Boeing XB-38 Flying Fortress

The History of the Boeing XB-38 Flying Fortress

The success and availability of the Boeing B-17 Flying Fortress during World War II (1939-1945) meant that there were many related programs focused on getting more out of Boeing products. The XB-38 was the company's short-term program to test the feasibility of replacing the original B-17's air-cooled radial piston engine with an Allison inline-piston type.

A B-17 airframe was taken from existing inventory and modified in this way, and the prototype entered service on several flights before several major problems completely ended the program.

The engine of choice is an Allison V-1710-97 liquid-cooled turbocharged inline V12 producing 1,425 horsepower. These were arranged on four separate nacelles with two engines per wing (as in the original B-17 arrangement). The main physical difference between the turbines is their streamlined appearance, since air cooling is no longer required for liquid-cooled engines.

This gave the B-17 its unique appearance, as the three-bladed propellers were now mounted on large conical spinners. Aside from this physical change, the bomber has retained much of its original form (and function).

In testing, the plane can fly at 327 mph and fly at 226 mph. Range is 3,300 miles and service is capped at 29,600 feet. The plane was built faster than previous iterations of the B-17. The compromise, however, was to lower the service cap, which was poor quality for a strategic bomber.

By comparison, the popular B-17G production model tops out at 287 mph and cruises at 182 mph, but has a significantly higher service ceiling of 35,600 feet.

Two major issues led to the end of the XB-38 program: First, the V-1710 engine was standard equipment on several other war-critical fighters, including the Lockheed P-38 Lightning and North American P-51 Mustang (Type A). Therefore, if the XB-38 goes into mass production, the availability of these engines will be called into question as demand for the engines elsewhere is already high. Second, the only prototype was lost on the ninth flight in its testing phase. On June 16, 1943, one of the engines caught fire, prompting rescue efforts by the crew, and the plane crashed.

Due to no effort, the XB-38 was written off and the project was cancelled.

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