text: angle of the surface must be sufficiently great 
  to prevent stall and subsequent loss of effec- 
  tiveness at ordinary sideslip angles. The high 
  Mach numbers of supersonic flight produces a 
  decrease in lift curve slope with the consequent 
  reduction in tail contribution 
  In 
  order to have sufficient directional stability at 
  high Mach numbers, the typical supersonic 
  large 
  exhibit 
  configuration will 
  vertical tail surfaces. 
  
  greater aerodynamic force and, generally, a 
  continued destabilizing influence. 
  
  Figure 4.23 illustrates a typical buildup of 
  the directional stability of an airplane by 
  separating the contribution of the fuselage 
  and tail. As shown by the graph of C. versus 
  6, the contribution of 
  the fuselage is de- 
  stabilizing but 
  instability decreases at 
  large sideslip angles. Tbe contribution of the 
  vertical tail alone is highly stabilizing up to 
  the point where the surface begins to stall. 
  The contribution of the vertical tail must be 
  the complete airplane 
  large enough so that 
  (wing-fuselage-tail combination) exhibits the 
  required degree of stability. 
  
  relatively 
  
  tail 
  operates is affected by the othei components 
  of the airplane as well as powe; effects. The 
  dynamic pressure at the vertical 
  tail could 
  depend on the slipstream of a propeller or the 
  boundary layer of the fuselage. Also, 
  the 
  is in- 
  local flow direction at the vertical tail 
  fluenced by the wing wake, fuselage crossflow, 
  induced flow of the horizontal 
  tail, or the 
  direction of slipstream from a propeller. Each 
  of these factors must be considered as possibly 
  affecting the contribution of the vertical tail 
  to directional stability. 
  
  The flow  field in which  the vertical 