Helicopters

The rotor of a Helicopter may, like a propeller, be powered by a variety of methods such as an internal-combustion engine or jet turbine. Tip jets, fed by gases passing along hollow rotor blades from a centrally-mounted engine, have been experimented with. Attempts have even been made to mount engines directly on the rotor tips. Helicopters obtain forward propulsion by angling the rotor disc so that a proportion of its lift is directed forwards to provide thrust.