Military Wiki
Keystone B-3A (S/N 30-281), the first B-3A built.
Role Light bomber
Manufacturer Keystone Aircraft
Primary user United States Army Air Corps
Number built 63 B-3A/B-5
Variants Keystone B-4
Keystone B-5
Keystone B-6

The Keystone B-3A was a bomber aircraft developed for the United States Army Air Corps in the late 1920s.

Design and development

It was originally ordered as the LB-10A (a single-tail modification of the Keystone LB-6), but the Army dropped the LB- 'light bomber' designation in 1930.

Although the performance of the B-3A was hardly better than that of the bombers flown at the end of World War I, it had come a long way. In terms of its safety, it was far superior to its oldest predecessors.

Operational history

The B-3A was the last biplane operated by the US Army; it remained in service until 1940. A few years after it was first produced, the introduction of all-metal monoplanes rendered it almost completely obsolete.


The last of the 17 LB-6s ordered (S/N 29-27) was converted with a re-designed single fin and rudder and two 525 hp R-1750E engines. Delivered to Wright Field on 7 July 1929, it was wrecked on 12 November 1929.
This version used Pratt and Whitney R-1690-3 Hornet engines and was slightly smaller, both wingspan and fuselage. a total of 63 were ordered (S/N 30-281/343). It was re-designated as the B-3A before any deliveries were made, and the final 27 were built as B-5A.
36 delivered as B-3A (S/N 30-281/316). The first aircraft was delivered in October 1930.
Ordered as B-3A, re-engined with Wright R-1750-3 Cyclone engines, 27 built (S/N 30-317/343).


 United States

Specifications (B-3A)

General characteristics

  • Crew: 5
  • Length: 48 ft 10 in (14.9 m)
  • Wingspan: 74 ft 8 in (22.8 m)
  • Height: 15 ft 9 in (4.8 m)
  • Wing area: 1,145 ft² (106.4 m²)
  • Empty weight: 7,705 lb (3,495 kg)
  • Loaded weight: 12,952 lb (5,875 kg)
  • Max. takeoff weight: lb (kg)
  • Powerplant: 2 × Pratt & Whitney R-1690-3 radial engines, 525 hp (392 kW) each


  • Maximum speed: 114 mph (98 kn, 183 km/h)
  • Cruise speed: 98 mph (85 kn, 158 km/h)
  • Range: 860 mi (760 nmi, 1,400 km)
  • Service ceiling: 12,700 ft (3,870 m)
  • Rate of climb: 530 ft/min (2.7 m/s)
  • Wing loading: 11.31 lb/ft² (55.42 kg/m²)
  • Power/mass: 0.0811 hp/lb (133 W/kg)


  • Guns: 3 × .30 in (7.62 mm) machine guns
  • Bombs: 2,500 lb (1,100 kg); 4,000 lb (1,800 kg) on short runs

See also


  1. "Fact Sheet - Keystone B-3A." National Museum of the United States Air Force. Retrieved: 18 September 2011.
  • Andrade, John. U.S. Military Aircraft Designations and Serials since 1909. Leicester, UK: Midland Counties Publications, 1979, pp. 43, 135. ISBN 0-904597-22-9.
  • The Illustrated Encyclopedia of Aircraft (Part Work 1982-1985). London: Orbis Publishing, 1985, p. 2255.
  • Maurer, Maurer. Combat Squadrons of the Air Force, World War II. Maxwell AFB, Alabama: Air Force Historical Studies Office, 1982. ISBN 0-89201-097-5.

External links

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