C of G issues

[gkey]

Yesterday I did my first long x-country in GKEY. We flew from Cold Lake (Alberta) to Brandon (Manitoba) and back. Total time 6 hours (940 nm). GKEY performed like an angel.

We never needed to do a C of G in this plane before, because so far it was not needed with just two people in it, but we found something interesting - these are the numbers we used:

Empty weight = 3099 lbs
Pilot = 195 lbs
Front Pax = 165 lbs
Centre seat pax #1 = 147 lbs
Centre seat pax # 2 = 144 lbs
Aft cargo = 35 lbs
Zero Fuel weight = 3785 lbs
Fuel = 780 lbs
Take off weight = 4565 lbs

The max TO WT for this plane is 4630 lbs.

The C of G worked out to be 137.7 which means we were a little outside of the curve to the left, and nose heavy.

Just for giggles, I then worked out a typical C of G with only me and my "first" CFI, who weighed close to 300 lbs, and full fuel 888 lbs. To my surprise, we were then even more left to the curve - 136.7 - and I remember the plane flew just great!

I see in the tech logs that this plane has had several alterations and mods made, like radio's, new seats, new equipment, Robertson STOL kit etc., and each time the C of G was recalculated just by math alone. It has never been physically re-weighed or C of G audited.

Is it possible that the C of G works out left of the curve because of wrong calculations with these many previous mods?