rcmaster-RCU

My Feedback: (11)

I have plans that I would like to enlarge proportionally to create bigger model, but I am not sure how to figure out the percentage of enlargment. The plane has a 50" span and I want to blow it up to a 76" span plane proportionately. Basically I am trying to turn a 40 sized plane into a 1.20 sized plane. Do you go off the square area of the plans to simplify things and play with the percentage numbers till you get what you want? I think this works, but I just want to know how to do it right.

Appreciate the help,

Alex.

amtpdb

Hi
76/50=1.52 so 152 percent larger. You can check this by taking the 50" and multiply it by 1.52(152 percent). You will get 76.
Don

ptulmer

My Feedback: (5)

Well, the first thing I would do is determine the wingloading of the 40 size. Now, use that number to determine the best wingloading of a 1.20 size. That's not as simple as it sounds because wingloading will typically increase with scale. Then try to scale the plan to achieve that first goal. If you can, try to scale it with a number that scales the lumber sizes to a useful number.

Here's a link that shows how to determine wingloading. http://webpages.charter.net/rcfu/HelpsHints/WACalc.html

I'm telling you the quick easy route with CAD. Since you didn't state how you were scaling, I'm making an assumption, but with a little effort, you can stick the wing outline into CAD to achieve similar results. But it still requires that you educate yourself about loading!

Now, the biggest shortcut is to enlarge by a scale factor of 1.75. I checked a "stik" plan of mine. That gets the closest to the specs of commercial "stiks".