So you have a set of planes to convert a Sportster 40 in to a twin but you have a Sportster 60 you what to do it to?

There should be a constant between the Sportster 40 and the twin version, maybe the fuselage length or the wing chord. Find the constant and then measure the same on the Sportster 60 and do the math.

Say both the wing chords of the Sportster 40 and the twin conversion are 10 inches long--you have you constant. Now measure the Sportster 60 and we'll say it's 12 inches. Divide 12 by 10 and you get 1.2. You would then enlarge the plans by 120%.

-Bob George