so absorbing my last post, here's my conclusion.
increased temperature explains why a plane apparently experiences less resistance and hence can go faster (measured in knots) at lower altitudes. i guess the gases in air gain mobility when they are warmer. whereas they are more viscous when they are colder. so the plane can push air aside more easily at low altitudes even though it encounters more of it.
in terms of thrust, i imagine having more air flowing through the jet engine gives the plane relatively more power (net of drag). so my guess is the engines also can make the plane go faster at sea level than up high. on the other hand, maybe the air flow at lower levels also causes engine perturbation and heat. indeed, it is also hotter at sea level. which would explain the lower operating speed limits imposed by the manufacturers. a hotter engine deteriorates more quickly. metal is liable to bend etc.
this would mean the break up speed limit is defined in terms of the aircraft frame. and the operating speed limit is defined in terms of the engine.
okay. that concludes my discussion of aeronautics or is it avionics.
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