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 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
The Lycoming O-360 is a family of four-cylinder, direct-drive, horizontally opposed, air-cooled, piston aircraft engines. Engines in the O-360 series produce between 145 and 225 horsepower (109 to 168 kW), with the basic O-360 producing ...
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
Rosamond Lake is a natural dry lake bed in the Mojave Desert of Kern- and Los Angeles County, California. The shores of the lake are entirely within the borders of Edwards Air Force Base, approximately from Lancaster. The lake is adjacent ...
on
Edwards Air Force Base in the
Mojave Desert
The Mojave Desert ( ; mov, Hayikwiir Mat'aar; es, Desierto de Mojave) is a desert in the rain shadow of the Sierra Nevada mountains in the Southwestern United States. It is named for the indigenous Mojave people. It is located primarily ...
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
The Lockheed AH-56 Cheyenne was an attack helicopter developed by Lockheed for the United States Army. It rose from the Army's Advanced Aerial Fire Support System (AAFSS) program to field the service's first dedicated attack helicopter. Lock ...
.
In 1975, Lockheed donated the CL-475 to the
National Air and Space Museum. The helicopter was loaned to the
United States Army Aviation Museum
The United States Army Aviation Museum is an aviation museum located on Fort Rucker near Daleville, Alabama. It has the largest collection of helicopters held by a museum in the world.Phillips 1992, p. 37.Purner 2004, p. 204. The museum feature ...
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