The nature of limitations imposed on the performance of a helicopter rotor

Abstract

A systematic theoretical approach to the investigation of helicopter rotor performance limitations is outlined. The essence of the method is a digital computer programme devised to solve the equations of motion of a typical articulated blade, part of a rotor system in a state of steady flight. This solution is the starting point from which the detailed rotor performance is calculated, a process which involves, in addition to the main performance programme, an interrelated system, the whole forming a hierarchy. Each member programme is designed for a particular function and the flow of data is routed according to the required form of output. The main programme and the next in order of importance, computing downwash distribution in the rotor disc plane from a knowledge of blade loading and wake geometry, are described in some detail along with their mathematical models. A brief history of development of the method precedes a formal comparison of computed output and experimental data. Some indication is given of refinements introduced during this stage. Detailed discussion is restricted to downwash distribution and its effects, first upon blade bending stresses. An interpretation of the mechanism modifying power requirements follows, and is combined with further description of an attempt to reconcile blade loading and downwash distribution in a consistent blade motion solution. It is shown how, by linking four programmes in a closed loop, rapid progress is made towards convergence.