# Keystone B-3

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

## Design and development

The B-3 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 flight safety.

## Operational history

The B-3A was a member of the last family of biplanes 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, in both wingspan and length. 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

    Ordered as LB-10A, 36 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 sq ft (106.4 m$^2$)
* Empty weight: 7,705 lb (3,495 kg)
* Gross weight: 12,952 lb (5,875 kg)
* Powerplant: 2 × Pratt & Whitney R-1690-3 radial engines, 525 hp (392 kW) each
Performance
* Maximum speed: 114 mph (183 km/h, 98 kn)
* Cruise speed: 98 mph (158 km/h, 85 kn)
* Range: 860 mi (1,400 km, 760 nmi)
* Service ceiling: 12,700 ft (3,870 m)
* Rate of climb: 530 ft/min (2.7 m/s)
* Wing loading: 11.31 lb/sq ft (55.42 kg/m$^2$)
* 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