Formula for scaling plans

On Sat, 06 Jan 2007 16:43:32 -0800, Geoff Sanders wrote in :

I'm sure that I don't understand your question, but I'll try to tell you what I think it means and what the answer is to the question as I understand it.

If you want 1/4 squale, multiply all measurements by 0.25 (or divide all measurements by 4).

If you want plans that are 1/4 larger than the original, multiply by 125% (or divide by 0.8).

For any dimension, just keep using the same technique and all will be well. All of your numbers should come out diminised or increased by the same amount.

Marty

This link should help

The main thing to remember is that areas increase as the square of the linear dimensions.

If your scaling increases wing span from say 50" to 60", the increase in linear dimensions is 60/50 = 1.2. Therefore the areas increase by 1.2 x 1.2 = 1.44 times, a 44% increase.

So if you want a 25% increase in wing area you increase the plans by the square root of 1.25 = 1.118, also expressed as an 11.8% increase. Similarly if you increase the plans by 10% in linear dimension, you get an area increase of 1.10 x 1.10 = 1.21, or a 21% increase.

It works the same way scaling down of course: if you want to reduce areas by

Square root of the area change = change in linear dimensions (span, length, etc.)

Square of linear dimension change = change in area

So pull your head out (there's apretty mental picture..), get it washed off, and bang away on your calculator! ;-)

And if you are using the Windows calculator on your PC, there is no square root function on the keypad, but actually there is - use x^y, x is the number, y = 0.5. Raising a number to the power of 0.5 is the same as taking the square root.

Mike D.

All your comments are fine, but what I can't remember is the simple high school algebra to determine the wingspan when scaling up a downloaded three view of 4.5" span into 1/5 scale (20%) or the full size plane's

I just GOTTA quit gobbling these here Brain Be Gone pills!

On Sun, 07 Jan 2007 11:46:41 -0800, Geoff Sanders wrote in :

If a span of 4.5" represents 409" then the scale of your three-view is 4.5/409 = 1.1%. If you can live with 22% for your plane, multiply all dimensions by 20. That will give you a wingspan of 90".

OK, suppose you insist that the plane has to be 20% of the original.

What multiplier do you need to change the 4.5" span into 20% of the original 409"?

By what do we need to multiply 4.5 to get 81.8?

Let "x" stand for the unknown quantity.

Multiply all of your measurements from the 3-view by 18.1777 and that will give you the dimensions for your new drawing.

Marty

three-view is 4.5/409 =

That's it! Thanks, Marty!

Ooooohh, gett

On Sun, 07 Jan 2007 16:21:23 -0800, Geoff Sanders wrote in :

You're most welcome. I'm glad that's what you were looking for. I'm OK with algebra. I never absorbed trig and have made a few futile efforts to remedy that without success in the last year or so.

I know what you mean. Unfortunately. :o(

Marty

Ah, that's what you're looking for! Obviously I thought you were looking for scaling info regarding areas, spans etc. Oh well... glad to be of no help this time! ;-)

Ahh, but what if you didn't have the balls to publicly admit it? Then you'd never have that cool plane to build.

How do you know I'm building a "cool" plane? I'm intending to build a French plane! ;-)