text: exist in both compressible and incompressible 
  cases. 
  
  It is important to note that compressibility 
  effects are not limited to flight speeds at and 
  above the speed of sound. Since any aircraft 
  will have some aerodynamic shape and will 
  be developing lift 
  there will be local flow 
  velocities on the surfaces which arc greater 
  than the flight speed. Thus, an aircraft can 
  flight 
  experience compressibility effects at 
  speeds well below the speed of sound. Since 
  there is the possibility of having both subsonic 
  and supersonic flows existing on the aircraft 
  it 
  is convenient to define certain regimes of 
  flight. These regimes are defined approxi- 
  mately as follows: 
  
  The example of subsonic incompressible flow 
  is simplified by the fact that the density of 
  flow is constant throughout the tube. Thus, 
  as the flow approaches a constriction and the 
  streamlines converge, velocity 
  increases and 
  static pressure decreases. In other words, a 
  convergence of the tube requires an increasing 
  velocity 
  to accommodate the continuity of 
  flow. Also, as the subsonic incompressible 
  flow enters a diverging section of the tube, 
  velocity decreases and static pressure increases 
  but density remains unchanged. The behavior 
  of subsonic incompressible flow is that a con- 
  vergence causes expansion (decreasing pressure) 
  while a divergence causes compression (in- 
  creasing pressure). 
  
  Subsonic-Mach numbers below 0.75 
  Transonic-Mach  numbers from 0.75 to 
  
  1.20 
  
  Supersonic-Mach numbers from 1.20 to 