text: “Inertia coupling” problems are relatively 
  new to fixed-wing aircraft but a similar effect 
  in the helicopter rotor has resulted in some 
  of its most important characteristics. This 
  aerodynamic-dynamic coupling effect is so im- 
  portant that it must be considered in discussing 
  both stability and control. The helicopter 
  derives both longitudinal and lateral control 
  by tilting 
  the main rotor and thus producing 
  a pltchmg or rolling moment as indicated in 
  figure 4.35. The magnitude of the rotor thrust 
  the angle of tilt, and the height of the rotor 
  hub above the c.g. determine the control 
  moment produced. 
  It should be noted that 
  low control effectiveness would result when 
  is low. Some helicopters 
  the rotor 
  
  with 
  lowing 
  problem of roll coupling: 
  
  (ZZ) Increase directional stability. 
  (b) Reduce dihedral effect. 
  (c) M’  h  1‘  mnmze t e mc mation of the inertia 
  
  axis at normal flight conditions. 
  
  undesirable  (d) Reduce  aerodynamic 
  
  coupling. 
  
  rate, roll duration, and 
  angle of attack or load factor for performing 
  rolling maneuvers. 
  
  (e) Limit  roll 
  
  thrust 