Leading edge (Kreuger) flaps and trailing edge (Fowler) flaps, when extended from the basic wing structure, literally change the airfoil shape into the classic concave form, thereby generating much greater lift during slow flight conditions.įrom experiments conducted on wind tunnel models and on full size airplanes, it has been determined that as air flows along the surface of a wing at different angles of attack (AOA), there are regions along the surface where the pressure is negative, or less than atmospheric, and regions where the pressure is positive, or greater than atmospheric. Advancements in engineering have made it possible for today’s high-speed jets to take advantage of the concave airfoil’s high lift characteristics. As a fixed design, this type of airfoil sacrifices too much speed while producing lift and is not suitable for high-speed flight. The most efficient airfoil for producing the greatest lift is one that has a concave or “scooped out” lower surface. The weight, speed, and purpose of each aircraft dictate the shape of its airfoil. Many thousands of airfoils have been tested in wind tunnels and in actual flight, but no one airfoil has been found that satisfies every flight requirement. They vary, not only with flight conditions, but also with different wing designs.ĭifferent airfoils have different flight characteristics. It is neither accurate nor useful to assign specific values to the percentage of lift generated by the upper surface of an airfoil versus that generated by the lower surface.
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