RE Museum - Helicopters
Helicopters: aircraft with spinning wings
The helicopter's spinning blades not only lift it into the air, they are also its means of propulsion - rather like a combined wing and propeller. And if the engine fails, the blades can be kept spinning to glide the machine to the ground (this is known as autorotation).
Each of the long, thin blades - the number varies from two to six - has the aerofoil shape of an aircraft wing and the leading (front) edge is angled upwards.
To lift the aircraft off the ground the blades are rotated and their pitch - the angle at which they meet the airstream - is gradually increased. As a result air pressure decreases above each blade and increases underneath it, providing an upward force. When the lift beneath the blades is greater than the weight of the helicopter, it rises into the air.
Once the helicopter is airborne, flight is controlled by adjusting the amount and direction of lift by altering the pitch of the blades. The pitch can be altered by two controls - collectively by the collective pitch lever, or separately by the cyclic pitch column.
The collective pitch lever angles all the blades at the same pitch. It is used by the pilot for vertical ascents and descents. As the pitch is increased and more lift is generated, the throttle is usually opened up automatically to provide the necessary extra engine power.