text: The dorsal fin has a powerful effect on pre- 
  serving the directional stability at large angles 
  of sideslip wliich would produce stall of the 
  vertical tail. The addition of a dorsal fin to 
  the airplane will allay the decay of directional 
  stability at high sideslip in two ways. The 
  least obvious but most important effect is a 
  large increase in the fuselage stability at large 
  the effective 
  sideslip angles. 
  aspect rario of the vertical 
  is reduced 
  which increases the stall angle for the surface. 
  twofold effect, the addition of the 
  By this 
  dorsal fin is a v 
  
  In addition, 
  
  tail 
  
  useful’ device. 
  
  Poluer effects on static directional stability 
  the power effects on static 
  are similar 
  The direct effects are 
  longitudinal stability. 
  confined to the normal force at the propeller 
  plane or the jet inlet and, of course, are de- 
  stabilizing when 
  is 
  located ahead of the c.g. The indirect effects 
  of power induced velocities and flow dirkccion 
  changes at the vertical tail are quite significant 
  for the propeller driven airplane and can pro- 
  duce large directional 
  trim changes. As in 
  the lontitudinal case, the indirect effects are 
  negligible for the jet powered airplane. 