On 29th August 1947, the American experimental rotorcraft XH-20, powered by a ramjet-motor, performed its maiden free flight.
In early 1946, development of the experimental ramjet-powered rotorcraft was launched by the McDonnell Aircraft Corporation. Initially, the company financed all work on the aircraft, which at the time was designated Model 38. However, in July of the same year, the project attracted the interest of US military authorities
Shortly afterwards, McDonnell was awarded an official contract to develop a lightweight ramjet helicopter. The rotorcraft was built by a team led by Marvin Marks, as part of a cooperation between the company and several research units subordinated to the United States Air Force. Officially designated XH-20 by the military, but commonly known as ´Little Henry´, the aircraft was ready for testing in the spring of 1947.
The XH-20 was powered by ramjet engines located in the tips of its rotor blades. This solution eliminated the need for a tail rotor to compensate for torque, as well as for a transmission system. The rotorcraft was designed as a low-cost research prototype with an open-frame construction.
In May 1947, the XH-20 performed its first tethered flight. At that time, fuel for the ramjet engines was delivered through a flexible hose connected to ground-based tanks.
As part of its further development, the rotorcraft was fitted with self-contained fuel tanks. On 29th August 1947, the XH-20 successfully completed its first free flight, lifting a few metres off the ground.
However, further evaluation of the rotorcraft led to the conclusion that the ramjet engines were too noisy and consumed too much fuel for the project to progress beyond the research stage. Plans to build a two-seat variant of the helicopter, designated XH-29 Big Henry (or Model 79 by the company), were soon abandoned, and the ramjet rotorcraft programme was terminated in 1951.
Two prototypes of the XH-20 experimental rotorcraft were built. One of them is now on display at the National Museum of the United States Air Force, which is located at Wright-Patterson Air Force Base.
Cover photo: XH-20 Little Henry (San Diego Air and Space Museum Archive, 00022952, via Flickr Commons)
