Cessna Wing Skins

Thanks for clarifying that Tom
You had me worried

Tony

In article .net,
"Tom Cummings" wrote:

I didnot find any corrosion. There is no A.D. for this. I just think the
I.A. is being thorough. I didn't mean to cause a false alarm.
The A.I. is not aware of the three little rivits or he would have pointed
them out to me. He is out of town this weekend and I thought I 'd check with
this group before he gets back on Monday.
Tom
"tony roberts" wrote in message
news:nospam-01806A.22502923042005@shawnews...
Did you find corrosion? I'm not aware of any AD that requires removal of
the skins.
I would have thought that you A & E would be doing this if it was
necessary. - and would know how to do it.
Here is Canada, if my understanding is correct, you would be allowed to
remove the skins, but not allowed to reinstall them.
Sorry I'm unable to answer your question but I have one of my own.
Is there an AD? If so, maybe I'm going to have to do the same thing in
my 172H.

Tony

--

Tony Roberts
PP-ASEL
VFR OTT
Night
Cessna 172H C-GICE


In article .net,
"Tom Cummings" wrote:

My Cessna 172 M (1973) is being annualed. The top wing skin panels above
the
wing tanks (Standard tanks) have to come off to inspect the area for
corrosion. We got all the screws removed. According to the service
manual,
that is all that is supposed to be securing the panel. (Dozens of screws
around the perimeter of the skin and six screws around the fuel filler
neck
is all that is stated to be removed). The skins would not remove after
careful tugging and pulling. (the fuel cap was removed for this).Then I
finally found three rivit type fasteners also around the filler neck.
They
apparently hold the skin in place in addition to the six screws but there
is
not any reference in the manual about removing them or drilling the heads
of
the rivits off. If they are indeed rivits, they are flush head type
because
they are smooth with the skin's surface. The heads are about 1/8th inch
in
diameter. I was hoping they could be merely some alignment pins. I
removed
the small inspection cover over the fuel transmitter (sender) to get a
better grip on the panel near the filler neck. When trying to gently lift
the skin panel upward, it is obvious that the three rivits are attached
to
the panel and to a flange underneath the panel that apparently secures
the
filler neck. The panel would not pop clear of them. So I don't think they
are alignment pins.
Anyone familiar with this to advise drilling these three fasterners to
free
the panel?
Thanks,
Tom Cummings




--

Tony Roberts
PP-ASEL
VFR OTT
Night
Cessna 172H C-GICE

Don't drill out those rivets! They are only holding a circular
gasket flange ring on the top skin. After all the screws are out, you
have to be a little less gentle with that skin and lift it enough that
the gasket flange ring will clear the tank neck and allow the skin to
slide out from under the leading edge skin and cabin roof skin.
Cessna wants those skins off every 1000 hours, and there's good
reason. We have found broken tank restraining straps, missing strap
chafe protection, rubber tank support and top skin straps rotted away
and the tank rubbed through (or almost through) against aluminum
structure, fuel stains around the filler neck weld indicating a crack
that could suddenly get serious, and so on. (Line boys with their big
fuel nozzles tend to let the tank neck take the hose weight, and that
cocks the tank neck and cracks the weld.) Once the mechanic has done a
couple of these inspections they're not a big deal. The skins are much
harder to get back into place thatn they are to take out, especially if
the tank was moved a bit; the filler neck will no longer line up with
the skin when the skin's screw holes are lined up with the wing's
holes.
You'll need a couple of new gaskets for the filler neck, at
typical Cessna prices.

Dan

Thank you very much Dan for the info.
Tom
wrote in message
ups.com...
Don't drill out those rivets! They are only holding a circular
gasket flange ring on the top skin. After all the screws are out, you
have to be a little less gentle with that skin and lift it enough that
the gasket flange ring will clear the tank neck and allow the skin to
slide out from under the leading edge skin and cabin roof skin.
Cessna wants those skins off every 1000 hours, and there's good
reason. We have found broken tank restraining straps, missing strap
chafe protection, rubber tank support and top skin straps rotted away
and the tank rubbed through (or almost through) against aluminum
structure, fuel stains around the filler neck weld indicating a crack
that could suddenly get serious, and so on. (Line boys with their big
fuel nozzles tend to let the tank neck take the hose weight, and that
cocks the tank neck and cracks the weld.) Once the mechanic has done a
couple of these inspections they're not a big deal. The skins are much
harder to get back into place thatn they are to take out, especially if
the tank was moved a bit; the filler neck will no longer line up with
the skin when the skin's screw holes are lined up with the wing's
holes.
You'll need a couple of new gaskets for the filler neck, at
typical Cessna prices.

Dan

wrote:
Cessna wants those skins off every 1000 hours, and there's good
reason. We have found broken tank restraining straps, missing strap
chafe protection, rubber tank support and top skin straps rotted away
and the tank rubbed through (or almost through) against aluminum
structure, fuel stains around the filler neck weld indicating a crack
that could suddenly get serious, and so on.
snip

I'll second that assessment. Tank skins need to be pulled far more
often than most people bother to pull them. The OP's mechanic is doing
his job.

See our recent experience on my site. Click through:

Aviation-Articles-Maintenance-Fuel Tank Repair

-Doug

--------------------
Doug Vetter, CFIMEIA

http://www.dvcfi.com
--------------------

Good article. Your airplane has an older style fuel cap and flange
arrangement than the original poster, and his skins are more difficult
to remove. His advantage is not having that recessed pit around the cap
that collects water and dirt; the cap flange is flush with the wing.
His disadvantage is getting that gasket back into place while replacing
the skin; a bit of fuellube will hold it in place. I suspect his tank
skin is being hard to remove because someone used Form-A-Gasket or
something tough to seal the gasket last time, and it's stuck good.
172s used all-brass floats by the time our L and M models came
out. They're OK, but we had one fail because the arm stop was
misadjusted and the float was tapping the top of the tank when the tank
was full of fuel. It wore a hole in the float, which filled and sank.

Dan

wrote in message
ups.com...
Good article. Your airplane has an older style fuel cap and flange

That is correct Dan. My cap is flush with wingskin. Once I get it the skin
loose,
the skin will slide across the neck.

a bit of fuellube will hold it in place. I suspect his tank
skin is being hard to remove because someone used Form-A-Gasket or
something tough to seal the gasket last time, and it's stuck good.

Yes, I saw the hardened sealant when I removed the screws. There is
definitely
no way or place to pry or use a tool to losen the skin without ruining any
components so
it is going to be interesting.
\The Cessna manual calls for some specific types of sealant to use, one
being
a Dow Corning product, and others.
I have not ordered any gaskets yet as I am waiting to see if I to need any
other
components such as tank restraining straps, chafe protection, rubber tank
supports,
top skin straps, and the sealant.
Tom

Good one. Thanks!

On 24 Apr 2005 20:01:30 -0700, wrote:

Don't drill out those rivets! They are only holding a circular
gasket flange ring on the top skin. After all the screws are out, you
have to be a little less gentle with that skin and lift it enough that
the gasket flange ring will clear the tank neck and allow the skin to
slide out from under the leading edge skin and cabin roof skin.
Cessna wants those skins off every 1000 hours, and there's good
reason. We have found broken tank restraining straps, missing strap
chafe protection, rubber tank support and top skin straps rotted away
and the tank rubbed through (or almost through) against aluminum
structure, fuel stains around the filler neck weld indicating a crack
that could suddenly get serious, and so on. (Line boys with their big
fuel nozzles tend to let the tank neck take the hose weight, and that
cocks the tank neck and cracks the weld.) Once the mechanic has done a
couple of these inspections they're not a big deal. The skins are much
harder to get back into place thatn they are to take out, especially if
the tank was moved a bit; the filler neck will no longer line up with
the skin when the skin's screw holes are lined up with the wing's
holes.
You'll need a couple of new gaskets for the filler neck, at
typical Cessna prices.

Dan