Figure 3-5

CHAPTER 3

HELICOPTER AERODYNAMICS WORKBOOK

TORQUE

The next major force we will discuss affecting the fuselage is torque. As the main rotor

blades rotate, the fuselage will rotate the opposite direction if unopposed. An antitorque system

is necessary to counteract this rotational force. This system must generate enough thrust to

counteract main rotor torque in climbs, directional control at this high power setting, and

sufficient directional control in autorotation and low speed flight. Available types are the

conventional system, fenestron (fan-in-fin), and NOTAR (fan-in-boom). When a helicopter

incorporates two main rotor systems, like the CH-46, rotating the systems in opposite directions,

effectively equalizing the torque from each system, compensates for the torque effect. We will

focus on the conventional system (figure 3-5).

Figure 3-5

A conventional system requires little power, produces good yaw control, and works just like

the main rotor system. Since the tail rotor is subject to the same drag forces, power is required to

overcome these forces. Therefore, different pitch angles on the tail rotor blades require different

power settings. As pitch angle is increased, power required will increase.

Figure 3-6

3-6 HELICOPTER POWERED FLIGHT ANALYSIS