Lockheed CL-475

The CL-475 was a light experimental helicopter designed to test and develop the concept of “rigid rotors” in helicopters.  Conventional helicopters have articulated rotors, with the rotor blades attached to the hub using hinges to accomodate the forces placed on the blades by allowing them independently to flap or twist to some extent.  Rigid rotors are firmly attached to the rotor shaft with the flexibility of the rotor blades designed to handle these loads.  Rigid rotors are simpler, more precisely controlled, and more stable, but prone to vibration and failure if not designed carefully.  The single CL-475 successfully proved this concept although it has not become the dominant mode of helicopter rotor design.

After successful flight testing the CL-475, registered N6940C, was donated to the National Air and Space Museum and in turned loaned to the Army Aviation Museum for display.  Although it was not used by the military, the CL-475′s rigid rotor technology was used by Lockheed in subsequent military projects such as the AH-56.

 

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