Capt. Pit Bull-
The Vmca will vary quite a bit with different factors. It is given as a reference speed in many manuals so as to provide the flight crew with SOME speed to use. The actual Vmca will vary with CG location, temperature and pressure altitude, and with assumed temp thrust or derates.
Gary- The Vmca won't be much different than Vmcg. In most cases it will be a few knots less due to the fact that you may use 5 degrees of bank, while on the ground you can't. Look in the performance section of your AFM. The "chase charts" will show the variables.
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