Induced drag based on leading edge suction for a helicopter in forward flight

Abstract

Estimating induced drag for a helicopter in forward flight is a three-dimensional, unsteady aerodynamic problem complicated by fluid compressibility and wake geometry. Based on an acceleration potential approach, the chordwise velocity and the derivative d$/dt of the velocity potential at the leading edge of a thin rotor blade in subsonic flow were re-examined in this paper to assess unsteady and compressibility effects on the induced drag using a leading-edge suction model. The chordwise velocity was shown to have a singular and a continuous component. The d$/dt was shown to be continuous and hence does not contribute to induced drag. The induced drag calculated from the leading-edge suction model and the more traditional model to be referred to as the induced angle model were compared to quantify the differences in the two approaches. The results show that variations can be significant. While these variations cannot substantiate the validity of either approach, it is clear that the leading edge suction model is simpler to apply with fewer assumptions. b A A d