Helicopters require a completely different method of control than airplanes and are much harder to master. Flying a helicopter requires constant concentration by the pilot and a near-continuous flow of control corrections.
A conventional helicopter has a main rotor above the fuselage which consists of two or more rotor blades extending out from a central rotor head assembly. The rotor blades are moved by the pilot to control the movement of the helicopter. This is achieved using a "swash plate", which is mounted on the main rotor shaft below the rotor head.
Each rotor blade has a cross-section similar to that of an airplane wing and generates lift as the blade is rotated through the air. The amount of lift produced is determined by the pitch angle (and speed) of each rotor blade as it moves through the air. The pitch angle of the blades is controlled by the pilot in two ways, using collective pitch ("collective") and cyclic pitch.
Collective pitch control either raises or lowers the swash plate without tilting it. As the swash plate rises or falls, the pitch of all rotor blades is changed at the same time and to the same degree. Because all blades are changing pitch together, or 'collectively', the change in lift remains constant throughout every full rotation of the blades. Therefore, there is no tendency for the helicopter to move in any direction other than straight up or down.
Cyclic pitch control can be used to move the helicopter in all directions other than up and down. This is achieved by tilting the angle of the swash plate. As the swash plate is tilted the pitch angle of a rotor blade is increased at a given point in the rotation, and decreased when the blade has spun through 180 degrees. As the pitch angle changes, the lift generated by each blade changes as it sweeps through it's rotation. As a result the helicopter tips towards whichever side is experiencing the lesser amount of lift. Moving the cyclic stick forward makes the helicopter fly forwards while bringing the stick back slows the helicopter and even makes it fly backwards. Moving the stick to the left or right makes the helicopter roll in these directions.
So now we have up and down, using the collective control, and pitch (forward/backward) and roll (left/right) using the cyclic control. Using these controls we can do everything apart from turn the nose of the heli around, i.e. control the yaw angle.
This is achieved using the tail rotor - a vertically mounted blade positioned at the very rear of the helicopter's tail boom. This rotor counteracts the tendency of the fuselage to rotate in the opposite direction to that of the rotors (so-called "torque reaction"). If this torque isn't controlled, the helicopter would just spin hopelessly. As the tail rotor spins it generates thrust, analogous to an airplane propeller, the sideways thrust negating the torque reaction. The pitch angle of the tail rotor blades can be changed by the pilot to control the amount of thrust produced, thereby allowing the nose of the heli to be turned in the air.
"You don't fly a helicopter, you just stop it from crashing...."
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