HELICOPTER AERODYNAMICS WORKBOOK
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,
focus on the conventional system (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.
3-6 HELICOPTER POWERED FLIGHT ANALYSIS