RE: kit building, tail vs nose weight
G'day
I have had two Butterflys. Great planes.
As for the way to calculate the difference - if you measure from the CG to where the weight in the tail is and multiply the weight by the distance, then an equivalent weight on the front will be the distance to the weight on the front by the weight.
So if you remove 5 grams from the tail and it is .5 metre back from the CG then it creates a moment of 5gm x 0.5 metre or 2.5 gm.metres. Then to balance it on the nose at say a distance of .2 metre you need a weight such that 0.2m x WEIGHT = 2.5. WEIGHT then works out at 2.5 / .2 or 12.5 gm
All these numbers are just made up but you can see from this rough example that you need 12.5 grams at the front to balance 5 grams at the back.
Did this help at all?
Basically to make a beam balance the weight x distance from the centre must be the same on both sides.
Mike in Oz