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Net Forces on an Airplane


The external forces on an airplane in flight heading westward are as follows:

gravity, thrust, drag, and lift.

They are not all along the same line.



The gravity represents the weight of the aircraft.

The drag is caused by air resistance on the aircraft.

The thrust is due to the engine and propeller.

How does lift work?

According to Daniel Bernoulli who presented his fact in 1738.

Fast moving fluids (such as air), exhibit less force than slow moving fluids.



where p is the pressure, r is the density, and v is the velocity.

A large velocity v results in a small pressure p, and conversely a small velocity v results in a large pressure p.

If we produce a surface such that air takes longer to travel over the top than the bottom, the surface will produce a net upward force. Such a surface is called an airfoil and the net force is called lift.


(Dr. Bob Gardner, East Tennessee State University)