A cross section of a typical airplane wing will show the top surface to be more curved than the bottom surface. This shaped profile is called an aerofoil or airfoil.
Due to this aerofoil structural design, the difference pressure below and above the aerofoil able to produce a larger lifting force.
According to Bernoulli Principle:
- Air moves with higher speed over the top of aerofoil.
- This creates a region of lower pressure over it and a region of higher pressure below it.
- This difference in pressure produce a resultant force acting upwards on the wings.
Drag is the resistance of air (the backward force), thrust is the power of the airplane's engine (the forward force), lift is the upward force and weight is the gravity downward force.
When it is in straight and level flight the opposing forces of lift and weight are balanced. During a descent, weight exceeds lift and to slow an airplane drag has to overcome thrust.