Boeing XB-15 / XC-105
US Army men like Colonels Hugh Knerr and C.W. Howard were working steadily in the 1930s to ensure, to the best of their capabilities, that a strategic bomber would be available. This thinking had led to the introduction into service of such bombers as the Boeing B-9, and the Martin B-10 and B-12. While it was appreciated that these did not represent the ideal, they prepared the way for the procurement of a true strategic bomber.
In 1933 came the US Army's requirement for a design study of such an aircraft, then identified as the XBLR-1 (Experimental Bomber Long Range): a range of 8046km was included in the specification to provide long-range strategic capability. Both Boeing and Martin produced design studies, but it was Boeing which received the US Army's contract for construction and development of its Boeing Model 294, under the designation XB-15. When this large monoplane flew for the first time, on 15 October 1937, it was then the largest aircraft to be built in the USA.
It introduced features including internal passages within the wing to permit minor engine repairs or adjustments in flight, two auxiliary power units within the fuselage to provide a 110-volt DC electrical system, sleeping bunks to allow for 'two-watch' operation, and the introduction of a flight engineer into the crew to reduce the pilot's workload. Intended to be powered by engines of around 1491kW, the actual powerplant was four 746kW Pratt & Whitney Twin Wasp Senior radial engines, which meant that performance was far below that estimated. Purely an experimental aircraft, it was, however, provided with cargo doors and flown as a cargo transport during World War II under the designation XC-105.
Engines: 4 x Pratt & Whitney R-1830-11 Twin Wasp Senior, 746kW
Take-off weight: 41731 kg / 92002 lb
Empty weight: 17105 kg / 37710 lb
Wingspan: 45.42 m / 149 ft 0 in
Length: 26.7 m / 87 ft 7 in
Height: 5.51 m / 18 ft 1 in
Wing area: 258.26 sq.m / 2779.88 sq ft
Max. speed: 314 km/h / 195 mph
Ceiling: 5760 m / 18900 ft
Range: 8256 km / 5130 miles