Larry,
The DA100 puts out 9.8hp, where your 3W56B2 puts out 5.5hp, so you are looking at a reduction in power of 56% of the original. If you reduce the weight of your scaleddown Pegasus by the same amount, you should end up with equal power loading (ref. birdofplay's comment above).
I would run a cubic loading calc on the DA100 powered Pegasus, and use the same cubic loading value at a .56 weight reduction factor to calc your new scale ratio. I don't have the figures in front of me, but if we say that cubic loading is:
weight/ (wing area)^1.5, and 'A' = DA100 Peg wing area, and 'a' = 3W Peg wing area,
then
W/(A)^1/5 = .56W/ (a)^1.5,
.56(A)^1.5 = (a)^1.5,
and a/A = .56 inv ^1.5, or .6794,
then this would result in an area reduction of 68% of the original. You can figure your new wing span using this reduction in area, and holding the aspect ratio constant.
BTW, I agree with Tony, that the scale ratio is not critical, and close enough is good enough. More important is the AUW. Don't want to build a smaller Pegasus that is too heavy (!!), but you want to keep it robust. Easy on the heavy ply, use carbon where you need it.
Have fun!
Don.
