TABLE OF CONTENTS A singular characteristic of rotorcraft operation is the wide cyclic variations in airfoil section angles of attack along the span of the rotor blade, especially as the vehicle operates at increasingly higher advance ratios. The requirement to maintain roll trim at the high advance ratios creates the situation wherein the blades operate with relatively high dynamic pressures and correspondingly low angles of attack on the advancing side of the disk ( ? ? ?/2) and low dynamic pressures and correspondingly high angles of attack on the retreating side of the disk ( ? ? 3 ?/2). Two speed-limiting phenomena occur as a result of this disparity in aerodynamic operation: 1) the increasingly higher airspeeds on the advancing side create transonic-flow conditions with attendant critical Mach-number drag rises; and 2) the increasingly higher angles of attack on the retreating side create airfoil-stall conditions. Furthermore, each of these conditions is highly dynamic in nature.
The inclusion of the effects of these two phenomena in practical aeroelastic analysis of rotor blades has continued to be a particularly demanding challenge. One reason for the intensity of this challenge is the lack of a well-developed technology base within the fixed-wing field that could be tapped, as has been the case with other aeroelastic problems. Typically, the fixed-wing vehicle does not routinely operate in dynamic conditions of transonic flow and/or stall. The effects of accelerating Mach numbers on transonic flow appear to...
