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To counteract this drift, one or more of the following features may be used: 

• The main transmission is mounted so that the rotor mast is rigged for the tip-path plane to have a built- in tilt opposite tail thrust, thus producing a small sideward thrust. 

• Flight control rigging is designed so that the rotor disc is tilted slightly opposite tail rotor thrust when the cyclic is centered. 

• The cyclic pitch control system is designed so that the rotor disc tilts slightly opposite tail rotor thrust when in a hover. 

Counteracting translating tendency, in a helicopter with a counterclockwise main rotor system, causes the left skid to hang lower while hovering. The opposite is true for rotor systems turning clockwise when viewed from above. 

## PENDULAR ACTION 

Since the fuselage of the helicopter, with a single main rotor, is suspended from a single point and has consider- able mass, it is free to oscillate either longitudinally or laterally in the same way as a pendulum. This pendular action can be exaggerated by over controlling; therefore, control movements should be smooth and not exagger- ated. [Figure 3-3] 

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## CONING 

In order for a helicopter to generate lift, the rotor blades must be turning. This creates a relative wind that is opposite the direction of rotor system rotation. The rotation of the rotor system creates centrifugal force (inertia), which tends to pull the blades straight outward from the main rotor hub. The faster the rotation, the 

greater the centrifugal force. This force gives the rotor blades their rigidity and, in turn, the strength to support the weight of the helicopter. The centrifugal force gen- erated determines the maximum operating rotor r.p.m. due to structural limitations on the main rotor system. 

As a vertical takeoff is made, two major forces are act- ing at the same time—centrifugal force acting outward and perpendicular to the rotor mast, and lift acting upward and parallel to the mast. The result of these two forces is that the blades assume a conical path instead of remaining in the plane perpendicular to the mast. [Figure 3-4] 

<img src='content_image/584687.jpg'>

## CORIOLIS EFFECT (LAW OF CONSERVATION OF ANGULAR MOMENTUM) 

Coriolis Effect, which is sometimes referred to as con- servation of angular momentum, might be compared to spinning skaters. When they extend their arms, their rotation slows down because the center of mass moves farther from the axis of rotation. When their arms are retracted, the rotation speeds up because the center of mass moves closer to the axis of rotation. 

When a rotor blade flaps upward, the center of mass of that blade moves closer to the axis of rotation and blade acceleration takes place in order to conserve angular momentum. Conversely, when that blade flaps down- ward, its center of mass moves further from the axis of 

Centrifugal Force—The apparent force that an object moving along a circular path exerts on the body constraining the obect and that acts outwardy away from the cen- ter of rotation. 

