text: A summation of the forces acting perpen- 
  dicular to the plane of rotation (tip path plane) 
  will determine the rotor thrust (or lift) char- 
  acteristics while summation of the moments 
  resulting from forces acting in the plane of 
  rotation will determine the rotor torque char- 
  acteristics. As a result of this analysis, the 
  rotor thrust (or lift) 
  is found to be propoc- 
  tional to the air density, a nondimensional 
  thrust coefficient, and the square of the tip 
  speed, or linear speed of the tip of the blade. 
  The thrust coefficient is a function of the aver- 
  age blade section lift coefficient and the rotor 
  solidity, which is the proportion of blade area 
  to disc area. The lift coefficient is identical to 
  that used in airplane aerodynamics while the 
  solidity is analagous to the aspect ratio in air- 
  plane aerodynamics. The 
  is 
  found to be proportional to a nondimensional 
  torque coefficient, the air density, the disc 
  area, the square of the tip speed, and the blade 
  radius. The torque coefficient is dependent 
  upon the average profile drag coefficient of the 
  blades, the blade pitch angle, and the average 
  lift coefficient of the blades. The torque can 
  be thought to result from components of profile 
  and induced drag forces acting on the blades, 
  similar to those on an airplane. 