text: Once the configuration of a transonic air- 
  craft is fixed, the pilot must respect the effect 
  of angle of attack and altitude. The local flow 
  1 velocities on any upper surface increase with an 
  increase in angle of attack. Hence, local sonic 
  flow and subsequent shock wave formation 
  can occur at lower free stream Mach numbers. 
  A pilot must appreciate this reduction of force 
  divergence Mach number with 
  lift coefficient 
  since maneuvers at high speed may produce 
  compressibility effects which may not be en- 
  countered in unaccelerated flight. The effect 
  of altitude 
  is important since the magnitude 
  of any force or moment change due to com- 
  pressibility will depend upon the dynamic 
  pressure of 
  the airstream. Compressibility 
  effects encountered at high altitude and low 
  dynamic pressure may be of little consequence 
  in the operation of a transonic aircraft. How- 
  the same compressibility effects en- 
  ever, 
  countered at low altitudes and high dynamic 
  pressures will 
  create greater trim changes, 
  heavier buffet, etc., and perhaps transonic 
  flight restrictions which are of principal inter- 
  est only to low altitude. 
  
  can be quite weak, the pressure waves can be 
  of sufficient magnitude to create an audible 
  disturbance. Thus, “sonic booms” will be a 
  simple consequence of supersonic flight. 
  
  The aircraft powerplant: for supersonic flight 
  must be of relatively high 
  thrust output. 
  Also, in many cases it may be necessary to 
  provide the air breathing powerplant with 
  special inlet configurations which will slow 
  the airflow to subsonic prior to reaching the 
  compressor face or combustion chamber. Aero- 
  dynamic heating of supersonic flight can pro- 
  vide critical 
  the gas 
  turbine engine as well as critical structural 
  temperatures. 
  
  The density variations in airflow may be 
  shown by certain optical techniques. Schlieren 
  photographs and shadowgraphs can define the 
  various wave patterns and their effect on the 
  airflow. The Schlieren photographs presented 
  in figure 3.11 define the flow conditions on an 
  aircraft in supersonic flight. 
  I 