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Unformatted text preview: DRAG, C L- α , AND PITCHING MOMENT OF A FINITE WING IN STEADY, SUBSONIC, COMPRESSIBLE FLOW SIMONE MARRAS Abstract. In this notes we review the formulas needed for the computation of the slope of the C L- α lift curve of a finite wing subject to compressible effects. How these effects influence the drag and pitching moment is also mentioned. 1. Nomenclature a ∞ or a ∞ ,i : slope of infinite span wing in incompr. flow a ∞ ,c : slope of infinite span wing subject to compressibility effects a : slope of finite span wing a c : slope of finite span wing subject to compressibility effect Λ le : sweep angle at leading edge A : aspect ratio of a finite span wing α : angle of attack α L =0 : angle of attack of zero lift M,M loc : Mach and local Mach number respectively M ∞ : free stream Mach number M crit : critical Mach number C L ,C D ,C M lift, drag, and moment coefficients respectively C D base zero lift drag coefficient C D i coefficient of induced drag C L α generic symbol for the slope of the C L- α curve 2. Formulae Compressibility effects start to be evident when the Mach number (M) reaches the approximate value of 0.36. Practically speaking, although the aerodynamics of the aircraft at this regime begins to be affected by compressibility (e.g. increasing strength of pressure waves moving aft the aerodynamic surfaces and thus intro- ducing mechanical disturbances at low Mach; shocks when M → 1), in terms of stability and controllability, no effects are evident until M approaches 0.6 , when deterioration of controllability begins.when deterioration of controllability begins....
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This note was uploaded on 08/06/2009 for the course DESIGN IN aa taught by Professor Simonemarras during the Spring '09 term at Universitat Politècnica de Catalunya.
- Spring '09