That spar/nail thing again

Post-War Aeronca Champ airplanes
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Aerco
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That spar/nail thing again

Post by Aerco »

Hi guys - I got involved in repairing a 1965 7ECA (0-200) that had a knock on its wingtip. Glass fiber tip and rib got cracked; fixed all that. Now my supervising mechanic and IA has seen a service letter No C-139 where it details how many nails may be how loose in how many ribs etc. The copy of the letter he printed out does NOT specifically list the 7ECA. It goes from 7EGA to 8GCBC. I just found of a copy of this same service letter, identical in every way, except it does list the 7ECA. The airplane I am working on has a serial no of 159. The service letter lists serial numbers from 1350-80 etc.

Could this all be a simple typo? Clerical error? Did somebody misread G for C??

Regardless, my IA feels that it ought to be done: inspect everything, replace loose nails and put a dollop of epoxy on the head of each; he says this was mentioned in some service letter - I do not know which. Is this correct?

Seems to me the only way to do this properly is to recover the wings; the paint on this thing (acrylic urethane) just flakes off in big sheets. Trying to dope a couple of dozen inspection panels onto that is next to impossible.

What is the legal situation here? Does the 7ECA require all this? And even if not legally required, is it advisable?




Any input gratefully received.

bob turner
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Re: That spar/nail thing again

Post by bob turner »

The only required action is an AD. As near as I can tell, that S/B was never converted to an A/D. I did not check the T-Data file. That said, the nails transmit the lift from the ribs to the spars, and are important.

There is a move afoot to treat S/Bs as mandatory, but that sort of violates the Administrative Procedures Act.

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skyking3286
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Re: That spar/nail thing again

Post by skyking3286 »

In the first spar nail controversy, people went to Chicago and looked at the original engineering for the wings and found that all the calculations had nothing said about the nails. They concluded that one reason they are there is to make the assembly go better. Another is to eliminate the fretting of the lower spar surface as the ribs move. But as far as lifting the whole weight of the plane on some nails in wood, the calculations didn't assume that at all.
As long as you have nails there and the lower spar surface isn't damaged, you are good to go. I have one nail that is bent over (way to go...) and it hasn't changed in twenty years. Every annual if the IA sees it, I figure it's a good thing to check if they are really seeing what they need to see. And then I explain it's been that way for twenty years and get the usual strug of the shoulders and we move on.
Mark Peterson
Harvey Field, WA
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Paul Agaliotis
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Re: That spar/nail thing again

Post by Paul Agaliotis »

Peter,
The ECA is included just below the line you discribed. The 7ECA serial no.1 thru 1350-80 aer included. Also SL 406rA is covering alot of the same issues and it refers you back to SL C-139.
A good rule of thumb, if you get it into the dirt you need to take a good look at it. Most problems are at the OB side of the strut doubler plates. They break in compression, and ARE NOT compression wood. Two completely different wood defects.
Paul
Mailing Adress : Paul Agaliotis 2060 E. San Martin, San Martin,Calif. 95046

bob turner
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Re: That spar/nail thing again

Post by bob turner »

I am confused. You worried about nails, or the spar inspection?

What Paul seems to be saying is there is a reason for inspecting the spar itself outside of the doubler at the lift strut. It sounds like an excellent place for the Rainbow kit. And apparently most failures have occurred after wingtip impact, the failure being after a compression fracture.

My problem with this whole deal is the AD. It mandates inspection of every square inch of every surface of that spar every year, impact or no. Installing the Rainbow kit is an acknowledgement that the AD cannot properly be accomplished without it, but it is a realistic way of looking at the problem area - you cannot see a compression fracture under the doubler plate!

The AD breeds contempt. A wingtip strike should involve at least the Rainbow kit, if not the removal of fabric and leading edge in a fairly large area outboard of the strut fitting.

Opinion, of course. Thanks for the info on the nails.

Aerco
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Re: That spar/nail thing again

Post by Aerco »

skyking3286 wrote:In the first spar nail controversy, people went to Chicago and looked at the original engineering for the wings and found that all the calculations had nothing said about the nails. They concluded that one reason they are there is to make the assembly go better. Another is to eliminate the fretting of the lower spar surface as the ribs move. But as far as lifting the whole weight of the plane on some nails in wood, the calculations didn't assume that at all.
.

I find this unlikely - without taking into account the effect of the nails, how would the rib loads be transferred to the spar, except by direct contact of the rib on the spar? Such ribs have been designed - Gypsy and Tiger Moths have the ribs resting directly on the upper and lower surface of the spar and are screwed to those surfaces with metal clips. The Aeronca ribs have no flange or "pad" that bears directly on the spar and could transfer the load. The rib loads can ONLY be transferred safely by the nails. They most definitely have an "engineering" reason for being there, even if there is no record of it. Likely it was decided that previous experience was sufficient data to know that the nails were adequate to carry the shear loads into the spar.

But they are necessary.

Paul Agaliotis
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Re: That spar/nail thing again

Post by Paul Agaliotis »

Bob,
In my opinion the fabric needs to be removed after a ground strike. I have one in the shop right now. The Rainbow kit is a problem for me. I can see more issues from water getting past the plates than the ease of access. Pulling the fabric off is the best action.
The failure is seen on the top of the spar, and I've only had one cracked. It looks like a pencil line on the top surface at the OB end of the doubler plates. I first thought is was a pencil line, but after sanding down 1/8th of an inch I still had that pesky pencil line!
This AD is just a mess. After performing an intensified inspection in the required areas they make a general statement to inspect and reject spars with any defect, repairabe or not. Most of the time it's the end grain splitting from the bolts in the butt attach fittings, this is an example of a repairable defect.
The nails will break the spars. They don't back out. But if you can get them out, without breaking the heads off, they pull out a big chunk of spar.
I think ACA didn't want to mess with the wood spars, they never built any wings with them. But if they can vilify the wood spars they might just sell some wings. All at no cost to them, only the operators.
More and more TC holders are generating revenue by the AD process. This process is to ensure safety, not the bottom line of the company.
Paul
Mailing Adress : Paul Agaliotis 2060 E. San Martin, San Martin,Calif. 95046

bob turner
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Re: That spar/nail thing again

Post by bob turner »

We agree.

The AD is unrealistic, difficult to accomplish, and expensive. An impact at the wing requires much more intensive inspection than the AD. No impact means go back to Cub-like inspections.

Paul Agaliotis
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Re: That spar/nail thing again

Post by Paul Agaliotis »

Bob,
Agreed.
It's a frustrating situation. For years we have repaired the nails, welded the seats, and changed the venturi and floats in the MS carbs. All with no operational incidents, and as soon as the companies change hands we get hit with these AD's that we have been dealing without the AD. The FAA ask for our input and then disregard it.
I filed a MDR on an issue that resulted in an AD. When it turned out to be a manufacturing error that caused the problem I tried to tell the FAA the AD wasn't needed. I was told it was just easier to let it go and continue a needless inspection. Now I only inform the FAA of any findings if required by the document I'm using.
Paul
Mailing Adress : Paul Agaliotis 2060 E. San Martin, San Martin,Calif. 95046

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skyking3286
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Re: That spar/nail thing again

Post by skyking3286 »

Good for you...

About the nail issue.... I mention it not to say that the nails aren't needed. But we don't need to obsess about one nail either. If
a nail is being pushed out, then it's well worth the time to inspect what is causing the flex to work on that nail. For non-aerobatic
Chiefs and Champs, it's seldom an issue. Unless..... :shock:
Mark Peterson
Harvey Field, WA
A copy of my old Chief website is preserved here:

http://www.reocities.com/mrpeters.geo/index.html

Paul Agaliotis
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Re: That spar/nail thing again

Post by Paul Agaliotis »

Mark,
I've pulled flying wings apart that had the majority of the nails missing or suspect. It's a problem that I have been repairing since 1978 and still and will be a problem long into the future.
The AD is good in the fact that it exposes the information to all. But the fix is worse than the loose nails. Installing the pallet nails puts such a big hole in the spar it's bound to split. They should just thru-bolt them, that's just about as crazy.
If it provided a higher level of safety I could understand, but it just doesn't.
Paul
Mailing Adress : Paul Agaliotis 2060 E. San Martin, San Martin,Calif. 95046

Richard
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Re: That spar/nail thing again

Post by Richard »

Rainbow Ron, said he's working on a STC to use small wood screws instead of nails to hold the ribs in place.

Richard

clipperfixer
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Re: That spar/nail thing again

Post by clipperfixer »

Richard,
I am just now completing the LH wing of my Champ. After reading all I can take on the spar nail thing I opted to go with Ron's STC for installing screws in the rib to spar interface. The STC is available now. Anyway I like it a lot. I have no experience to go on as far as nailing the ribs to the spars, or longevity of the installation. I guess I just had to make my own decision.

bob turner
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Re: That spar/nail thing again

Post by bob turner »

This is a very useful forum for me. Sometimes it seems like a forum is a better source of technical information than almost any other - I hope this doesn't go the way of that neat aerobatics forum that nobody posted to.

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