What is Oil Canning?

What is Oil Canning? How is It Spotted? What Problems Dose It Cause? Dose It
Affect Airworthiness? If So How Is It Resolved or Fixed?

Think of the old-timey oilers - the ones with the long, narrow spout, with
the reservoir at the bottom. The bottom of that reservoir was convex-shaped.
Another example would be on the top of a jelly jar - you know, the ones that
once the seal is broken, the middle of the lid pops up a tiny bit.

If you press on either the oil can or the jelly jar lid, it will go in an
out a bit, and spring back to its original form. So, if you have a panel on
the plane that you can press, and it springs in and out, that's "oil
canning."

By itself, it's not bad, and (no A&P here...) is not an airworthy issue. IF
however, a formerly straight and tight panel starts to oilcan, you might
have it checked to see if you overstressed a wing or tail that would cause
one of the spars or ribs to bend a bit, creating "looser" metal in that area
of the panel, which could then cause the oil canning effect.


"MRQB" wrote in message
...
What is Oil Canning? How is It Spotted? What Problems Dose It Cause? Dose
It
Affect Airworthiness? If So How Is It Resolved or Fixed?

"MRQB" wrote in message ...
What is Oil Canning? How is It Spotted? What Problems Dose It Cause? Dose It
Affect Airworthiness? If So How Is It Resolved or Fixed?

"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 .
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).

Regards,
Bruce N30464

"MRQB" wrote in message ...
What is Oil Canning? How is It Spotted? What Problems Dose It Cause? Dose It
Affect Airworthiness? If So How Is It Resolved or Fixed?


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.
Some builders, I've heard, will heat the sheet with a heat lamp
before and during the installation process so that the sheet will
tighten afterward as it cools and come smooth and resist oilcanning.
Don't quote me on that.
Best thing is to build an airplane with lots of curved sheets
that won't vibrate, but it's a lot more work.

Dan

"MRQB" wrote in message ...
What is Oil Canning? How is It Spotted? What Problems Dose It Cause? Dose It
Affect Airworthiness? If So How Is It Resolved or Fixed?

We experienced this in our Arrow a couple of years ago. It would
occur usually after landing while parking the aircraft. A gear
collapse many years ago hadn't been repaired quite robustly enough, so
we had it reinforced and that took care of it. On any a/c with damage
history, I wouldn't ignore it.