View Full Version : Mcrit over wings or not?

4th Feb 2008, 17:16
In my books they talk of Mcrit as point on the WINGS where airflow reaches M1.0. However on an aircraft like the 747 airflow will reach M1.0 over the hump before the wings.

So is:

Mcrit the speed when airflow over a point on the WINGS reach M1
Mcrit is the speed when airflow over a ANY point on the aircraft reaches M1.


David Horn
4th Feb 2008, 20:34
My understanding is that Mcrit is the highest speed at which no parts of the aircraft are supersonic. So in the context of this definition it wouldn't really matter whether the first part to go supersonic is the wing, or in the case of the 747, the hump.

Brian Abraham
4th Feb 2008, 23:04
Extensive discussion here by people who have some grip on the subject http://www.pprune.org/forums/showthread.php?t=83506

Post #29 by Flamgat in the above thread includes Boeings definition

"Critical Mach number is a term aerodynamicists use to quickly compare the "drag rise" or "compressibility drag" of several wing design alternatives. At Boeing, we define critical Mach number as the Mach number, at a constant lift coefficient, where the drag coefficient is 20 counts greater than the drag coefficient at the incompressible Mach number."

Mad (Flt) Scientist
5th Feb 2008, 01:19
I suspect it could legitimately be used to mean anything, depending on how it was phrased.

"Mcrit" of the aircraft
"Mcrit" of the wing (3d)
"Mcrit" of the section (2d)

And so on...

It doesn't really have much importance as a practical concern, once the design has started, anyway....