Helicopter tail rotor

Fig. 6-10. Bell Helicopter Company engineers hold an 8-foot length of boron/epoxy shafting which will comprise one of three sections that make up the final helicopter tail rotor driveshaft system. An aluminum shaft system would require five shorter sections, with additional end fittings and bearing supports, to transmit an equal amount of power over an equal distance. The lighter weight and superior stiffness of the composite material thus permits an overall system weight reduction of 30%. Courtesy of Textron s Bell Helicopter Co.)...

Typical structural items fabricated from cfrp for a helicopter are shown in Figure 23.20. The tail rotor drive shaft for the Eurocopter Tigre helicopter (Figure 23.21) is filament wound by Urenco using cfrp. 

A conventional helicopter requires a tail rotor to provide anti-torque and keep the craft from spinning in... 

Igor Sikorsky is most often associated with the development of the helicopter and is called the father of the modern helicopter. Sikorsky s VS-300, the first operational helicopter, made its first free flight in 1940. It introduced the practical use of the tail rotor to the helicopter airframe. Its purpose was to counteract the action of torque on the body of the aircraft and keep it from spinning wildly out of control in the opposite direction of the blades overhead. 

Rotary-Wing Aircraft. Helicopters use the same principles, with two exceptions. The engine in the helicopter is usually hooked directly to the propeller or rotor. It is also hooked in sync with the shaft that turns the rear or tail rotor. The tail rotor is necessary for the directional control of the aircraft. When the collective, the control system that governs lift, is pulled up, it sends directions for the rotor blades to change their pitch and take a larger bite out of the air to lift the machine. Without the tail rotor, torque takes effect, and this causes the aircraft body to rotate in the opposite direction of the rotor blades. The pitch (or amount of bite into the air of the blades) of the tail rotor is controlled by the foot pedals. 

The lateral thrust of the tail rotor of a helicopter has to compensate for the main rotor torque. For maximum effectiveness, it is operated with a rotational speed as high as permitted by the blade tip velocity, but well below the speed of sound. In general, the noise- and vibration-generating mechanisms are similar to those of the main rotor. While there is no cyclic blade pitch, the interaction with the main rotor outflow has to be taken into account. Due to the comparatively small diameter of the tail rotor, its rotational speed is significantly higher than that of the main rotor and thus the emitted noise and vibrations have higher frequencies, see Staufenbiel et al. [168]. 

Advanced composites have been used most extensively in helicopters. Sikorsky s S-75 helicopter, for example, is about 25% composite by weight, mostly graphite-epoxy and aramid-epoxy composite materials. Composites are used in rotors, blades, and tail assemblies. Future military helicopters are likely to comprise up to 80% advanced composites by structural weight. Graphite-epoxy composites are likely to be used in the airframe, bulk-heads, tail bones, and vertical fins, while the less stiff glass-epoxy composites will be used in rotor systems. 

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