and flexibility exist, flutter could occur at 
flight speeds below the limit airspeed. 
Compres&ility pmblems may define the limit 
airspeed for an airplane in terms of Mach num- 
ber. The supersonic airplane may experience 
a great decay of stability at some high Mach 
number or encounter critical structural or 
engine inlet temperatures due to aerodynamic 
heating. The transonic airplane at an excessive 
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