Boeing XB-15 model

Preceding the Model 299/B-17 on the design board but not to the air, Boeing’s Model 294/XB-15 was built in response to the USAAC’s early 1930s Project A requirement for a heavy bomber able to fly 5,000 miles while carrying a one-ton bomb load. This was a very ambitious set of specifications, given that the Air Corps was only then just phasing in its first monoplane bomber, the Martin B-10. Indeed, it was not until the advent of the B-36 that the USAAF could field a bomber capable of such combat radius unrefueled.

First flown in October 1937, the XB-15 had been designed with Allison V-3420 liquid cooled engines, but delays with that powerplant forced the use of R-1830s; as the -1830 was little more than third as powerful as the Allison engine, the XB-15′s designed top speed of 200mph was never to be achieved.

Boeing XB-15 model
Photo: XB-15 in flight with a P-26. Flying June 1941 p.24
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