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Old Dec 22, 2009, 05:11 PM
Physics hate's my ideas
GreenAce92's Avatar
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CG on positive stagger biplane.. 3D biplane

Got a bird coming up here pretty soon, in design stages but anyhow, for starters, imagine lets say a spitfires' wings, top wing is farther ahead than the other, say that the TE of the top wing is at the middle of the chord of the bottom wing. Where would the CG be?
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Old Dec 22, 2009, 06:49 PM
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it depends on the pitching moment of the airfoil you're using, but probably between 1/4 and 1/3 chord... also, put the upper wing 1.25 chord up, and 1/4 forward
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Old Dec 22, 2009, 11:06 PM
Physics hate's my ideas
GreenAce92's Avatar
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So a flat plate basically say 2 rectangles uhh say 8x30 30being the span so top wing is ontop and bottom wing is mounted with leading edge halfway back from top wing's chord or the le of bottom wing is 4in back from the le of top wing
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Old Dec 22, 2009, 11:44 PM
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Quote:
Originally Posted by GreenAce92 View Post
Got a bird coming up here pretty soon, in design stages but anyhow, for starters, imagine lets say a spitfires' wings, top wing is farther ahead than the other, say that the TE of the top wing is at the middle of the chord of the bottom wing. Where would the CG be?
It depends mostly on the tail size and location actually. Doesn't depend on the airfoil.
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Old Dec 22, 2009, 11:57 PM
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You first figure the C/G on both wings.
The lets say the top wing is 2"s ahead of the bottom wing.
Then the C/G would be 1" back from the top wing C/G.
And 1" forward of the bottom wing C/G.
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Old Dec 23, 2009, 03:18 AM
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Assuming rectangular wings as you mention in post 3, I just use the measurement from the leading edge of the top wing to the trailing edge of the bottom wing and then set the CG at around 30% of that width. It's always worked for me as a ball park CG.

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Old Dec 23, 2009, 09:20 AM
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From Lennon On Bipes. Has always worked for me.

Les
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Old Dec 23, 2009, 12:32 PM
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bipe cg

if normal model power wing sections are being used, its just in front of
1/2 way across the front wing, as a starting point, Robin Andrew,UK
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Old Dec 23, 2009, 04:41 PM
Physics hate's my ideas
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Ooo! Great diagram! thanks!
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