How does a helicopter control blades that keep rotating?

A helicopter rotor keeps turning while its blades need controlled changes in pitch: the angle at which each blade is set. Controls on the nonrotating airframe cannot simply be attached directly to a spinning blade. A swashplate provides a mechanical connection between those stationary and rotating parts.

The assembly has a nonrotating part linked to the controls and a rotating part linked to the rotor. Bearings allow relative rotation while the two parts move and tilt together. Pitch links connect the rotating part to mechanisms that turn each blade around its spanwise axis. Blade pitch is therefore a different motion from rotation of the entire rotor around its mast.

Raising or lowering the assembly changes the common pitch setting of the blades. This is collective pitch. Tilting it makes a pitch link encounter changing height as it travels around the mast. Each blade’s pitch then varies once per revolution, producing a cyclic component. Both changes can be present together.

An ideal prescribed pattern is θ = C + A cos ψ, where C is collective pitch, A is cyclic amplitude and ψ is angular position around the rotor from a chosen reference. With C = 8° and A = 3°, sampled positions 0°, 90°, 180° and 270° give pitches 11°, 8°, 5° and 8°. Increasing C shifts the whole pattern; increasing A widens its range.

This example describes control transfer and an imposed pitch pattern, not a flight-control recipe. Aerodynamic forces, blade flapping and the phase between pitch input and rotor response determine the actual flight behavior. The location of greatest prescribed pitch alone does not establish the direction a helicopter will tilt.