The Four Main Forces
The four main forces acting on an airplane are lift, drag, gravity, and thrust. All of
these forces have effects on the performance of the airplane.
Lift is created by the airfoil. It is what allows the aircraft to fly. Most of the lift
created by the airfoil can be attributed to Bernoulli's Principle. The rest of lift is
created by the impact of air against the lower surface of the wing. The amount of lift
is in a direct relationship with the speed of the airplane. As it increases speed, the
amount of lift acting upon it increases. Lift can also be manipulated by increasing or
decreasing the angle of attack but, if the angle of attack is increased to much the
aircraft will stall.
Drag is the force which opposes the forward motion of the aircraft. There are two
kinds of drag inducing drag and parasite drag. Inducing drag is caused by the
development of lift while Parasite drag is the result of all of the un-aerodynamic
features of the airplane.
Gravity is the force that pulls the aircraft, and everything else, towards the earth.
In order to fly, the force of lift has to exceed the force of gravity.
Thrust is the force which opposes drag. In for the aircraft to move forward, thrust
must be greater than drag.
These four forces can be divided into two groups of opposing forces. Lift opposes gravity,
and thrust opposes drag. Also, according to Bernoulli's Principle, as the speed of the aircraft
increases so does the amount of lift.
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