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Old Feb 09, 2013, 12:43 AM
JohnAV8R is offline
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Clark Y airfoil flies inverted


I made this small wing for an indoor flyer. It has a 15% Clark Y air foil, foam ribs, and is only covered on the top surface with saran wrap.

I dropped the wing and noticed that it quickly flipped onto its back and glided away rather well. I tried this again trying to keep it upright for a test glide, but it always quickly rotates upside down and then goes into a flat glide (wing is up side down).

Is this characteristic inverted flight only because there is no covering on the bottom, or is it the air foil?

I have a small Winglet 2 which flies very nicely and it has a curved bottom airfoil which is different from the top airfoil.
John
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Old Feb 09, 2013, 01:37 AM
slebetman is offline
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It's the airfoil. If you look at an inverted Clark-Y or any high camber airfoils you'll notice that the inverted camber becomes a reflex - which is what is needed for a flying wing to fly.

But it's not really efficient. It works, and actually works very well but can't compete with a properly designed flying wing airfoil with an S shaped camber line.

Still, if you're just building a sport model for fun it's usually good enough.
Old Feb 09, 2013, 02:46 AM
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As slebetman wrote, you can flip a Clark-Y, but it will have four or five times the drag of a good selected airfoil. Also, due to leaving the top(?) of the wing open, the airfoil is something different than a Clark-Y. It's rather a sort of cambered plate...

Cheers
Andrés
Last edited by andrecillo76; Feb 09, 2013 at 03:45 AM.
Old Feb 09, 2013, 03:32 AM
Stuart A is offline
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Quote:
Originally Posted by andrecillo76 View Post
As slebetman wrote, you can flip a Clark-Y, but it will have four or five times the drag than a good selected airfoil. Also, due to leaving the top(?) of the wing open, the airfoil is something different than a Clark-Y. It's rather a sort of cambered plate...

Cheers
Andrés
.....which is why it's flipping.
Old Feb 09, 2013, 11:53 AM
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It flips inverted so as to become stable, although as said above, it is not efficient.
It does this because there is no tailplane opposing the pitching moment of the wing section. Have seen many times in thermal comps a model which lost its tail (usually from a mid-air) coming down slowly and semi controlled (flap and aileron because there is no elevator) but inverted.
One time in the 80's I saw a model landed on the spot this way.

John
Old Feb 09, 2013, 01:24 PM
JohnAV8R is offline
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Thank you gentlemen for the answers. I’m never too old to learn something new.
John


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