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landing gear. Throughout the rest of this discussion, the term “drag” includes induced, profile and parasite drag. 

An important consequence of producing thrust is torque. As discussed earlier, Newton’s Third Law states: for every action there is an equal and opposite reaction. Therefore, as the engine turns the main rotor disk in a counterclockwise direction, the helicopter fuselage wants to turn clockwise. The amount of torque is directly related to the amount of engine power being used to turn the main rotor disk. As power changes, torque changes. 

To counteract this torque-induced turning tendency, an antitorque rotor or tail rotor is incorporated into most helicopter designs. A pilot can vary the amount of thrust produced by the tail rotor in relation to the amount of torque produced by the engine. As the engine supplies more power to the main rotor, the tail rotor must produce more thrust to overcome the increased torque effect. This control change is accomplished through the use of antitorque pedals (See page 3-4). 

## Translating Tendency (Drift) 

During hovering flight, a single main rotor helicopter tends to move in the direction of tail rotor thrust. This lateral (or sideward) movement is called translating tendency. [Figure 2-27] 

To counteract this tendency, one or more of the following features may be used. All examples are for a counterclockwise rotating main rotor disk. 

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• The main transmission is mounted at a slight angle to the left (when viewed from behind) so that the rotor mast has a built-in tilt to oppose the tail rotor thrust. 

• Flight controls can be rigged so that the rotor disk is tilted to the left slightly when the cyclic is centered. Whichever method is used, the tip-path plane is tilted slightly to the left in the hover. 

• The transmission is mounted so the rotor shaft is vertical with respect to the fuselage, the helicopter “hangs” left skid low in the hover. (The opposite is true for rotor disks turning clockwise when viewed from above.) 

• The helicopter fuselage will also be tilted when the tail rotor is below the main rotor disk and supplying antitorque thrust. The fuselage tilt is caused by the imperfect balance of the tail rotor thrust against the main rotor torque in the same plane. The helicopter tilts due to two separate forces, the main rotor disk tilt to neutralize the translating tendency and the lower tail rotor thrust below the plane of the torque action. 

• In forward flight, the tail rotor continues to push to the right, and the helicopter makes a small angle with the wind when the rotors are level and the slip ball is in the middle (See page 12-2). This is called inherent sideslip. For some larger helicopters, the vertical fin or stabilizer is often designed with the tail rotor mounted on them to correct this side slip and to eliminate some of the tilting at a hover. (By mounting the tail rotor on top of the vertical fin or pylon, the antitorque is more in line with or closer to the horizontal plane of torque, resulting in less airframe (or body) lean from the tail rotor.) Also, having the tail rotor higher off the ground reduces the risk of objects coming in contact with the blades, but at the cost of increased weight and complexity. 

## Pendular Action 

Since the fuselage of the helicopter, with a single main rotor, is suspended from a single point and has considerable mass, it is free to oscillate either longitudinally or laterally in the same way as a pendulum. This pendular action can be exaggerated by overcontrolling; therefore, control movements should be smooth and not exaggerated. [Figure 2-28] 

The horizontal stabilizer helps to level the helicopter in forward flight. However, in rearward flight, the horizontal stabilizer can press the tail downward, resulting in a tail strike if the helicopter is moved rearward into the wind. Normally, with the helicopter mostly into the wind, the horizontal stabilizer experiences less headwind component as the helicopter begins rearward travel (downwind). When 

