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Dec 14, 2019, 12:48 PM
ET
eteet's Avatar
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Sagitta XC repair


Hey Guys,

I got a little aggressive on the winch pedal and did some damage to the wing root of my Sagitta. Which is a shame since it is a beautiful model (I didn't build it!).

The aft joiner box split and I need to get it back together. Actually the term joiner box is a bit grandiose since there is almost no structure holding that aft tube in the wing. The brass tube is bent so that needs to come out and another installed. Does anyone know of a way to get that out without cutting into the wing? I'm assuming it was put in with epoxy so I've thought of trying to heat it up and sliding it out. But I don't think that would work. Any ideas?

Putting the new brass tube in just seems to be a matter of gluing it in and clamping it down. Of course if I have to cut it out the repair will be a bit more extensive.

As for the joiner; a friend in my local club has recommended using a Dixie Pin, which I guess is hardened steel. The joiner seems to be 5/16". Is that correct?

Anyway, looking for some advice before I start cutting.

Thanks in advance,

Eric
Last edited by eteet; Dec 18, 2019 at 08:15 AM. Reason: Reworded discription of damage.
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Dec 15, 2019, 12:21 AM
If it flies - I want one!
Petem's Avatar
Oops!
Eric, first, 5/16" is correct for the kit/plan.
Not clear from your pics - is it the front (main) joiner tube or the rear one that has broken out?
If the main one, if built to the plan it should have been built into the spar box, with ply side shear webs fore and aft, spruce top and bottom - again hard to see from your pics.
Suspect some exploratory surgery will be needed just to see what the damage is in the spar structure. The tubes and joiner boxes are short, so very highly stressed at the point where the tubes end - your fix will need to be very solid.
When I built mine (circa 1986!) from the kit I was unhappy with the arrangement of two equal-sized joiner bars, with no real supporting structure for the rear one. I installed diagonal drag spars over and under the rear joiner tube, going out to meet the main spar a few bays out.
All the best for the repair,
Pete
Dec 15, 2019, 08:45 AM
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Hi Pete,

Thanks for the information. It's the rear joiner box that split so I guess I got off somewhat easy. I have to start digging around inside the wing and see what needs to be done.

Thanks for the help,

Eric
Dec 17, 2019, 12:47 PM
volare est vivere
ray foley's Avatar
hi there from Toledo!

Hey Eric;

You really need to strip the covering off the top and bottom of the wing to properly assess the damage.

Be prepared to replace the entire top spar as well as the joiner tube and any support plywood in the joiner box area and the root rib also.

I know it is a pain but how else can you be sure the repair is comprehensive and durable?

ciao rjf
Dec 17, 2019, 06:05 PM
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eteet's Avatar
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Hi Ray,

Luckily for me it wasn't the joiner box that split but the structure that holds the rear joiner tube. As of now I've ordered a set of plans, a new set of steel joiners and a 11/32nd brass tube.

I've looked a some build pics of the wing and the structure that holds the aft brass tube is minimal, which is probably why it broke. OTOH, the repair should be easier because of that. I'll try to add some extra wood in that area to strengthen it up. Shear webs? The more I look at the wing the more thankful I am that the damage isn't worse.

I'm still working up the courage to start cutting into the wing. I'll try to add some pics and maybe turn this into a mini re-build thread. Should be good for some laughs for people who really know what they are doing.

Thanks for your reply,

Eric
Last edited by eteet; Dec 17, 2019 at 06:10 PM.
Dec 17, 2019, 10:10 PM
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Gratter's Avatar
Might want to think of wrapping the outside of the root area with some carbon fiber or fiberglass once the inside work is complete.
Dec 18, 2019, 07:58 AM
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eteet's Avatar
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Quote:
Originally Posted by Gratter
Might want to think of wrapping the outside of the root area with some carbon fiber or fiberglass once the inside work is complete.
I thought about going around the repair with some Kevlar tow. I'll see what it looks like as the repair progresses. Looking at pictures of XC builds it seems like that area is ridiculously weak.

I think the aft joiner is more of a locator pin than structural piece.
Last edited by eteet; Dec 18, 2019 at 08:16 AM.
Dec 18, 2019, 04:50 PM
If it flies - I want one!
Petem's Avatar
Quote:
Originally Posted by eteet
Looking at pictures of XC builds it seems like that area is ridiculously weak.
I think the aft joiner is more of a locator pin than structural piece.
Yes, I agree. If the aft joiner was sized as a locator pin it would be fine, but being the same size as the main joiner means it must bend at the same time or break out - and there is no structure other than the ribs to take the load out to the main spar. As mentioned earlier, I modified mine in the build with a 3/8"x1/8" diagonal drag spar top and bottom, passing over the end of the rear joiner tube and scarfing to the main spar four or five bays out. Shear webbed fore and aft, and the wing root sheeting extended to cover both spars as a box. That wing is still flying happily with its third owner.
Sorry no pics, they didn't have cameras back when I built it!
Cheers,
Pete
Dec 18, 2019, 07:15 PM
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This is where I am now. Not nearly so much damage as I first thought. With just a little heat the epoxy holding the tube released and it slid right out. I'm feeling lucky!

Waiting for my brass tubing to arrive.
Dec 22, 2019, 07:44 PM
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eteet's Avatar
Thread OP
I got lucky with this. I thought the aft joiner would have a full blown box like the fwd one but it only had minimal structure, so there was less to repair.

Pics tell the story. Thanks to all who offered assistance, the advice was well taken.

Happy Holidays to all!!

Eric
Dec 22, 2019, 07:46 PM
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Now, on to my next winter project.

I'm thinking; motor.
Last edited by eteet; Dec 22, 2019 at 07:56 PM.
Dec 23, 2019, 12:04 AM
If it flies - I want one!
Petem's Avatar
Lovely job, congratulations! Now repeat after me: 'tap, tap, tap - gently does it...'
Cheers, and enjoy your flying,
Pete
Dec 23, 2019, 09:41 AM
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Quote:
Originally Posted by Petem
Lovely job, congratulations! Now repeat after me: 'tap, tap, tap - gently does it...'

Pete
Yes, tap tap tap.
Dec 24, 2019, 01:11 PM
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Randy Reynolds's Avatar
We all want to correct the many design flaws in the original Sagitta XC. However consider how well that area held up to the wrenching torque that was applied as the wing rod caused the brass tube to bend and yet the inner two ribs are still in place. Might not be such a bad design after all.

I wish I could get my XC's back to their design weight where they would fly easily. However mine are loaded with all the officially approved modifications and beefed up sections, etc. My first one after plenty of repairs and mods wound up at over 13 pounds. It was a handful to launch! The Sagitta design is an icon no matter the size.
Dec 24, 2019, 01:43 PM
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eteet's Avatar
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Quote:
Originally Posted by Randy Reynolds
However consider how well that area held up to the wrenching torque that was applied as the wing rod caused the brass tube to bend and yet the inner two ribs are still in place. Might not be such a bad design after all.
I have to agree. The area looks flimsy but with all that bending only one plywood rib broke. I'm going to a stronger steel on the joiner, I hope that isn't a mistake. The joiner bending is better than a different part breaking.

Tap, tap tap....

Eric


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