Lockheed XH-51

The Lockheed XH-51 (CL-595, Model 186) was a three-bladed, single-engine experimental helicopter designed by Lockheed-California, a division of Lockheed Aircraft, utilizing a rigid rotor and retractable skid landing gear . The XH-51 was selected as the test vehicle for a joint research program conducted by the United States Army and United States Navy to explore rigid rotor technology.