Boeing XB-38 Flying Fortress Strategic Heavy Bomber Aircraft Prototype
The Boeing XB-38 was a study involving the classic B-17 Flying Fortress heavy bomber arranged with liquid-cooled inline piston engines - only one example was completed and lost during testing.
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The success and availability of the Boeing B-17 "Flying Fortress" heavy bomber in World War 2 (1939-1945) meant that there were many related projects centered on getting more out of this Boeing product. The XB-38 was a short-lived program by the company to test the feasibility of replacing the original B-17's air-cooled radial piston engines with Allison inline piston types. A B-17 airframe was pulled from the existing stock and modified in this way and the prototype served in several flights before several major issues ended the program in full.
The engine of choice became the Allison V-1710-97 turbosupercharged V12 liquid-cooled inline piston engine of 1,425 horsepower. These were set across four individual nacelles with two engines per wing (as in the original B-17 arrangement). One major, physical difference in the installations was in their streamlined appearance as air-cooling was no longer necessary in the liquid-cooled powerplants. This gave the B-17 a unique look as the three-bladed propellers now sat on large, conical spinners. Beyond this physical change, the bomber retained much of its original form (and function).
In testing, the aircraft was able to make 327 mph and cruise at 226 mph. Range was out to 3,300 miles and service ceiling reached 29,600 feet. The aircraft was made faster than previous iterations of the B-17. However, the trade-off was in a lower service ceiling which was a poor quality for a strategic bomber to have. In comparison, the popular B-17G production model reached a maximum speed of 287 mph and cruised at 182 mph but the service ceiling was substantially higher at 35,600 feet.
Two key issues served to end the XB-38 program: Firstly the V-1710 engine being a standard fit on several other important fighter products of the war including the Lockheed P-38 "Lightning" and the North American "P-51" Mustang (A-models). As such, the availability of these powerplants would be in question should the XB-38 have entered serial production for there was already much demand for the engines elsewhere. Secondly the sole prototype was lost during the ninth flight of its test phase. On June 16th, 1943, one of the engines caught fire resulting in a bailout by the crew and the aircraft crashing. With nothing to show for the efforts, the XB-38 was written off and the project cancelled.