The same basic laws govern the flight of both fixed and rotary wing aircraft and, equally, both types of aircraft share the same fundamental problem; namely that the aircraft is heavier than air and must, therefore, produce an aerodynamic lifting force to overcome the weight of the aircraft before it can leave the ground. In both types of aircraft the lifting force is obtained from the aerodynamic reaction resulting from a flow of air over an aerofoil section. The important difference lies in the relationship of the aerofoil to the fuselage. In the fixed-wing aircraft, the aerofoil is fixed to the fuselage as a wing whilst in the helicopter, the aerofoil has been removed from the fuselage and
attached to a centre shaft which, by one means or another, is given a rotational velocity.