Originally Posted by
DC-8
the heavier aircraft would require more thrust for a given speed, so this would also increase VMC, wouldn't it?
No. VMC is demonstrated and calculated for a defined thrust level; whether the aircraft NEEDS that much thrust for level flight, or any other purpose isn't an issue.
What would happen in a test/demonstration is that you'd set the thrust per the test definition, then adjust climb/dive angle to maintain the target speed. Since VMC is usually tested at light weights, you can end up in quite a nose-high attitude trying to hold the speed constant. (To the extent that the so-called "dynamic VMCA" demonstration actually allows a relaxation of the demonstration conditions, to avoid having to go to dangerously high attitudes)