Repair of compromised Longeron

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SamP

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Hello All,
I'm the proud owner of a new Sonex. Unfortunately, there are some issues with the previous owner's work. In a few instances, he redrilled holes next to others and near edges, seriously compromising the structural integrity of the piece (in this case, horizontal stabilizer spar).

The most straightforward solution is to replace the piece completely. I've also been told that filling the holes with welded material (though I think it would compromise the heat temper).
I'm also considering using a doubler over the area to bridge the weak spot. Anyone have any thoughts? If I use a piece as thick as the damaged part, I think that should be sufficient to handle all the loads.

IMG_3718[1].jpgIMG_3717[1].jpgIMG_3716[1].jpg
 

rdj

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The title says longeron, but your text says the horizontal stabilizer spar was damaged. Which is it? A doubler might be a possibility on a longeron, but if the spar is damaged I would certainly look at replacing it. Just thinking a fix is sufficient doesn't cut it for spars.
 

FritzW

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...considering using a doubler...If I use a piece as thick as the damaged part, I think that should be sufficient to handle all the loads.
Not necessarily. Can you tell us exactly where the part is? I've got a set of Sonex plans to cross referance. Without knowing exactly what you're dealing with; nobody can give you a worthwhile answer.

P.S. Those pictures look very familiar...
 

TFF

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Replace might require the most work but the least amount of thinking. A doubler would be extra weight and that stuff looks thick. It will also need to be though out, so it does what you want strength wise. Hard to tell what is going on in there.
 

Mad MAC

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What exactly is the material specification
A marked up drawing would help us understand where the actual damage is.

So the following is an educated guess based on the information provided so far.

Welding would a poor solution, around the filled hoe it would reduce the temper to O then eventually T4, although reducing the filled hole to O state would allow local yielding at a low stress (likely normal operational loads), so even when it did age to T4, it won't strain at the same rate as the rest of the angle (so one would still get a stress riser at the filled hole, but no one would know just how much of a stress raiser it is).

For the bolt which the head is in plan view in the first pic.
Its the last bolt in that flange so the bolt strength will define the critical loads at that point assuming what ever is on the back of the bolt doesn't introduce a compression or tension load. So one would trim the "figure 8ed" hole out sufficiently to allow the packer of sufficient length to be tied independently to the doubler (to avoid a floating packer and the bolt bending that comes with it).

The other bolt. Well that one is a bit more of a B******d not prone to a simple analysis. However the angles are constant section, with a large fastener pitch, which suggests that there may be a possibility that with a bit of analysis one could just trim out the hole and relocate the bolt. Or alternately as before but with a doubler as well to restore the strenght. I would be reluctant to just put a doubler straight over the damaged hole because the possibility of not easily inspectable cracking originating from the swoff damage and the increase in resultant bolt bending.
 
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FritzW

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...The most straightforward solution is to replace the piece completely.
I think that that's your best answer. While your in there you can straighten up whatever is so wonky that the part had to be re-drilled in the first place.
 

wsimpso1

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I am qualified to analyze and design such things, and I would think seriously about disassembling the subject structure, replacing what I must, and reassembling it correctly.

There are several problems with using doublers over the current assembly. Hole margins are still compromised, and new holes will be needed in some places, with likely more hole margin compromises, which makes cracking likely to develop over time, even with the reinforcing doublers. Look up fracture mechanics online for more insight. Then these are substantial members that would have to be doubled. Since these doublers would be needed "inside", if the assembly sees bending (likely) the doublers will not double the stiffness and strength, so the original structure will still be carrying more than half of the loads.

Then there are the little issues of those drill chips caught between the parts. That greatly interferes with load transfer between the parts in the assembly and exposes the bolts to seeing the live loads as the chips crush and imbed. Bolts and rivets exposed to live loads WILL fatigue and fail.

Additional point about replacing "the piece" in question. When the hole drilled in one piece is out of position, the mating holes in other pieces are also out of position, which means other pieces will also need replacement. The fasteners should also be replaced as they have been exposed to fatigue as well.

If it were mine (easy for me to say, as it is not mine) I would tear the assembly down and rebuild it correctly per the plans. You should take that as serious advice. If it is not at your home base, and a rebuild would be very difficult from its current location, I would advise that you remove the offending assemblies, rebuild them from home, and then reinstall. Obtaining or building an entire new assembly may be a better option. I would not ferry flight that airplane as is, even if it has flown already.

One other scary thought. If the builder did these nasty things to this structure that you have found, how many other sins have you not found yet? This warrants some serious inspection of the entire airplane structure. Perhaps you have already done so.

Billski
 
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mcrae0104

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Sam, why not contact the folks at Sonex?
 

Tiger Tim

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I know this is a Sonex, but for reference there are a number of known fatal accidents on Zenith aircraft caused by nearly this exact same issue ('compromises' made during the construction/installation of the stabilizer).
 

wsimpso1

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I've also been told that filling the holes with welded material (though I think it would compromise the heat temper).
Do not even think about that in aluminum. Most of the Sonex is 6061-T6. Immediately after welding, it is O, which is annealed. With natural aging it will likely go to T-4. and that is a long ways, strengthwise, from T-6.

The other way to handle holes you do not want to is to fill them with a rivet of similar alloy. Like all rivets, it would need to be upset to fully fill the holes. And you would have to go through all of the fracture mechanics of the hole with it filled. Not for the amatuer. Go through it with an engineer that knows fracture mechanics, you might still have to tear it down and rebuild it...

Oh, and we KNOW what Sonex will say, do we not? "We can not endorse any scheme that violates the plans"

Tear it down and rebuild per the plans is the smart way...

Billski
 

Daleandee

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Those pictures look very familiar...
They should ... I had posted a couple anonymously on another thread:

http://www.homebuiltairplanes.com/forums/showthread.php?t=30208&page=2&p=434798&viewfull=1#post434798

FWIW ... I'd dismantle the entire tail and start over. It's a piece of work but I had to do some of that on a second hand kit that I bought. When you get it in the air you'll have the peace of mind knowing that you are flying a safe well built airplane and not something that has been hacked together and then patched over.

Dale
N319WF
 
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FritzW

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...When you get it in the air you'll have the piece of mind...
That's what it's all about. I'm sure most of us have flown, or a least worked on, a homebuilt airplane. If your worried about something that's not right (see photos above) you wont enjoy flying the airplane.

Spend a 100 hours rebuilding the ass-end, your enjoyment level will increase by an order of magnitude.
 

SamP

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Thanks all for looking and offering your opinions. I wanted to get generalizable information as well actionable info directly associated with my current problem.

I had asked on a Sonex Forum, so that's why they look familiar. I wanted to poll a larger audience, to see if there were other solutions. I hadn't heard about the use of same metal rivets as a means to fill and strengthen the beams, so glad I looked farther afield.

I had contacted Sonex as well, which suggested I replace the longeron and spar (yes, both are damaged). This is for step SNX-T01, for those with Sonex plans.

I'm glad fracture mechanics were brought up. My college classes didn't dive too deeply into those, and I couldn't find any good literature on doubler design.

Piece of mind and safety says I'll be getting the rivet remover tool out and doing some disassembly.

Thanks again for the tips.
 

Daleandee

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That's what it's all about. I'm sure most of us have flown, or a least worked on, a homebuilt airplane. If your worried about something that's not right (see photos above) you wont enjoy flying the airplane.
Realized after seeing my quote in your post that "piece" should have been "peace" and my wife would go bonkers seeing me do something like that.

Thanks for reiterating the point that if it takes time and money to fix it ... then that's what needs to happen. When I bought a second hand kit the previous builder hadn't done much before he realized that he didn't know what he was doing. Truth be told, I didn't either when I started but I had a great mentor and I dug in and tried to learn all I could from people that I believed I could trust on how to put this thing together.

I have a copy of AC 43.13-1B - Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair and it is a good resource. Another suggestion is Kit Airplane Construction by Ron Wanttaja. EAA also has EAA HINTS FOR HOMEBUILDERS which has some excellent videos available.

Dale
N319WF
 

Mad MAC

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I'm glad fracture mechanics were brought up. My college classes didn't dive too deeply into those, and I couldn't find any good literature on doubler design.
For doubler repair design have a dig around online for the course notes for Boeing Structural Repair for Engineers II (https://www.myboeingtraining.com/Courses/58/464-structural-repair-for-engineers---part-ii), its is a good primer for designing repairs (although written from the point of view that the user can run sufficient numbers to create a repair to send off to Boeing to approve without much thinking AC43-13-1 is pretty crude for repairs and struggles to prove efficient repairs for more complex damage (like this case).
 

Jimstix

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A couple of things come to mind to fix your edge distance and mis-drilled holes issues: 1) replace the fitting with a bigger one - one having sufficient edge distance, 2) add doublers to carry the loads around the offending substructure, and 3) use the next larger sized rivets or bolts along with items 1 & 2. ("When in doubt, make it stout") That said, it might be a good idea to have extra eyeballs on the fix to keep the demons of stupidity at bay.
 
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