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Boeing Y1B-9

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Boeing YB-9/Y1B-9
Y1B-9 test flight, 1932.
Type Bomber aircraft
Manufacturer Boeing
Maiden flight 1931-04-29
Retired 1934
Status No surviving examples
Primary user United States Army Air Corps
Produced 1930-1933
Number built 7

The Boeing B-9 was the first all-metal monoplane bomber designed for the United States Army Air Corps. The first service model, dubbed the YB-9, was originally tested and developed by Boeing as XB-901 and first flew on April 29, 1931. The YB-9 was an enlarged alteration of Boeing's Model 200 Commercial Transport. The Pratt & Whitney R-1830-13 radial engines used on the YB-9 gave it a top speed of 163 mph (262 km/h).

The second test model, named the Y1B-9 (Y1B- indicating funding outside normal fiscal year procurement), used liquid-cooled Curtiss V-1570-29 'Conqueror' engines. The increased power from these engines, combined with increased streamlining of the engine nacelles, increased its top speed to 173 mph (278 km/h). With the exception of the B-2 Condor, liquid-cooled engines were never used on production bombers for the United States military. The air-cooled radial engine was simpler and more reliable than the liquid-cooled engine, and less vulnerable to enemy damage.

The Y1B-9A was an improved version of the YB-9, featuring more powerful engines and a redesigned vertical stabiliser. Utilising two Pratt & Whitney R-1860-11 'Hornets', the plane was faster than any contemporary Pursuit aircraft. The Y1B-9 was the first closed-cockpit plane flown by the Army. Its high speeds made open cockpits extremely impractical. Five were ordered by the Army in September 1931.

Specifications (Y1B-9A)

General characteristics

  • Crew: 4
  • Length: 51 ft 6 in (15.7 m)
  • Wingspan: 76 ft 10 in (23.4 m)
  • Height: 12 ft 8 in (3.86 m)
  • Wing area: 954 ft² (88.6 m²)
  • Empty weight: 8,941 lb (4,056 kg)
  • Loaded weight: 13,932 lb (6,320 kg)
  • Max takeoff weight: 14,320 lb (6,500 kg)
  • Powerplant:Pratt & Whitney R-1860-11 "Hornet" radial engine, 600 hp (450 kW) each




  • Alain Pelletier (2002). "End of the Dinosaurs: Boeing's B-9, Breaking the Bomber Mold". Air Enthusiast 101. 
  • Wagner, Ray (1982). American Combat Planes. New York: Doubleday. ISBN 0-930083-17-2. 
  • Jones, Lloyd (1974). U. S. Bombers. Fallbrook: Aero. ISBN 0-8168-9126-5. 
  • Boeing B-9. Encyclopedia of American Aircraft. Retrieved on April 10, 2005.
  • Boeing Y1B-9. USAF Museum. Retrieved on August 1, 2004.

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pt:Boeing Y1B-9