Rotor Dynamics and Helicopter Stability: Development of a Unified Mathematical Theory of the Steady and Disturbed Motion of a Helicopter with Particular Emphasis on the Dynamical Aspects of the Problem

The aerodynamic force on an element dx1 of the rotor blade produces a moment about any point, and the component of this moment along the flapping hinge determines the flapping motion of the blade. The air force on an element being i4 dX4‘+Jt d/Y4’+k1 dZ,‘, the moment dG’, say, about the hinge F is given by