In sideward flight, the tip-path plane is tilted sideward in the  direction that flight is desired, thus tilting the total lift-thrust  vector sideward. In this case, the vertical or lift component  is still straight up, weight straight down, but the horizontal  or thrust component now acts sideward with drag acting to  the opposite side.  For rearward flight, the tip-path plane is tilted rearward and  tilts the lift-thrust vector rearward. The thrust is then rearward  and the drag component is forward, opposite that for forward  flight. The lift component in rearward flight is straight up;  weight, straight down.  Newton’s third law of motion states “To every action there  is an equal and opposite reaction.” As the main rotor of a  helicopter turns in one direction, the fuselage tends to rotate  in the opposite direction. This tendency for the fuselage to  rotate is called torque. Since torque effect on the fuselage is  a direct result of engine power supplied to the main rotor,  any change in engine power brings about a corresponding  change in torque effect. The greater the engine power, the  greater the torque effect. Since there is no engine power  being supplied to the main rotor during autorotation, there  is no torque reaction during autorotation.  The force that compensates for torque and provides for  directional control can be produced by various means. The  defining factor is dictated by the design of the helicopter,  some of which do not have a torque issue. Single main  rotor designs typically have an auxiliary rotor located on  the end of the tail boom. This auxiliary rotor, generally  referred to as a tail rotor, produces thrust in the direction  opposite the torque reaction developed by the main rotor.  [Figure 2-25]  Foot pedals in the flight deck permit the  pilot to increase or decrease tail rotor thrust, as needed, to  neutralize torque effect.  Other methods of compensating for torque and providing  directional control include the Fenestron$^{®}$ tail rotor system,  an SUD Aviation design that employs a ducted fan enclosed  by a shroud. Another design, called NOTAR$^{®}$, a McDonald  Douglas design with no tail rotor, employs air directed  through a series of slots in the tail boom, with the balance  exiting through a 90° duct located at the rear of the tail boom.  [Figure 2-28] The spinning main rotor of a helicopter acts like a gyroscope.  As such, it has the properties of gyroscopic action, one of  which is precession. Gyroscopic precession is the resultant  action or deflection of a spinning object when a force is  applied to this object. This action occurs approximately 90°  in the direction of rotation from the point where the force  is applied.  [Figure 2-29]  Through the use of this principle,  the tip-path plane of the main rotor may be tilted from the  horizontal.  Gyroscopic Forces Torque Compensation Figure 2-28.  Aerospatiale Fenestron tail rotor system (left) and the McDonnell Douglas NOTAR$^{®}$ System (right). 2-19