Oil canning forming in the wing from the sun

[Dferr34]

Hey guys, yesterday while fueling up my 1949 Cessna 170A out in the sun, I heard my wing making a popping noise. I stepped up on the tire and saw on top of the leading edge had several dents in it all the way across on both wings. Has anyone ever saw this happen before? I would think this has to be destroying lift. Please see attached photo.

Thanks, Don

[GAHorn]

When was that leading edge w/VG’s installed..? and by whom?

[Dferr34]

I installed them, my mechanic approved and signed off. I saw this happen once before with out the VG's installed but it was just in one spot and not that bad.

[sfarringer]

Has the leading edge always been painted a dark color?

[GAHorn]

By chance has it ever been re-fueled using a gas-can…held by someone who rested their elbow on top of the leading-edge…perhaps causing a dent…which sometimes “flexes” due to temperature changes…??

When refueling it’s important to not use the thin-skins to support hoses or other…. (although I have no-idea what has caused this…. I have sent a pvt email to a sheet metal expert to ask his opinion….Hopefully we’ll have a response.)

It’s difficult to imagine this occurring on-it’s-own…especially so near “D”-ribs.

[Bruce Fenstermacher]

Hard to tell. Are we looking at a leading edge cuff installed or standard leading edge? VGs won't have a thing to do with the issue

[GAHorn]

I wasn’t blaming VGs at all… I was considering that SOME leading edges are installed OVER the original leading edge….and that might be identified by virtue of having VGs attached. (This L.E. certainly does not look like the “over-laid” one’s I’ve seen.)

[Dferr34]

Sorry, guys, I guess I didn't explain it very well. Maybe I shouldn't have said they were dents; they are more of a buckle in the wings. This only happens when the sun is heating the wings. I do not have a leading edge cuff; it is just a standard wing. It is obviously just from heat expansion. Once the plane is in the shade, it goes away altogether. I was just up at the hangar today and when I inspected the wings, they looked perfect. A few local guys at the hangar saw the photos and how the wings look today and we were discussing that it may be an issue because of the dark blue paint heating up the wing surface and creating expansion and buckling. I guess my solution would be to paint that top surface a lighter color. I have only had the plane for a little over a year and this was the color scheme when I bought her. Thanks again.

[GAHorn]

Don’t blame yourself for Our meanderings… I’ve never witnessed anything like this …and while dark colors certainly absorb heat from sunlight… I’ve never heard of this on any airplane despite being painted dark colors.

[voorheesh]

While waiting for input from a metal expert, some questions: Where are you located? How hot is it when the skin deforms? How much time in heat before condition? Is direct sunlight always involved? Can you or your mechanic verify this is original skin and not a section that was replaced? Unless you are dealing with extreme heat (say excess of 120deg f), this should not be happening. The paint is dark, but I don’t see how that would cause this. It may have occurred before you bought it and that patch of metal developed a “memory” meaning it distorts when a certain temperature is reached. Whatever the cause, I recommend getting it repaired, even if it means replacing that small section. (Replacement would allow inspection of underlying wing structure). It may or may not affect lift, but I would hesitate to fly it while deformation is happening until you get a good explanation. When I was working, we had to ferry a couple of planes due to bird strikes and other damage much worse than yours. Manufacturer engineers always allowed ferry, but once had to apply a temporary surface patch to make wing leading edge, upper surface laminar. Our company always took any wing discrepancies very seriously. (Bigger airplanes, but still wings). Good luck and kudos for not just looking the other way.

[GAHorn]

Don,…. I’m in agreement with a friend whom I respect greatly…. that for the skin to deform as much as that…. the underlying primary structure might be suspect.

You might wish to open up panels, remove fairings, (wing root esp)…and with a bright light look for cracks and movement of the spar, the attach points, wing-attach points/blocks/bolts for movement, corrosion, etc.. Just to be SURE you don’t have primary structure issues.

[Dferr34]

Hey guys, I went to the hangar and took a few photos of the inside right at the wing strut. I also rolled the plane out in the sun for a while but I guess it wasn't hot enough, so nothing happened, no wrinkles. The plane is scheduled to go in for annual this coming week, I'll be sure to mention all this and show the photos to mechanic. Also, I'm curious does anyone else have an Cessna A model with a dark colored wing, and if so, have you ever checked for any of these issues in the direct hot sunlight?

Don

[ghostflyer]

I have a cessna 170a and the wing is painted metallic silver,but saying that the aircraft has sat in the sun for hours with the air temperature at 42 deg C [Note centrigade ]and when I have gone to refuel it ,I have burnt myself on the skin. I now carry a rubber mat that has a hole cut into it so the fuel nozzle can refuel the aircraft . Never seen dimpling like that ,yes a little oil canning but nothing like that. I would be looking closely at the main spar or sheared rivets on the spar.

[hilltop170]

The stock leading edge on my 1951 170A is painted a darker red back to the spar, top and bottom. It lives in Texas and has seen its share of hot sun and weather. I have never seen deformations that come and go like that.

[voorheesh]

I had a 1950 Cessna 170 A for about 15 years. The wing was painted bright red and operated in the hot California Central Valley. Never experienced skin deformity. I hangared it in Fresno, but it would spend time parked in direct sunlight while traveling. Incidentally, does your upper skin display any unusual oil canning in cooler weather when it returns to normal? Or is it as stiff as other sections that do not have the problem when hot? I’m hoping you get this resolved during your upcoming annual and that it turns out to be a minor issue.