text: The power-boosted control system employs a 
  ‘mechanical actuator 
  the 
  mechanical linkages of a conventional control 
  system. The principle of operation is to pro- 
  vide a fixed, percentage of the required control 
  forces thus reducing control 
  forces at high 
  speeds. The power-boosted control system 
  requires a hydraulic actuator with a control 
  valve which supplies boost force in 
  fixed 
  proportion 
  to control force. Thus, the pilot 
  is given an advantage by the boost ratio to 
  assist in deflecting the control surface, e.g., 
  with a boost ratio of 14, the actuator provides 
  14 lbs. of force for each 1 lb. of stick force. 
  The power-boosted control system has the 
  obvious advantage of reducing control forces 
  at high speeds. However, at transonic speeds, 
  forces due to shock 
  the changes in control 
  waves and separation still take place but to a 
  lesser degree. The 
  of hinge 
  moments is reduced but the aberrations in 
  stick forces may still exist. 
  
  in parallel with 
  
  The gearing between the stick position and 
  control surface deflection is not necessarily a 
  linear relationship. The majority of powered 
  control systems will employ a nonlinear gear- 
  ing such that relatively greater stick deflection 
  per surface deflection will occur at the neutral 
  This sort of gearing is to 
  stick position. 
  advantage for airplanes which operate at flight 
  conditions of high dynamic pressure. Since 
  the airplane at high 4 is very sensitive to small 
  deflections of the control surface, the nonlinear 
  gearing provides higher stick force stability 
  with 
  less sensitive control movements than 
  the ‘system with a linear gearing. Figure 4.21 
  illustrates a typical linear and nonlinear control 
  system gearing. 
  The power-opsrdted, irreversible control system 