Simplified Helicopter Ground Resonance Stability Boundaries

Abstract

A method is developed or drawing ground resonance stability boundaries in the (?1, ?) plane for arbitrary values of the parameters ??, A1 and Aa. The current values of ?1 and ? are expressed simply and directly in terms of the co‐ordinates (Y, Z) of points lying on a parabola whose equation involves ??, A1 and A3. The position of the intersections of this parabola with a certain unique curve in the (Y, Z) plane determines into which of three classes each stability boundary falls. All stability boundaries split up into two separate branches, and only in one class of boundaries do the branches align themselves in such a way as to permit the possibility of stability for all rotor speeds ?. A method is given showing how ??, A1 and A3 may be determined to achieve this effect.