text: NAVWEPS 00-601-60 
  HIGH SPEED AERODYNAMICS 
  
  in pressure without apparent changes in den- 
  sity. Such a condition of airflow is analogous 
  to the flow of water, hydraulic fluid, or any 
  other incompressible fluid. However, at high 
  flight speeds the pressure changes that 
  take 
  place are quite large and significant changes 
  in air density occur. The study of airflow at 
  high speeds must account for these changes 
  the 
  there will be  1 in air density and must consider that 
  1 air  is compressible and that 
  
  “compressibility effects.” 