In flight, outside air cannot enter the pressurized wing and is forced to flow around the leading edge. This results in the prevention of air escaping from the wing, and in the formation of an aerodynamically correct wing. Lift equals Weight and Thrust equals Drag. When the wing, with its curved upper surface and flat lower surface, moves through the air, it forces the air to flow around it. Air flowing over the curved upper surface has to travel further, and therefore faster, than air going under the wing.
Air traveling at a higher velocity creates a lower pressure than air traveling at lower velocity.
This higher pressure air traveling beneath the wing produces an upward force called lift. Weight is produced by gravity which is equal to the weight of pilot and aircraft. When lift and thrust exceeds weight and drag, the craft will climb. When weight and drag exceeds lift and thrust, the craft will descend. Thrust is produced by the propeller driven by the engine.