text: NAVWEPS DO-ROT-80 
  APPLICATION OF AERODYNAMICS 
  TO SPECIFIC PROBLEMS OF FLYING 
  
  usually means remaining over a particular 
  spot on the ground, it shall be considered 
  here as flight at zero airspeed. This is necessary 
  because the aerodynamic characteristics of the 
  rotor depend on its motion with 
  respect to 
  the air and not the ground. Hovering in a 20 
  knot wind 
  is aerodynamically equivalent to 
  flying at an airspeed of 20 knots in a no-wind 
  condition, and the characteristics will 
  be 
  identical in the two conditions. 
  
  Thus, the velocity due to rotation varies line- 
  arly from zero at the hub to a maximum at 
  the 
  the tip. A 
  forces acting on it is shown in figure 6.15. 
  
  typical blade section with 
  
  The first point to realize is that the rotor is 
  subject to the same physical laws of aero- 
  that govern flight of 
  dynamics and motion 
  the fixed-wing airplane. The manner in which 
  the rotor is subject to these laws is much more 
  complicated due to the complex flow con- 
  ditions. 