Historical Perspective ‘little henry’ left big legacy Innovative XH-20 was first ramjet-powered helicopter By Henry T. Brownlee Jr. Iafter the diminutive helicopter in a popular children’s book consisted of an open steel frame for the pilot and a two-bladeThe XH-20 design was simple. The concept demonstratortransport, field messenger service and rescue operations.t wasn’t very big, so engineers referred to it as “Little Henry,”of the day. But the XH-20, at 290 pounds (130 kilograms), could lift almost rotary assembly 20 feet (6 meters) in diameter, with ramjets twice its weight and fly up to 50 mph (80 kilometers per hour). mounted on the tips and fed from two fuel tanks beside the pilot. Designed and developed by McDonnell Aircraft Corp., one of McDonnell Aircraft designed the twin “Tom Thumb” 10-pound Boeing’s heritage companies, Little Henry was the world’s first (4.5-kilogram) ramjet engines specifically for the XH-20, and ramjet-powered helicopter. during the rotor testing phase experimented with several ramjet A pioneer in naval jet fighter aircraft, McDonnell Aircraft realized designs to achieve maximum efficiency. the potential of jet propulsion for rotary wing aircraft as early A ramjet is a jet engine without moving parts that develops as 1943 when, under the leadership of Constantine L. “Zakh” thrust by the continuous burning of fuel injected within a stream- Zakhartchenko, the company’s chief engineer for helicopters, it lined tube, which increases the velocity of air rammed in by flight. began examining self-propelled rotor blades for helicopters. When the ramjets on the tips of the XH-20 rotor were ignited, Three years later, in 1946, McDonnell Aircraft submitted an the centrifugal force of the spinning rotor pulled the fuel into the unsolicited proposal to the U.S. Air Force’s Air Materiel Command ramjets through a fuel line that ran through the rotor blade to at Wright Field in Ohio. It subsequently was awarded a contract to the fuel tanks. Because power for the rotor was generated at determine the feasibility of a small, lightweight ramjet rotor helicop- the tips of the rotor, the need for a tail rotor and other heavy ter that could be used for a variety of military missions, including parts—normally required on a helicopter for counter-torque artillery reconnaissance, communications, wire laying, light cargo or torque compensation—was eliminated. 10 BOEING FRONTIERS / OCTOBER 2012
Frontiers October 2012 Issue
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