This may seem like a dumb question to some however, seeing how I have never done this before I thought I would ask. I currently have lots of plans in the 60-90 2-cycle size. I just bought a new Desert Aircraft 50. What I would like to do is to increase the size of these plans to be suitable for my new 50. For example, I have plans for a Kaos 90. What is the mathematical formula to come up with the correct percentage to blow up the plans to fit the 50. Would this formula work on any size plane as long as you know what the displacement of the current plan is and what you want to go to? Any help would be greatly be appreciated. Thanks in advance...

Spencer

It goes by wing area. Find out what area you want for the new engine ( this part is just research and comparisons. There's no formula) and blow up the plan to match. It's a square root relationship. If the new size is 1.6 times the area of the 90 Kaos then the linear scaling dimension is sq rt ( 1.6 ) = 1.27. So you'd ask Kinkos or whoever to blow up your photocopy by 1.27 times.

I suppose there IS a guide for how much area. You'd have to graph 60's, 90's, 1.20's and up to your engine and maybe a little larger and then join the points with a graph curve to figure out what area you want for the new engine. But it's only approximate as different folks want different models.

The numbers are up to you as I don't have anything over a 46 that I fly but a graph of that sort will answer a lot of questions.

The weight will be one major factor to watch out for. Especially if you have a particular thrust to weight ratio you want to achieve.

Thanks guys. I'll have to give it a try and see what I come up with.

I took a .40 size SS bipe and scaled it to a Quadra 42 size.

I took the rated horsepower of the two engines:

40 - 0.7hp
Q42 - 3 hp.

The ratio is 3/0.7= 4.29

Then I took the cube root (3 dimesions to scale) = about 1.6

So I scaled the dimension by 1.6. It worked great. The bipe actually has better power/weight than the original.

Example: If you scale by 2, the plane will be twice as wide, twice as long and twice as high. So it should take 8 times the power to pull it. Do it the other way around, take the cube root of the power ratios and you get the ratio to scale each dimension.