The Lockheed CL-475 is a two-seat, single-engine light helicopter developed by
Lockheed to explore rigid rotor technology. The CL-475 has a three-bladed main rotor and a two-bladed tail rotor. Only one was built.
Design and development
In 1958
Irv Culver presented an idea for how to rigidly attach the rotor blades of a helicopter to the hub, to the Lockheed management. In 1920,
Juan de la Cierva
Juan de la Cierva y Codorníu, 1st Count of la Cierva (; 21 September 1895 in Murcia, Spain – 9 December 1936 in Croydon, United Kingdom) was a Spanish civil engineer, pilot and a self taught aeronautical engineer. His most famous accomplish ...
had tried the same concept, but had trouble controlling the rotor, because of excessive gyroscopic moments. Culver's research led him to believe that there was a way to control the excessive pitch and roll moments by incorporating a feedback system into the rotor. Culver's solution to high control moments was a device known as the "compliance factor". It kept the blades forward less than a degree, which would apply a corrective feathering input to the opposite blade. This essentially was the moment feedback system. Before presenting his ideas, he had built a radio-controlled model that demonstrated the feasibility of the concept. Lockheed gave him use of part of a flight test hangar, a flight test engineer and two mechanics.
[Cefaratt, Gil, "Lockheed: The People Behind the Story", Turner Publishing Company, 2002, .]
The CL-475 is a two-seat helicopter with a fabric-covered steel and aluminum structure. The glazed cockpit provides side-by-side seating for two occupants. The landing gear is designed in a tricycle configuration, with two large wheels mounted alongside the bottom of the fuselage, and a nosewheel mounted underneath the cockpit. The helicopter is powered by a 140 hp (104 kW), four-cylinder, air-cooled
Lycoming O-360-A1A piston engine. Designed to test a rigid-rotor concept, it originally utilized a two-bladed wooden rotor.
After completion at Burbank, the CL-475 was taken to
Rosamond Lake on
Edwards Air Force Base
Edwards Air Force Base (AFB) is a United States Air Force installation in California. Most of the base sits in Kern County, but its eastern end is in San Bernardino County and a southern arm is in Los Angeles County. The hub of the base is E ...
in the
Mojave Desert for testing. It was first flown on 2 November 1959, but the pilot reported severe vibrations. For six months, Lockheed experimented with three and four-bladed wooden rotors, but stability was finally achieved by using metal blades in a three-blade configuration and the addition of a gyroscopic control ring connected directly to the swashplate.
[Francillon 1987] In the mid-1960s, the helicopter was test flown by a number of government and military agencies, and also the military. The stability offered by the rigid rotor control system made the helicopter easy to fly,
and the lessons learned from the CL-475 rigid rotor were later used to develop the
Lockheed XH-51 and
AH-56 Cheyenne.
In 1975, Lockheed donated the CL-475 to the
National Air and Space Museum
The National Air and Space Museum of the Smithsonian Institution, also called the Air and Space Museum, is a museum in Washington, D.C., in the United States.
Established in 1946 as the National Air Museum, it opened its main building on the Nat ...
. The helicopter was loaned to the
United States Army Aviation Museum at Fort Rucker, Alabama,
but is currently in the museum's storage.
[United States Army Aviation Museum. ]
Rotary Wing Collection
''. United States Army Aviation Museum Association. 2 January 2003. Accessed on 13 July 2009
Specifications
See also
References
Notes
Bibliography
*
* Francillon, René J. ''Lockheed Aircraft Since 1913''. Annapolis, Md: Naval Institute Press, 1987.
{{Lockheed Martin aircraft
CL-0475
1950s United States experimental aircraft
1950s United States helicopters
Single-engined piston helicopters
Rigid rotor helicopters
Aircraft first flown in 1959