Let me start by saying that I generated 4 pages of notes that I turned into 5 pages of finished calulations for determining the proper placement of the alternate MAC Phazer engine in lieu of the Revmaster R2300. Then I got some raw data from Gen Bradley and Jake Thiessen on their finished weights and balances. It turns out that the airworthy examples of the type have a 14% variance in their empty CG, and an 8% variance in empty weight. Also, the moment arm for the pilot, pax, baggage and fuel vary by between 2" and 6". So I scrapped all the preceeding math and started again.
At least repetition has made me better at this. Now it only took me three pages of notes to generte 2 pages of finished calculations. And I have produced a *range* of valid values for the location of the engine forward of the datum point, that are valid for a range of weights and balances. Let me jump past the calculations that I've got written up in my folder, and get to the answer. The engine C.G. should be at between -70.86" and -79.71".
Next up, truss calculations for the motor mount. I may just go build the empennage instead. Becuase I would very much like ot stop looking at blank sheets of white paper for a couple of days.