Swashplates

A swashplate is a mechanical assembly that translates rotational motion into linear motion or, in aircraft and hydraulic machines, translates control inputs into variable pitch or displacement. The term is most widely associated with rotorcraft and with axial piston hydraulic machines.

In helicopter flight control, the swashplate sits between the rotor mast and the rotor blades. It consists of two bearing assemblies: a stationary part attached to the airframe and a rotating part that turns with the rotor. The pilot’s cyclic and collective inputs tilt and/or lift the swashplate, and a set of pushrods or control links transmit the resulting motion to the blade pitch horns. There are two common configurations: rotating swashplates, which rotate with the rotor, and fixed (non-rotating) swashplates, which remain stationary relative to the airframe while still transmitting cyclic changes to blade pitch. The design allows a single mechanism to impart precise cyclic changes (tilting to control directional attitude) and collective changes (uniform pitch change across all blades) to the rotor system.

In hydraulic machinery, the swashplate (also called a tilt-plate) is used in axial piston pumps and motors. An inclined swashplate converts the rotary motion of a drive shaft into the axial reciprocating motion of pistons. The tilt angle controls displacement and output flow, enabling variable displacement when the angle is adjustable. Fixed-angle swashplates provide constant displacement. These devices may be actuated hydraulically, mechanically, or electrically.

Swashplates are valued for compactness and high stiffness, enabling smooth, controllable changes in pitch or displacement across a range of speeds and loads.