Four force acting on an aircraft in flight:
(a) Lift, (b) Weight, (c) Thrust, (d) Drag
The four forces acting on an aircraft in flight are:-
(a) Lift is a positive force caused by the difference in air pressure under and above a wing. The higher air pressure beneath a wing creates lift and is affected by the shape of the wing. Changing a wing's angle of attack affects the speed of the air flowing over the wing and the amount of lift that the wing creates.
(b) Weight is the force that causes objects to fall downwards. In-flight, the force of the weight is countered by the forces of lift and thrust.
(c) Thrust is the force that propels an object forward. An engine spinning a propeller or a jet engine expelling hot air out the tailpipe are examples of thrust. In bats, thrust is created by muscles making the wings flap.
(d) Drag is the resistance of the air to anything moving through it. Different wing shapes greatly affect drag. Air divides smoothly around a wing's rounded leading edge and flows neatly off its tapered trailing edge, this is called streamlining.