text: just above the speed of sound only slight modi- 
  fications to ordinary subsonic inlet design pro- 
  duce satisfactory performance. However, at 
  supersonic flight speeds, the inlet design must 
  slow the air with the weakest possible series-or 
  combination of shock waves to minimize en- 
  ergy losses and temperature rise. Figure 3.20 
  illustrates some of the various forms of super- 
  sonic inlets or “diffusers.” 
  
  create very large changes in control surface 
  hinge moments. Such large changes in hinge 
  moments create very undesirable control forces 
  and present the need for an “irreversible” 
  con- 
  trol system. An irreversible control. system 
  would employ powerful hydraulic or electric 
  actuators to move the surfaces upon control by 
  the pilot and the airloads developed on the 
  surface could not feed back to the pilot. Of 
  course, suitable control forces would be syn- 
  thesized by bungees, “4” springs, bobweights, 
  etc. 
  
  One of the least complicated types of inlet 
  is the simple normal shock type diffuser. This 
  type of inlet employs a single normal shock 
  wave at the inlet with a subsequent internal 
  subsonic compression. At low supersonic Mach J 
  numbers the strength of the normal shock wave 
  is not too great and this type of inlet is quite 
  practical. At higher supersonic Mach num- 
  bers, the single normal shock wave is very 
  strong and causes a great reduction in the total 
  In addition, 
  pressure recovered by the inlet. 
  the wasted 1 
  it 
  energy of the airstream will appear as an addi- 
  tional undesirable rise in temperature of the 
  captured inlet airflow. 