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Old Mar 23, 2010, 11:22 PM
RCHN #202
Dowquest's Avatar
United States, CA, El Cajon
Joined Nov 2007
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Choosing Wing Sweep angle

I've built several Flying Wings over the past year or so, and always settled on my wing sweep angle more for balancing ease. But... What are the design characteristics/ considerations, and flight handling properties of wings of various sweep?
i would think I would be overgeneralizing to say less sweep is for slower aircraft, and higher sweep is for high speed, so could someone throw some light on the subject?
I am interested in scratchbuilding a sloper wing, and want to know how the whole sweep angle and aspect ratio come into play. I've read that you want your gliders to have a higher aspect ratio, but what about sweep?
Thanks in advance
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Old Mar 24, 2010, 10:06 AM
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Joe'n Kody's Avatar
Yeppoon Queensland
Joined Oct 2009
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Swept back wings are for high speed flight. High spped is up to and above the speed of sound. What the definition is for high speed for an RC model is, I don't know. The best info I have read on the subject is from Martin Simons book, "Model Aircraft Aerodynamics". One advantage of sweep back is it slightly reduces the dihedral angle required. Stability can become a problem as speed decreases. Building a swept wing requires very precise building to enable the full potential of the design to be realized. Personaly, I wouldn't bother building such a model unless it was for a scale event. If you want a flying wing for a sloper, why not build a "Plank" wing. These are very easy to build and are extremely stable. They can turn on a wingtip and can be very fast when needed. You can also see them better in the sky compared to a Zagi type plane. If you are interested in building one, PM me for more details and plans that are available.
Joe n' Kody
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Old Mar 24, 2010, 10:17 AM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
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There a few threads below in the 'Similar Threads' list that may help.

I know that seep back can have a dihedral effect, i.e. increase stability, also give a slightly larger CG range, (although still quite small).

It may depend on what you want from a model, best soaring/lift, best aerobatics, or somewhere in between. I don't thing it has too much affect regarding speed when at model size, especially for the same frontal area.

Don't forget swept forward wings as well.

One place to ask again is the Modeling Science forum though you may get a lot of technical jargon, (they love that), but they do know what they are talking about, (I hope )
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Old Mar 24, 2010, 11:52 AM
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Quote:
Originally Posted by eflightray View Post
There a few threads below in the 'Similar Threads' list that may help.

I know that seep back can have a dihedral effect, i.e. increase stability, also give a slightly larger CG range, (although still quite small).

It may depend on what you want from a model, best soaring/lift, best aerobatics, or somewhere in between. I don't thing it has too much affect regarding speed when at model size, especially for the same frontal area.

Don't forget swept forward wings as well.

One place to ask again is the Modeling Science forum though you may get a lot of technical jargon, (they love that), but they do know what they are talking about, (I hope )
It sounds good anyhow!
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Old Mar 24, 2010, 02:57 PM
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Hong Kong
Joined Jun 2002
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All Windrider flying wings using the same angle, I feel the angle we are using is the best all around for lift, aerobatics and speed.

Ming Lou
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Old Mar 24, 2010, 04:44 PM
RCHN #202
Dowquest's Avatar
United States, CA, El Cajon
Joined Nov 2007
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Quote:
Originally Posted by Ming View Post
All Windrider flying wings using the same angle, I feel the angle we are using is the best all around for lift, aerobatics and speed.

Ming Lou

Ming,
it looks like you're around 30 degrees. I've scratchbuilt wings from the high 20's to 40 degrees. all have flown exceptionally well. Maybe I need to push into the 150+mph envelope to notice.
What I'm trying to understand is what is the difference in handling characteristics and performance. You say your's is the best, why?
What does yours do that a wing of 35 degrees won't do? There are manufacturers that have wings of differing sweeps for different purposes, is your wing a compromise of multiple disciplines?

Not trying to be argumentative, just trying to nail down the difference.
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Old Mar 24, 2010, 08:08 PM
RCHN #202
Dowquest's Avatar
United States, CA, El Cajon
Joined Nov 2007
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Here's a link for some reading 2nite. hopefully will answer some questions, found it off the related links. Thanks.

http://www.b2streamlines.com/EffectiveDihedral.pdf


Uhhh,, covers a bit more than wing sweep. Pretty technical, I'll have to let it soak in overnight.........
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Old Mar 25, 2010, 12:33 AM
B for Bruce
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The 'Wack, BC, Canada
Joined Oct 2002
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The speed of sound doesn't scale to our sizes. So sweep is not needed to lessen the drag for the transonic region. The only thing that is left is the wing's stability. If you don't use it already google for and download the Excell spreadsheet version of the Panknin flying wing equations. With that tool you can set the design of the wing and the CG location along with some airfoil parameters for the root and tip airfoils and it'll tell you how much washout you require for the wing to fly in a stable manner.

If you play with it for a while with different designs you'll soon see that the more the sweep angle the less washout you need for a given CG location at the same MAC point. This makes sense since on a swept flying wing the more rearward portion is acting as a stabilizer. And the longer the "tail moment arm" courtesy of the sweep angle and span the less negative lift force you require to balance the design.

Never mind searching. Here's the link to b2streamlines' flying wing links. The Panknin page is near the bottom and on that page is links to the Exel spreadsheet. If you don't have Microsoft Office then google for "Open Office". It's a freeware MS Office compatible package that'll run the spreadsheet for you and well worth the install.
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Old Mar 25, 2010, 09:52 AM
RCHN #202
Dowquest's Avatar
United States, CA, El Cajon
Joined Nov 2007
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BMatthews, your link didn't come through, but through the magic of Google I found it. Thanks.
http://www.b2streamlines.com/Panknin.html

So from your post, I'm taking the basic thought of more sweep = more stability + less tip washout. less sweep = less stability + more tip washout .
From my experience, I think alot of the stability can be addressed with forward cg/ balancing of the model. making the more swept models easier to balance due to more real estate in front of the cg. I also use this calculator for a starting point on my wings. starting at 20%
http://fwcg.3dzone.dk/
Would you agree?
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Old Mar 25, 2010, 01:00 PM
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I've run across some articles on the affect of wing sweep, dihedral and other parameters in the RC Soaring Digest. You can find these issues at http://www.rcsoaringdigest.com/pdfs/ A lot of articles specific to planks / flying wings is in the "On the Wing" series in that magazine.

As examples, download and look at:
Sept 96 - experiments of design changes having to do with wing sweep,
Jun 97 - Virtues and problems of excessive wing sweep are discussed
Mar 2000 - Sweep & dihedral change effective dihedral
Mar 01 - planforms with sweep work best using twist between the root and tip

There is an index ("INDEX through 2005") you can download and search for more articles at http://www.rcsoaringdigest.com/ toward the end of the page.

Great stuff on aerodynamics in the magazine.

Alan

Added Later: Bruce found the article I was originally looking for
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