The Development Of Transonic Airfoils For Helicopters

This paper presents two approaches to the design of helicopter main rotor blade airfoils which attempt to satisfy specific design criteria in the transonic regime. The successful design of such airfoils results in significant performance improvements. Examples of power required savings are discussed. One of the two design approaches is offered by Dr. F. X. Wortmann which is a simplified three-step method to achieving shockless flow for the low-lift, high Mach number and the high-lift, moderate Mach number conditions. The second methods, developed at the Netherlands National Aerospace Laboratory (NLR) aims at the same objectives by use of a transonic hodograph method. Airfoils designed by the two methods are described and their qualities are discussed. Performance of a helicopter using such airfoils is analytically determined and compared with more conventional designs.