The XH-51A helicopter was developed as an experimental vehicle designed and built by the LOCKHEED-California Co. under a joint U.S. Army-Navy contract to explore the potential of the rigid rotor system. This 4000-pound XH-51A helicopter had fixed wings and an auxiliary jet engine in addition to rotor blades. This basic helicopter was converted to a compound helicopter configuration by installing a 70-square-foot wing and a J-60 jet engine to supplement rotor lift and thrust respectively.
Engine used in this aircraft was Pratt and Whitney J-80-2P, 2000# thrust.
Close view of main rotor of XH-51A Compound helicopter in photo.
Photo by Gene Munson from Army Aviation Museum at Fort Rucker.
Source: Papers presented at VFS (then AHS) Annual Forums 19, 21 and 24.