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Determining weight and wing loading

Old 03-11-2011, 02:34 PM
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Default Determining weight and wing loading

Is there a chart or formula for determining the weight and wing loading of a plane as the design is scaled up?


Example

Cherokee
Wingspan: 60 in
Weight: 6.75
Wing Area: 606 in²
Wing Loading: 26 oz/ft²

Now if I wanted a IMAA 80" one what would the weight and wing loading be?

I have a motor with 23 pounds of thrust, what size would I need to have a 1:1 powered plane?

If I want a 120" wing span one what would it's weight and wing loading be?

If I wanted to go to the AMA 55 pound limit how big of a Cherokee would that be?

I've always figured this by looking at similar designs in the size I wanted but I was wondering if there is a helpful rule of thumb or a chart on some web page with this information. I do know that weight goes up exponentially with size so the 120" one which is twice the 60" size wont come out weighing 13.5 pounds just as it's wing loading wont be 26 oz/ft² either.
Old 03-11-2011, 03:06 PM
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Default RE: Determining weight and wing loading

Lots of good info here: www.astroflight.com/pdfs/ScaleSpeed.pdf
Old 03-11-2011, 04:35 PM
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Default RE: Determining weight and wing loading

OMG, just what I was looking for! The first post too. Thank you so much sandal!

Thought I'd have to wait a week and weed through the usual dumb answers,

"The kit should say what the plane will weigh"

"I don't think anyone makes a 120" Cherokee"

"Just find a model that is like the size of the one you want to build and go by that"
Old 03-11-2011, 06:30 PM
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Default RE: Determining weight and wing loading

Ah there it is.

Thanks Bob Boucher!
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Old 03-11-2011, 07:08 PM
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Default RE: Determining weight and wing loading


The cubeing factor for weight was great!


Don't think I'm ready to fly scale though.

Lets see take the GP Cherokee 40 set up "SCALE"

60"
11.1 pounds weight "Got to ad 4.3 pounds of lead to her"
40oz sqf wing loading
powered by a .20 spining a 12.6" X 10 prop at 6,561 RPM makeing 2.9 pounds of stadic thrust.

Those are some ugly numbers! I can see it now "Dude, what's wrong with your plane?"
Old 03-11-2011, 08:08 PM
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Default RE: Determining weight and wing loading

I still need to find out how to scale up.


I think it's scale cubed times weight.

Lets see a 60" at ten pounds scaled up to a 86" wing span.

86" is 1.43/1 of the 60"
1.43X1.43X1.43 = 2.92
2.92 X 10 = 29.2 pounds

Wing loading

Lets say our 60" plane has a 25oz sqf wing loading for it's 921" wing area.

25oz sqf X 1.43 scale = 35.7 oz sqf for the 86" one.

29.2 pounds / 35.7oz sqf = 13.08 sqf
13.08 sqf = 1,884 sqi wing era

So the 86" plane specs will be

86" span by 22" cord wing
weight 29.2 pounds
wing loading 35.7 oz sqf
35.7 oz sqf = 29.8 MPH stall speed and 89.6 MPH top speed
29.2 pounds = 3,650 watt electric motor or 50cc gas engine

120"
weight 80 pounds
wing loading 50 oz sqf
35mph stall speed, 106 mph top speed
110cc engine.

OK I think that sounds about right.






Old 03-12-2011, 12:03 AM
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Default RE: Determining weight and wing loading


ORIGINAL: AmishWarlord
Lets see take the GP Cherokee 40 set up ''SCALE''

60''
11.1 pounds weight ''Got to ad 4.3 pounds of lead to her''
40oz sqf wing loading
powered by a .20 spining a 12.6'' X 10 prop at 6,561 RPM makeing 2.9 pounds of stadic thrust.

Those are some ugly numbers! I can see it now ''Dude, what's wrong with your plane?''
Looking at the numbers, I sometimes wonder how full size planes can stay in the air at all. They are very heavy and underpowered compared to RC models. For a model to fly well, it often needs to be quite a bit lighter than "scale weight", and it needs much more power. I believe the main reason for this is that we have to stand on the ground watching the plane from a distance. Sitting in the cockpit things would have been different because we would be able to feel what the airplane was doing.
Old 03-12-2011, 05:33 AM
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Default RE: Determining weight and wing loading


I found a really good site with some more info.

http://members.cox.net/moormanrc1/WingLoading.htm

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