Question.
If I want to enlarge 40 size plans to 60 size plans, what do I multiply the 40 size plans by? I've got a 60 size Sportster that I want to make into a twin engine. I've got the 40 size plans for that. Thanks.
Don

Well, the engine proportions alone would dictate that you multiply by 1.5, but...

I would probably go with a somewhat smaller ratio, say 1.25. Also, look around at commercial kits that exist in both .40 and .60 size, to get a feel for how some proven designs have been done. The details depend on what kind of performance you're seeking, and so you have to consider what construction details will change, and how the added weight will affect performance.

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

The engine displacement is in cubic inches so theoretically, you would take the cubic proportion to determine the linear multiplier. Going by this, the multiplier would be approximately 1.15. If the wingspan of the .40 size plane is 56 inches, the wingspan of the .60 size plane would be about 64 inches. I don't know how this compares to actual measurements of kits on the market but I would bet it is pretty close.

Thanks for the input guys. Now I wont feel so stupid at Kincos when I get the plans enlarged.