Stability Derivatives of Helicopter Rotors

Citation

Dykes, John Christopher (1938) Stability Derivatives of Helicopter Rotors. Master's thesis, California Institute of Technology. doi:10.7907/N0GE-EA65. https://resolver.caltech.edu/CaltechETD:etd-10282005-161504

Abstract

At present there are only three published papers dealing with the stability of helicopters, all based on helicopters with rigid rotors. Since all rotors are, in practice, constructed with the blades free to "flap", these analyses are not sufficiently general.

Below, the blade motion equation has been written in terms of small incremental accelerations and velocities; for which an approximate solution is obtained. This is then used to calculate the actual forces and moments that are produced on the rotor; by taking suitable mean values, it has been found possible to express these forces and moments without reference to the actual position of the blades at that instant, but only as functions of the position of the whole helicopter. The aerodynamic mechanism of the rotor has therefore been expressed in a a series of equations, and the stability of the helicopter now becomes solely a dynamical problem.

It appears that a helicopter is most likely to become unstable when hovering; this analysis is confined to this case.

Calculated values for a helicopter of the same size as the "C.30" autogyro, are given to show the dimensions of the various forces and moments.

Thesis Files