text: stability. As shown in figure 4.17, a down- 
  spring consists of a long preloaded spring at- 
  tached to the control system which 
  tends to 
  rotate the elevators down. The effect of the 
  downspring is to contribute an increment of 
  pull force independent of control deflection or 
  airspeed. When rhe downspring is added to 
  the control system of an airplane and the air- 
  plane is retrimmed for the original speed, the 
  airspeed stick force gradient is increased and 
  there is a stronger feel for airspeed. The down- 
  spring would provide an “ersatz” 
  improve- 
  ment to an airplane deficient in airspeed stick 
  force stability, Since the force increment from 
  the downspring is unaffected by stick position 
  or normal acceleration, the maneuvering stick 
  force stability would be unchanged. 