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Old Sep 16, 2014, 04:45 PM
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Need advice: Vertical stabilization with dihedral

I'm building a 7ft flying wing with a 4ft non-tapered center section and 1.5ft tapered wing ends with ~12 dihedral. Does anyone know if this kind of dihedral could act as vertical stabs? My preference is to not have vertical stabs mostly for looks but also because of how often I tend to beat them up on rough landings, but of course adding them wouldn't be the end of the world.
Any advice would be greatly appreciated.
Thanks and happy flying

Alex
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Old Sep 16, 2014, 05:10 PM
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Quote:
I'm building a 7ft flying wing with a 4ft non-tapered center section and 1.5ft tapered wing ends with ~12 dihedral.
What planform: chevron, plank or forward swept? (Delta not included because of provided dimensions)

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Old Sep 17, 2014, 10:00 AM
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If the tips aren't very far behind the CG they aren't going to be very effective for yaw stability.
Can you provide a picture?
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Old Sep 17, 2014, 03:40 PM
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These pictures should answer questions of dimension and wing style. What do you think?
thanks
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Old Sep 17, 2014, 05:18 PM
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Quote:
Originally Posted by nuteman View Post
If the tips aren't very far behind the CG they aren't going to be very effective for yaw stability.
Can you provide a picture?
That being said, I suspect from the appearance of the plane in the pictures, it should do just fine as it is. Doubt it needs any fins since it has no vertical surfaces at all.
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Old Sep 17, 2014, 08:13 PM
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Looks like a sailplane wing!
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Old Sep 18, 2014, 12:34 AM
Fremont, CA
United States, CA, Fremont
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You might have problems with yaw stability and turning. For turning you need some side drag at the back.
Here's what I suggest: Attach a temporary vertical fin to the wing with velcro as shown in the pic. Start flying with the fin about 12" behind the prop. Then gradually reduce the fin distance until you don't like how it handles. If you discover that you don't need the fin, all the better.
You might need twin booms and fins to straddle the prop.
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Old Sep 18, 2014, 01:16 AM
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Hmm... From the pics looks like you've got mild sweep and the tip sections (with dihedral) will provide plenty of roll stability with some yaw stability (because of the vertical component of side area and because of the sweep). It's likely to be marginal because of the very mild sweep.
Try it out and see if it is controllable (nothing like the empirical proof of a crash ).
If you want to play it safe:
If you swept those tip sections back significantly (like at least another 20 degrees - 30 degrees to be safe) then you'd likely have plenty of yaw stability with no need for additional vertical surfaces.
Or do as djacob7 suggested.

By the way: Nice lookin' plane!

Let us know which option worked out for you.
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Old Sep 18, 2014, 05:33 PM
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That's more or less a plank.The only one I know of that flew without a central fin had drag rudders.
I seem to recall reading that tip fins aren't very efficient with a plank layout
The prop should provide some stability,might be better if you can set it behind the wing- but that leads to balance/cg issues.
Maybe a touch of reflex?

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