Depression after Washing

On Jul 5, 3:58 pm, More_Flaps wrote:

Why did your push-pull test not detect it? I prefer to give a shake
and feel the nature of surface response.

That's why I have a push-pull test now. Didn't do it until
after I flew that airplane and took it apart after I got it here.
Found a lot of other stuff, too: lower strut attach bolts with no
nuts, and backing out of their holes; cracks in lots of places; scary
stuff galore. The owner trucked it away. In pieces.

Dan

On Jul 5, 4:26 pm, Peter Clark
wrote:
On Sat, 5 Jul 2008 09:45:11 -0700 (PDT),
wrote:

evasive action. We run several 172s and have seen cracks, up to four
of them, in a spar; we now forbid students to push down on the things.
No more cracks.

Just out of curiosity, is this before or after Cessna put the
reinforced spars (R and S models?) in at the factory? I don't believe
the newer models are prone to this kind of issue, but wouldn't do it
in practice anyway - using the towbar is always better for the
aircraft, and done by hand I don't think it's possible to damage a
172/182 nosewheel.

There's a Service Bulletin dealing with this, and it's dated to
before the R/S models went into production, so it's safe to figure
that Cessna fixed the problem in these models. The SB calls for
stopdrilling and monitoring every 100 hours, and fixing it by
installing a doubler either right away or when the cracks go too far.
The problem with waiting is that the centre section needs to be
replaced if the cracks reach the flanges.
I'll know more later. We're getting a new or newer one, maybe
two, soon. Interesting to see what they've improved, and what they
haven't but should have.
Which reminds me: there are other places that crack, not
readily visible. The rudder hinge brackets (on the rudder itself, not
the fin) will break in the bend radii. The top hinge is the worst, as
it has the loads of the lead balance weight wobbling around in the
turbulence to deal with. Got to use a tiny mirror and lots of light to
see the break. We spin these airplanes all the time, and in a spin
the tail wiggles around a lot, so maybe the non-spinning pilot won't
have a problem with these. Spins are also hard on gyros, whacking the
internal gyro cases against their stops and Brinelling the bearings.
But that's all part of flight training, and we charge enough to cover
things like that. We go through more propellers, too, operating off
rougher strips and picking up small stones.
These rudder brackets also wear against the fin lugs, since the
spacing at the factory was often screwed up so that the bottom hinge's
top bracket doesn't ride on its bearing flange like it's supposed to,
letting the middle and/or upper hinges take the thrust loads so they
wear thin. No thrust flanges on those bearings; just aluminum against
aluminum, and sitting outside in the wind those hinges get full of
grit and the wind wiggles the rudder and the brackets eat themselves.
I've asked Cessna to issue some teflon washers to shim the bottom
bearing and get the load off the others, but they pay no attention to
a hick from rural Canada. The law here says we have to use only the
stuff from the parts manuals, and they don't list any such washers.
The rudder bar springs put tension on the rudder cables. Those
cables aren't pulling perpendicular to the hinge line becease the
rudder is tilted back, so the rudder is pulled down, increasing the
load on the hinge thrust faces.

Dan

wrote in message
...
On Jul 4, 4:56 pm, "Mike" wrote:

Obviously, you haven't seen some of the things I have seen. One of
the
more tender, and more invisible spots on some airframes is where the
horizontal stabilizer connects to the fuze. Many designs allow a
tremendous moment arm for any non-balanced load on the stabilizer to
stress the attachment points. This shows up as cracked spars on
Cessnas,
and I have seen stressed and cracked fittings from another airframe.
How
can this happen? Well on Cessnas it happens from folks using improper
procedures to back the plane into a parking spot. It can also happen
from
innocent (but ignorant) bystanders, mowers, animal activity, or any of
thousands of other posibilities.

I always give each side a good heave up and down for this very reason, so
such can easily be checked on the preflight for impending failure.

A good heave up and down on the end of the stab of a 172
flexes the center of the forward spar, eventually cracking it. A
gentle bit of push-pull is all that's needed, to see if there's
unusual tip travel. I bet your spar is cracked now. Many are. Cessna
calls for stopdrilling the crack unless it has reached the spar
flange, in which case it has to be repaired. I once flew a 172 that I
subsequently found had a broken spar, busted clear through both
flanges so that the skin was all that was holding it. The thing could
have killed me if I gotten into turbulence or had to take violent
evasive action. We run several 172s and have seen cracks, up to four
of them, in a spar; we now forbid students to push down on the things.
No more cracks.
172s suffer cracking at the bottom of the aft doorposts. Some
models crack inside the forward doorposts. Do I need to point out that
these doorposts are what the wing pulls on to lift the airplane, along
with the struts? No preflight will find those. The wing spar attach
lugs are known to crack at the bolt holes. In older 172s the forward
elevator bellcrack bracket would break loose, reducing elevator
control. In newer 172s (rod-style gear; 1973 or so and on) the landing
gear retaining bolt sometimes shears and totals the airplane on
landing. As the years go by, these older airplanes will become the
subjects of ADs addressing age-related airframe failure, probably
after a couple come apart in flight. Sooner or later.

1. By "good heave" I don't mean raising the nosewheel off the ground. I
just mean applying enough pressure both directions to listen for any
irregularities.

2. I don't have a 172.

On 2008-06-30, John Smith wrote:
It really isn't as bad as you make it out to be.
You polish on rainy spring days, before the real flying season begins
and let it go the rest of the year. Maybe touch it up in August on days
when it is too hot to fly.

Coming in to this thread very late...

Actually, it is as bad as that unless you live in the desert. I owned a
polished plane (Cessna 140). It was only half polished, too - just the
lower half of the fuselage, the tailplane, and flaps. The rest was
painted.

To keep it looking nice required a whole day of polishing, a minimum
period of once every two months. By whole day I mean at least 12 hours.
(I rarely did it all in a day, usually I spent a weekend doing it so I
could do other stuff too). This was for an itty bitty plane and only
half polished with the more difficult to polish bits (things like upper
wing surfaces) painted. A completely polished Cherokee, for example,
would be at least three days work every two months to keep looking nice.
The plane absolutely must be hangared too. We also used Nuvite, the
final polish grade of that stuff also leaves a bit of a coating that
keeps it shiny for much longer.

The result with our C140 was of course stunning, especially when the
plane was parked on a rural turf airfield, with the polished underside
and tail reflecting the green grass, trees and blue sky. But it was a
BIG commitment to keep it that way. On the plus side you really get to
know the skin of the plane well and each session of polishing is a
rather thorough inspection.

--
From the sunny Isle of Man.
Yes, the Reply-To email address is valid.

The result with our C140 was of course stunning, especially when the
plane was parked on a rural turf airfield, with the polished underside
and tail reflecting the green grass, trees and blue sky. But it was a
BIG commitment to keep it that way. On the plus side you really get to
know the skin of the plane well and each session of polishing is a
rather thorough inspection.

(Note: I've deleted .piloting from this reply. That group is gone, I'm
afraid.)

This is an asset of a cosmetically well-maintained plane that rarely gets
mentioned. The act of thoroughly cleaning/polishing/waxing an aircraft
gives you the opportunity to really inspect your plane, and lets you detect
problems early on.

For example, just the other day I was cleaning the 'Coupe when I bumped into
the exhaust pipe -- and it moved! Turns out a clamp was loose, and we were
able to simply tighten it up, rather than "discovering" it in flight when it
could have potentially become a serious problem.

Just another reason to look askance at planes with two summers' worth of
dead bugs on the struts...
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
Ercoupe N94856
www.AlexisParkInn.com
"Your Aviation Destination"

On 2008-07-11, Jay Honeck wrote:
For example, just the other day I was cleaning the 'Coupe when I bumped into
the exhaust pipe -- and it moved!

This is why I was taught, on preflight, to give the exhaust stack a firm
shake. (Unless the engine was just run, of course.)
--
Jay Maynard, K5ZC http://www.conmicro.com
http://jmaynard.livejournal.com http://www.tronguy.net
Fairmont, MN (FRM) (Yes, that's me!)
AMD Zodiac CH601XLi N55ZC (got it!)

This is why I was taught, on preflight, to give the exhaust stack a firm
shake. (Unless the engine was just run, of course.)

Reminds me of an (otherwise good) movie we watched at "Movie Night at the
Inn" a few months ago. George Peppard stars in "The Blue Max", a story
about German World War I aviators. After he lands his plane, he jumps out
and is engaged in conversation with another pilot.

The scene cuts away, and then back -- and they show Peppard with his hand
laying casually on the cylinders/exhaust stack! Everyone in the movie
night crowd let out a yelp of disbelief and sympathetic pain. Needless to
say, the guy in charge of continuity in *that* movie really dropped the
ball...

:-)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
Ercoupe N94856
www.AlexisParkInn.com
"Your Aviation Destination"

"Jay Honeck" wrote

The scene cuts away, and then back -- and they show Peppard with his hand
laying casually on the cylinders/exhaust stack! Everyone in the movie
night crowd let out a yelp of disbelief and sympathetic pain. Needless to
say, the guy in charge of continuity in *that* movie really dropped the
ball...

Funny! I'll have to look for that, next time I see it.

I really enjoyed The Blue Max. Great flying scenes and camera work, as I
recall.
--
Jim in NC

On Fri, 11 Jul 2008 12:00:56 +0000 (UTC), Dylan Smith
wrote:

On 2008-06-30, John Smith wrote:
It really isn't as bad as you make it out to be.
You polish on rainy spring days, before the real flying season begins
and let it go the rest of the year. Maybe touch it up in August on days
when it is too hot to fly.

Coming in to this thread very late...

Actually, it is as bad as that unless you live in the desert. I owned a
polished plane (Cessna 140). It was only half polished, too - just the
lower half of the fuselage, the tailplane, and flaps. The rest was
painted.

To keep it looking nice required a whole day of polishing, a minimum
period of once every two months. By whole day I mean at least 12 hours.
(I rarely did it all in a day, usually I spent a weekend doing it so I
could do other stuff too). This was for an itty bitty plane and only
half polished with the more difficult to polish bits (things like upper
wing surfaces) painted. A completely polished Cherokee, for example,
would be at least three days work every two months to keep looking nice.
The plane absolutely must be hangared too. We also used Nuvite, the
final polish grade of that stuff also leaves a bit of a coating that
keeps it shiny for much longer.

The result with our C140 was of course stunning, especially when the
plane was parked on a rural turf airfield, with the polished underside
and tail reflecting the green grass, trees and blue sky. But it was a
BIG commitment to keep it that way. On the plus side you really get to
know the skin of the plane well and each session of polishing is a
rather thorough inspection.

I once had the care of a polished all aluminium cessna 150A.(lovely
thing)
polishing it took a weekend. what caused it to be painted eventually
was the realisation that the night time condensation appeared to
penetrate the wax polish. this continued the activity in surface
pitting that had developed all over the aircraft.
the eventual cure to the pitting was the wash and phosphoric acid prep
done prior to alodining the aircraft and painting it.

since painting, not a problem since.

in hindsight if I wanted an all aluminium finish aircraft I'd paint it
that colour.

Stealth pilot

"Jay Honeck" wrote in message news:vyVdk.249112$yE1.134425@attbi_s21...
This is why I was taught, on preflight, to give the exhaust stack a firm
shake. (Unless the engine was just run, of course.)

Reminds me of an (otherwise good) movie we watched at "Movie Night at the Inn" a few months ago. George Peppard stars
in "The Blue Max", a story about German World War I aviators. After he lands his plane, he jumps out and is engaged
in conversation with another pilot.

The scene cuts away, and then back -- and they show Peppard with his hand laying casually on the cylinders/exhaust
stack! Everyone in the movie night crowd let out a yelp of disbelief and sympathetic pain. Needless to say, the
guy in charge of continuity in *that* movie really dropped the ball...

:-)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
Ercoupe N94856
www.AlexisParkInn.com
"Your Aviation Destination"

Well, they would land many of those old birds dead stick, modulating the mags on and off, so maybe by the time he
deplaned, etc, it would have been cool enough. What kind of plane was it?