It is the component of the sum of all those tiny forces added up (actually, integrated vectorially) which is perpendicular to the flight path of the aircraft. What we call Lift is just an abstraction we create to help visualize and do aerodynamics calculations. At each point on the surface of anything in a fluid, the fluid pushes on the surface, normal (perpendicular) to the surface, with whatever pressure exists at that point. In some cases it is defined as the longest chord line through the airfoil from leading to trailing edge, in some cases it is defined by the bottom of the airfoil, etc.Īs to the question "How?", all Aerodynamic forces are generated by the pressure of the air pushing on the surface of the airfoil. Yes, it is the angle that the Airfoil makes with the relative wind (or the flight path through the air), but how the "Airfoil" is defined can vary. In fact, for asymmetrical airfoils, it is only a matter of convention as to how to define Angle of Attack. Whether the airfoil is symmetrical or not simply determines what that zero $C_L$ intersection AOA will be. The line (of course!) continues below the zero $C_L$ line.Īlso, the $C_L$ curve for any airfoil, symmetrical or not, must cross the $C_L$ = 0 line at some angle of attack. The graphic above only shows the positive $C_L$ portion of the complete curve.
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