LOCKHEED XH-51 RIGID ROTOR EXPERIMENTAL HELICOPTER RAW FOOTAGE (SILENT) GG45561

Creator: Lockheed Aircraft

Description: This silent footage shows the Lockheed XH-51 (Model 186), a single-engine experimental helicopter designed by Lockheed Aircraft, utilizing a rigid rotor and retractable skid landing gear. The XH-51's rigid rotor design and extra rotor allowed it to achieve speeds that were not possible with previous rotor designs. Lockheed began developing its rigid rotor concept with the CL-475 helicopter design in 1959. The choice of a rigid rotor meant that the helicopter was more agile than it would have been with a flapping rotor. The performance of the CL-475 encouraged Lockheed to seek further development. Lockheed submitted the CL-475 to the Army as a candidate to replace the Bell OH-13 Sioux and Hiller OH-23 Raven observation helicopters. Lockheed also tested the commercial market waters without success. However, in February 1962, Lockheed's Model 186, a new design based on the CL-475 rigid rotor, was selected as the winner for a joint Army-Navy program to evaluate the rigid rotor for high-speed flight capability.