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A supercritical airfoil is a special airfoil designed to reduce the drag when operating near supersonic speeds. When a plane flies near supersonic speeds, the air moving over the wing goes faster than the speed of sound before the plane does. This causes a shock wave to form on the wing, which creates a lot of wave drag. By designing the airfoil so that the top is mostly flat and the bottom has a curve at the back, as shown here, the point on the wing where the air reaches supersonic speeds is farther back on the wing, which creates a smaller shock wave and leads to less wave drag on the wing.