text: propellers is obtained by rotating 
  the blade 
  angle well below the low pitch stop and 
  applying engine power. The action is to ex- 
  tract a large amount of momentum from the 
  airstream and thereby create negative thrust. 
  The magnitude of the reverse thrust from pro- 
  pellets is very large, especially in the case of 
  the turboprop where a very large shaft power 
  can be fed into the propeller. 
  In the case of 
  reverse propeller thrust, maximum effective- 
  ness is achieved by use immediately after the 
  the runway. The 
  airplane is in contact with 
  reverse thrust capability 
  the 
  is greatest at 
  high speed and, obviously, any delay in pro- 
  ducing deceleration allows runway to pass by 
  at a rapid rate. Reverse thrust of turbojet 
  engines will usually employ some form of 
  vanes, buckets, or clamshells in the exhaust to 
  turn or direct 
  the exhaust gases forward. 
  Whenever the exit velocity is less than the in- 
  let velocity (or negative), a negative momen- 
  tum change occurs and negative thrust 
  is 
  produced. The reverse jet thrust is valuable 
  and effective but it should not be compared 
  with 
  the reverse thrust capability of a com- 
  parable propeller powerplant which has the 
  thrust at low velocities. As 
  high 
  jet reverse 
  with 
  thrust must be applied 
  immediately after 
  ground contact for maximum effectiveness in 
  reducing landing distance. 