*** Posted by kim ***
[I am well aware that you are talking about the SUDDEN appearence of the airnoise around the plane. Please tell me why are you facinated by this phenomina?
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Facination is not the right word. Morely: an interrest in the technics behind the suddennes of the airnoise.
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.......That's the loudest plane I've been on but I did not remember any distinct noises around the plane caused by drag too much on take off. Infact I think the noise you are refering to may be caused by the flaps in the take off position, after a short while they are retracted.
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Flaps should be most noisy during use, and in that way it should be more silent when they gets retracted under the climb, wich is opposite to my experiences.

Obviously, the noiselevel caused by air passing the plane, will rise with the speed of the plane, and one could expect to hear the sound of passing air relatively early (a couple of houndred km/t's?), and there after increase more or less quick towards the highest peak at top travelling speed.
However it is my experience that the airnoise do appear relatively late in the acceleration and rises to its toplevel very quick, whereafter it stays for the rest of the acceleration and flight.- Strange to me!

Does it happen in the same way around mach 1 and the "sonic boom" (the boom appears quite sudden and is hard to pass (while it dosnt rise in level thereafter)???

Kim Nielsen.