Lycoming XR-7755-3, Radial 36 Engine


Display Status:

This object is on display in the Boeing Aviation Hangar at the Steven F. Udvar-Hazy Center in Chantilly, VA.

Lycoming XR-7755-3, Radial 36 Engine

Collection Item Summary:

The XR-7755-3 is the largest, most powerful reciprocating aircraft engine in the world. During World War II, the U.S. Army Air Forces requested an engine with high takeoff power and low fuel consumption for a yet-to-be designed long-range bomber and transport. Lycoming began designing the engine in early 1944, and it was ready for testing by mid-1946. It featured nine dual-lobe overhead camshafts, which shifted axially for takeoff and cruising efficiency, and a two-speed, geared, dual-rotation propeller drive.

Lycoming built two XR 7755-3 prototypes. The company and the Army successfully tested them, but neither engine ever flew in an airframe. The proven reliability of the new gas turbine engines introduced after World War II made the XR 7755-3 obsolete before it could be fully developed. This artifact is the sole survivor.

Collection Item Long Description:

Data Source

National Air and Space Museum


Do not reproduce without permission from the Smithsonian Institution, National Air and Space Museum

Credit Line

Transferred from the U.S. Air Force Museum.


Diameter 154.9 cm (61 in.), Length 308.2 cm (121.35 in.)

Country of Origin

United States of America



Physical Description

  • Type: Reciprocating, Radial, 36 cylinders, nine 4-cylinder rows, liquid cooled
  • Power rating: 3,729 kW (5,000 hp) at 2,600 rpm
  • Displacement: 127 L (7,755 cu in)
  • Bore and Stroke: 162 mm (6.375 in.) x 171 mm (6.750 in.)
  • Weight: 2,783 kg (6,130 lb)


PROPULSION-Reciprocating & Rotary

Inventory Number