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Old Nov 20, 2012, 05:06 PM
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FlyBoy20's Avatar
United Kingdom, Wales, Swansea
Joined Aug 2012
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Question
Flat-bottomed airfoils..

Forever wanting to DIY and re-cycle a model, I've been thinking about this 6" chord built-up balsa glider wing I have - can it be pressed into service for something else a bit more exciting, I wondered? It's a 5 footer with dihedral at the tips, so in theory I could make two 30" wings from it.

The problem is it's a flat-bottomed section, and I was wondering if it would be OK for inverted flight. Any suggestions..?
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Old Nov 20, 2012, 05:10 PM
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jasmine2501's Avatar
United States, AZ, Mesa
Joined Jul 2007
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Quote:
Originally Posted by FlyBoy20 View Post
Forever wanting to DIY and re-cycle a model, I've been thinking about this 6" chord built-up balsa glider wing I have - can it be pressed into service for something else a bit more exciting, I wondered? It's a 5 footer with dihedral at the tips, so in theory I could make two 30" wings from it.

The problem is it's a flat-bottomed section, and I was wondering if it would be OK for inverted flight. Any suggestions..?
There's a few types of flat-bottom airfoils - some are ok inverted and some are not.

If there's 3 angles in your wing, one central and two up-turned tips, then I wouldn't try to make two wings out of it, I would only make one, by cutting off the tips. Would probably do it that way even if the center section was straight.

Can we get some photos? What kind of planes do you like?
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Old Nov 20, 2012, 05:12 PM
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Canada, BC, Port Coquitlam
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Any type airfoil has the capability to fly inverted.

Symmetrical airfoil would be better but flat bottom Clark Y type airfoils will still fly inverted, albeit not ideal.

With that flat bottom, you'll fly with a very high angle of attack when inverted. Hard to control. IMO, if your intention is aerobatics/inverted flying, forget the flat bottom wing.
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Old Nov 20, 2012, 07:54 PM
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United Kingdom, Wales, Swansea
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Originally Posted by jasmine2501 View Post
..If there's 3 angles in your wing, one central and two up-turned tips, then I wouldn't try to make two wings out of it.. What kind of planes do you like?
The centre section is a straight 30", the two tips being 15" each - which I could join together. Hey presto, two planes from one.

I like most sorts of planes, especially ones with floats. If I got really ambitious, I'd make a bipe.
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Old Nov 20, 2012, 07:57 PM
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Originally Posted by easyrider604 View Post
..With that flat bottom, you'll fly with a very high angle of attack when inverted. Hard to control. IMO, if your intention is aerobatics/inverted flying, forget the flat bottom wing.
I wasn't thinking of any really clever aerobatics, just the ability to fly upside down at a pinch.

Maybe I'll have a re-think.
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Old Nov 21, 2012, 09:01 AM
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Most airfoils will fly upside down through newton's third law. They may not do it to well though. The closer an airfoil is to symmetrical and the lower the angle of incidence, the better inverted performance you'll get.
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Old Nov 30, 2012, 12:41 PM
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Originally Posted by FlyBoy20 View Post
Forever wanting to DIY and re-cycle a model, I've been thinking about this 6" chord built-up balsa glider wing I have - can it be pressed into service for something else a bit more exciting, I wondered? It's a 5 footer with dihedral at the tips, so in theory I could make two 30" wings from it.
Well, I did make two-for-one planes, and flown both. I'd love to show you pictures, but don't know how to upload, and can't see any links...help needed!
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Old Nov 30, 2012, 01:07 PM
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Just had reply regarding pictures..doh

As I said - I've built and flown both. The little one is now well and truly stuck up a high tree - for the second time. Flew good for a while though. The wing came fluttering down so I can build another...

The Jumbo wheeled job has now flown just once since fitting the proper wheels and also aelerons. Goes up like a rocket with the HK Donkey motor and 7x5 prop, and throttling back to 1/2 it should cruise around for ages on the 1300mAh. Only tried one bit of aerobatics, and does a nice tight loop. I was planning to do a few circuits and bumps, but one of the wheels fell off on the first landing.

I've now Araldit-ed it on instead of hot glue, so I shouldn't have to come home so soon next time...
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Old Nov 30, 2012, 01:41 PM
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If you have to use a flat bottomed wing, and also want it to do aerobatics, next build, reduce the wing incidence angle to a minimum.
It will reduce the amount of down elevator you would have to hold while inverted.

But better still, make a fully symmetrical section wing.
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Old Nov 30, 2012, 02:39 PM
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Originally Posted by eflightray View Post
..But better still, make a fully symmetrical section wing.
I'll have to see what I can do with the old Decathalon wing. That's nearly symmetrical..
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