So here is my 2 cents worth based on the topless 912s QuikR (Trike / Weight Shift Aircraft)
If we take the aircraft Empty Weight = 220kg
Max pilot / pass weight 220kgs
Seat Load 110kgs
Min pilot weight 55kgs
Defining the CofG envelope
If we suspend the totally empty trike from its hang point, and drop a plumb line from the hang point down to the carriage keel. We will call this point “Station Zero” (ST0), it represents the most rearward CofG (center of Gravity) possible. In this configuration the control bar, in straight and level flight, would be in its most reward neutral position.
The Quick has a 55kg minimum pilot weight. The effect of this will be to move the neutral point forward - essentially to a point where it provides sufficient rearward movement of the control bar for control of the aircraft. This is what defines our most rearward CofG (Centre of Gravity) limit. If we put 55kgs in the middle of the front seat of our hanging Quick and mark the new position of the plumb line on the carriage keel we will have “Station R” (STR) representing the most rearward CofG limit. This will be in front of ST0.
As we maximum load the trike we will have 110kg in the pilots seat located at say “Station 2” (ST2) and 110Kgs in the passenger seat “Station 1” (ST1). The remaining weight (10Kgs) we will have as fuel and as it is located near to the minimum weight CofG in our STR
We now have the most forward CofG possible. In straight and level flight the control bar is going to be at its most forward neutral position, with sufficient forward movement remaining to provide aircraft control . We can now define an envelope roughly assigning values to STO STR ST1 ST2 all measured as a value forward of ST0. And using the maximum weight of 450kgs and minimum weight of 220kgs. We are not really concerned with where exactly the cofg is as we will be changing it all the time in flight to effect control of the aircraft. So for the sake of simplicity we will say that the arms are measured in units and
ST0 = 0 units by definition
ST2 = 1 unit forward of ST0
STR = is calculated using the formula new ST Units = MASS CHANGE / NEW TOTAL MASS x ARM to added weight Station)
= (55kgs/275kgs) x 1 Unit =0.2 units
(because we added 55kgs to ST2 (the pilot seat 1Unit forward of ST0) to get STR
ST1 = is about halfway between ST0 and ST1 so ill just call it 0.5 units.
The max weight is 450Kgs by law and the minimum weight is 275kgs (carriage + pilot minimum weight) by design.
We now have an envelope for our trike that all though not 100% accurate interns of the exact location of the CofG is good enough for all our loading possibilities. (What it more accurate then you should probably not be in a trike ;-) .
Attached the file - you may want to adjust the fuel flow figures a bit - sorry I was a bit slack and did not look up the 912 fuel flow figures.