Spoilers and Ailerons

Wing

A wing, or airfoil, is a surface that produces a lifting force when it moves through air. A flat surface creates lift if it moves through air at the correct angle, like a kite. A curved surface produces more lift and less drag.

Wing Shapes

Most aircraft wings are curved on top and flatter underneath. Fixed-wing aircraft generally have one of these types of wing: 1) Delta, 2) Arrow-shaped, 3) Tapered, 4) Straight, 5) Swept-back, and 6) Variable geometry.

Delta wing - thin triangular wing that is especially aerodynamic.	Arrow-shaped wing found on combat aircraft; the angle it forms with the fuselage can be changed in flight.
Tapered wing - wing that is perpendicular to the fuselage and whose width decreases toward the tip.	Straight wing - long wing of consistent width and perpendicular to the fuselage; it is found on low-speed planes such as cargo and light planes.
Swept-back wing - arrow-shaped wing that is found on jet planes.
The F-14 Tomcat is a supersonic aircraft with a variable geometry wing. This aircraft wing geometry changes according to flying speed by swinging the wings forward and backward.

Small, slow airplanes usually have wings that stick straight out from the sides of the plane’s body, or fuselage. Straight wings are not suitable for high-speed flight, because they create too much drag. Wings that are angled backward, called swept wings, are better for high-speed aircraft, such as jet airliners. A delta wing is a triangular wing that is very efficient for supersonic flight. It produces little lift at low speeds, however, so delta-wing aircraft have to take off and land faster than other aircraft, and they are not very maneuverable.

A few planes have swing wings, which are straight at low speeds and swept back at high speeds. Their wings actually move, swinging backward as a plane accelerates. This is called variable geometry, or swing-wing technology. These planes are rarely built, however, because the swing-wing mechanism is heavy and complicated.

Creating Lift

When a wing slices through air, two things happen to the air. First, the air flowing over the curved top of the wing speeds up. As Bernoulli’s principle states, when air speeds up, its pressure falls. Low air pressure above a wing and higher pressure below it produce an upward force. Second, a wing deflects air downward. According to Newton’s third law of motion, forcing air downward produces an equal and opposite force that pushes the wing upward. The total upward force on a wing is lift.

If a wing is tilted up at the front, it deflects air downward even more powerfully and produces more lift and more drag. The angle between a wing and the airflow is called the wing’s angle of attack. If the angle of attack is increased too much, the wing will stall. When a wing stalls, the smooth flow of air over it breaks up, and lift suddenly disappears.

Boosting Lift

An airplane needs big wings to produce large amounts of lift when it is flying slowly during takeoff and landing. Big wings that produce a lot of lift, however, also produce a lot of drag. Excessive drag makes the wings inefficient when the plane is cruising at high speed, because the engines have to burn more fuel to overcome it.

Designers solve this problem by creating the best wings for high-speed cruising but changing their size and shape for takeoff and landing. As an airliner prepares for takeoff or landing, flaps slide out from the trailing edges of its wings, and slats slide out from the leading edges. Flaps and slats are called high-lift devicesbecause they produce extra lift. Flaps produce more lift by making a wing bigger and more curved. When slats are extended, they make the leading edge of a wing more curved. This shape enables the wing to be tilted to a greater angle of attack without stalling. The higher angle of attack produces extra lift.

The simplest flaps hinge downward from the wing’s trailing edge. Fowler flaps slide backward and then tilt down. They increase the size and curve, or camber, of a wing. Flaps are nearly always on a wing’s trailing edge, but Krueger flaps are on the leading edge. The increased curve in the wing shape produced by flaps may cause a wing to stall and lose lift if the smooth airflow over the wing breaks away from the drooping flaps.

When a slotted flap slides out, a gap opens up between the flap and the rest of the wing. Air from below the wing comes up through the slot and flows over the top of the flap. This extra airflow helps to stop the wing from stalling. There are also slotted slats. Air coming up through the slot from below flows over the top of the wing and enables the wing to work safely at a higher angle of attack without stalling.

A blown flap is a device that blows air from the engine over the flaps. The extra airflow produces more lift and delays stalling even more.

Spoilers and Ailerons

Spoilers on top of a wing serve the opposite purpose from flaps and slats. When a spoiler is raised, it spoils the wing’s aerodynamic shape, increases drag, and cuts the amount of lift. Spoilers are used to cut lift after an airplane has landed. They may be used to help a big, heavy plane turn. The spoilers on one wing are raised to help the ailerons.

Ailerons are panels in the trailing edge of an airplane’s wings that are used for turning the plane. One aileron tilts up, and the other tilts down. One wing produces more lift than the other and rises. The wing that produces less lift falls, and the plane rolls into a turn. Big airliners often have two sets of ailerons. The ailerons closest to the wingtips have more leverage for rolling the plane at low speeds. At high speed, the ailerons closest to the fuselage have enough leverage to turn the plane.

Date: 2016-01-05; view: 1058