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). 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. Translating Tendency (Drift) 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  Figure 2-27.  A tail rotor is designed to produce thrust in a direction  opposite torque. The thrust produced by the tail rotor is sufficient  to move the helicopter laterally.  2-15 $_{ }$B $_{l}$a d e r o t a tio n  B la d e r o t a t i o n Drift Tail rotor thrust Tail rotor downwash T o r q u e T o r q u e •  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. 