Modification of a generalized inverse simulation technique for rotorcraft flight

Abstract

Inverse simulation techniques have been employed for several years to analyse the manoeuvrability, operational suitability and conceptual design of helicopters. Much of the published work has used specially constructed (algebraic) models of the aircraft. Recently, integration methods have been used successfully with conventional simulation models, although with some important simplifying assumptions made regarding the dynamics of the main rotor, principally the omission of coupled lead/lag and rotorspeed degrees of freedom. This paper will present the current state-of-theart in helicopter inverse simulation—inserting a complete, validated, rigid-body rotorcraft model inside an integration-based algorithm. It is found that the additional rotor dynamics destabilize the inverse algorithm, resulting in severe oscillations in certain unconstrained states, most notably body pitch and roll angles. Analysis of the dynamics of the inverse system shows that these oscillations are manifest by lack of robustness in the inverse algorithm. Several new modifications to the inverse algorithm are shown to reduce these instabilities considerably.