trying2fly
Is there a formula or rule designating the distance apart that the two wings on a biplane should be?  Also is there a special distance the two wings should be staggered?  Finally..is the CG about 1/3 back from the leading edge of the "bottom" wing or the "top" wing?  thanx!!
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DualDesertEagle
I THINK since both wings contribute to the total lift it's gonna have to be 1/3 of the combined chord length. I would argue that 2 staggered wings of a given size produce the same amount of lift as a single one with the same wing area and thus both need to be taken into account for the CG.

I would even go as far as to say that if the upper wing (which often has a greater wing span than the lower one and, since it's usually a single, relatively unobstructed surface with no fuselage in the center, produces more lift even if it's the same wing span) generates 20% more lift than the lower one the CG would have to be shifted forward accordingly, but that's just pure logical thinking without actual knowledge about how it works in real life.



For the distance between the wings and how far they're staggered I'd simply go straight ahead and use the same ratio as real planes do, tho since there are even planes where the upper wing is staggered BACKWARDS I don't think the staggering makes much of a difference. The Wright brothers' plane didn't have ANY staggering after all.





I have no clue wether or not the following is correct, so use this at ur own risk, but I think the fomula for the CG would go somewhat like this:


Let's say we have 2 wing chords of the same length, for which I'll just use 3 feet for convenience.
Then let's say the fuselage is also 3 feet wide where the lower wings stick out of it
And finally let's say the lower wings have a span of 15 feet and the upper wing (mounted above the fuselage) has a span of 18 feet and is staggered about a foot forward.

So minus the width of the fuselage the lower wing has about 36 square feet of surface area and the upper wing has about 54, giving us 50% more lift than the lower wing

Now I'd say with no difference in lift between the 2 wings the CG should be half a foot aft of the upper wing's 1/3 and half a foot ahead of the lower wing's 1/3, but we've got 50% more lift on the upper wing, so the CG would actually have to be 4 inches aft of the upper wing's 1/3 and 8 inches ahead of the lower wing's 1/3.

Does that make sense to everyone? And much more importantly, and this question is directed at the guys who've built biplanes before, is that actually correct?
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solentlife
For me ... things like this come down to the age old maxim :

If it looks right ... it likely IS right.

Distance apart ... stagger of wings ?

Personally I think major consideration of vertical separation of the wings was not only avoiding one wing interfering with the other - but also VISIBILITY of the poor old pilot !! 
As to stagger ... look at WW1 and many did not have staggered wings ... it coming later. In fact there are various that had reverse stagger ... no stagger ... huge amount of stagger ... so IMHO - it really comes down to what pleases the designer.
The Tiger Moth had its top wing altered to allow front pilot to bail out !! 

For planning a model ... I usually fall back on 3 views and use them as a guideline.
I'll fly anything if I can launch it ! Youtube : solentlifeuk
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trying2fly
Great advice as usual and I am very appreciative.  You inspire me....thanx!!!
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Sidewayskiwi
trying2fly wrote:
Is there a formula or rule designating the distance apart that the two wings on a biplane should be?  Also is there a special distance the two wings should be staggered?  Finally..is the CG about 1/3 back from the leading edge of the "bottom" wing or the "top" wing?  thanx!!

Looking at most WW1 biplanes the wing placement is 
vertically 1 1/2 x the fuselage vetical height 
Laterally the top wing is a 1/3 to a 1/4 of the chord line forward of the lower wing i believe this is to give some stability around the wings centre of pressure/lift  as if all the wings are right above each other the centre of lift would be at one point making the plane unstable 
also the top wing forward positioning gave better pilot visability without reducing centre section strength
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trying2fly
Super...this is the info I was looking for!!!  thank you so much!!!!!!!!!!
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