![]() ![]() Both the maximum thickness and the camber are usually expressed in terms of a percentage of the chord length for example, a 12% thick airfoil has a maximum thickness equal to 0.12 c. The camber is the maximum distance between the mean camber line and the chord line, measured perpendicular to the chord line. The maximum thickness, and where it occurs along the chord, is an important design feature of the airfoil. The thickness of the airfoil is the distance from the upper to the lower surface, measured perpendicular to the chord line, and varies with distance along the chord. The straight line connecting the leading and trailing edges is the chord line of the airfoil, and the distance from the leading to the trailing edge measured along the chord line is simply designated the chord of the airfoil, represented by c. The most forward and rearward points of the mean camber line are the leading and trailing edges, respectively. The mean camber line of an airfoil (see illustration) is the locus of points halfway between the upper and lower surfaces as measured perpendicular to the mean camber line itself. The cross sections of wings, propeller blades, windmill blades, compressor and turbine blades in a jet engine, and hydrofoils on a high-speed ship are examples of airfoils. ![]() The cross section of a body that is placed in an airstream in order to produce a useful aerodynamic force in the most efficient manner possible. The Columbia Electronic Encyclopedia™ Copyright © 2022, Columbia University Press. Other airfoils include propeller blades and the blades utilized in turbojet engines. In aircraft of the swing-wing type, in which the sweep of the wings is variable, the entire wing can be considered a control surface. Spoilers, which can be made to protrude from lifting surfaces to give controlled reduction of lift, often replace ailerons and elevators. Flaps are located near the ailerons to increase lift for takeoff and landing. The rudder, which is hinged to the rear of the vertical airfoil of the tail assembly, is used to produce yawing. Elevators, which are hinged to the rear of the horizontal airfoil of the tail assembly, are used to produce pitching, which occurs when an airplane in level flight points its nose upward or downward. Modern aircraft have fairly complex arrays of control surfaces, including elevators, a rudder, and flaps. Ailerons, control surfaces hinged to the trailing edges of wings, can produce rolling, which is rotational motion of the aircraft about a line running through its fuselage, or yawing, which is rotational motion about a line running from the top to the bottom of an aircraft. Airfoils that are manipulated to produce variable forces are called control surfaces. For example, the fixed wing surfaces of an airplane produce lift, which opposes gravity. Airfoil, surface designed to develop a desired force by reaction with a fluid, especially air, that is flowing across the surface.
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