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How does an airplane fly?
Traction (Thrust): this force propels the aircraft in the air. The thrust is created by a Propeller or Jet engine.
Trail : The Air resistance, which tends to slow the forward motion of an Aircraft
Weight (Gravity) : This is the force which attracts all objects towards the earth.
Bearing Capacity: An upward force is created by a movement of air below the wing. The air flow thus becomes faster above the wing and more slowly below. This mechanism creates a difference in pressure that keeps a plane in flight.
The Traction forward opposes the Trail backwards.
The upward lift opposes the downward weight.