Quote:"Oil canning" is merely the flexing or buckling in and out, of a thin
flat panel, such as a portion of aircraft skin, perpendicular to the
plane of the panel. It got the name from the old style oil cans which
would spurt a drop oil out the spout when you pushed on the bottom
with your thumb (flexing the bottom of the can). The cans are shaped
generally like half of a sphere with a thin, straw like spout. I'm
sure you've seen them even if you don't remember it just yet.
The effect is not always bad, since once the panel moves or "pops"
thru, it becomes stable again, or pops back when the force that caused
it is released (like the oil can bottom did). If it occurs at a place
where the airstream is buffeting the skin somewhere, it can cause
fatigue cracks quickly at rivets, etc. Lots of times it is harmless.
It just depends on where it is and what is causing it. It can be found
by the sound it makes (like a drum head). The oil cans would make a
clicking sound. Flap skins and firewalls are places that come to mind.
It can also be spotted at locations of "smoking" rivets. Fatigue
cracks are fun to find too Wink.
Only way to resolve it is to eliminate or change the force
causing it, or brace or modify the structure somehow. Most production
planes have had any severe cases resolved already. However, time or
bad repairs can cause it to occur. Obviously it can effect
airworthiness when it damages skins, etc; lots of times it is just a
nuisance (the noise).
It applies to airplanes made of sheet metal, specifically those
areas of the structure that have flat areas. If that flat area is
large enough, and has no stiffeners behind it, it will tend to flutter
in and out like the skin on a drum and cause rumbling noises.
Most of the time it's not critical, just annoying, and doesn't look
good on the airplane, since the skin will be a bit wavy. If the skin
vibrates enough, though, it could fatigue along its fastener points
(rivets) and crack.
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