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Airfoil Design

 Airfoil Design

An airfoil is a structure designed to obtain reaction upon its surface from the air through which it moves or that moves past such a structure.

  •  Air acts in various ways when submitted to different pressures and velocities; but this discussion is confi ned to the parts of an aircraft that a pilot is most concerned with in fl ight—namely, the airfoils designed to produce lift.
  •  By looking at a typical airfoil profi le, such as the cross-section of a wing, one can see several obvious characteristics of design.
  •  Notice that there is a difference in the curvatures (called cambers) of the upper and lower surfaces of the airfoil.
  • The camber of the upper surface is more pronounced than that of the lower surface, which is usually somewhat fl at.
  • NOTE: The two extremities of the airfoil profi le also differ in appearance. The end, which faces forward in fl ight, is called the leading edge, and is rounded; the other end, the trailing edge, is quite narrow and tapered.
  • A reference line often used in discussing the airfoil is the chord line, a straight line drawn through the profi le connecting the extremities of the leading and trailing edges.
  •  The distance from this chord line to the upper and lower surfaces of the wing denotes the magnitude of the upper and lower camber at any point.
  •  Another reference line, drawn from the leading edge to the trailing edge, is the mean camber line. This mean line is equidistant at all points from the upper and lower surfaces.
  •  An airfoil is constructed in such a way that its shape takes advantage of the air’s response to certain physical laws.
  • This develops two actions from the air mass: a positive pressure lifting action from the air mass below the wing, and a negative pressure lifting action from lowered pressure above the wing.

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