by Richard Sheffield
The Anti-Torque Rotor
Another force that affects the helicopter is torque. Torque is a force that is the reaction of the engine turning the rotor. When the engine turns the rotor, there is an equal-and-opposite reaction that tries to turn the body of the helicopter in the opposite direction. Anyone who has had an electric drill spin out of their hand when the bit became lodged knows what torque can do.
So to keep the body of the helicopter from spinning around and around once it leaves the ground, the AntiTorque Rotor was developed. This is the small propeller you see spinning at the end of the aircraft fuselage. When this rotor spins, it creates thrust in the opposite direction of the torque force. The amount of force generated by this rotor is controlled in a manner similar to the way the lift of the main rotor is controlled. The pitch of the Anti-Torque Rotor can be increased or decreased by using a pair of pedals at the pilot's feet. In this manner, the pilot can control the amount of force generated by this rotor and keep the aircraft pointed straight ahead. The pilot can also use this control to turn the aircraft while in a hover.
Figure 3-5. Anti-Torque Rotor Action
As the engine spins the rotor blades, the torque produced tries to spin the body of the aircraft in the opposite direction. The Anti-Torque Rotor produces thrust to push the tail and oppose the force of the torque. When these forces are balanced, the aircraft will remain pointed in a fixed position.
Figure 3-6. Cyclic Control
Pushing forward on the cyclic stick increases blade lift during the back portion of the cycle and decreases lift during the front part of the cycle (above). This results in a tilt in the rotor disc (below) and forward motion.