty weight: 7,951 lb (3,607 kg)
  • Gross weight: 13,209 lb (5,992 kg)
  • Powerplant: 2 × Pratt & Whitney R-1860-7 radial engine, 575 hp (429 kW) each


  • Maximum speed: 121 mph (195 km/h)
  • Range: 855 miles (1376 km)
  • Service ceiling: 14,000 ft (4,265 m)


See also

Related development

Related lists


  • John Andrade. U.S.Military Aircraft Designations and Serials since 1909, p.135. Midland Counties Publications, 1979. ISBN 0 904597 22 9.
  • The Illustrated Encyclopedia of Aircraft (Part Work 1982-1985), p.2255. Orbis Publishing, 1985.


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