Physics

# How Airplanes Fly

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Peggy Barnett's image for:
"How Airplanes Fly"
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Like a bird, an airplane can fly because it has wings. Without wings, an airplane would become a rocket, which quickly plummets to earth when deprived of the thrust required for its motion across the sky.

Wings are found on all types of airplanes: model, propeller, jet engine, and rocket motor. The wing's shape, rounded on the top, is designed to allow air to travel faster across the top of the wing than it does across the bottom, due, in part, to the fact that the rounded top is actually a longer distance than the bottom of the wing. The different speeds of the air motion on the wing lowers the air pressure on the top of the wing, which creates "lift", a condition in which the airplane reacts by reaching for the lower air pressure, which lifts the plane. Too steep of an incline in the ascent of an airplane disrupts the air flow over the wing, decreasing its "lift", and causing rapid loss of altitude.

Unlike birds, an airplane has one wing, which extends on both sides of the airplane, and two "flaps" on the edge of the wing, one on each side of the airplane. By moving the flap(s) down, the forward motion of the airplane can be reduced, due to the extension of the wing's top surface, which increases the amount of "lift" of the wing. Near the wing tips are ailerons, which can be moved up or down, and which direct the airplane to roll to the right or the left, depending on the ailerons' placement.

Most airplanes are heavy objects. In order for "lift" to operate on the wing, an airplane must first move forward rapidly enough to allow the air pressure to "lift" the wing. The necessary forward speed of the airplane is generated through the use of a propeller and engine, or through jet propulsion, both of which create thrust. Thrust is the force which propels the airplane forward.

Working in opposition to "lift" and thrust are gravity and drag. As the thrust of the airplane moves it forward, the normal force of earth's gravity, distributed equally over the entire airplane, center on a point within the structural design of the airplane. If the airplane has been designed properly, it will be neither nose-heavy (center of gravity in front of the wing), nor tail-heavy (center of gravity behind the wing), and will allow "lift" of the rapidly forward moving object to occur, in effect overcoming gravity.

Drag is created by the resistance of the air to having an object moved through it. Air sometimes sticks to objects, such as rivet heads, creating friction along the surface of the airplane, slowing its forward motion. Drag can also be created along the wing as the airplane "lifts". An airplane's design and maintenance will determine the amount of drag involved.

Take-off of an airplane occurs when gravity has less effect on the plane than "lift", and when the thrust overcomes the drag. Landing an airplane reverses only one of these conditions, by allowing gravity to assume control of the "lift", since the forward motion of the landing plane continues to create thrust, which is greater than the drag. In level flight, all forces, "lift", gravity, thrust, and drag, should be equal.

The tail of an airplane also contains a small wing, known as a horizontal stabilizer, which helps keep the airplane level during flight. Adjacent, at a right angle to the horizontal stabilizer, is a fin known as the vertical stabilizer, which controls side-to-side movements of the airplane. Without these necessary additions, once again, the wing would incline at too great an angle and disrupt the airflow over the wing, which would cause the airplane's rapid descent, turning it into a rocket.

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