text: At smaller blade angles near the Rat pitch 
  position, the drag added by the propeller is 
  very large. AC these small blade angles, the 
  propeller windmilling at high RPM can create 
  such a tremendous amount of drag that the 
  airplane may be uncontrollable. The propel- 
  ler windmilling at high speed in the low range 
  of blade angles can produce an increase in para- 
  site drag which may be as great as the parasite 
  drag of the basic airplane. An indication of 
  this powerful drag is seen by the hclieopter in 
  is ca- 
  autorotation. The windmilling 
  pable of producing autorotation rates ofdcscent 
  which approach that of a parachute canopy 
  with 
  the propeller windmilling at high speed and 
  small blade angle can produce an 
  drag coefficient of the disc area which compares 
  tha~t of a parachute canopy. The drag 
  with 
  and yawing moment caused by loss of power 
  at high engine-propeller speed is considerable 
  and the transient yawing displaccmcnt of the 
  loads for the 
  aircraft’ may produce critical 
  reason, automatic 
  vertical 
  this 
  feathering may be a necessity rather than a 
  luxury. 