| YB-9 | |
|---|---|
 | |
| General information | |
| Type | Bomber aircraft |
| Manufacturer | Boeing |
| Status | No surviving examples |
| Primary user | United States Army Air Corps |
| Number built | 7 |
| History | |
| Manufactured | 1930–1933 |
| Introduction date | 5 November 1931 |
| First flight | 13 April 1931 |
| Retired | 1935 |
TheBoeing YB-9 was the first all-metalmonoplanebomber aircraft designed for theUnited States Army Air Corps. The YB-9 was a much enlarged twin-engine development of Boeing's single-engineModel 200 Monomail commercial transport. Only small numbers were built as prototypes, but these entered service starting in September 1932 and were used until early 1935. No serial production was started.
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In May 1930,Boeing had flown itsModel 200 Monomail single-enginedmailplane. The Monomail was of radical design for the time, being a semi-monocoque,stressed skincantilevermonoplane with a retractable undercarriage. Air Corps bomber squadrons of the day were largely equipped with slow strut-bracedbiplanes built from steel-tube frames covered in doped fabric, such as theKeystone 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.[1][2]
Boeing built two prototypes of a new bomber as a private venture, which differed in the engines used, with the Model 214 powered by two liquid-cooledCurtiss V-1570-29 Conqueror engines while the Model 215 had twoPratt & Whitney R-1860 Hornet Bradial engines.[3] 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 thebombardier 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 retractabletailwheel undercarriage was used.[4][5]
The first of the two prototypes to fly was the radial powered Model 215 which, carrying civil markings and theaircraft registrationX-10633, made its first flight on 13 April 1931.[6][7] It was leased to the Air Corps for testing under the designationXB-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.[2][8]
TheY1B-9 (Y1 indicating funding outside normal fiscal year procurement), powered by two liquid-cooledCurtiss V-1570-29 'Conqueror' engines, first flew on 5 November 1931. The increased power from these engines, combined with improved streamlining of the enginenacelles, increased its top speed to 173 mph (278 km/h). The YB-9, meanwhile, had been re-engined with more powerful Hornet Bs, demonstrating slightly better performance than the Y1B-9, which was therefore also re-engined with Hornet Bs.[2][8]
The fiveY1B-9A service test aircraft (Boeing Model 246) had thePratt & Whitney R-1860-11 Hornet B engines which powered the re-engined YB-9 and Y1B-9 and a redesignedvertical stabilizer modeled on the247D transport. While enclosed canopies were considered and designed, the B-9 was never fitted with them.[8] Although it equaled the speed of existing Americanfighter aircraft,[9] no further aircraft were built, as theGlenn L. Martin Company had flown a prototype of a more advanced bomber, the XB-907, which was ordered into production as theMartin B-10.[6]
The first of the five Y1B-9As entered service with the20th and49th Bombardment Squadrons,2nd Bomb Group on 14 September 1932, with all examples built being in service by the end of March 1933. The new bomber proved impossible to intercept during air exercises in May 1932, strengthening calls for improved air defense warning systems. Two B-9s were destroyed during crashes in 1933, one of the accidents being fatal, while the remaining aircraft were gradually phased out over the next two years, with the last being withdrawn on 26 April 1935.[10]
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Data fromUnited States Military Aircraft since 1909[11]
General characteristics
Performance
Armament
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