TABLE OF CONTENTS A variety of three-dimensional theories has been formulated for rotorcraft unsteady airloads both in hover and forward flight. The range of applicability of any one of these theories is generally limited by virtue of the assumptions made in their respective formulations with regard to four basic issues: 1) frequency content, 2) inclusion of compressibility effects, 3) inclusion of the forward-flight condition, and 4) the type of wake geometry. Analyses addressing the hovering condition are typically concerned with the rotor flutter aeroelastic problem and relax the assumption regarding frequency content to the extent that it can be integral or nonintegral with respect to the rotor rotational frequency. Linearity is generally assumed to the extent that the airloads for different frequencies can be superimposed. These theories invariably take the Loewy theory as a starting point.
The emergence of quality analyses that address the inclusion of compressibility effects is relatively recent and is in part a result of the continuing proliferation of computer resources with profoundly increased speed and memory capabilities. With the complementary development of computational-fluid-dynamics (CFD) technology in general, application of CFD to the rotor problem is becoming an increasingly viable approach. CFD has the promise of simultaneously relaxing all of the restrictive assumptions currently being made in rotor unsteady aerodynamic problems, including those dealing with the nonlinearities of transonic and subsonic stalled flow.
On the other hand, analyses addressing the forward-flight condition are concerned principally with the harmonic loads aeroelastic problem. Generally,...
