Use of Computer Models In Helicopter Drag Prediction

The paper presents a brief review of the developments in airframe drag predictionn capability in the last decade. In particular, it details the inability of the first generation panel methods to more than adequately calculate the flow about helicopter fuselages and their failure, despite early promise to be able to predict absolute levels of drag. The development of a second generation of panel methods led the way to an improved flow modeling capability and, in particular, to the ability to model the behavior of vis-. cous flow and to predict and track the development of regions of separate flow. The paper shows, however, that even these models fall short in their ability to accurately predict drag. They do, however, provide the jumping off point for the development of a new generation of panel methods which take full account of the unsteady motion of the large-scale separated flow. These methods are discussed and early results on a series of bluff bodies and typical helicopter tail boom cross sections are presented. In most cases the correlation between predicted and measured drag is excellent.