Single-Rotor Helicopters

The single-rotor helicopter has one large rotor, usually mounted toward the front of the body and above the passenger compartment. A smaller rotor is attached to the tail of the helicopter.

The main rotor may have between two and eight blades. The tail rotor can have two, twelve, or more blades. It is mount­ed vertically on the side of the tail and is therefore at right angles to the main rotor. The tail rotor provides stability, acting against the tendency of the heli­copter to spin around in the opposite direction of the main rotor blades. This spin force is known as torque.

The tail rotor may be shrouded, or enclosed in a cover-it is then called a fenestron. This is quieter and safer, but less efficient. A tail rotor can use up to 5 percent of the engine’s power without helping the helicopter fly upward or for­ward. One way of improving efficiency is to angle the vertical stabilizer so that it counteracts the torque without taking power from the engine. Helicopter pilots call this “slipstreaming.”