How do they make hollow square wing joiners? - RC Groups
Thread Tools
Feb 06, 2013, 06:52 PM
One Idiot is plenty...
Dbox's Avatar

How do they make hollow square wing joiners?

Can't find any info or video on that subject.
Appreciate any input.
Sign up now
to remove ads between posts
Feb 07, 2013, 04:50 AM
Launchpad McQuack
Prop-er's Avatar

Pictures speak for themselves.
Feb 07, 2013, 06:24 AM
Deniable plausibility
Shedofdread's Avatar
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.
Feb 07, 2013, 06:37 AM
chetosmachine's Avatar
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.
Feb 07, 2013, 03:23 PM
chetosmachine's Avatar
I didn't remember I had this picture on my gallery:

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.
Feb 07, 2013, 06:25 PM
Deniable plausibility
Shedofdread's Avatar
I'd not seen that aeroplane of your's before - VERY nice... Oh, and cool name!
Feb 08, 2013, 12:49 PM
One Idiot is plenty...
Dbox's Avatar
Originally Posted by Shedofdread
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.
Feb 10, 2013, 11:42 AM
Mongo like wind. Wind Good.
V1VrV2's Avatar
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.
Feb 10, 2013, 08:36 PM
Entropy is happening!
Jim.Thompson's Avatar

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.

Feb 10, 2013, 11:58 PM
One Idiot is plenty...
Dbox's Avatar
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.
Feb 14, 2013, 01:45 PM
chetosmachine's Avatar
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!
Feb 14, 2013, 04:28 PM
Entropy is happening!
Jim.Thompson's Avatar
[QUOTE=chetosmachine;24135173].................................................. ...................Jim, the interest of hollow is that you can put ballast on it. No structural advantage.

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.


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Question Carbon wing joiner: diameter? How make outer tube? sroge The Builders Workshop 10 Jan 25, 2013 02:38 PM
Discussion How to make a very thin, airfoil wing? mongdex Foamies (Scratchbuilt) 7 Jan 15, 2013 05:32 PM
Question How do you make sealed hollow molded Ailerons or Flaps? tommyt Composites Fabrication 5 Oct 25, 2007 12:16 PM
Hollow Molded are they made?? CDignition Hand Launch 3 Feb 13, 2004 03:17 PM
How do they make hollow molded wings? TheTick Slope 4 Jul 25, 2003 12:56 AM