Milt, Yes I meant C of P, as in “high subsonic flight (actually transonic would be a better term) will give an aft movement in C of P, not C of G. thanks, and I corrected the post.
Herc Jerc, we seem to have some different understandings.
1. the buffet from flying above M crit is actually almost non existent at speeds slightly above m crit. Its once the shock get strong enough that it causes flow separation that mach buffet becomes a problem. Hence, Mmo is well above M crit, for most wing designs we see today.
2. Mack tuck would occur, if at all, above M crit. And when local flow just starts to become sonic, this is the definition of the beginning of transonic flight. If DP Davies says otherwise, please quote. I don’t have his book, and if this is wrong I’d like to know.
3. I can certainly imagine an airliner cruising above M crit. With third generation supercritical wings, the drag associated with flight above the M crit does not increase like non supercritical wings. Minimum fuel cost does not drive the choice of cruise speeds, even at $40 a barrel.
Milt, your quote “So over time M crit has become that Mach No at which there is a sharp increase in drag and a need to substantially increase thrust to go faster.”
That mach is known as the drag divergent mach number. M crit has always been where first sonic, or M1.0 flow occurs locally, somewhere. The sharp increase in drag occurs at various speeds above M crit, depending on the aerodyamics. As I said earlier above, supercritical wings were able to delay the increase in drag, allowing higher cruise speeds before this significant drag rise.
Hawk