So the 182 is in annual and all is ok except they found 5 rivets missing on top of wings between wing root and strut attachment point, 2 are skin to spar. They really checked closely to make sure nothing is moving, I.e. wing attachment bolts, strut attachment, etc. and all looked good. To be honest they have been gone awhile, my former mechanic was not to worried about it. I asked my current A&P how common was this and he said he sees 1 or 2 from time to time but not this many, they are also almost weirdly symmetrical from left to right. Anyone else ever seen this, delt with this? Of course now I’m worried about corrosion but there is no appreciable corrosion anywhere else on the plane

My first question is how many hours on the airframe and what has been its primary usage in its lifetime (BTW, what year is it?). Photos are super cool as well.

It’s a 66, it has about 2600hrs on it. Personal use its whole life. Guy I bought it from 2 years ago had it on and flew it off of his farm.

Rivets work at times. Sometimes you can get a bit shearing action on the high load areas. No not too terribly uncommon to see a couple of them pop off over time. It would lead me to believe that perhaps it may have had more than its share of firm landings. I would replace them all. They don't depart if something was not causing it, unless they had corrosion. There is also the case that they may not have been well set in the first place allowing them to work. Did you have little charcoal streaks from them before they popped?

Either way, replace them and look to see if there is any diagonal oil canning on the spar area near the points they left. The aircraft is 56 cars old, stuff happens, things work harden over time and break. Fix, move on.

There could be one or two hard landings in there, my son earned his private pilots license in the plane over the last year. As you suggested we’re replacing the rivets, moving on, and just gonna keep a careful eye on it

I remember a 310 that was being rebuilt in my shop... the guy that had been working on it said it was all ready to go, minus one rivet on the left side of the carry through that needed replaced. I ran the gun and he bucked. Got that one in and a couple more fell out.... long story short, I started digging and we put a whole new center section in. Kinda like what Dogpilot said....they don't just quit hanging on. There's a reason there somewhere.
John

If you've ever seen how flimsy a Cessna wing is without the skins on, you'll quickly realize that the skins are the structure. The rivets shouldn't move. They are compressed to clamp the skin on and should never even see shear stresses. If they do, cyclic loading/fatigue, cracks and/or smoking rivets and eventually departure are on the menu of outcomes.

You kind of have it backwards. Rivets have very little strength in tension, so they are not little clamps, but rather have their strength in shear. It is the basis of monocoque design. That way you can have a very light fastener actually have a net strength influence that is far greater than something that was using fasteners holding in tension. It is why Beechcraft bathtub bolts, the ones that old the wings on are so large and have to be inspected hourly. Whereas the bolts in Cessna wing fitting are not nearly so large, due to being mounted in shear. So in this case, as the wings get influenced up or down, the skin is trying to pull the entire length of the spar in a linear fashion, not being pulled off straight up. All the rivets are acting together, not singly, so the net strength is huge. The rivets are trying not to be guillotined rather than racked. It is a common misconception.

In this case, there was a localized bending moment near the main attach points, which over time, sheared the enough they worked out. Too bad I never kept the photos of the ultimate load test on the Caravan wing we did at Soloy. It neatly sliced off the rivets on the last 24" of the spar as it failed. Once they sheared, the spar failed.

dogpilot wrote:You kind of have it backwards.

Not actually. The axial tensile stress on a properly finished is at or just below the yield stress. They aren't Play Doh. They become springs when they are bucked due to Poisson's ratio. The difference in use (shear vs tensile) depends on the designer. They are designed for bearing critical loads or slip critical loads. The load transfer for the bearing critical joint is the same as for a bolt...the fastener in such a case never sees shear stress as long as the friction load transfer is not exceeded. This means that the river (or bolt) never sees cyclic shear unless.the friction load transfer slips (as in a lap or butt joint). No fatigue of the rivet. This design goal is very, very important in aero applications. It is simpler to analyze and more reliable if proper riveted design and execution are possible.

The slip critical design uses the simple (well, not quite so simple biaxial stress analysis) shear forces as a naive conservative approach where skill or other concerns are to be expected. In fact, a lot of riveted steel structures default to this standard because of variability in real execution. In fact, civil structures standards move to bolts to be able to apply dependable preloads on bearing critical applications or use a slip critical design with rivets.

So it depends.

Even now, things that go fast and go boom boom very often take advantage of the efficiency and reliability of bearing critical design in riveted designs, if they use rivets at all.

A Boeing design manual covers this in more detail. It is often a young engineer's first encounter with bearing critical design. It means a lighter, stronger joint.

So yes, the rivets can be looked at as little clamps.

To your point about being weak in tension, yes...rivets have little strength perpendicular to the plane of a lap or butt joint.

In college, I had the privilege of getting paid $5 an hour to run tests on riveted joints with composites for weeks. The yield numbers for bearing critical designs were higher than the shear strength of the rivets alone ...by up to around 30% more than the naive shear area would suggest, and cycle failures were up to orders of magnitude higher for bearing critical designs, attesting to the bearing critical vs. slip critical differences.

If the load is not transferred to the spar due missing rivets, the load will be higher on the surrounding rivets, obviously.

Gee! I always preferred tube and fabric but you guys make it really sound good. What little rivet setting I did, they got a couple sizes larger by the time I got it right.

Curious which rivets were used? Did Cessna use DD rivets (2024) or AD rivets (2117) when the aircraft was built?


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Been über busy lately. Folks may think the prices for T206H's may be high, but didn't deter a flood of people wanting my buddy's one. Took almost 4 days of offering it up to generate a sale, two with competing offers. Some folks must have money to burn at the moment. Back to the rivets. Wow, your university temp jobs where way better than mine. When I got called up for projects, it usually involved me sitting in a booth getting shocked by some sadistic graduate student. To make it worse, the monkey always got better scores than me. Of course he was highly motivated by the banana treats. Excellent write up, you should teach. Not arguing with you on any of it, but observationally, based on looking and repairing literally hundreds of dinged aircraft, focusing on the over-stressed ones. If you look at a localized bending moment on the spar. Visualize it as two sheets now describing a circle. One has a greater radius than the other, this causes a shearing action, not enough to fail the rivets, but enough to, lets say reduce the shank diameter. Do this enough and they will either shear or work themselves out. If they fail in a tension situation, you will get skin dimpling or actual pull throughs. I rarely saw this except in explosions.

Now one might think that explosions are rare, or at least hope they are. We would get the occasional one. Most notable a Baron with a leaking wing fuel tank, just seeping, not pouring out. Well apparently while heating up on the ramp, this seeping fuel turned into vapor in the magic 11:1 ratio. Upon turning on his strobes, the wing went wump! Not shredding, but becoming a comically plump version of a Baron wing. Yes in this case a whole lot of rivets pulled through.

dogpilot wrote:
Now one might think that explosions are rare, or at least hope they are. We would get the occasional one. Most notable a Baron with a leaking wing fuel tank, just seeping, not pouring out. Well apparently while heating up on the ramp, this seeping fuel turned into vapor in the magic 11:1 ratio. Upon turning on his strobes, the wing went wump! Not shredding, but becoming a comically plump version of a Baron wing. Yes in this case a whole lot of rivets pulled through.

That wasn't on the way to Jordan was it?