Rectangular Straight Wing
Tapered Straight Wing
Rounded or Elliptical Straight Wing
Wing Design
The amount of lift produced by an airfoil depends upon many factors:
The shape of a wing greatly influences the performance of an airplane. The speed of an airplane, its maneuverability and its handling qualities are all very dependent on the shape of the wings. There are four basic wing shapes that are used on modern airplanes: straight, sweep (forward and back), delta and swing-wing.
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Rectangular Straight Wing |
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Tapered Straight Wing |
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Rounded or Elliptical Straight Wing |
The straight wing is found mostly on small, low-speed airplanes. General Aviation airplanes often have straight wings. These wings provide good lift at low speeds, but are not suited to high speeds. Since the wing is perpendicular to the airflow it has a tendency to create appreciable drag. However, the straight wing provides good, stable flight. It is cheaper and can be made lighter, too.
Slight Sweepback Wing |
Moderate Sweepback Wing |
Great Sweepback Wing |
Forward Sweep Wing |
The sweepback wing is the wing of choice for most high-speed airplanes made today. Sweep wings create less drag, but are somewhat more unstable at low speeds. The high-sweep wing delays the formation of shock waves on the airplane as it nears the speed of sound. The amount of sweep of the wing depends on the purpose of the airplane. A commercial airliner has a moderate sweep. This results in less drag while maintaining stability at lower speeds. High speed airplanes (like fighters) have greater sweep. These airplanes are not very stable at low speeds. They take off and descend for landing at a high rate of speed.
The forward-sweep wing is a wing design that has yet to make it into mass production. An airplane (like the X-29) is highly maneuverable, but it is also highly unstable. A computer-based control system must be used in the X-29 to help the pilot fly.
Simple Delta Wing (top) and Complex Delta Wing (bottom) |
A delta wing looks like a large triangle from above. Because of the high sweep, airplanes with this wing can reach high speeds - many supersonic airplanes have delta wings. Because of the high sweep, the landing speeds of airplanes with delta wings are very fast. This wing shape is found on the supersonic transport Concorde.
The swing-wing design attempts to exploit the high lift characteristics of a primarily straight wing with the ability of the sweepback wing to enable high speeds. During landing and takeoff, the wing swings into an almost straight position. During cruise, the wing swings into a sweepback position. There is a price to pay with this design, however, and that is weight. The hinges that enable the wings to swing are very heavy.
High Lift Devices
When an airplane lands it is desirable to fly as slowly as possible. Ideally for landing, an airplane would have a large wing with a very cambered airfoil. However, airfoils designed to perform well at slow speeds are not good for flying at faster speeds, and vice versa. Airplane designers have developed a set of features that allow the pilot to increase the wing area and change the airfoil shape to compensate for this.
The trailing edge of the wing is equipped with flaps which move backward and downward. These are not to be confused with ailerons, which are also located on the trailing edge of the wing, but have an entirely different purpose. The flaps increase the area of the wing, and the camber of the airfoil. With this increase in area, the airflow has farther to travel which spreads the pressure difference between the top and bottom of the wing over a larger area. An equation for the lift force is
lift = pressure x area
Given this equation, if the area increases the lift increases also. Conversely, if the area decreases, so will the lift.
Slats are located on the leading edge of the wings. They slide forward and also have the effect of increasing the area of the wing, and camber of the airfoil.
Flaps and slats are used during takeoff and landing. They enable the airplane to get off the ground more quickly and to land more slowly. Some airplanes have such large flaps and slats that the wing looks like it's coming apart when they are fully extended!
Spoilers are devices that are located on top of the wings. Spoilers have the opposite effect from flaps and slats. They reduce lift by disrupting the airflow over the top of the wing. Spoilers are deployed after the airplane has landed and lift is no longer needed. They also substantially increase the drag which helps the airplane to slow down sooner.
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