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Old Aug 31, 2014, 09:29 AM
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Sean Moloney's Avatar
Sunshine Coast, Australia
Joined Jun 2007
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I'm not so sure a bulkhead would make much difference. The original fuse has an area of solid splooge at the base of the fin which would act similarly to a bulkhead. What's needed is a very strong bond between left and right halves along the top of the fuse from the base of the fin forward - a bulkhead has a very small surface area bonded to the sides which would break away quite easily.

What I did on the fuse I just built was, prior to joining, I added a couple of layers of carbon, about 50mm wide by 100 long, along the top of the fuse at the base of the fin that stuck above the parting plane about 25mm. When that carbon had gelled a bit I applied some spooge to its outside surface, then joined the fuse halves. This gave a large area of carbon bonding the top of the fuse at the base of the fin, in addition to the joggle. I reckon that should make a big difference.
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Old Aug 31, 2014, 03:53 PM
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timbuck's Avatar
gold coast australia
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Carbon Bulk head is probably not the word to use. More like a inner sleeve , like a molded insert. Might even find a type of tube that fits to make thing easier.

What you have done sounds perfect. As I don't think it needs muck to cross brace the seam.
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Old Aug 31, 2014, 05:06 PM
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Jim.Thompson's Avatar
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That sounds like the go Sean.
However, I wonder if you could use a balloon (or something similar) just in that section to positively clamp that carbon overlap onto the mating half without the need for prior gelling off?
Relying on the stiffness of this to support splooge at gel stage seems a bit doubtful to me.
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Old Aug 31, 2014, 11:40 PM
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Sean Moloney's Avatar
Sunshine Coast, Australia
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Quote:
Originally Posted by timbuck View Post
... More like a inner sleeve , like a molded insert. Might even find a type of tube that fits to make thing easier.
That was my initial idea too. I was tossing up with the way I did it, or a carbon sock around foam, but with the sock there's a possibility it could get pinched somewhere and stop the moulds from closing so I decided not to try it this time. I reckon it could work with a bit of experimentation though.

Quote:
Originally Posted by Jim.Thompson View Post
...I wonder if you could use a balloon (or something similar) just in that section to positively clamp that carbon overlap onto the mating half without the need for prior gelling off?
Relying on the stiffness of this to support splooge at gel stage seems a bit doubtful to me.
Using a balloon would be good but I can't think how that would work without the complication of plumbing to expand the balloon?

The way I did it I think worked really well. The curved joggle provides a surface to help conform the carbon to the right shape. It might be hard to imagine without seeing it. I have some pics I can post if you're interested.
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Old Sep 01, 2014, 08:52 PM
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New Zealand, Auckland
Joined Aug 2006
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Quote:
Originally Posted by Sean Moloney View Post
Using a balloon would be good but I can't think how that would work without the complication of plumbing to expand the balloon?
On my t tail fuses i build for ds, i use bladder to join the halves, inside a mold
Thats completely enclosed.
I plumb the hose into the mold through the elevator servo hatch
On the side of the fin

Im not sure you ever wanting to do the bladder thing, but theres a
Suggestion if you need it
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Old Sep 02, 2014, 08:20 PM
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Jim.Thompson's Avatar
Australia, NSW, Bellingen
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Another suggestion.

This may be totally superfluous Sean, as you seem to have arrived at a satisfactory solution to the join at the tail area problem, but thought I would describe it anyway.

A suitable length of carbon tube could be pre-made slightly larger in diameter than the internal diameter of the affected part of the tail boom.
A lengthwise slot could be cut in it to allow it to overlap and have some spring "pre-load" effect when placed inside the assembled fuse halves after the usual preparation and application of the joining splooge.
Making sure of course, to orient the join at the horizontal (or 90 deg.) position in the fuse.
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Old Sep 02, 2014, 08:51 PM
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I've repaired a fuse boom like that.

Wet out some carbon cloth on freezer bag plastic and wrap it around the boom just forward the break, over lapping the materials by about 10mm.
Once cured, it compresses enough to place back inside the boom to sleeve it.

Makes for a more aesthetic repair but I could see it working well for a join too

D.
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Old Sep 02, 2014, 08:51 PM
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timbuck's Avatar
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That would be strong.
I had a thought last night about doing the seam the way you are doing it sean , and just add expanding PU to that area just before you close it. This would ensure the seam is push out perfect. I'm sure 20 or 30g would do it.
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Old Sep 02, 2014, 09:02 PM
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Sean Moloney's Avatar
Sunshine Coast, Australia
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Quote:
Originally Posted by Jim.Thompson View Post
...A suitable length of carbon tube could be pre-made slightly larger in diameter than the internal diameter of the affected part of the tail boom.
A lengthwise slot could be cut in it to allow it to overlap and have some spring "pre-load" effect when placed inside the assembled fuse halves after the usual preparation and application of the joining splooge.
Making sure of course, to orient the join at the horizontal (or 90 deg.) position in the fuse.
I think that's quite a nice idea Jim. To mould the sleeve I'd need to find a tube that was of the right diameter, a piece of ali tube could possibly work. I couldn't use the Deepend's boom to make it because the area in question is the smallest diameter part of the boom, and the layup is thick.
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Old Sep 02, 2014, 09:04 PM
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Sean Moloney's Avatar
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Quote:
Originally Posted by timbuck View Post
That would be strong.
I had a thought last night about doing the seam the way you are doing it sean , and just add expanding PU to that area just before you close it. This would ensure the seam is push out perfect. I'm sure 20 or 30g would do it.
That could work nicely too. I've never used expanding PU though, I'd need to to some tests to get a feel for it.
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Old Sep 02, 2014, 09:37 PM
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Quote:
Originally Posted by Sean Moloney View Post
I think that's quite a nice idea Jim. To mould the sleeve I'd need to find a tube that was of the right diameter, a piece of ali tube could possibly work. I couldn't use the Deepend's boom to make it because the area in question is the smallest diameter part of the boom, and the layup is thick.
I would machine up a length of wood in a wood turning lathe for use as a mandrel to make the carbon tube.
If you don't have access to one I do. I could machine it up for you and bring it to Borah should you decide this is worth a try. You would just need to tell me the approximate internal diameter(s), plural if there is any considerable taper along that area.
If it is not completely round in section, some final hand work would make it sufficiently eliptical. Probably not necessary in practice though?

edit:
Actually, it would not even need a lathe to do this. I've a long history of hand shaping yacht spars and tool handles; it could be quickly hand shaped using the following in this order:
Power planer,
Hand plane,
Then cross (45deg/45deg) sanding with 40 grit "belts" of sanding paper while holding the extra length in a vice.
Final light sanding lengthwise.
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Old Sep 02, 2014, 10:31 PM
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Sean Moloney's Avatar
Sunshine Coast, Australia
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Thanks Jim, shaping up some timber would work well. If you'd really like to do it I can send you some dimensions, otherwsie I'd be happy to do it myself. It'd only be quite small and 15mins of sanding some MDF on my belt sander would have it done. But if you were keen and not too busy with other things I'd certainly be happy for you to do it!
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Old Sep 09, 2014, 11:58 PM
flo
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flo's Avatar
Near Munich Germany
Joined May 2003
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Hi Sean,
as im not a native english speaker i might have misunderstood the ongoing conversation but i might have some tips for you?

First of i read you have problems to cut your Layup on the parting lines.
I do this not when cured, but around at 8-9 hours into curing. Depending on temp.
At this stage the layup feels sort of dry, even hard but it is still flexible. like a plastic sheet.Then use a freshly sharpened chisel and push along the flange. If one gets the timing right, it takes like a minute for my Hannibal fuse per half
The blade might last about one fuse-mould side only so make sure you have enough chisels around.

For joining i did try a couple of things but had the best results using a seperate mould for the flange...
I ll post some pics to explain.

Only comment to ad would be that i do not make the flanges too strong a layup as there still needs some flex to get best results.
And to use peelply on the fuse and flange layup for better results.

I also did use a fg-"tube" (precured) in a couple of my builds and it does work great.
as the tube is inserted with a mix of splooge around the whole perimeter it gives an extremely strong bond between halfes ( big contact area around the perimeter) and the fuses are some of the strongest i have ever seen. It might get tricky if you really need strong taper into your shape...
I have overcome that problem by usinging staggered layers and just more splooge. that gives extreme wall thickness as well, and the wall thickness tappers down too so not to bad engeneering .
Hope to find some pics ot it

For an already build fuse / quick fix we usually wrap TESA Film ( brand name of a clear office tape which is extremely strong for its purpose) in multible layers from tail to wing. Overlaped each rev of course
One does not belive how strong this ends up as the tape serves multible purposes:
It protects the layup somewhat from direct impact .
It adds wall thickness
It stops the halfes from flexing and this prevents the joins to open.
Just make sure there are couple of layers - i usually would do 3 layers

Sounds funny but it really helps a lot-
probably not on a multi layup ds plane but on your regular sloper or on a prototype that came out with a less than perfect join on the halfes..

greets

flo
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Last edited by flo; Sep 10, 2014 at 12:04 AM. Reason: spelling
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Old Sep 11, 2014, 10:41 PM
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Sean Moloney's Avatar
Sunshine Coast, Australia
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Thanks for the tips Flo!
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