History
Between 1941 and 1942, the US Army Air Forces sought alternatives to the standard Wright R-1820 Cyclone radial engines used in the B-17, aiming for performance improvements. On March 4, 1942, Vega, a subsidiary of Lockheed, proposed modifying a B-17E (serial number 41-2401) to accommodate four 1,425-horsepower liquid-cooled Allison V-1710-89 V-12 engines. These engines offered 225 more horsepower per unit compared to the Wright R-1820-65 radials used in the B-17E. On July 10, 1942, Vega was awarded a contract to build, test, and deliver one modified B-17E under the designation XB-38.
The modifications to the original B-17E airframe were extensive. The most notable change was the replacement of the four radial engines with inline V-1710-89s, necessitating redesigned engine nacelles and cooling systems. As a result, the XB-38’s engine nacelles and propeller spinners extended noticeably farther forward than those of the standard B-17E. Radiators were installed in the leading edges of the wings between the engines, featuring large rectangular air inlets at the front for cooling. The aircraft’s wings also housed the necessary plumbing for the water-cooling system. Additionally, the standard B-17E’s 11-foot-1-inch diameter propellers were replaced with larger 12-foot-1-inch versions. To maintain power output at high altitudes, Vega engineers integrated General Electric turbo-superchargers. Despite these changes, the XB-38 retained much of the B-17E’s structure, including its defensive armament and bomb load capacity. The Allison V-1710 engines, which had already proven successful in fighters like the P-38 Lightning and P-40 Warhawk, were expected to offer superior high-altitude performance.
Modifications to the XB-38 took less than a year to complete, though some delays occurred due to urgent side tasks. The aircraft made its maiden flight on May 19, 1943, from Lockheed’s Burbank facility in California. During ground testing and its first five flights, the XB-38 showed promise, exhibiting relatively trouble-free operation and a slightly higher top speed than the standard B-17E. However, after its sixth flight, the aircraft was grounded to address serious exhaust manifold leaks. Once repairs were completed, testing resumed until June 16, 1943, when disaster struck.
During its ninth test flight, a high-speed evaluation at 25,000 feet, the XB-38’s No. 3 engine caught fire. The flames spread toward the wing’s fuel tank, and the crew was unable to extinguish the blaze. As the aircraft became uncontrollable, the test pilots were forced to bail out. Tragically, one pilot’s parachute failed to open, resulting in his death, while the other pilot was seriously injured. The aircraft crashed near Tipton, California, and was completely destroyed, bringing an abrupt end to the XB-38 program. The prototype had accumulated only 12 flight hours before its loss.
The cancellation of the XB-38 program was officially announced on August 12, 1943. The aircraft’s performance improvements over the standard B-17 were deemed too marginal to justify further development. Additionally, liquid-cooled engines introduced new maintenance concerns and were more vulnerable to battle damage compared to air-cooled radials. The R-1820 engines used in the B-17 offered greater durability in combat, as radial engines were less susceptible to catastrophic failure from enemy fire. Furthermore, the Allison V-1710 engines were in high demand for fighters such as the P-38 and early P-51 variants, further reducing the feasibility of using them in bombers.
Following the XB-38’s cancellation, Vega shifted its efforts to licensed production of the Boeing B-17F and B-17G models for the remainder of World War II. Production continued until July 28, 1945, when the final B-17 rolled off the assembly line.
