I have all the index units in tabular form
doesn't really matter which way you go .. arithmetic calcs will give a marginally "better" accuracy .. but the difference is not worth worrying about if the trim sheet is well designed .. and at the risk of potentially higher error rate. Overall, my experience suggests that the trimsheet is the better tool...
The best manual system with which I have been involved had
(a) initial trim calculations done by the freight shed folk to run up a conventional IATA style load sheet
(b) flight crew checked using a circular trim sheet (looked a bit like a nav computer). As the weight control engineer for the operator, I was against this initially (due to concerns regarding variable errors across the sheet) until I saw just how effective it was in operations .. captain ran through the can loads and the F/O ran the trim calcs. Very fast and very reliable .. changed my thoughts on the matter.
(c) .. but, if you don't double check that the cans actually get put in the right bays (ie as per the loadsheet) .. it all can become both academic and exciting
the reference point(or trim datum which you explain it is) was created to enable/create -ve & +ve moments for easier calculations
.. total, utter, and complete nonsense. It never ceases to amaze me how folk can dream up innovative ideas such as this. I am bemused that anyone could think that a mix of plus and minus makes for simplicity given that many pilots don't have a particular affinity for such things ?
For aircraft of this class, it is entirely conventional for the OEM to suggest a trim datum in the loading manual/weight and balance manual (or other similar names). No reason, of course, why you should use the OEM's suggestion but it will probably be as good as any alternative in most cases.
The trim datum's sole use is to get a datum position (for a graphical loading system) which will give you the most accurate trimsheet.
As I showed earlier, you can do whatever you want with the entry numbers .. can make all the entry positive, negative, or a mix according to your desires .. positive makes the most sense, though.
a method to generate the CG Given the weights and IU's
too easy .. I'll have a look at the TCDS later on today and (presuming that gives me all the info I need) I'll give you the IU equation for the system you are using and, more importantly, show you how to work it out yourself for the next time .. the equation can then be rearranged to make CG the dependent variable.
You can, quite easily, extend your present system to do the lot on the PC .. just a matter of comparing the CG with the forward and aft limits to determine if the loading is OK or not.
Freighter hacks unite !!