World War 2 In Review: Boeing XB-38 Flying Fortress

Essentially an Allison-powered B-17E, the XB-38 was a project developed by engineers at Lockheed-Vega. The ninth production B-17E 41-2401 had been delivered to Lockheed-Vega to help in setting up a Flying Fortress production line at their Burbank, California facility. This was the aircraft modified as the prototype for the XB-38 design.

The XB-38 Flying Fortress was a single example conversion of a production B-17E Flying Fortress, testing whether the Allison V-1710 V type engine could be substituted for the standard Wright R-1820 radial engine during early World War II.

Design and Development

The XB-38 was the result of a modification project undertaken by Vega (a subsidiary of Lockheed) on a Boeing B-17 Flying Fortress to fit it with liquid-cooled Allison V-1710-89 V-12 engines. It was to be an improved B-17, and an alternative if the normally fitted air-cooled Wright R-1820 radial engines became scarce. Completing the modifications took less than a year, and the XB-38 made its first flight on May 19, 1943. Only one was built, and it was modified from a regular production aircraft.

The XB-38 delivered a higher top speed, but its ceiling was lower. After a few flights it was grounded due to exhaust gas leaks from the engine manifolds. Once this had been fixed, testing resumed until the ninth flight on June 16, 1943 when the inboard starboard engine caught fire and the crew bailed out. The XB-38 was destroyed and the project was canceled, in part because the V-1710 engines were in high demand for Lockheed P-38 Lightning, Curtiss P-40 Warhawk and North American P-51A Mustang fighters.

Type: Strategic bomber

Manufacturer: Boeing (B-17E aircraft)/Vega (modifications)

Status: Cancelled

Primary user: United States Army Air Forces

Number built: 1

First flight: 19 May 1943

Retired: 16 June 1943

Developed from: Boeing B-17 Flying Fortress

Operators

United States: United States Army Air Forces

Specifications (XB-38)

Crew: 10

Length: 74 ft 0 in (22.56 m)

Wingspan: 103 ft 11 in (31.67 m)

Height: 19 ft 2 in (5.84 m)

Wing area: 1,420 sq ft (131.9 m2)

Empty weight: 34,750 lb (15,762 kg)

Gross weight: 56,000 lb (25,401 kg)

Maximum takeoff weight: 64,000 lb (29,030 kg)

Powerplant: 4 × Allison V-1710-97 turbosupercharged liquid-cooled V12 engines, 1,425 hp (1,063 kW) each

Maximum speed: 327 mph (526 km/h, 284 kn) at 25,000 ft (7,600 m)

Cruise speed: 226 mph (364 km/h, 197 kn)

Range: 3,300 mi (5,310 km, 2,870 nmi)

Service ceiling: 29,600 ft (9,020 m)

Guns: 10× .50 in (12.7 mm) Browning M2 machine guns

Bombs: 6,000 lb (2,700 kg)

Bibliography

Francillon, René J. Lockheed Aircraft since 1913. London: Putnam, 1982.

Hess, William N. and Jim Winchester. ""Boeing B-17 Flying Fortress:Queen of the Skies". Wings Of Fame. Volume 6. London: Aerospace Publishing, 1997. pp. 38–103.

Jones, Lloyd S. U.S. Bombers, B-1 1928 to B-1 1980s. Fallbrook, CA: Aero Publishers, 1962, second edition 1974.

Vega XB-38 41-2401 in flight, circa May–June 1943. Note the remotely-operated ventral turret. (Lockheed Martin)

Boeing-Lockheed Vega XB-38 in flight. (U.S. Air Force photo)

XB-38 variant of B-17 with V1710 engines, built by Boeing/Lockheed Vega.

Four weeks into the testing program while on its ninth flight, the XB-38 developed a fire in the right inboard engine nacelle. Efforts to extinguish the fire were unsuccessful and the aircrew bailed out. The co-pilot was killed when his parachute failed to open.

While the Allison powered Fortress was slightly faster than the Cyclone powered version, it was also heavier and had a projected lower maximum ceiling. In addition, the Allison engine was in demand for several USAAF Pursuit aircraft, including the P-38, P-39, and P-40 among others. With no clear advantage to changing the design, the decision was made to continue Flying Fortress production with Cyclone engines. Here is the XB-38 sharing the apron with a B-17F.