Aerodynamic Design of High Lift Devices: A Comparative Study of Airliner Flaps and Fighter Leading Edge Maneuvering Slats

Abstract

High-lift devices are essential aerodynamic features used to enhance aircraft performance during the low-speed regime, namely takeoff and landing, as well as in high-maneuverability flight regimes. In this paper, a comparative study of high-lift system design philosophies used in two classes of aircraft, commercial airliners and military fighters, is presented. Commercial aviation has an overriding interest in trailing-edge high-lift devices for fuel efficiency, safety, and economic maturity. Military fighter design has an overriding interest in leading-edge devices for enhanced aircraft maneuverability, controllability, and post-stall flight characteristics. The paper presents a systematic comparison of design philosophies used in high-lift system design in commercial transports and military fighters. Commercial aviation uses trailing-edge high lift devices on aircraft such as the Boeing and Airbus families for lift-to-drag ratio optimization, and to operate within acceptable margins of weight, size, and maintenance. Military fighter aircraft use trailing-edge and leading-edge devices, such as slats and Leading-Edge Vortex Controllers (LEVCONs), to achieve enhanced aircraft maneuverability, controllability, and post-stall flight characteristics. The LEVCON operation is presented, including the mechanism of vortex generation and delay of stall. The extent to which modern fighters integrate the leading-edge aerodynamic controls with digital flight control is discussed. A comparative analysis of airliner and fighter high lift system design philosophies is presented. Airliner high lift systems are designed to operate in a predictable, safe, and efficient regime of low-speed flight. Fighter high lift systems are designed to operate in a regime of extreme flight regimes, in particular high angles of attack. Finally, future trends in high lift system design are discussed including unmanned aerial vehicles (UAVs) and blended-wing-body configurations. A review of promising trends in adaptive wing geometries, smart materials, and active flow control actuators is presented, including the prospect of truly aerostructurally integrated intelligent high lift systems.