The International Cessna^® 170 Association

Hello,
Just working through the squawks on the annual and was informed that our right wing stringer is contacting the ribs in a couple of places neccesitating removal of the top wing skin and grinding down of the offending ribs to prevent contact. Doesn't sound cheap to me but haven't got the estimate back yet. Also the bolt (AN8-23A) is showing corrosion grade 2 or 3 corrosion and needs replacement likely.

The cause was a likely hard landing before we bought the plane this fall I guess.
Does that make sense? Any thoughts or experience on costs or other things to make sure and do while we are dealing with the problem.

Thanks for the help,
The last 4 months worth of repairs have made me regret not getting the full "annual inspection" versus a "prebuy inspection" at the time of purchase.
So it goes.
Thanks,
Gordon Bunting
N2354D

That is some interesting stuff. I have seen wing ribs contact the stringer before and never thought a thing of it. If all they are going to do is "grind it down" then why don't they get a dremell tool and cut it down on the aircraft?? Removing the top wing skin seams way way over the top. Maybe there is more to the story?? Are there cracks in ribs, skins or stringers? I have seen winkled skins from hard landings that i may be concerned about.

I've been around C-170 for quite a long time and this is certainly a new one on me. This is a skin stressed wing and I can't imagine that deskinning it without a fixture (jig) to maintain proper aerodynamic shape is at all a good idea. I would strongly suggest you get another opinion before authorizing the work.
You know, all the early Cessnas have practically the same wing.That is, the C-170, C-172, C-175, C-180,And C-182. I've never heard of it on any of them.
Perhaps you could get some information from the Cessna Pilots Association. They don't normally have much to do with the C-170 but, since there is so much similarity with the other models they may be able to help.

To be perfectly honest, this sounds like bull s--- to me and I think you need a different IA.

Seems your shop is in need of some extra work. As stated you need another opinion with a knowledgeable Cessna IA.

Thanks alot for all the comments- seems to be a general trend to a second opinion which sounds good to me. I'll let you know how it develops.
Gordon

You have got to be kidding. What is it going to hurt? If it hit that hard you might have other worries. Sounds like the IA I knew that spent hours adjusting spark plug gaps so they fired evenly on both ground electrodes in the tester. Claimed it was a FAA requirement.
Is this for the top or bottom skin? Do you have any oil canning or kinked stringers? Has the wing been repaired or rebuilt before?
I have seen a 206 that hit hard enough to badly wrinkle the empanage, Shear all but one of the front horizontal attach point rivets, Break gear bolts and saddles but only added a slight amount of oil can to the bottom of the wing. Sounds like someone wants to start making Yacht payments.

Indopilot has the right idea. I think you'd best see if this guy has a boat financed. I just today checked with a friend of mine who is an A&P IA who used to work for years at big Cessna dealership and has been working on Cessnas since Clyde was a kid. He's never heard of this problem either. Get a hold of the Cessna Pilots Assn. and ask them.

Under the circumstances, I'd also get a second opinion on the necessity for new bolts.

Gordon,
If the wing has been previously repaired, and new blank stringers were used, it is possible the new stringers were located slightly different than original; the stringers are riveted to the skin before the skin is placed onto and riveted to the ribs. They didn't pay attention to the rib/stringer clearance and deal with it during assembly.
Unless either the stringer or rib looks pre-loaded (like there is pressure on either), I would'nt be concerned about it,. The fact that the rib relief is contacting the stringer is not necessarily a big deal, there is no movement to cause chaffing, it's a rigid structure with both the rib and stringer solid riveted to the skin in close proximity. Just make a note to closely inspect for cracks every year or more often if your worried about it.
As for removing the top skin to correct this problem; you have to remove the bottom skin as well to be able to reassemble with solid rivets, and the wing needs to installed into a fixture during this process. Don't let anybody try to convince you to let them reinstall the top skin with blind rivets.

Del and everyone else who commented,
Thanks alot for the info. It really helps. It is what makes this forum such a good website and value. I'll let you know how it goes. Take care, Gordon

As a side note- here are pics of the rib/stringer contact in question as well as a crack on the right belly skin that is of issue as well. Looking back at the 337's the only left wing repair performed was a probable groundloop repair that involved a new left top main skin, tip rib and tip skin bottom in 1975. It sounds like the contact likely occurred at that time with replacement of the main skin. I also submitted these pics to the tech support at CPA.
Thanks alot for all your help,
Gordon

After looking at the picture of your so called problem, I can't immagine that there could be any chafing between the srtinger and the rib. And if there was, so what? I certainly would not allow anyone to pull a top skin off of my wing for something like that. I really think you should find another mechanic who is more practical. This one is going to be a dollar pit.

The good news is that the inside of that wing doesn't look bad at all. And very little corrosion is evident in that view.
The bad news is that the belly wrinkles are probably an old ground-loop that went un-repaired. The stop-drilled-holes didn't work, were too small, and incorrect repair anyways. I'd recommend you leave that wing alone and focus on the damage inside that landing gear box/belly area.

George,
I have been waiting for that shoe to drop since I purchased the plane. So much for a thorough pre-purchase exam. I have spent the last couple of nights trying to find the part number for that particular skin but am still not sure which skin it is. Looking at the service repair manual it seems like the only fix for that skin is replacement of the whole skin versus patching. Can you rule out bulkhead damage via the inspection holes or do you need to remove the skin first??

Any thoughts on the repair recommendations for this would be appreciated and or suggestions on folks to do it in the Northwest. The last groundloop damage recorded in the logs is 1975 with damage to the left wingtip. I'm guessing that is when this damage occurred. Would have been nice for someone to have fixed it before now.

As a side question, despite lots of good advice to the contrary from this website we ended up going with a pre-purchase exam versus a full annual inspection. Interestingly, this never showed up on the inspection. It is my fault to not have been more thorough but at a certain level I'm still a little pissed with the guy who helped out with the inspection. Think a call would be appropriate?

Thanks for your help,
Gordon

If the question is with regards to the crack, it looks like its needed some attention for sometime. George is correct in that the stop drill holes are too small. When stop drilling consider putting in a larger hole at the head of the crack as the metal may have weakened where the damage is not yet apparent to the naked eye. If this was missed during the pre-sale inspection, check you wallet, there's more to come. If this was my plane, I would inspect for the extent/ cause of the crack (metal flexing or accidental damage) and correct that situation. I would install an internal doubler plate for the skin and tie it in to the bulkhead angle with another doubler forward and on top of the skin doubler. But thats me, if I had this aircraft as a project and I was not concerned about flying it for a long time , I would replace the skin.

With respect to the pictures of the wing ribs, I find their condition to be unsettling to me as to the why and where.