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James Hammond Sigma II joiner broken


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Darren_O

I know the answer but I'm hoping against hope.

Is it fixable because the chances of finding another are next to nothing:(

Or does anyone do custom joiners? It's roughly 36 wide X 13 deep X 375 long with about 2° dihedral. 

IMG_20200830_165844_484.jpg

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isoaritfirst

Think you are missing a dimension Darrren. 

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mikef

Is that 36mm x 13 mm?  It looks hollow with a squared off figure 8 section.  If so, do the holes go right through the length?  A clear picture end-on to the failure might help.

It looks like carbon/epoxy?

Later edited 18 to 13.

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Darren_O

Holes right through, measurements adjusted for decimal places and missing measurement, apologies. Looks to be carbon to me.

 

IMG_20200830_180504466.jpg

IMG_20200830_180808151.jpg

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mikef

I assume that your top picture above is one of the outboard ends.  It seems to show the central web detached from the bottom flange?  How did that happen?

I'm thinking that, if the joiner is constant width and thickness, a sacrificial hard balsa mould and lay up a new 'solid' joiner might be the way to go - if you can't buy a new one.

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satinet

I don't think it's practical to repair it. 

You might have to look at making your own. I think the extra weight of a solid joiner won't matter. 

Have a look on rcgroups. 

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Darren_O

That's definitely beyond my limited workshop right now.  I'll stow the old girl away until we move and I build my workshop I've always promised myself.

Thanks for the link, I'll bookmark it for when I'm better equipped:)

 

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Peter G

It looks very much like the Predator (P3) joiner. I don't have one to measure but wouldn't be surprised if the joiner was common to Predators and possibly Strega's as well as the rather rare Sigma 2. Maybe a predator owner could confirm?

May be worth a try with RCRCM stockists or in wanted / for sale?

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Robert099

Just checked, Predator is 36 x 12 x 357 long and as Peter notes I think it is then same as the Strega.

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isoaritfirst

36 x 12 rather than 13 , i would say would be a useable option. It could be reworked perhaps with a layer of cloth. 
unless of course you are going for high power wince launches 😁

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isoaritfirst

Wince 🤣 don’t you just love auto correct

 

🤣🤣

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satinet

As an idea you might be able to tack it back together and pull a bundle of carbon tows through the two holes it to make it in to solid joinner. E.g gold the tows in half and tie fishing line to it.

Then repair the crack from the outside.

But you will need to get the right dihedral angle and perhaps more importantly keep it straight in the other dimension and avoid a twist.

 

Dunno might be easier to make a new one.

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  • 3 weeks later...
Darren_O
On 30/08/2020 at 18:30, mikef said:

It seems to show the central web detached from the bottom flange?  How did that happen?

 

Insufficient pre flight check....
Previous landing was a little rough. The clevis had popped off the bell crank resulting in the only elevator control was full up or full down as the clevis pushed past the bellcrank. After careering around the sky in serious trouble for 5 mins I managed to bring it round to land. I say land....the wings nearly clapped. Result was the joiner splintered slightly, only way to remove it from the fuselage was in half.

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