Why does COP move aft, mach tuck?

[Raskolnikov]

I understand that mach tuck is caused by the COP moving aft at/above mach crit.

I'm having a hard time finding a source explaining what causes the aft movement of the COP at and above mach crit.

Some explanations I've come across:
1. The shock wave starts at the leading edge and moves aft over the upper camber, pushing the COP aft.

2. The increase in airspeed above mach crit causes an increase in the lift vector, since AS is part of the lift equation. This increase in the lift vector increases the nose down force. This increased lift vector is pushed aft by the shockwave, increasing the moment arm between the CG and COP, causing an increase in nose down force.
(So if #1 and/or #2 is correct is there no lift forward of the shock wave?)

3. The shockwave itself causes an increase in lift; suggesting a large increase in lift in front of the shock wave.

#3 was given with no explanation as to how. If this one is true wouldn't it be theoretically possible to experience mach tuck without aft movement of the COP? Just increase the Lift vector significantly forward of the shockwave with no movement of the COP and the nose would go down? This would even make it possible for a forward movement in COP and mach tuck if the increase in lift forward of the shockwave was significant enough.

Can someone please explain the aft movement of COP at mach tuck and site a good reference?

 

[BobDDuck]

I'm digging WAY back in my memory here but I'm pretty certain the center of pressure moves back at speeds below mach crit as well. Mach crit is simply the point where the pressure is so far back on the wing that without secondary measure (mach trim ect) it's not possible to prevent mach tuck. That said the explanation is simple when you look at it that way: Laminar flow separation rejoins further back on the wing at higher airspeeds.

But then again, I'm going from memory of about 12 years ago.

 

[Mike Massimini]

It's "1", above - although it's a bit more complicated sometimes (I'm reaching "way back myself - 1975/76 fluid mechanics ). BTW, "3" would move COP forward.

 

[Raskolnikov]

Thanks! Number seems to make the most sense.

 

[cime_sp]

Best way I understood it was since wing is thickest at the root and camber is greatest there, Mach Critical is reached there first. This causes a lowering of lift inboard and Center of lift moves outboard. Since the wing sweeps back as it moves outboard this causes CL to move rearward and Mach tuck to occure.