Have anyone ever wondered about the fact that why helicopters fly at a constant height above ground even though their rotor blades keep moving constantly.
When the engine of the helicopter is started (which has a certain power), the rotor blades begin to rotate. As a result they push the air molecules beneath them downwards (for those who have little idea the rotor blades of the helicopter are slightly bent downwards rather than absolutely perpendicular to each other). One of Newton’s laws of motion states that to every action there is an equal and opposite reaction. So when the blades force the air molecules downwards, the air molecules push the rotor blades upwards. So an unbalanced force is created and the chopper moves upwards. Once it reaches a certain height, the upward force provided by the air molecules on the rotor blades is balanced by the downward force of the chopper’s weight. Thus a constant height is maintained while flying.
The height maintained by the chopper while flying depends on the power of its engine, which in turn provides velocity. More the power more is the velocity.
While landing the chopper, velocity of the rotor blades is gradually decreased so the chopper moves down due to its weight which is greater of the two forces at that moment.