An airfoil is a specific shape, notably that used in airplane wings, which helps generate lift. In addition to airplane wings, which are the most well-known airfoils, fans, propellers, and some stabilizers are also in the shape of an airfoil. In nature, the airfoil is a very common shape, found in plants and in creatures that fly through the air or swim through the water.
The basic principle by which an airfoil operates is referred to as lift. The shape of an airfoil is such that wind can pass both above and below it. The shape of the top is designed so that, as air passes over it, it speeds up, decreasing the air pressure in that region according to Bernoulli’s principle. Air below the airfoil is not affected, so its speed is the same as it was when it first contacted the airfoil.
Air with a higher pressure tends to move towards air with a lower pressure, and this difference in pressure causes force to be exerted beneath the airfoil, generating lift. The faster the air is moving – or the faster the airplane is moving through the air – the greater the difference in air pressure, and therefore the greater the pressure being exerted. At a certain speed, enough force is being exerted that an object – such as a plane – will overcome the force of gravity and lift off of the ground.
An airfoil may also be used to generate lift in a downward direction, by changing its shape. In this case, rather than lift helping an object to overcome the force of gravity, it increases the downward force to compensate for other upward forces. A good example of this can be seen on the wings or “spoilers” found on some cars, which help increase the car’s traction at high speeds so that the car remains well seated on the ground.
An airfoil may come in many different shapes, depending on the purpose for which it is intended. The design of airfoils for specific tasks is one of the major focuses of aerodynamics, and new and improved airfoil designs continue to be created. Some airfoil shapes, such as those meant for aircraft traveling below the speed of sound, are rounded on one end curving down to a point. Others, such as those intended for supersonic aircraft, are much sharper in shape.
Certain airfoil shapes may be chosen in order to reduce drag and allow a greater overall speed, to increase drag to slow down the vehicle, or to react to different types of currents. Some airfoil designs are symmetric, with a round curve on both sides, to allow an aircraft to function equally well when flying straight or when flying inverted.