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Old Jan 23, 2013, 08:29 PM
Flutter-Bys are fun
Conehead's Avatar
United States, MI, Honor
Joined Dec 2005
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Another great glue for depron is Foam-Tac made by Beacon.

You put it on what you want to glue, put the pieces together to get the glue on both pieces, seperate them for about 10-20 minutes, then press back together. Max bond takes place within 24 hours.
It stinks to high heaven, but I love the smell. Sort of a "high" on glue that you used to get from dope when we used silkspan, I guess some still do.

Conehead
Orrin Eldred

2DogRC has it, others also have it. TnT Landing gear I think.
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Old Jan 23, 2013, 09:03 PM
Dr John
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Lake Placid, Florida
Joined Dec 2001
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Quote:
Originally Posted by Chrizz View Post
Hi again!

While at talking Depron...
Here's another thing that's good to take into consideration: Depron is a laminate.
It consists of two layers of some kind of plastic-foil with foam in between. Its strengh is also the result of that.
This is worth talking into consideration when building: i.e. if sanding the surface of a sheet of Depro, it will loose some of its strengh, rigidity, in a non-proportional way, when the plastic-foil thins of.
Another interesting fact, when comparing the weight of different Depron thicknesses (1mm, 3mm, 6mm...), is that the weight increase isn't proportional to its thickness. I.e. 1x6mm is lighter than 2x3mm because of its laminate construction.
It's not "just" foam...
I belive you will find that the "foil" is a skin that is formed during the extrusion process. It is all the same stuff but the skin closes the pores on the surface. There is a higher concentration of weight in the skin and it does add strength. That is why 3mm is well over half the weight of 6mm, ect. I build a lot of thin wings by sanding a basic airfoil into a 6mm wing. If I don't think a carbon spar will make it strong enough I will glass with 3/4 oz glass cloth and WBPU.

Dr John
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Old Jan 24, 2013, 03:49 AM
What could possibly go wrong?
nickchud's Avatar
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Joined Apr 2006
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Thanks Dr John

I've noticed that WBPU with a bit of sanding gives a lovely surface for painting whilst restoring all the fray that results from sanding off the original skin.

What about the weight penalty of glass cloth? For my fairly large (6' ws) Depron EZ I'm considering making spars from Depron strips between the top and bottom surfaces. Before putting the top on, I wonder if glass cloth around these spars will be effective in terms of rigidity per weight. Alternatives are cf or balsa strips. My instinct tells me that it's a very good idea.

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Old Jan 24, 2013, 07:48 AM
Dr John
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Lake Placid, Florida
Joined Dec 2001
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Nick
Once you sand through the skin you are into open pores and a rough surface. The glass WBPU will be heavier than the original skin but also much stronger. A lighter way to get a smooth surface but without the strength benifit of glass is to work thinned light weight spackle into the surface with a wet finger and sand with 220 after it dries.

If I was building a 6' wing with Depron I would make the spar with solid foam and cap top and bottom with CF. This will give you a increadibly strong structure with minimum weight.

Dr John
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Old Jan 24, 2013, 08:49 AM
What could possibly go wrong?
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Market Harborough
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Thanks John

when you say "glass WBPU" does that mean including glass cloth? My current Seabee project has lots of compound curves. I've been using 50-50 spackle and WBPU to repair all the open pores and seal the surface. Seems to be working well, though I'm not counting on it for structural strength. For that, I'm sure the glass cloth is necessary, with a weight penalty.

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Old Jan 24, 2013, 09:01 AM
Dr John
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Lake Placid, Florida
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Yes Nick
"Glass WBPU" means fiberglass cloth applied with WBPU. WBPU or spakle will give a smooth surface for painting without the glass cloth but for the increase in strength you will need the glass and the weight penalty that comes with it.

Dr John
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Old Jan 24, 2013, 10:34 AM
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Joined Mar 2008
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CG for a Shinden

Where'd you put the CG on this? The span is 57" with a MH45 airfoil. The canard (Charles might call it an elevator trim tab) span is about 14".
I oversized the wing quite a bit from scale to get it to slope better, the rest is scale.

Should I set the CG where a flying wing would be? Using a flying wing calculator, that'd be 6 inches from the LE.
Seems like the CG should be forward of that, but how far?
The Canard has a hand shaped symmetric airfoil.

Where's the CG calculator for canards?

I hope to maiden it this weekend!

Dave
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Old Jan 24, 2013, 11:45 AM
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Tampere, Finland
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A couple of free flight plans put Shinden CG pretty close to wing leading edge at fuselage. They show a big range, though: slightly forward of leading edge - about 15% behind leading edge.

... or it could be something totally different if the proportions of your Shinden don't match the proportions in those particular plans.
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Old Jan 24, 2013, 12:19 PM
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The CG for flying wings estimated the CG to be 6 inches from the LE.
From there, I imagine I'm trying to factor in the lift generated from the canard which is exactly to scale (not shown in this picture) although my symmetrical airfoil there may be different.

Good to hear the CG from other models is at 15% back. That's telling me I should move the CG forward, but not a lot.

I used the flying wing airfoil (MH45) and larger wing so that the canard would have to serve as little more than an elevator trim tab. It will have an effect; And I must remember the first rule of canards; The canard must stall before the wing does.

I think if it's a bit nose heavy, and I maiden her in strong lift (20+mph) I'll have success. CG at 15%. I'll move the battery tonight.
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Old Jan 24, 2013, 01:17 PM
What could possibly go wrong?
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Market Harborough
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Here's a reliable CoG calculator for canards. I usually put in the static margin at 10%. And I set the incidence of the canard at 2 deg more positive than the wing.

Best of luck!

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Old Jan 24, 2013, 02:58 PM
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Another change I made to the shin den was to make the canard full flying (easier to repair...slope landings are brutal)

I am stuck at the mixing options;
1. canard as elevator, with ailerons (the way it ought to be)
2. canard as elevator with elevons
2a. elevator on throttle stick to trim it
or
b. elevator on elevator channel mixed with appropriate % elevon assistance
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Old Jan 24, 2013, 04:49 PM
What could possibly go wrong?
nickchud's Avatar
Market Harborough
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I haven't progressed beyond the Keep It Simple, Stupid stage.

I mean, option 1 works, why fix it?

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Old Jan 24, 2013, 06:02 PM
Lighting Up the Darkness
United States, GA, Loganville
Joined Jan 2013
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Dihedral or no Dihedral....

Great COG tool. Thanks so much for the link....and speaking of keeping it simple.....

I am about to start a GWS slow stick conversion as outlined early on in this group by Charles. I do have a J3 cub wing that has a flat airfoil that I could cut down for the canard, per the detailed recommendation. But I just happened to have this little foam wing (survivor of something tragic!), I know it's big enough and I think the throws would be sufficient, but as you can see, it is not flat. There is an incident of dihedral, fairly significant. What do you think of this as a candidate for the canard?

I've seen swept back, and swept forward canards, but I believe they were flat airfoils. Not sure how the dihedral factor would effect the behavior of the canard.
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Old Jan 25, 2013, 04:28 AM
What could possibly go wrong?
nickchud's Avatar
Market Harborough
Joined Apr 2006
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Hmmm Where's Don when you need him?

Maybe Charles can answer that one. I don't have much experience with dihedral canards. My canard wings have flat bottomed airfoils and the main wings are usually symetrical or semi-symetrical. I don't like the under-cambered airfoils, but lots of other people have used them for canard type planes.

Horses for courses. Some configurations fly like aerobats, some like racers, some like gliders and some like trainers. It all depends what you want.

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Old Jan 25, 2013, 09:17 AM
Lighting Up the Darkness
United States, GA, Loganville
Joined Jan 2013
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Thanks Nick! I believe I'm going to try this horse and just see what kind of course it takes me on. If its squrally, unstable, or otherwise unfun in the air, I'll change it out for a flat canard!
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