Aerodynamics

April 16, 2000

A fluid, such as a gas like air or a liquid like water, can flow over a solid object. The same amount of fluid that hits the front of the object must pass by the rear of the object. Otherwise, the fluid would build up in the front or rear. 

The bottom of a wing, or airfoil, is flat or only slightly curved, but the top is highly arched. This shape causes air to travel farther over the top of the wing and shorter over the bottom. The air must move faster over the top and slower underneath. The slower air has more sideways pressure (because it has less forward pressure), and the faster air has less sideways pressure (because it has more forward pressure), pushing the wing upward. 

Also, a wing has a rounded front and a pointed back and is tilted upward in the front. The air hits underneath the wing and pushes the wing up. (The movable pieces on the back edge of the wing, called ailerons, tilt up or down to change the angle of the wing for landing and taking off.)

If a fluid flow has constant speed and no sideways motion, it is called streamline flow. If the flow has sideways motion or different speeds, it is called turbulent flow. A wing is made to have streamline flow, in order to reduce friction.

A solid object slows a fluid by friction, and this is called drag. The total force that pushes up on a wing is called lift. Some forward force, like a jet engine or hand, is needed to push the object through the fluid, and this is called thrust. 
An airplane can rotate around the direction of motion, along the body of the airplane, called roll. It can rotate around the wings, horizontal to the body, called pitch. And it can rotate around the tail, vertical to the body, called yaw. An airplane must be able to prevent these rotations. 

A fluid, such as a gas like air or a liquid like water, can flow over a solid object. The same amount of fluid that hits the front of the object must pass by the rear of the object. Otherwise, the fluid would build up in the front or rear. 

The bottom of a wing, or airfoil, is flat or only slightly curved, but the top is highly arched. This shape causes air to travel farther over the top of the wing and shorter over the bottom. The air must move faster over the top and slower underneath. The slower air has more sideways pressure (because it has less forward pressure), and the faster air has less sideways pressure (because it has more forward pressure), pushing the wing upward. 
Also, a wing has a rounded front and a pointed back and is tilted upward in the front. The air hits underneath the wing and pushes the wing up. (The movable pieces on the back edge of the wing, called ailerons, tilt up or down to change the angle of the wing for landing and taking off.)

If a fluid flow has constant speed and no sideways motion, it is called streamline flow. If the flow has sideways motion or different speeds, it is called turbulent flow. A wing is made to have streamline flow, in order to reduce friction.

A solid object slows a fluid by friction, and this is called drag. The total force that pushes up on a wing is called lift. Some forward force, like a jet engine or hand, is needed to push the object through the fluid, and this is called thrust.