"dominik lenné" wrote in
:

Hi,

I wonder whether the lift over resistance coefficient diagram (aka
polar diagram or lilienthal diagram) of a given airplane changes much
with altitude.

The rationale behind the question is, that I read somewhere, that
commercial aircraft are flying in the so called "coffin corner", that
is so high they can't go faster because of compression and can't go
slower because of stall.

Why should they do this, when they could well be a little lower and
comfortly fly at the point of optimal angle of access, well away from
stall.

Do optimal point and stall point come closer together with increasing
height?





Are you sure you are refering to commercial aircraft ?

sure sounds as if you thinking of the U-2 with its VERY narrow
flight envelope at close to max.