Configurations of Rotary Wing Aircraft - Helicopter Assembly


An autogyro is an aircraft with a free-spinning horizontal rotor that turns due to passage of air upward through the rotor. This air motion is created from forward motion of the aircraft resulting from either a tractor or pusher configured engine/propeller design. [Figure 1]

Configurations of Rotary-Wing Aircraft
Figure 1. An autogyro

Single Rotor Helicopter

An aircraft with a single horizontal main rotor that provides both lift and direction of travel is a single rotor helicopter. A secondary rotor mounted vertically on the tail counteracts the rotational force (torque) of the main rotor to correct yaw of the fuselage.

Single main rotor helicopters are the most common type of helicopter. They need an anti-torque device (tail rotor or other anti-torque system) to counteract the twisting momentum produced by the main rotor, which is powered by one or more engine(s). The most common anti-torque device is a tail rotor, which is designed to compensate the torque produced by the main rotor. [Figure 2]

Configurations of Rotary-Wing Aircraft
Figure 2. Single rotor helicopter

Dual Rotor Helicopter

An aircraft with two horizontal rotors that provide both the lift and directional control is a dual rotor helicopter also referred as tandem helicopter. The rotors are counterrotating to balance the aerodynamic torque and eliminate the need for a separate antitorque system. Usually the rear rotor is mounted at a higher position than the front rotor, and the two are designed to avoid the blades colliding, should they flex into the other rotor’s pathway. The rotor discs are slightly tilted toward each other to provide control along the vertical axis during the hover.

This configuration, which is mainly used for larger helicopters, has the advantage of being able to support more weight with shorter blades. The smaller rotor disc area is compensated by having two rotors. The anti-torque function is performed by the counter-rotating rotors, with each cancelling out the other’s torque, so all of the power from the power-plants is employed for lift. Tandem helicopters are typically powerful and fast. The design of the drive and control system are more complicated than the ones of a single main rotor helicopter. [Figure 3]

Configurations of Rotary-Wing Aircraft
Figure 3. Dual rotor helicopter


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