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Old Jul 30, 2011, 01:42 PM
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Kent, UK
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3.2m thermal 'wing

Time for another 'wing!

I'm planning for this to be just over 3.2m span and will use it off the flat as a power assisted thermal ship.

The plan is driven by what I can cut from readily available foam panels without waste. As it happens, the layout is almost exactly the same as a 2.4m 'wing I built a few years ago.

This new model will be bagged foam, probably with a carbon 'd' box for rigidity. The 2.4m wing had no spar and flutters easily. I'd like this new version to be a lot stiffer so that maybe I can make a slope pod with ballast tube and/or winch launch it.

I've attached my initial sketch and hope some of the usual suspects will chip in. I'm going to use the HS 522, as it seems to come up trumps for several studies Edwinzea has done.

First question...

Is there any benefit from a 3 stage washout like the later CO 'wings? I will need to cut each semi span in three sections anyway. so hope someone can inform me as to whether it will be worth steeping the twist rather than doing linear washout.

I look forward to hearing from you all!
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Old Jul 30, 2011, 01:58 PM
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Colorado
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Quote:
Originally Posted by miniphase View Post
Time for another 'wing!



Quote:
Is there any benefit from a 3 stage washout like the later CO 'wings?
Yes. The washout produces a dead spot on the wing that produces no lift but plenty of drag. Thus 'wings do have parasite drag even though they don't have all those nasty non-wing parts. Non-linear washout reduces the size of this dead spot and moves it toward the tip where it adds to the directional stability.

--Norm
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Old Jul 30, 2011, 02:02 PM
Designing something...
United States, CA, Cameron Park
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Nice! But why so small? Just kidding! I'll definitely be watching this thread.

Brian
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Old Jul 30, 2011, 02:06 PM
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Kent, UK
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Originally Posted by nmasters View Post
Non-linear washout reduces the size of this dead spot and moves it toward the tip where it adds to the directional stability.

--Norm

next question....how do I calculate it Norm?

I was planning on 2 degrees linear root to tip, how would I go about translating this to a non linear twist?
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Old Jul 30, 2011, 02:45 PM
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You could just guess but I think I have his article on my hard drive. I have people expecting me to act like a responsible grownup for a few hours so it'll be a while before I can look for it. latter
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Old Jul 30, 2011, 03:08 PM
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No problems Norm.

I won't be cutting the cores for a few days yet, enjoy your stint of responsibility....I prefer to give such duties a wide berth!
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Old Jul 30, 2011, 03:55 PM
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Originally Posted by cpdude View Post
Nice! But why so small? Just kidding! I'll definitely be watching this thread.

Brian

I hope to get it thermalling high enough to make it look very small Brian
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Old Jul 30, 2011, 06:00 PM
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Blackstock, South Carolina
Joined Sep 2007
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Perty. But I'm all thumbs when it comes to foam. Doesn't anyone make a good size thermal FW out of balsa?
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Old Jul 30, 2011, 06:23 PM
Designing something...
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@Fly Wheel - Yes! Well, I guess that depends on what you mean by "good size" Anyway, Take a look at some of my posts. You can decided.

Brian
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Old Jul 31, 2011, 01:07 AM
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Australia, SA, Windsor Gardens
Joined May 2001
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@fly wheel and CPdude. Well not quite balsa. But the liteply is pretty lite, and much stronger. You can actually use little spring clamps on the ribs without crushing them.

@ miniphase, looks good, i'd put a nice little bat tail on there but i'm just partial to them
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Old Jul 31, 2011, 01:40 AM
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Originally Posted by nmasters View Post
You could just guess but I think I have his article on my hard drive.
The article I was thinking of was Jochen Haas' piece describing his design procedure for highly tapered 'wings with BSLD and no vertical fins. Obviously that's not what you need for this project but others watching may find it to be for them.

So I looked elsewhere and found two references to segmented washout on Hans-Jurgen Unverferth's 'wings. Twist Distributions for Swept Wings, Part 1 mentions washout in three segments:

Zero twist on the first 1/3 of the half span
then 1/3 of the total washout on the second 1/3 of the half span
then 2/3 of the twist in the last third of the half span.

But as far as I can tell both the CO2 and the CO5 had a two segment washout schedule: no twist on the inboard half and all the washout on the outboard half.

--Norm

P.S. There's an article about the winglets that Burt Rutan designed for the LongEZ that you should see.
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Old Jul 31, 2011, 02:22 AM
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Kent, UK
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Thanks Norm

The CO8 used the 1/3rd step, the Zanonia site shows this in a bit more detail http://www.zanonia-flyers.de/

So my intuition tells me that if I have no twist for the first 1/3rd of half span, then I'll need a bit more on the outboard 1/3rd

Hopefully Edwin will chip in, he stepped the washout on his last swept 'wing
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Old Jul 31, 2011, 03:47 AM
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Originally Posted by Fly Wheel View Post
Perty. But I'm all thumbs when it comes to foam. Doesn't anyone make a good size thermal FW out of balsa?
Here's one for inspiration!

http://www.rc-network.de/forum/showt...%28-Kr%E4he%29

The text isn't English, but lots of photos.
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Old Aug 02, 2011, 01:13 PM
the answer 42 is
Switzerland, AG, Lenzburg
Joined Jan 2006
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Hey Paul

I stop visiting the FW forum for three days and you come with something new already :P I also planning on starting my 3m project this week :P if everthing goes right.

I tested the non linear washout in XFLR5 and it gives better glide ration and less induced and viscose drag, as norm has already pointed. I also teste it on my A.J.R.V. and it works pretty well.

I can calculate the wash outs for you(shame on you, you did not asked me ) :P please give me more details on the profiles, to make a good XFLR5 model. do you want to use the same thickness allong the wing??

Are you making a three piece wing??

good luck

EZ

PS. I should read the whole thread before postin, shouldn't I??
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Last edited by Edwinzea; Aug 02, 2011 at 01:18 PM. Reason: I forgot something :P
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Old Aug 03, 2011, 01:44 AM
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Kent, UK
Joined Nov 2004
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Hi Edwin

HS 522, constant thickness.....I'm thinking two piece wing purely because I don't enjoy messing around with joiners, but I'll se how I feel as the build progresses.

I've now got some time away from work so foam cutting will begin shortly!
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