This article covers the main components of a traditional helicopter configuration, including the rotors, engine, fuselage and stabilizing surfaces.
The main rotor is probably the most important and sophisticated component of a helicopter. It produces thrust that lifts the helicopter off the ground, propulsion for forward flight, and facilitates pitch and roll control. Most main rotors have two to eight blades (rotary wings) connected in the center at a hub. The hub attaches the blades to the rest of the aircraft and provides the means for pitching the blades (also called feathering), which controls the helicopter. Unlike smaller UAVs you may have seen, traditional helicopters keep their rotors spinning at a constant speed, rotor speed is not used as a control mechanism (control is achieved purely by pitching / feathering the blades).
The main rotor gives the helicopter the ability to fly at low airspeeds and takeoff / land in many locations, without a runway. However, it has the disadvantage of making the helicopter quite complex relative to a fixed wing aircraft.
Without a tail rotor (or other anti-torque mechanism), the “reaction torque” from turning the main rotor would cause a helicopter to spin out of control. The tail rotor counters that torque to keep the helicopter facing in a consistent 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, which is accomplished by changing the pitch (not speed) of the tail rotor blades. 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 the pitch behavior of the aircraft. 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 leverage these large stabilizers to set a desirable aircraft pitch angle in forward flight, in addition to stabilizing the overall pitch behavior.
The vertical fin, also located on the tail of the aircraft, stabilizes the aircraft’s yaw angle (reduces undesired nose left/right movement). It can also be used to reduce the required tail rotor thrust at high speeds (unload the tail rotor).
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.