Keystone B 3

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.

Variants

LB-10

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 Wright R-1750E engines. Delivered to Wright Field on 7 July 1929, it was wrecked on 12 November 1929.

LB-10A

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). All were re-designated as the B-3A before any deliveries were made, with the final 27 built as B-5A with Wright engines.

B-3A

36 ordered as LB-10A and delivered as B-3A (S/N 30-281/316). The first aircraft was delivered in October 1930.

B-5A

Ordered as B-3A, re-engined with Wright R-1750-3 Cyclone engines, 27 built (S/N 30-317/343).

Operators

 United States

United States Army Air Corps

2d Bombardment Group, Langley Field, Virginia

20th Bomb Squadron - operated B-3A and B-5A 1931-1932

49th Bomb Squadron - operated B-3A and B-5A 1931-1932

96th Bomb Squadron - operated B-3A and B-5A 1931-1932

4th Composite Group, Nichols Field, Luzon, Philippines

28th Bomb Squadron - operated B-3A 1932-1937

2nd Observation Squadron- operated B-3A 1938-1940

5th Composite Group, Luke Field, Territory of Hawaii

23d Bomb Squadron - operated B-5A 1932-1937

72d Bomb Squadron - operated B-5A 1932-1936

6th Composite Group, France Field, Panama Canal Zone

25th Bomb Squadron - operated B-3A 1932-1936

7th Bombardment Group, March Field, California

9th Bomb Squadron - operated B-3A 1931-1934

11th Bomb Squadron - operated B-3A 1931-1934

31st Bomb Squadron - operated B-3A 1931-1934

19th Bombardment Group, Rockwell Field, California

30th Bomb Squadron - operated B-3A 1932-1936

32d Bomb Squadron - operated B-3A 1932-1935

Air Corps Advanced Flying School , Kelly Field, Texas

42d Bomb Squadron - operated B-3A and B-5A 1935-1936

 Philippines

Philippine Army Air Corps

10th Bombardment Squadron

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

Performance

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)

Armament

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