ABSTRACT
The alternative types, with contra-rotating main rotors, allow all the power to be used to lift the helicopter but at the cost of extra complication. Contrarotating helicopter rotors can be tandem (Boeing-Vertol), co-axial (Kamov) or inter-meshing (Kaman). Aeroplanes and helicopters both obtain their lift from the movement of air over their airfoils. Aeroplanes use their forward speed to obtain airflow over their wings; helicopters rotate their rotor blades through the air, allowing them to obtain lift without requiring forward speed. The combination of collective and cyclic control inputs, and the effects of the helicopter’s forward speed on the rotating airfoils, result in very complex airflows and motions of the blades throughout each revolution. Helicopters with contra-rotating rotors are particularly dependent on the integrity of their transmissions, highly stressed complex machinery which requires impeccable maintenance. Tandem-rotor helicopters have a number of gearboxes, connecting shafts and couplings to transmit engine power and to ensure that the two rotors are synchronised.
