Lumenier RB2205C-12 2400KV SKITZO Ceramic Bearing Motor
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Old Dec 27, 2011, 05:42 PM
Shedofdread is offline
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Deniable plausibility
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How did you go about selecting the amount of washout used? The old-fashioned way, or by one of the tailless design packages?
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Old Dec 27, 2011, 05:46 PM
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...opps
Old Dec 27, 2011, 06:35 PM
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This wing was designed before I even knew what computers were. I used the black art method .... guess, untill it flew. I did find out quickly that 2 degs. of washout made the tow exciting. But, they flew very fast. I must have made 12 wings that only lasted 1 flight. Once I had success with the tow everything was right with the world. Computers have made things so much easier.

Vern Attached is one of my wing works of art
Old Dec 27, 2011, 06:46 PM
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I was under the impression that such swept flying wings, with tip rudders, where typically designed with no washout. Is this current one at zero degrees washout?

Kent
Old Dec 27, 2011, 07:19 PM
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Kennt, there's an overview of a number of european tailless rc models:

http://www.aerodesign.de/modelle/3S_NF.htm

It's from Hartmut Siegmanns website http://www.aerodesign.de .

You can find planform sketches of many models there with additional informationon the washout used.

biber
Old Dec 27, 2011, 07:41 PM
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Thanks biber. Those are great links and all new to me. I'm clearly going to have to learn some German.

For example, does this wing have 1.0 degree washout at the end of the inner elevon and 2.5 degree washout at the tip?

Kent
Old Dec 27, 2011, 07:52 PM
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Incidences according to the description are:

0.0° at 0/3 (half-)span (center)
-1.0° at 1/3 (half-)span
-2.5° at 2/3 (half-)span
-4.5° at 3/3 (half-)span (tip)

biber
Old Dec 27, 2011, 07:56 PM
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Of course, I see it now
Thank you.
Old Dec 29, 2011, 07:55 AM
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I built a vacuum bagged wing using a HS 522 airfoil.I studied Hartmut's website ( right click and translate ). Not good as knowing German but a big help. I made it very light with a glass skin and minimal carbon spar. It was electric powered but weighed about 27 oz. It was a great thermal bird! I only used 3 degrees washout and should have used more. It flew with up trim on the elevons. Handling was relatively good but it took full stick in turbulence.I was inspired by an article by Neil Pollock in Feb/ March 2006 Quiet Flyer. I did a little build thread here http://www.rccanada.ca/rccforum/showthread.php?t=82290
Old Dec 29, 2011, 10:57 AM
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Quote:
Originally Posted by Vernon Hunt View Post
. It has progressive twist, ending at 4.5 degs....
I hope it doesn't flutter like my first version 13 years ago.
Vern
So from your previous comments, when you used less washout, you had handling problems on tow but it was a cleaner/faster ship. Is that about right?

Flutter is a tough nut to crack. I also had a "flapping" swept wing like this until I added so much carbon and glass that it wouldn't fly. Just like bending forces, I think that flutter resistance is best handled by focusing reinforcements at the root area. Any thoughts?

Kent
Old Dec 29, 2011, 04:38 PM
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Kent,

Less washout makes the glider very squirley on tow. Maybe if I had taken it to a slope it would have proven to be a very good fast flyer. But, I was looking for a soaring ship I didn't need to drive for an hour to fly.
The first skinny wing had no spars.... so it flapped on tow. Once off tow it was a dream to fly. So I started to put spruce spars in (I had no carbon) this did wonders in eliminating flapping. I now use carbon tow 1/3 of the way back from the leading edge, top and bottom.
I sand a shallow ditch about 1/32" deep and 1/2" wide with a narrow sanding block. That way the carbon fills the ditch and does't leave a lump in the sheet balsa when bagged. Along with that I now I put carbon tow just ahead of the line that the ailerons and flaps are cut. Sometimes I'll put 1 strip off carbon tow at the trailing egde to keep it straight and ridgid.
The root needs to be strong but light, so I use 1/4" plywood with carbon tow top and bottom bagged before setting it into a ditch carve into the 2 halves. There's not much room in these narrow chord wings so careful planning in where the spars and wiring for the servos go.

I hope this makes sense. I bagged some of my wings with 2 oz. carbon cloth, but that became so expensive I went back to using balsa. Now carbon cloth is crazy expensive and I haven't used any for years.

Vern Flying wings need to be light for great flatland flying.....
Old Dec 29, 2011, 05:33 PM
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Any anhedral Vern? also any suggestions on optimum hook position relative to cg?
Old Dec 29, 2011, 07:30 PM
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Paul,

Yes, 1 deg. of anhedral per side. That seemed to work pretty well. I put my hooks about 1/2" ahead of the CG.
How's your thermal wing coming along?

Vern
Old Dec 29, 2011, 07:43 PM
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I'm obviously the noob in this group. I've noticed that these wings often have anhedral in the tips, which in conventional aircraft would make it roll unstable.

Can someone explain this one to me? A link to a German website would be fine. No doubt some thing to do with the sweep.

Thanks,
Kent
Old Dec 29, 2011, 08:06 PM
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Winglets are basically a very extreme form of polyhedral.

Adding to that, sweep does act like dihedral, whenever the swept wing does create lift.
So at low speed, the dihedral effect of the sweep contributes noticably to the whole and at high speed it hardly does at all.

With sweep and winglets you have lots of effective dihedral already and in many cases less would be better.
Then you build some anhedral into it to have just the needed amount.

biber


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