Preface

Abstract

Application of smart structures technology to rotorcraft systems Helicopters are susceptible to high vibratory loads, aeromechanical instabilities, excessive noise levels, poor flight stability characteristics, and high dynamic stresses. Compared to fixed-wing aircraft, helicopters suffer from high operating cost, poor ride quality, low fatigue life of structural components, less reliability, inferior handling qualities and a restricted flight envelope. To reduce these problems to an acceptable level, numerous passive and active devices, and many ad hoc design fixes, are resorted to with resultant weight penalties and reduced payloads. The primary source for all these problems is the nonsteady and complex aerodynamic environment in which the rotor must operate and the complex coupled structural and mechanical systems comprised by the rotor, body, transmission system and engine. To counter some of these deficiencies, and also to further expand the flight capabilities of military and civilian helicopters, many new design modifications and devices are being contemplated. These appear to show incremental and modest gains in terms of performance improvement and reduction in operating costs. If the objective is to achieve ` a jet smooth ride' with helicopters at a comparable operating cost, for example, one has to try revolutionary ideas. One innovative idea that may give a substantial jump in performance at a small price is to apply the technology of smart structures to rotorcraft. For such an application, numerous light-weight sensors and actuators are embedded or surface-mounted at different stations on the blades, and optimal distributed forces applied with the help of modern control theory. At this stage, the technology of smart structures is primitive and requires a focused basic research effort that will help clarify the projected gains. This issue will review the state-of-the-art on the application of smart structures technology to the rotor systems. Inderjit Chopra Professor and Director Center for Rotorcraft Education and Research Department of Aerospace Engineering University of Maryland College Park MD 20742 USA