Modelling of dynamics of the Hiller hub for a small helicopter∗

A relation between aerodynamic forces and the Coriolis forces of small unmanned helicopters differs from that of big helicopters. In this paper, a cross influence between the blade pitch angle and the servo blade flapping angle is studied. A full mechanical equations of a rigid body motion was taken as a basis for a description of the flapping motion process in the blades and servo blades subsystems of the Hiller hub in the main rotor. It was found that the dimensionless variables in the equations can be divided into groups by their decimal orders. The equations were truncated up to the second order of approximation error. It is shown that the torque from the blade pitch angle to the servo blade flapping can not be neglected.