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Tandem Wing Spacing and Reynolds

Old 12-08-2010, 04:51 AM
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DKNguyen
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Default Tandem Wing Spacing and Reynolds

Hello.

I was wondering if anyone knew where to find material (or just outright knows) the spacing required for two tandem wings to not intefere with each other.

Reason I ask is because I suspect that it tandem wings might work better at low reynolds numbers than higher ones because turbulent flow is dampened more easily. If that were true (it may very well not be since turbulence might only affect the localized downwash, and not the overall downwash which would be the same whether the downwash wash turbulent or laminar) it would mean that at small sizes, tandem wings might have much more reasonable spacings for their size compared to larger sizes without having interference effects.
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Old 12-08-2010, 07:39 AM
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JetPlaneFlyer
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I'd guess downwash angle would be a bit less at low Re due to the fact that the CLmax of the wing will be less at low Re than at high Re.. less lift = less downwash.

As for wing spacing. The disturbed air from a wing trails behind the plane for a huge distance. You just need to look at the spacing airliners need to leave between each other to get some idea, for instance behind 'super jumbo' size airliners separation needs to be between 4 and 8 nautical miles!. So in practical terms it's impossible to space wings far enough apart to avoid downwash effects.
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Old 12-08-2010, 10:03 AM
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DKNguyen
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Originally Posted by JetPlaneFlyer View Post
I'd guess downwash angle would be a bit less at low Re due to the fact that the CLmax of the wing will be less at low Re than at high Re.. less lift = less downwash.
Oh yes, I never thought about it that way. But the effect of that is more about how laminar flow tends to separate from the wing. My question isn't about the initial strength of the downwash generated by less or more lift, whatever the cause. It's more about the dampening the downwash at high vs low reynolds numbers.

Originally Posted by JetPlaneFlyer View Post
As for wing spacing. The disturbed air from a wing trails behind the plane for a huge distance. You just need to look at the spacing airliners need to leave between each other to get some idea, for instance behind 'super jumbo' size airliners separation needs to be between 4 and 8 nautical miles!.
What I meant to ask is more along the lines of this:

Taking your above example (which occurs at very high reynolds numbers), wouldn't the much stronger viscous forces at work at much lower reynolds numbers dampen out that disturbed air much more quickly? Sort of like how a pendelum slows down a lot more quickly in water than it would in air. Though it may still be large too be practically useful would it not be much much less?
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