text: Since the only control forces are those of the 
  tab, this device makes possible the deflection 
  of large surfaces with relatively small control 
  forces. 
  
  A variation of the basic servo tab layout is 
  figure 4.18. 
  the sprirzg tab arrangement of 
  When the control horn is connected to the 
  control surface by springs, the function of the 
  tab is to provide a given portion of the required 
  control forces. The spring tab arrangement 
  can then function as a boost to reduce control 
  forces. The servo tab and spring 
  tab are 
  usually applied to large or high speed subsonic 
  airplanes to provide tolerable stick forces. 
  
  CONTROL REQUIRE- 
  MENT. 
  The airplane should have sufficient 
  longitudinal control power to attain the maxi- 
  mum usable lift coefficient or limit 
  load factor 
  during maneuvers. As shown in figure 4.19, 
  forward movement of the c.g. increases the 
  of an airplane and 
  longiturjinal 
  requires larger control deflections to produce 
  changes in 
  the 
  example shown, the maximum effective de- 
  flection of the elevator is not capable of trim- 
  ing the airplane ‘at C,,,, 
  for c.g. positions 
  ahead of 18 percent MAC. 