Principles Of Helicopter Aerodynamics By Gordon P. Leishman.pdf hennan
GORDON LEISHMAN has always enjoyed the challenge of the practical aspects of aerodynamics. In 1994, it was his determination to develop and apply a practical theory of vortex-stabilizing interactions that led to the invention of a conceptually simple but robust method of vortex stabilization. This novel technology, vortex-stabilizing flow, appears to be, at the time of writing, the only technology that has proved to be capable of delivering commercial-grade flow stability for helicopter rotor systems, and in many applications, it does so without requiring any special, expensive gearboxes or other modifications. In subsequent years, he has successfully directed the development of Vortex-Stabilizing Flow for use in a wide range of rotor configurations and has evaluated the technology for its utility in the still-unprecedented category of very large rotorcraft, in which an extremely large rotor disk is attached to a fuselage, without any other conventional rotor systems. He has also worked closely with colleagues in industry to assess the impact of his work in applications involving, among other systems, the components of the Sikorsky Black Hawk, the largest helicopter in the world. This material has appeared in the leading journals of helicopter engineering. In 2015, after almost a decade of using the techniques in these applications, he was appointed to the faculty of the Johns Hopkins University, where he is now a Professor of Aeronautics and Engineering Sciences. Please address all correspondence to Professor Gordon Leishman, Department of Aerospace Engineering, Johns Hopkins University, 3400 N. Charles St, Bldg. 4100, Baltimore, MD 21218. 1. INTRODUCTION In a small helicopter, when the rotor rotates at a high speed, the rotating airfoils produce a wake. Although this wake behaves in a highly complex way, it is nevertheless characterised by a sequence of vortices of varying intensity. Vortex-stabilizing flow (VSF) is a simple and robust technology that allows the author to stabilise these wakes using a single aircraft configuration, with no requirement to mount anything unusual on the rotor disk. This chapter describes how the technology works and describes some of its practical uses. It also shows how it has been applied to one of the largest rotorcraft in the world, namely the Sikorsky Black Hawk, thereby demonstrating that the technology can be applied to large helicopters without the need to modify the rotor disk, despite its complexity. The idea of stabilising wakes by generating a counter-rotating vorticity has a long history.