Unless we are talking about MAC and cheese, or the Mickey D kind of MAC, the aircraft MAC is the Mean Aerodynamic Chord.  This MAC is the width of the wing when measured through the center of the wing in the forward-aft direction.  On a plane like a Piper, this is just the width of the wing.  With a more complicated wing design like the Lancair it is the average of this measurement.  That is where the word “Mean” comes from.  This measurement has nothing to do with the “neutral point”.  It really just describes how effectively wide the wing is.  The CG (Center of Gravity) is the point around which the airplane balances (or would balance) if it is sitting on its wheels.  (Maybe that is a “neutral point”?)  This CG is calculated when the plane is motionless on the ground and on scales.  It is not the CG that the plane is operating with when it is in flight because the horizontal stabilizer is usually designed to place a down force on the plane, which will have the effect of moving the CG backward in cruise.  That is why the CG is specified to be in the front 25% of the wing width (MAC) in the specs.

When we determine thru the Weight and Balance calculations, the CG, we have no idea what the CG of the plane will be in flight because as the angle of attack moves the Center of Lift forward and aft, and the horizontal stabilizer adds and removes loads, we have no way of calculating or knowing how these forces are moving.  Hopefully the aircraft designer did all this when he specified the CG range that we should keep the plane in when it is on the ground and on its wheels.  I suggest we stay inside these recommendations.

Bill B