"The Natural Philosopher" wrote in message
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On 30/05/2021 23:56, Joey wrote:


"Vir Campestris" wrote in message
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On 28/05/2021 20:02, Joey wrote:


"The Natural Philosopher" wrote in message
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On 27/05/2021 20:59, Vir Campestris wrote:
but those are not really affected by any changes in engine
'efficiency'
In reality long haul airliners fly quite close to 'coffin corner'
slightly above stall speed

A long way above stall speed actually.

and slightly below mach 1 at as high an
altitude as they can because that reduces drag.
snip

I tried and failed to find a reference for that.

Given that an airliner's stall speed clean is over 150kt (easily found)
and the air pressure at cruising height is under a quarter that at sea
level (also easily found) I would expect them to be fairly close.

They arent, for a reason, FAR too dangerous.

Well they are : from 150kt to 450kt at ground level, you are up to 250kt
at say 40,000ft, and the speed of sound has come down.

2:1 ratio as you say in another isnt anything like fairly close.