The airfoil is designed to increase the velocity of the airflow above its surface, thereby decreasing pressure above the airfoil. In this narrow section, the fluid moves at high speed, producing low pressure.Īn important application of this phenomenon is made in giving lift to the wing of an airplane, an airfoil. As the pipe narrows it must contain the same amount of fluid. In the wide section of the gradually narrowing pipe, the fluid moves at low speed, producing high pressure. This principle was first used to explain changes in the pressure of fluid flowing within a pipe whose cross-sectional area varied. In other words, Bernoulli found that within the same fluid, in this case air, high speed flow is associated with low pressure, and low speed flow with high pressure. A reference line often used in discussing airfoils is the chord, an imaginary straight line joining the extremities of the leading and trailing edges.īernoulli's Principle: To understand how lift is produced, we must examine a phenomenon discovered many years ago by the scientist Bernoulli and later called Bernoulli's Principle: The pressure of a fluid (liquid or gas) decreases at points where the speed of the fluid increases. The aft part is narrow and tapered and is called the trailing edge. The forward part of an airfoil is rounded and is called the leading edge. Generally the wing of small aircraft will look like the cross-section of the figure above. Wings, horizontal tail surfaces, vertical tails surfaces, and propellers are all examples of airfoils. When an airfoil is moved through the air, it is capable of producing lift. An airfoil is a device which gets a useful reaction from air moving over its surface.
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