Swashplate

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A swashplate is a device used in mechanical engineering to translate the motion of a rotating shaft into a linear back and forth motion. Conversely it can translate a reciprocating motion into a rotating one and can be used to replace the crankshaft in engine designs.

The swashplate consists of a disk attached to a shaft. If the disk is aligned squarely on the shaft then rotation of the shaft will turn the disk with it and no swashplate effect will be seen. Even a slight displacement of the disk from the square position, however , will cause the disk edge to appear to describe an oscillating linear path when viewed from a non-rotating point of view away from the shaft. The greater the angle of the plate to the shaft the more exaggerated the apparent linear motion will be. The apparent linear motion can be turned into an actual linear motion by having a follower, stationary with respect to the shaft but which presses against the top or bottom edge of the plate. The device has many similarities to the cam.

The swashplate engine uses a swashplate in place of a crankshaft to translate the motion of a piston into rotary motion. Internal combustion engines and Stirling engines have been built using this mechanism.

The axial piston pump drives a series of pistons aligned coaxially with a shaft through a swashplate to pump a fluid.

The helicopter swashplate is a similar but slightly different device. Here the swashplate is a pair of plates that bear on each other on the main rotor shaft. One rotates with the rotor and one is fixed with respect to the body of the helicopter. Motions in the alignment of the fixed plate are translated into similar motions in the alignment of the rotating plate, allowing continuous adjustment to be made to the rotor blades while they are in motion and allowing the pilot to control the helicopter.