Dec 22, 2009, 05:11 PM Physics hate's my ideas USA, NY, Dunkirk Joined May 2007 3,912 Posts Discussion 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?
 Dec 22, 2009, 06:49 PM Registered User Joined Sep 2009 46 Posts 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
 Dec 22, 2009, 11:06 PM Physics hate's my ideas USA, NY, Dunkirk Joined May 2007 3,912 Posts 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
Dec 22, 2009, 11:44 PM
Sink stinks
United States, GA, Atlanta
Joined Apr 2005
4,642 Posts
Quote:
 Originally Posted by GreenAce92 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.
 Dec 22, 2009, 11:57 PM Registered User Livermore, CA Joined Sep 2004 8,583 Posts 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.
 Dec 23, 2009, 03:18 AM Old age is not for sissies Dayton Intl, Ohio, United States Joined Jan 2000 8,344 Posts 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. Azarr
Dec 23, 2009, 09:20 AM
Registered User
San Diego, California
Joined Dec 2004
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From Lennon On Bipes. Has always worked for me.

Les