How a helicopter works

Helicopter aerodynamics and rotor control phase delay


The concept of helicopter control phase delay is that the maximum aerodynamic force applied to a helicopter rotor blade takes some time before it manifests as a control input. This is referred to as phase delay by some texts, and gyroscopic precession by others. For typical helicopters this delay is about 90 degrees of blade rotation.

This animation shows how the swashplate moves, in response to pilot control inputs, and where the motion has to occur in order to account for phase delay.