This article discusses the main components of a traditional helicopter. It includes the rotors, engine, fuselage and stabilizing surfaces.
The main rotor is the most sophisticated component of a helicopter. It produces thrust that lifts the helicopter off the ground, propels the helicopter in forward flight and facilitates pitch and roll control. Most main rotors have two to eight blades connected in the center at a hub. These blades can be thought of as wings that rotate. The hub attaches the blades to the rest of the aircraft and provides the means for feathering the blades, which controls the helicopter. Unlike smaller UAVs you may have seen, traditional helicopter rotors spin at essentially constant speed. Rotor speed is not used as a control mechanism. Control is achieved purely by feathering the blades as described here.
The main rotor allows the helicopter to hover, fly at low airspeed and takeoff / land in locations without a runway. A normal airplane or jet wing requires significant speed to generate enough lift to fly. Main rotor blades always operate at such speed, even when the aircraft is hovering. Unfortunately, this advantage comes with drawbacks. A main rotor is much more complex to design and analyze compared to fixed wing, and has efficiency and top speed limitations.
Without a tail rotor, the “reaction torque” from turning the main rotor would cause a helicopter to spin out of control. The tail rotor counters that torque and keeps the helicopter facing in a desirable direction. By over and under compensating for that reaction torque, the tail rotor provides yaw control. This yaw control is achieved by varying the thrust of the tail rotor via feathering the blades as described here. The tail rotor typically spins over 5x faster than the main rotor.
The primary responsibility of the fuselage is to house the pilots, passengers and cargo. The fuselage adds weight and drag to the helicopter that must be overcome, primarily by the main rotor.
The horizontal stabilizer, located on the tail of the helicopter, improves pitch behavior. Early helicopters had little or no horizontal stabilizer. That was feasible, but larger stabilizers reduced pilot workload and are used in all modern helicopters. Designers may use large stabilizers to set a desirable aircraft pitch angle in forward flight, in addition to stabilizing the overall pitch behavior. In some helicopters, the control system can change the pitch angle of the stabilizer. An example is the Bell UH-1Y.
The vertical fin, also located on the tail of the aircraft, stabilizes the aircraft’s yaw angle. It reduces undesired nose left / right movement. It also reduces tail rotor thrust requirements at high speeds.
Most helicopter include one or two turboshaft engines, typically mounted near the main rotor. These engines have an output shaft that spins much faster than the desired main (or tail) rotor speeds (but at a constant speed, like the rotors). The drive system includes gear reduction and facilitates turning the rotor shafts at specific, lower speeds. The tail rotor normally spins about 5 times faster than the main rotor.