I believe the correct calculation is "multiply the distance from
aircraft CG (NOT firewall) to engine CG by the engine's weight".
Frank

Chuck Caldarale wrote:

Wait a moment (pun intended) - all CG calculations must be based
on a fixed location, not the aircraft CG. The aircraft CG is quite
variable, depending on fuel, passengers, baggage, engine weight,
etc. The firewall is certainly one of the many fixed points that
can be used, and usually one of the easiest.

 - Chuck Caldarale

That is what I thought Chuck and the CG can indeed be calculated by using 
the firewall as the reference point. I think Frank's point is; you don't want 
to move the CG... just find that combination of engine weight and position that 
keeps it in the same place. IMHO using the current CG position makes those
calculations easier as there are no positive and negative values to be added
up and divided by the gross weight giving the new position of the CG
relative to the firewall. A drawing would help explain this I think.

Paul Lamar
 
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