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Old 11-22-2017, 05:18 PM   #1
pbrannan
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Default Repairing broken ribs

My newly acquired Marquart project has several broken ribs. Most have taken a hit on the rib tail. AC43.13-1B figure 1-11 shows what needs to be done in most cases, has little to say about how it should be done.

For instance, cutting the the scarf joints needs to be precise. I'll need to make some sort of scarf jig that allows me to get the same cut. Does anyone know of any detailed documentation about HOW to do these repairs?

Thanks,

Pat


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Old 11-22-2017, 06:12 PM   #2
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Default Repair

No jig needed except to hold the parts straight while gluing. Hand saw, then sanding block. The part you are adding can be done on a disc sander with miter guide or just a piece of masking tape on the table for reference. With modern epoxy glues fit is not critical as it once was with older glues.


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Old 11-23-2017, 02:09 AM   #3
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Any photos of what you have to work with?
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Old 11-23-2017, 04:30 PM   #4
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This is the worst either somebody dropped something on this or picked up the wing with the cap strip. I'm not sure I can get my correct angle on the scarf joint forward of the spar into the stringers on the leading edge.

I've been doing a lot of reading, I have every wood aircraft book I could find, and I think I have a bead on what has to be done and a few ideas about how to do it. I will need to pull the nails and somehow carve away the existing gussets. Then the new gussets conforming to faa scarf joint ratios the thickness of the capstrip from the end of the 10:1 scarf joint. The new gusset will have to extend .75 inches past the cracked cap strip on the nose rib.

Exactly what tools and how to do all of this is the question.
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Old 11-23-2017, 04:38 PM   #5
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Two things I would be thinking of. One, sand off all the gussets on the top, cut out the whole top piece and put a new one in and re-gusset. The best feel good way. If you have the old piece, you could glue it in and back it up with another piece of spruce underneath. Or go hybrid, sand off gusset, go back a bit and make your scarf, and go all the way to the nose rib. Match gussets to the scarf per AC43. Those are interesting drag/ anti drag braces.
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Old 11-23-2017, 04:39 PM   #6
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You will want the airfoil's curve to be preserved when you replace that section. As short as it is I'd lean toward starting with a taller section and shaping the top to match the other ribs.
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Old 11-23-2017, 05:52 PM   #7
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Are those drag "straps" standard on Chargers?
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Old 11-23-2017, 07:08 PM   #8
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I think replacing the whole top strip sounds like the plan in this case. I'll soak and bend a piece to match the profile, then cut new gussets and clamp it on. Some horizontal reinforcement clamped along the compression pieces should keep me from breaking the bottom.

Yep, the drag strips are that way in the plans. .063 x .5 4130. Seems like they will be very strong. Turnbuckles called for are AN150-16S which are rated at 1600 lb. According to my calculations the straps themselves wouldn't yield until 1987 lbs. I'm not sure about the various pins and fittings. I'm also not so sure about the tail.

QUOTE=planebuilder;187549]Are those drag "straps" standard on Chargers?[/QUOTE]
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Old 11-23-2017, 08:56 PM   #9
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Do you have the plans to make a new rib of the section you want to replace ?
Also it appears that the nose rib has a piece broken and sticking up.
Guess you could glue it back in place with gussets on each side.
If that is the worse your in good shape.
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Old 11-23-2017, 09:14 PM   #10
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I used an xacto razor saw then cleaned up with a block plane
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Old 11-23-2017, 09:37 PM   #11
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A good start might be to watch some of the informative and helpful videos produced by the EAA for home builders. Happy Thanksgiving to our wonderful neighbors to the south! Phil
http://www.eaavideo.org/category/videos/wood
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Old 11-24-2017, 04:29 AM   #12
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Looks like a fairly easy repair. Lost of options here. Iíd lean towards replacing the whole
Top piece. Make it so there is no ďrepairĒ. Itís the correct way to go and no one can bitch it isnít to Plans. Itís also the most ďpiece of mindĒ way to go. Plus after you scarf and add doublers and gussets etc itís more work than just taking the factory gussets off, replacing the broken piece and installing new Plans size gussets. Looks like you have a great start! Letís see what all else youíre working with. Howís the fuselage etc
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Old 11-24-2017, 12:30 PM   #13
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I made a couple of repairs retaining the gussets by removing the nails from the gussets, using a 1/4 inch chisel to remove the wood between them and to clean up the inside surface of the gusset and replacing the cap strip. I would do the cap strip splice in the section behind the break...plenty of room to get the proper angle. Just remove the wood between the gussets in the nose rib as well as the gusset just behind the break. It would be easy to steam some cap strip and bend it to fit.

You can easily remove the nails by putting the blade of your pocket knife under the head and twisting to lift the head and then use your wire cutters to roll the nail out.

Steve H

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Old 11-24-2017, 04:05 PM   #14
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Dennis: the plans are in the public domain and available for free, so having a rib plan on hand should be simple.

pbrennan: any more pictures you want to post of details in the wings would be very very welcome -- I can see the end of rib construction on the horizon, and if my spars ever show up, I'll be building my wings next. I've already learned that my brief glance at the orientation of the drag strips was wrong (I was picturing them running vertically instead of horizontally).


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