There are four aerodynamic forces affecting an airplane while in flight, they are 1.Lift 2. Weight 3.Thrust 4. Drag. Lift is cause by different wind velocity under and over an airfoil shape of the wing of an airplane. According to Bernoulli's principle as velocity increases pressure decreases, as velocity decreases pressure increases. This pressure difference create a force known as "Lift". Weight is the downward force cause by gravitational force exerted by earth on an airplane. Thrust is a forward force created by combustion engine usually cause by the expansion of gases as it passes through the nozzle of an engine. Drag force is opposite of thrust, cause by friction air on the body and surface of an airplane