text: destabilizing and the greatest contribution 
  will occur at high power and low dynamic 
  pressure as during a waveoff. 
  
  As in the case of longitudinal static stability, 
  freeing the controls will 
  reduce the effective- 
  ness of the tail and alter the stability. While 
  the rudder must be balanced to reduce control 
  pedal forces, the rudder will 
  tend to float or 
  streamline and reduce the contribution of the 
  vertical tail to static directional stability. The 
  floating tendency is greatest at large angles of 
  sideslip where large angles of attack for the 
  vertical tail tend to decrease aerodynamic bal- 
  ante. Figure 4.24 illustrates the difference be- 
  tween rudder-fixed and rudder-free static di- 
  rectional stability. 
  
  High Mach ntrmbers of supersonic flight reduce 
  the contribution of the vertical tail to direc- 
  tional stability because of the reduction of lift 
  cnrve slope with Mach number. The third 
  chart of figure 4.24 illustrates the typical decay 
  of directional stability with Mach number. To 
  produce the required directional stability at 
  high Mach numbers, a viziy large vertical tail 
  area may be necessary. Ventral fins may be 
  added as an additional contribution 
  to direc- 
  tional stability but landing clearance require- 
  ments may limir their size or require the fins to 
  be retractable. 