



Discussion
wing area X % scale =?
Maybe I didn't put i down quite right, but what I would like to know is this?
If you are going to increase the overall size of a plane by say 150%, and you have a given wing area (sq in) , how do you figure the new area out? A x 150%, just doesn't seem right. TIA 




Thanks,
I was thinking it had something to do with being "squared" , just not sure on what and how. Now I have learned my one new thing for the day!! 


Florida
Joined Aug 2004
4,474 Posts

Your thinking was correct. The increase would be 1.5 squared or 2.3 times the original area. If you wanted to have the new size to have 150% as much area as the original you would increase the linear dimensions by the square root of 1.5 or 1.2247 times.




OK, here's one more question. I'm trying to find sq.in (wing area) of a model which is 8.79% scale. Full size plane is 202 sq.ft. So do I take 8.79 x 8.79= 77.26/202=2.61 x144=375.84 sq.in.?




You need to convert the % to a decimal. So 8.79% is actually .0879.
So it's the size change squared times the full size area in sq feet times the conversion from sq ft to sq inches. Or; .0879^2 x 202 sq feet x 144 sqin/sqft = 225 sq inches 



Thanks for the help guys, but I'm doing something wrong here.
Where I think I'm going wrong is in figuring the scale. The full size plane has a WS of 40ft or 480" and 400sq/ft. . Model has WS of 53" sqft? I took 53/480=9.056 So, using BMatthews formula .0905^2 x 400 sq/ft x 144 sqin/sqft = 471.7sqin Now if I take 44.5" WS/480 =10.78 then .1078^2 x 400sqft x 144sqin/s1ft =669.3sqin? shorter wing with more sqin? WRONG. It has to be something simple I'm missing, HELP Please. 


Staffs, UK
Joined Nov 2003
12,173 Posts

You're calculating the scale factor NOT the percentage change. Effectively your division is upside down which is why the calculations go astray.
Scale factor is Original size / Model size. 480 / 53 = 9.056 Percentage change is Model size/Original size (x 100) 53 / 480 = .1104 (or 11.04 %) 44.5 / 480 = .0927 (or 9.27%) The percentage change also equals 100 / scale factor. I.e. if scale factor is 4 that's 100/4 or 25%, if scale factor is 8 that's 100/8 or 12.5%. For 53" span you got a scale factor of 9.056, which is a percentage change of 100/9.056 or 11.04 Steve 



slipstick, Thanks much, I knew something was astry, just could not pin point it.
To some it may seem a "Stupid"question, but I can't be the only one who doesn't/didn't know! It may help others later on, in a their quest for knowledge! Having gotten the solution,I see where I went wrong The dividend is the number that is being divided. The divisor is the number that the dividend will be divided by. Had to look it up, it's been a long time since I have seen the inside of a classroom!! 
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