Designated XBLR-1, the Boeing XB-15 started life as a very long-range bomber, having been funded in fiscal year 1935 after winning a design competition before the XB-17 came on the scene. A couple of requirements to meet the 1933 BLR specifications, for which the XB-15 was designed, were a range of 5,000 miles and an ability to drop four 2,000-pound bombs. The resulting Boeing Model 294 was ordered in July 1935.
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The one and only XB-15 left the runway for the first time on October 15, 1937. (The Boeing-funded Model 299 XB-17 Flying Fortress had made its first flight on July 28, 1935, having been designed, rather radically, to meet an August 1934 design competition for an Army Air Corps multiengine bomber.)
From the beginning, the XB-15’s GFE engines did not provide enough power, and the later Douglas XB-19 suffered from the same GFE plague. Incorporating a high aspect ratio and a high-lift wing, the XB-15 demonstrated a 200mph top speed at somewhat less than its 15,900-foot service ceiling. Four Pratt & Whitney R-1830-11 engines drove 3-blade controllable-pitch propellers, but no attempt was made to include turbo-superchargers.
Passages within the wing allowed minor repairs/adjustments to be made while in flight. The fuselage provided complete living and sleeping quarters, and a flight engineer was introduced for the first time in an American airplane. Two, small gasoline-powered engines powered the 110V electrical generators.
The XB-15 broke the official World Altitude Record for lifting weight when it carried a payload of 31,176.6 pounds to an altitude of 8,200 feet. On January 24,1939, a great earthquake devastated Chile. The U.S. responded by dispatching the XB-15 with 3,250 pounds of medical supplies via Panama and Lima, Peru, to Santiago-a 4,933-mile trip that was accomplished in less than 50 hours (29 hours, 53 minute flying time).
