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Old Feb 06, 2013, 06:52 PM
One Idiot is plenty...
Dbox's Avatar
Planet Earth
Joined Jun 2005
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Question
How do they make hollow square wing joiners?

Can't find any info or video on that subject.
Appreciate any input.
Thanx.
Yuri
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Old Feb 07, 2013, 04:50 AM
Launchpad McQuack
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Netherlands, Moordrecht
Joined Sep 2004
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https://sites.google.com/site/projek...nder-laminiert

Pictures speak for themselves.
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Old Feb 07, 2013, 06:24 AM
Deniable plausibility
Shedofdread's Avatar
Derbyshire, UK
Joined Aug 2008
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Great link - thanks for posting

Never sure re the pros and cons of hollow joiners. Some say they fail in a crash thus protecting the wing but I'd be concerned about in-flight failure (clearly though many are fine).

Just my '2p' but I use a structural foam (Core-Cell) and it stays in there.
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Old Feb 07, 2013, 06:37 AM
chetosmachine's Avatar
Madrid, Spain
Joined Sep 2004
1,102 Posts
I make my joiners both hollow and with foam in them; I tried to use acetone to solve foam but the inside was quite rugged and not worth it.
Now I mold them with some brass slugs on the inside with 2 layers of plastic with vaseline between the plastics. After cure, a very hard pull will remove the brass, then remove all plastic and the fit for the brass ballast is quite good.
I never broke a joiner, even when full ballasted(2250g) in rough conditions.
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Old Feb 07, 2013, 03:23 PM
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Madrid, Spain
Joined Sep 2004
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I didn't remember I had this picture on my gallery:
https://picasaweb.google.com/1067359...96989020031602

The left one has a foam core (30kg/m3 expanded poly, CNC hot wired); the right is hollow and has some balsa and carbon on the vertical walls.
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Old Feb 07, 2013, 06:25 PM
Deniable plausibility
Shedofdread's Avatar
Derbyshire, UK
Joined Aug 2008
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I'd not seen that aeroplane of your's before - VERY nice... Oh, and cool name!
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Old Feb 08, 2013, 12:49 PM
One Idiot is plenty...
Dbox's Avatar
Planet Earth
Joined Jun 2005
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Quote:
Originally Posted by Shedofdread View Post
I'd not seen that aeroplane of your's before - VERY nice... Oh, and cool name!
Chetosmachine is Master Magician from Spain
Thank You Chetos.
I got some ideas now.
Yuri
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Old Feb 10, 2013, 11:42 AM
Mongo like wind. Wind Good.
V1VrV2's Avatar
Joined Apr 2004
424 Posts
Silicone (not foam, sometimes rohacell) inserts inserted in molds laminated as described above. Whole assembly placed in oven, silicone expands under heat and compresses laminate. After cooled, remove silicone inserts. Done.
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Old Feb 10, 2013, 08:36 PM
Entropy is happening!
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Australia, NSW, Bellingen
Joined Aug 2008
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Yuri,

I have only made foam cored wing joiners. As of yet, I am unaware of the advantages of hollow over foam cored. More ignorance than anything else.

I put one plywood shearweb in mine in the centre. I've seen pics of them with two.
Also, a bit off the point, but I made mine with carbon tow which worked. However, it is very challenging to do without getting some voids. I read recently on Sean Moloneys Deepend thread where he uses uni-carbon, which must to a large extent, minimise or avoid this problem.

Not a good pic I know! Better one later.

Jim.
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Old Feb 10, 2013, 11:58 PM
One Idiot is plenty...
Dbox's Avatar
Planet Earth
Joined Jun 2005
5,186 Posts
Interesting techniques with silicon ,however there are to many of different silicons to give it a try

Uni carbon has great epoxy absorption,as far as I concern and usually
I have never had any voids problem with it.

Thanx for more info guys.
Yuri
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Old Feb 14, 2013, 01:45 PM
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Madrid, Spain
Joined Sep 2004
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Thank you for the nice words men! =)
Vendetta is my latest creation and I am only making them for me and my partner, but this may change -or may not-.

Jim, the interest of hollow is that you can put ballast on it. No structural advantage.
I have not tried the silicon because my aluminium mold distorts a bit when I put it in the oven. To be fair, it was the first time I was making a hollow joiner and may be something moved and made me closing the mold harder than usual so I did not force things at all.
With the brass cores and 2 plastics with vaseline between them it's not hard to demold and I can post cure the joiner out of the mold. My brass is a special measure and not good quality; one important thing is the better the quality on the inserts, the easier the release. While this may be obvious, it's easy to think something is supposed to be straight and when you measure it...... surprise!
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Old Feb 14, 2013, 04:28 PM
Entropy is happening!
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Australia, NSW, Bellingen
Joined Aug 2008
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[QUOTE=chetosmachine;24135173].................................................. ...................Jim, the interest of hollow is that you can put ballast on it. No structural advantage.
...............................QUOTE]

Yes! So obvious but I did not think of it, thanks. Very neat little trick.

I have just obtained some silicone (2 part RTV) for another task. I will have plenty left over and I might get around to trying it out for manufacturing a hollow joiner.
The choosing of a type of silicone for a particular job is challenging. I was on the phone for a long time choosing this one. In the end, it was a young sounding woman who knew her stuff best, and immediately understood my description of the application, helped with a couple of pictures.
However, I like your brass (rod?) forming idea. I would try spiral wrapping the rod with drop sheet plastic - I've used this method successfully for making small tubes. The Carbon would then need to be a mix of uni and tow to shape the layup around the round rod.
That is, or course, if round is used.

The joiner I have in my current plank (see my blog) is 40 x 12 mm. Plenty of scope for hollow cavities.

Jim.
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