Boeing YB-9
| YB-9 | |
|---|---|
 |
|
| Y1B-9 test flight, 1932. | |
| Role | Bomber aircraft |
| Manufacturer | Boeing |
| Designer | John Sanders |
| First flight | 13 April 1931 |
| Introduction | 5 November 1931 |
| Retired | 1935 |
| Status | No surviving examples |
| Primary user | United States Army Air Corps |
| Produced | 1930-1933 |
| Number built | 7 |
| Developed from | Boeing Monomail |
The Boeing YB-9 was the first all-metal monoplane bomber aircraft designed for the United States Army Air Corps. The YB-9 was an enlarged alteration of Boeing's Model 200 Commercial Transport.
In May 1930, Boeing had flown its Model 200 Monomail single-engined mailplane. The Monomail was of radical design for the time, being a semi-monocoque, stressed skin cantilever monoplane with a retractable undercarriage. Air Corps bomber squadrons of the day were largely equipped with slow wood-and-canvas biplanes such as the Keystone B-6, and Boeing decided to design and build a twin-engined bomber using the same techniques used in the Monomail to re-equip the Air Corps.
Using its own money, Boeing decided to build two prototypes of its new bomber design as a private venture. The two aircraft differed only in the engines used, with the Model 214 to be powered by two liquid-cooled Curtiss V-1570-29 Conqueror engines while the Model 215 had two Pratt & Whitney R-1860 Hornet B radial engines. Both aircraft were low winged cantilever monoplanes with a slim, oval cross-section fuselage accommodating a crew of five. The pilot and co-pilot sat in separate open cockpits, with the co-pilot, who doubled as the bombardier sitting forward of the pilot. Two gunners, each armed with a single machine gun sat in nose and dorsal positions, while a radio operator sat inside the fuselage. Like the Monomail, a retractable tailwheel undercarriage was used.
The first of the two prototypes to fly was the radial powered Model 215 which, carrying civil markings and the aircraft registration X-10633, made its maiden flight on 13 April 1931. It was leased to the Air Corps for testing under the designation XB-901, demonstrating a speed of 163 mph (262 km/h). Testing was successful, and both the XB-901 and the as-yet incomplete Model 214 were purchased as the YB-9 and Y1B-9 respectively on 13 August 1931, with an order for a further five for service testing following shortly.
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