Lockheed XH-51

The Lockheed XH-51, developed by Lockheed Corporation in the early 1950s, was the first American helicopter to employ a tip‑jet rotor system. Designed under the company’s S-51 program, the prototype first flew on 21 March 1952, demonstrating a novel approach to power transmission that eliminated the need for a conventional gearbox and tail rotor. The XH-51’s single‑engine, twin‑blade rotor was driven by compressed air exhausted from small jets at the blade tips, providing smoother torque characteristics and reduced mechanical complexity. Although the tip‑jet concept suffered from high fuel consumption and noise, the aircraft proved the feasibility of alternative propulsion methods and influenced later designs such as the French Sud‑Est S.E.3120 Alouette III and the experimental Piasecki X‑49.

Only two XH-51s were built, serving primarily as testbeds for aerodynamic and structural research at the United States Army Aviation Center. Their data contributed to the development of more conventional turbine‑powered helicopters and informed Lockheed’s subsequent V‑22 Osprey tilt‑rotor program. Today, the XH-51 remains a notable milestone in rotorcraft history, illustrating the innovative spirit of post‑war aviation engineering. Its preservation in several museums continues to inspire new generations of engineers and pilots.

Lockheed Corporation

Classification

Production & History

Design & Classification