Aerodynamics
How planes fly: the four forces of flight
In cruise, the four forces are in balance. To climb, descend, speed up or slow down, the pilot changes that balance.
Lift
The wing has a curved profile and a small angle of attack. Air speeds up over the top, pressure drops and the wing is pulled upward.
Weight
Gravity acting on the structure, fuel, cargo and passengers. It decreases during the flight, because fuel is burned.
Thrust
Turbofan engines push a large mass of air backward. By Newton's third law, the plane moves forward.
Drag
The air's resistance against the plane. That's why the landing gear and flaps are retracted in cruise.
