Where Mmo, or the mach operating limit applies at altitude, of course Vmo applies at lower levels. Flutter may be a consideration, but with non-reversible controls, not so likely.
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You can push up the power if you like, but you do have aircraft limitations to consider before you go too far.
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To paraphrase CONFiture, if I firewall the throttles at low level (clean config, obviously) in a typical modern airliner, what's the envelope wall I'll hit? Is it indeed flutter?
So ... we don’t really know what’s happening … and what we could encounter ?
But the risk looks serious enough that Airbus put in place the High Speed Protection in order to prevent any uncommanded as well as commanded (!) excessive exceeding ...
Their words still remain a bit vague:
There is an increased potential for aircraft control difficulties and structural concerns, due to high air loads
Should we consider that control difficulties would be reached
before structural concerns … ?
If so, where would be that limit in term of exceeding VMO + ?
No pressure to answer that question which is obviously over stretched for a day to day operation.
Just my own curiosity.