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Wing Panel Wrinkle

seattleworm

Well Known Member
Sponsor
My RV7 got about 70 hours. Last weekend I had a passenger to take some video, and I noticed a obvious wing panel wrinkle. Since I could not see it from left seat without really reach out, I didn't notice this until now. The wrinkle probably has been there from day 1. I checked the wing panel while on the ground, the wrinkle is not obvious, but noticeable when looking hard. When pushing the panel, you can see some sort of oil canning behavior (panel is not very tight). I don't remember seeing this kind wrinkle from other RV videos, it could be just that the light and angle make the wrinkle so obvious. The plane flies really well, and there is no vibration on the panel during flight, so I don't think it will cause any safety problem, but just wonder if anybody noticed something similar. Picture is shown below, you can see the winkle at the bay right after the fuel cap

w89h5h.jpg
 
My RV7 got about 70 hours. Last weekend I had a passenger to take some video, and I noticed a obvious wing panel wrinkle. Since I could not see it from left seat without really reach out, I didn't notice this until now. The wrinkle probably has been there from day 1. I checked the wing panel while on the ground, the wrinkle is not obvious, but noticeable when looking hard. When pushing the panel, you can see some sort of oil canning behavior (panel is not very tight). I don't remember seeing this kind wrinkle from other RV videos, it could be just that the light and angle make the wrinkle so obvious. The plane flies really well, and there is no vibration on the panel during flight, so I don't think it will cause any safety problem, but just wonder if anybody noticed something similar. Picture is shown below, you can see the winkle at the bay right after the fuel cap

w89h5h.jpg

... This is very normal in flight or if sitting on a set of wing jacks. The first time I saw this I was not happy as well and after pursuing a solution found it was present in most others RV aircraft. When inverted it goes away.:rolleyes:
Very nice photo! Thanks, Allan...:D
 
Oil Canning

Shawn:

This would not be noticeable on the ground, since the panel in question is probably more in tension. When in the air however, the upper skin is more in a compression condition and then the smallest of variations of excess skin panel verses the rib hole spacing would show up as this oil canning, as it's called.

I have seen Army UH-60 Blackhawk, and CH-47 Chinook, tail booms, and fuselages respectively, severely oil can under stress, when picking up heavy sling loads . When the sun light is just right along the skin, you can see the slightest deviations the height of the skins.
 
Thanks all for confirming this is not something I should worry about. Amazing picture of the B52, wondering what kind temperature is on the skin to get these wrinkles :D
 
When I skinned my RV-6 wings, I heated them while drilling and riveting. 22 years later they are still drum tight. Of course that was before the kit came with the holes included. That won't help much now. Although heating them while riveting should help some.

The only time I got concerned about wing skin wrinkles was while looping my old Globe Swift. They wrinkled quite a bit during a 3g pull-out.
 
The only time I got concerned about wing skin wrinkles was while looping my old Globe Swift. They wrinkled quite a bit during a 3g pull-out.

Uh....and for future reference (while used airplane shopping), the serial number of that airframe would be....? :p:D
 
When I skinned my RV-6 wings, I heated them while drilling and riveting. 22 years later they are still drum tight. Of course that was before the kit came with the holes included. That won't help much now. Although heating them while riveting should help some.

How hot? What was ambient? What was the temperature of the skeleton?

And how did you keep them hot while riveting?
 
How hot? What was ambient? What was the temperature of the skeleton?
And how did you keep them hot while riveting?

We probably did a little overkill. We had the skins so hot that I got a minor sunburn on the side of my face. We used a "salamander" type heater blowing directly on the skin. Can't control the temperature of the skeleton but with the heater blowing directly on the skins, they were definitely hotter.
 
Uh....and for future reference (while used airplane shopping), the serial number of that airframe would be....? :p:D

The last time I saw that aircraft, it had been purchased by the President of the Swift Association and modified with a Cont. IO=360, sliding canopy, sticks, clipped wing tips and all the other mods popular with those guys.
When I sold it, it was original configuration.
 
When I skinned my RV-6 wings, I heated them while drilling and riveting. 22 years later they are still drum tight. Of course that was before the kit came with the holes included. That won't help much now. Although heating them while riveting should help some.

The only time I got concerned about wing skin wrinkles was while looping my old Globe Swift. They wrinkled quite a bit during a 3g pull-out.

I just built mine in an un-airconditioned garage in New Mexico in June;)
 
So I have

CTE 12.9 ?in/in-?F

What's the longest piece of wing skin, 5'? (Don't have a plane handy to measure :) ).

Let's say ambient is 70 ?F
I doubt anyone could work on a part in excess of 140 ?F, so let's use that.

Run the numbers and you get ~ .05" over the entire length of the skin.

AN426AD3 rivets use a #40 hole, with is .098". (BEFORE dimpling, which makes it even larger).

Thus, the change in length of a 5' piece of skin, end-to-end, heated so hot you can hardly touch it (if at all...I think hot water heaters use 120 as a maximum before scalding is a danger) is 1/2 the diameter of rivet hole.

I submit the underlying structure would be flexible enough to negate any possible effect here, and what you're really seeing is just good craftsmanship in overall alignment, drilling, etc. :)
 
Fuselage wrinkles

For those of you interested in the technical side of this fuselage side wrinkling phenomena, airframe structures engineers call this web deformation a characteristic of a diagonal tension field beam. That is the the structure supporting the skin panel is being pulled inward allowing the panel to buckle in compression and take its load as in-plane tension. This design trick allows for a very light aluminum structure. As flight loads change these wrinkles disappear and reappear. As you guys who fly these aluminum airplanes know this happens and has to happen on the wings too as they take on the bending loads of flight. This is not the term used for wing skin buckling but skin buckling is accounted for and judiciously used in wing design. I know it must be disconcerting to look out on your wings and see those wrinkles appear, especially since your rear-end is on the line, but be assured that if you built your airplane according to the plans, your airplane is safe for the design loads Van has specified. The next time you take an airline flight on an aluminum winged aircraft (composite wings do not normally buckle) gaze out on the wing and watch the wing skin wrinkles (buckles) appear and disappear as the aircraft transitions from one flight regime to another or takes on gust loads. Of course, you will see the same thing happen on your airplane.

George
retired airframe structures engineer for the USAF
 
Even the best have wrinkles!

1fdbbb3e9cb7d8f7d261970d99523ec4.jpg

The F-18 wrinkles up pretty good on a cat shot too. If the sun is just right, the moment the cat fires and the load is transferred to the center barrel, it looks like a twisted up beer can. Buddy of mine got a pretty good picture of it I'll try and locate.
 
I can't see anything but a mountain like nothing I have ever seen in Georgia.

Beautiful


cary
 
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