While the cat's away...

[azure]

I dropped by my hangar this afternoon to check up on my mechanic and got a bit of a scare. He mentioned that most of what he had found was minor -- yoke was loose, gear shim needed adjustment, replace alternator wire, yoke shaft was rubbing on instrument panel (been that way since I bought it and I'd asked him several times to look at it and adjust/lube/whatever it takes), reposition rat's nest of wiring underneath panel. We decided to put off replacing the partly torn fuselage cowl seal as I am not at present having any problems with engine cooling.

Then he said there was a "showstopper". (Almost a "heart stopper".) It turns out he had found corrosion on my wing spar carrythrough, the bane of Cardinal owners. That was my #1 concern that I thought had been addressed in the pre-buy, but he said that he needed to rip out the headliner and do a thorough inspection of the carrythrough to be sure that what he was seeing wasn't just the tip of a very nasty iceberg.

I even called the plane's former mechanic in NY to find out when the carrythrough had been last inspected -- Joe didn't expect my guy to find anything significant.

Well my mechanic called me back about an hour ago and said that it looks like the carrythrough is okay, but that I should replace all the insulation up there as it's saturated with mouse poop and pee. In fact, the corrosion he's seeing seems to be due to the mouse excretions as well, and he is sure now that it's all superficial <whew>. He'll wipe it down, apply some more Corrosion-X, and replace the insulation and then put it back together again. First annual complete.

But it got me to thinking about just how long that mess of brine and ammonia had been sitting there, and what would have happened had it gone on indefinitely. The former mechanic admitted that he had only done a quick visual inspection at previous annuals, and never the thorough lookover it would have taken to discover it. I can't help thinking that my guy's being new to the airplane (and therefore much more cautious) may have saved the Branded Bird a few years down the line from a fate that has befallen too many Cardinals.

 

[wabower]

It's scary to think how much rodent residue is being carried around in these planes. There are no inspection holes in the tail sections of many Cessnas. Every time I see one deskinned it looks like a 9-room critter condo.

I dropped by my hangar this afternoon to check up on my mechanic and got a bit of a scare. He mentioned that most of what he had found was minor -- yoke was loose, gear shim needed adjustment, replace alternator wire, yoke shaft was rubbing on instrument panel (been that way since I bought it and I'd asked him several times to look at it and adjust/lube/whatever it takes), reposition rat's nest of wiring underneath panel. We decided to put off replacing the partly torn fuselage cowl seal as I am not at present having any problems with engine cooling.

Then he said there was a "showstopper". (Almost a "heart stopper".) It turns out he had found corrosion on my wing spar carrythrough, the bane of Cardinal owners. That was my #1 concern that I thought had been addressed in the pre-buy, but he said that he needed to rip out the headliner and do a thorough inspection of the carrythrough to be sure that what he was seeing wasn't just the tip of a very nasty iceberg.

I even called the plane's former mechanic in NY to find out when the carrythrough had been last inspected -- Joe didn't expect my guy to find anything significant.

Well my mechanic called me back about an hour ago and said that it looks like the carrythrough is okay, but that I should replace all the insulation up there as it's saturated with mouse poop and pee. In fact, the corrosion he's seeing seems to be due to the mouse excretions as well, and he is sure now that it's all superficial <whew>. He'll wipe it down, apply some more Corrosion-X, and replace the insulation and then put it back together again. First annual complete.

But it got me to thinking about just how long that mess of brine and ammonia had been sitting there, and what would have happened had it gone on indefinitely. The former mechanic admitted that he had only done a quick visual inspection at previous annuals, and never the thorough lookover it would have taken to discover it. I can't help thinking that my guy's being new to the airplane (and therefore much more cautious) may have saved the Branded Bird a few years down the line from a fate that has befallen too many Cardinals.

 

[azure]

It's scary to think how much rodent residue is being carried around in these planes. There are no inspection holes in the tail sections of many Cessnas. Every time I see one deskinned it looks like a 9-room critter condo.

And my mechanic also reported plenty of surface corrosion visible through the inspection panels -- enough to wonder whether the airplane had ever been based near the ocean. Well, it had been 25 years ago (San Diego), but since then it's been in upstate NY far from the coast, and also all the interior surfaces had been pretty heavily treated with Corrosion-X. My guy then opined that he'd learned from working on military aircraft that in areas like MI where the roads are heavily salted all winter long, some of the salt water splashed up by tires gets aerosolized and carried up at least into the lower atmosphere, 3-4000 AGL and could account for some of it. Anyone know if there's any truth to that?

After what he found, I have to wonder how much of that is due to critter crud instead... seems more likely to me anyway.

 

[wabower]

The most recent examples I've seen have been a 1952 170-B (hail) and a 1954 180 damaged in hangar by falling fluorescent fixture during BKD tornado. Both tails had quite a bit of surface corrsosion from rodents, but nothing serious or scary, and in both cases the plane would probably have flown for many more years without a problem.

And my mechanic also reported plenty of surface corrosion visible through the inspection panels -- enough to wonder whether the airplane had ever been based near the ocean. Well, it had been 25 years ago (San Diego), but since then it's been in upstate NY far from the coast, and also all the interior surfaces had been pretty heavily treated with Corrosion-X. My guy then opined that he'd learned from working on military aircraft that in areas like MI where the roads are heavily salted all winter long, some of the salt water splashed up by tires gets aerosolized and carried up at least into the lower atmosphere, 3-4000 AGL and could account for some of it. Anyone know if there's any truth to that?

After what he found, I have to wonder how much of that is due to critter crud instead... seems more likely to me anyway.

 

[azure]

Oh, he didn't say this corrosion was serious, just "widespread". More than he would expect on an airplane hangared in upstate NY. So I was wondering if the "aerosolized street brine" theory had any merit to it. It's the first I'd ever heard of it, it's something another military mechanic had mentioned to him that he'd never heard of before either, and I'm just wondering if it's truth, or urban legend.

 

[flyingcheesehead]

So I was wondering if the "aerosolized street brine" theory had any merit to it. It's the first I'd ever heard of it, it's something another military mechanic had mentioned to him that he'd never heard of before either, and I'm just wondering if it's truth, or urban legend.

Well, it sounds plausible to me. If you can have corn in the sky, certainly salt spray can get carried up. Having picked up plenty of salt spray on my truck's windshield from the roads in winter with the nearest vehicle a good mile in front of me, I know that the salt can get into the air pretty easily. I also went to retrieve a truck that wasn't far from an interstate once - Time from when it was abandoned there until I picked it up was about 3 weeks, but there was enough salt spray that the brakes were already rusted to the drums, and the drums were VERY rusty until we got it rolling and used 'em some.

Besides, in some places they're now spraying brine instead of spreading rock salt. Ohio's definitely doing it, not sure about NY or MI.

 

[azure]

Flying corn has to be a pretty freak occurrence though, and take some hefty winds to get it up that high. Salt spray is obviously a LOT easier, and I don't doubt that trace amounts of the stuff can get lifted by the wind even a lot higher than the 4000 AGL my mechanic talked about. My question isn't whether it can get up there, but whether there's enough of it at typical cruise altitudes to cause noticeable or even measurable corrosion in aircraft over a period of years -- and specifically, whether it could cause enough surface corrosion to make someone wonder if a midwestern bird had been based along the coast.

 

[flyingcheesehead]

Flying corn has to be a pretty freak occurrence though, and take some hefty winds to get it up that high. Salt spray is obviously a LOT easier, and I don't doubt that trace amounts of the stuff can get lifted by the wind even a lot higher than the 4000 AGL my mechanic talked about. My question isn't whether it can get up there, but whether there's enough of it at typical cruise altitudes to cause noticeable or even measurable corrosion in aircraft over a period of years -- and specifically, whether it could cause enough surface corrosion to make someone wonder if a midwestern bird had been based along the coast.

I would think it'd be a bigger issue when the bird was parked outside on a ramp than when it's up high, especially if the airport is near a major road. I base that on the amount of time a plane is on the ground vs. flying, and the likelihood of salt presence going down as altitude goes up. But, it's certainly possible that it could pick some up in the air too...

 

[azure]

I'd think so too, and yet another reason to hangar vs. keeping it at a tie-down. But if the stuff is really and truly aerosolized, it might not make a big difference whether it's outside the hangar or inside. And even if most of the windborne brine is kept out by hangar doors, there are plenty of times that the doors are up for extended periods, such as during maintenance and annuals.

 

[Trapper John]

Flying corn has to be a pretty freak occurrence though, and take some hefty winds to get it up that high. Salt spray is obviously a LOT easier, and I don't doubt that trace amounts of the stuff can get lifted by the wind even a lot higher than the 4000 AGL my mechanic talked about. My question isn't whether it can get up there, but whether there's enough of it at typical cruise altitudes to cause noticeable or even measurable corrosion in aircraft over a period of years -- and specifically, whether it could cause enough surface corrosion to make someone wonder if a midwestern bird had been based along the coast.

I suppose if this subject has been studied, you'd find info at the FHWA or researched published by a state university Civil Engineering/Transportation Engineering department.

But I'd think if there were much salt making it up into the air and we were flying through it, we'd see it deposited on the windscreen or leading edges. I've never seen that, though.

To aerosolize a material and get it to stay in the air, the particle sizes need to be less than 10 micrometers. Whether vehicles rolling along highways can do that to CaCl2, MgCl2, CMA or other deicers, I have no idea.

 

[RichNY]

Azure
I took over the hangar that your plane had been in. BTW, thanks, I was on a waiting list for years. When it rains or the snow melts off the roof, the hangar
has a lot of water inside. Over the years, this damp environment could have been partly to blame for the corrosion you're seeing. I have not seen any signs of mice in the hangar thus far but I'm always looking. Hope this helps.

 

[Cap'n Jack]

I'd think so too, and yet another reason to hangar vs. keeping it at a tie-down. But if the stuff is really and truly aerosolized, it might not make a big difference whether it's outside the hangar or inside. And even if most of the windborne brine is kept out by hangar doors, there are plenty of times that the doors are up for extended periods, such as during maintenance and annuals.

I'm not disputing the brine theory, but offering another theory for consideration. Is it possible that someone set off a dry powder fire extinguisher upwind of the plane? That material is fine enough that it can carry some distance and it is very corrosive. Aside from extinguishers, other corrosive materials could have been sprayed as well.

 

[Tom-D]

Well my mechanic called me back about an hour ago and said that it looks like the carry through is okay, but that I should replace all the insulation up there as it's saturated with mouse poop and pee. In fact, the corrosion he's seeing seems to be due to the mouse excretions as well, and he is sure now that it's all superficial <whew>. He'll wipe it down, apply some more Corrosion-X, and replace the insulation and then put it back together again. First annual complete.

Unless that rat **** is cleaned up and the area of aluminum is etched with Alumaprep and primed with zinkcromate the corrosion will continue.

 

[steingar]

If it makes the OP feel any better, I've spotted some corrosion on the Free bird. It had an extensive wings off restoration, and has spent nearly almost its entire time hangared since. Had to come from somewhere, and I doubt I have critter problems. It is in annual right now, so we'll see.

 

[kmead]

I did a pre-purchase on a Mirage on a private field a number of years ago. The poor airplane hadn't flown in years. The mice had made such a mess that I couldn't get most panels off of the wings. There was about an inch of debris (mouse leftovers) inside the wings, they chewed up all of the wiring too. It was fun to watch them running around. The real show-stopper was the fuel selector cut-out accessed in the RH wing root. The mouse urine had reacted with the fuselage skin in a way that it looked like a bomb went off, the wing would need to be de-mated and major repairs made.

I was relieved when the sale didn't move ahead, I really didn't want that big of a job at the time. I also wonder if a future buyer found the problems too.

Kevin

 

[azure]

Unless that rat **** is cleaned up and the area of aluminum is etched with Alumaprep and primed with zinkcromate the corrosion will continue.

He says he's gonna wipe it down thoroughly and apply corrosion-x. Why would the corrosion continue once the residue is gone?

 

[azure]

Azure
I took over the hangar that your plane had been in. BTW, thanks, I was on a waiting list for years. When it rains or the snow melts off the roof, the hangar
has a lot of water inside. Over the years, this damp environment could have been partly to blame for the corrosion you're seeing. I have not seen any signs of mice in the hangar thus far but I'm always looking. Hope this helps.

Rich, good to hear from you! Yep, that's pretty much what my hangar is like too. But I don't see how dampness by itself could lead to corrosion. The humidity is high all over the Great Lakes and the NE all winter long. It seems you would need an agent that reacts with aluminum to do that (like NaCl or CaCl2).

Though I guess dampness combined with all the other crap that finds its way into the ramp environment could work together. It all depends on airport policies and how compliant the pilots are. Joe seemed to think there shouldn't be any serious problem at 1B1.

 

[Ted]

It sounds like your mechanic did the right thing by performing a more thorough inspection. Get it taken care of and move on with life, but it probably is a good idea to do a more thorough look-see at annual. This is just one of the many reasons why routine inspections are very important.

Mice and rodents are really, really annoying. We suffered them significantly with British cars (wasps, too... for some reason wasps are attracted to British cars).

 

[wabower]

It figures. Wasps prefer to build their nests on stationary objects that are unlikely to move anytime soon.

It sounds like your mechanic did the right thing by performing a more thorough inspection. Get it taken care of and move on with life, but it probably is a good idea to do a more thorough look-see at annual. This is just one of the many reasons why routine inspections are very important.

Mice and rodents are really, really annoying. We suffered them significantly with British cars (wasps, too... for some reason wasps are attracted to British cars).

 

[Ted]

It figures. Wasps prefer to build their nests on stationary objects that are unlikely to move anytime soon.

Most aircraft provide a more appropriate home than Japan in that regard.

Then again, most Jaguars provide an even more appropriate home.

 

[Tom-D]

He says he's gonna wipe it down thoroughly and apply corrosion-x. Why would the corrosion continue once the residue is gone?

The C-177 carry thru is a large cast aluminum piece that is anodized for protection, when that is removed by the rat pee, it will continue to corrode unless it is etched, an protected.

sprayed on corrosion protection will only seal the rat pee on to the surface. Etching removes the residue and washes it away, and the zinkcromate will be a permanent protection.

Remember urine is an acid, seal it to the surface and it continues to corrode

 

[azure]

The C-177 carry thru is a large cast aluminum piece that is anodized for protection, when that is removed by the rat pee, it will continue to corrode unless it is etched, an protected.

sprayed on corrosion protection will only seal the rat pee on to the surface. Etching removes the residue and washes it away, and the zinkcromate will be a permanent protection.

Thanks Tom, that's good to know. Well I talked to my mechanic and he said that he was going to treat the spots of corrosion with Alodine first. I looked it up and couldn't find what it's made of exactly, but it does seem to be a kind of chromate conversion treatment. Does that do the same thing as zinkcromate?

 

[Gary]

I looked it up and couldn't find what it's made of exactly, but it does seem to be a kind of chromate conversion treatment. Does that do the same thing as zinkcromate?

MSDS for Alodine 1201 is here:

http://ac0ok.net/projects/f3bhsd/alodine1201MSDS.pdf

Pretty much a solution of chromic acid and hydrofluoric acid. It is corrosive and in concentrated solutions, pretty nasty. It is not the same as zinc chromate.

http://facilities.fit.edu/documents/forms/MSDS/Richards 1017.pdf

The Alodine will clean the aluminium and give it a chemical coating of an aluminium/chrome complex (the nice golden color) That coating takes paint much better than bare aluminium or the aluminium oxide coating that forms natrually.

Gary

 

[Yellowbird]

Good catch on the spar. I had mine inspected as part of the prebuy inspection when I bought the plane. Nothing significant was found, but the seller had it cleaned and treated per my request. I got my first good look at the spar when I redid my interior a couple of years ago. It wasn't bad, but there were a few spots that predated the prebuy cleaning/treatment that I didn't like. I ended up scrubbing the whole thing clean again, and then alodining/priming it before putting the new interior in.

I never saw any evidence of mice, but I did have bird nests in the tailcone a couple of times.

I dropped by my hangar this afternoon to check up on my mechanic and got a bit of a scare. He mentioned that most of what he had found was minor -- yoke was loose, gear shim needed adjustment, replace alternator wire, yoke shaft was rubbing on instrument panel (been that way since I bought it and I'd asked him several times to look at it and adjust/lube/whatever it takes), reposition rat's nest of wiring underneath panel. We decided to put off replacing the partly torn fuselage cowl seal as I am not at present having any problems with engine cooling.

Then he said there was a "showstopper". (Almost a "heart stopper".) It turns out he had found corrosion on my wing spar carrythrough, the bane of Cardinal owners. That was my #1 concern that I thought had been addressed in the pre-buy, but he said that he needed to rip out the headliner and do a thorough inspection of the carrythrough to be sure that what he was seeing wasn't just the tip of a very nasty iceberg.

I even called the plane's former mechanic in NY to find out when the carrythrough had been last inspected -- Joe didn't expect my guy to find anything significant.

Well my mechanic called me back about an hour ago and said that it looks like the carrythrough is okay, but that I should replace all the insulation up there as it's saturated with mouse poop and pee. In fact, the corrosion he's seeing seems to be due to the mouse excretions as well, and he is sure now that it's all superficial <whew>. He'll wipe it down, apply some more Corrosion-X, and replace the insulation and then put it back together again. First annual complete.

But it got me to thinking about just how long that mess of brine and ammonia had been sitting there, and what would have happened had it gone on indefinitely. The former mechanic admitted that he had only done a quick visual inspection at previous annuals, and never the thorough lookover it would have taken to discover it. I can't help thinking that my guy's being new to the airplane (and therefore much more cautious) may have saved the Branded Bird a few years down the line from a fate that has befallen too many Cardinals.

 

[Tom-D]

MSDS for Alodine 1201 is here:

http://ac0ok.net/projects/f3bhsd/alodine1201MSDS.pdf

Pretty much a solution of chromic acid and hydrofluoric acid. It is corrosive and in concentrated solutions, pretty nasty. It is not the same as zinc chromate.

http://facilities.fit.edu/documents/forms/MSDS/Richards 1017.pdf

The Alodine will clean the aluminium and give it a chemical coating of an aluminium/chrome complex (the nice golden color) That coating takes paint much better than bare aluminium or the aluminium oxide coating that forms natrually.

Gary

Alodine will NOT clean aluminum. it is only a 6% solution of chromic acid and will not treat any surface that is not chemically clean before application.

Alodine produces a artificial hydroxide film that protects the aluminum. some times it is clear, and some times it looks like a coffee stain.


You use Alumaprep, to clean and remove any corrosion products/urine left behind. Then you apply the Alodine, and rinse it very well

read this

http://www.airmod.com/articles/PDF/cpafeb07.pdf

 

[Gary]

Alodine will NOT clean aluminum. it is only a 6% solution of chromic acid and will not treat any surface that is not chemically clean before application.

Yes - you are correct Alumiprep is a far better cleaner, It is recommended prior to Alodine. That being said the hydrofluoric acid will oxidize any organics present.

Alodine produces a artificial hydroxide film that protects the aluminum. some times it is clear, and some times it looks like a coffee stain.

Minor point - the reaction with Alodine and aluminium is chemical, the chromic acid reacts with the aluminium to form a aluminium/chrome metallic complex, the reaction is catalyzed by the hydrofluoric acid and ferrocyanide. No hydroxides are involved, not sure on the color issue, may depend on the particular aluminium alloy.

Alumiprep is phosphoric acid based, no hydroxide formation using Alumiprep 33.

You use Alumaprep, to clean and remove any corrosion products/urine left behind. Then you apply the Alodine, and rinse it very well

read this

http://www.airmod.com/articles/PDF/cpafeb07.pdf

Correct.

Gary

 

[Tom-D]

aluminium/chrome metallic complex, Gary

Fancy name for hydroxide film..

that is the only recommended repair for the loss of the anodizing.

read the 100 service manual for the C-177

 

[Tom-D]

Alumiprep is phosphoric acid based, no hydroxide formation using Alumiprep 33.
Gary

You are talking about 2 different chemicals, Alumiprep, and Alodine.

One is a cleaner, the other is a corrosion preventative.

 

[azure]

Okay, so Alumiprep is to etch the surface to remove all the bound residue, and either Alodine or zinkcromate (why the weird spelling, is that a brand name?) are to protect it from further corrosion.

Which is better? I have Cessna's document on cleaning the spar and inspecting for minimum serviceable thickness, and it recommends Alodine.

Also, can the etching action of Alumiprep be controlled? If you remove too much of the surface, the spar is toast.

My guy said he removed about 2 cups worth of poop and found a couple blistered spots once he'd wiped it all away. He's concerned now about whether the spar is serviceable.

 

[Gary]

Okay, so Alumiprep is to etch the surface to remove all the bound residue, and either Alodine or zinkcromate (why the weird spelling, is that a brand name?) are to protect it from further corrosion.

Which is better?

It's a two step process, not an either/or. The Alumiprep 33 is foremost a cleaner and corrosion remover, it is highly unlikely Alumiprep will "etch" enough aluminium to be a problem:

http://www.xs4all.nl/~henk0008/Henkel/ALUMIPREP. 33 (US).pdf

The Alodine 1201 is a chemical conversion treatment for corrosion resistance and provides a good base for painting (if necessary):

https://tds.us.henkel.com//NA/UT/HN...6E852571ED0055ED8E/$File/ALODINE® 1201-EN.pdf

Depending on the application, after you have used the Alumiprep and Alodine, you could then apply a zinc chromate paint for further protection/corrosion resistance.

This all depends on the application, the extent of corrsion and the desired level of corrosion resistance.

Gary

 

[Ted]

My guy said he removed about 2 cups worth of poop and found a couple blistered spots once he'd wiped it all away. He's concerned now about whether the spar is serviceable.

Here's a question - what's his background with wing spars? At this point, it might be worth consulting a specialist who deals with this more regularly to at least get some background information. A phone call might be worth a lot in this case.

 

[azure]

It's a two step process, not an either/or.

Just for clarification: I was asking which is better, Alodine vs ZnCrO4, NOT Alumiprep vs Alodine. I know it's a two-step process. Etch first, then apply protectant. Good to know that Alumiprep won't remove too much.

Again, I'm asking because Cessna recommends Alodine but Tom-D said "zinkcromate" is best. Yes, he can apply Alodine first and then chromate, I'm trying to figure out how you determine whether you need both, and if only one, whether chromate is better than Alodine.

And no, my guy is not an expert in spars. I'm trying to get him all the information I can, and he also has access to Cessna experts at Michigan Aviation in PTK.

 

[Yellowbird]

Okay, so Alumiprep is to etch the surface to remove all the bound residue, and either Alodine or zinkcromate (why the weird spelling, is that a brand name?) are to protect it from further corrosion.

Which is better? I have Cessna's document on cleaning the spar and inspecting for minimum serviceable thickness, and it recommends Alodine.

Also, can the etching action of Alumiprep be controlled? If you remove too much of the surface, the spar is toast.

Alumiprep is used to clean, but it doesn't really remove any material (at least not beyond the first few molecules).

When I did my spar, I used a scotch-brite pad and a small polishing wheel in a Dremel moto-tool to remove the spots of corrosion and the old anti-corrosion treatment. I then scrubbed the spar with a fresh scotch-brite pad soaked in diluted Alumiprep to thoroughly clean the surface. After rinsing, I wiped the spar down with a couple of coats of alodine, rinsing again after all was done. The final step was to spray a few coats of primer. (I used zinc phosphate primer, which is supposed to be more health-friendly than zinc chromate.)

Before

During

After

 

[Tom-D]

Just for clarification: I was asking which is better, Alodine vs ZnCrO4, NOT Alumiprep vs Alodine. I know it's a two-step process. Etch first, then apply protectant. Good to know that Alumiprep won't remove too much.

Again, I'm asking because Cessna recommends Alodine but Tom-D said "zinkcromate" is best. Yes, he can apply Alodine first and then chromate, I'm trying to figure out how you determine whether you need both, and if only one, whether chromate is better than Alodine.

And no, my guy is not an expert in spars. I'm trying to get him all the information I can, and he also has access to Cessna experts at Michigan Aviation in PTK.

Don't confuse the corrosion treatment with paint.

Alumiprep is a cleaner, basically a acid type soap.
http://www.aircraftspruce.com/catalog/cspages/alumiprep.php

Alodine is a chemical treatment, made from chromate crystal,
http://www.aircraftspruce.com/menus/cs/metalprepsupplies.html

And the Zink chromate is a paint
http://www.aircraftspruce.com/menus/cm/primer.html

 

[azure]

Got it, thanks.

As it turns out, this is all probably academic. I sent him the Cessna minimum serviceable limits for the spar CT from the CFO website. The corrosion is on the center "web" part of the spar, the part where the limit is strictest. I'm waiting now to hear the bad news, but I don't expect the spar to be serviceable.

 

[azure]

Well I had a good look at my spar ct today... ugly, looks very bad. Scott, yours looked pristine compared to mine even before you did any work, if that photo is any basis to judge. My mechanic showed me blistered spots where you can remove tiny aluminum shavings with your thumbnail. It's all on the "web" part that connects the upper and lower flanges. The Cessna minimum spec for that section is 0.22", and he's not sure what it was originally but he suspects that it is (was) quarter-inch aluminum. He doesn't think that any of the blisters go more than .015" into the metal. He's mainly concerned that underneath the blistering, the corrosion has gone intergranular and he only knows of tests that can prove a positive, not how to rule it out.

He's taken some pictures that he will forward to a Cessna tech rep for a second opinion. He's asked mechanics from PTK to come over and look at it but everyone has refused. Despite being a Cessna authorized repair station, no one there has experience with Cardinal spars.

 

[Cap'n Jack]

Fancy name for hydroxide film..

that is the only recommended repair for the loss of the anodizing.

read the 100 service manual for the C-177

Hydroxide film? Nope. Hydroxide refers to an OH group. A chromium/aluminum complex isn't a hydroxyl group. Look it up in a chemistry book.

Don't confuse the corrosion treatment with paint.

Alumiprep is a cleaner, basically a acid type soap.
http://www.aircraftspruce.com/catalog/cspages/alumiprep.php

Alodine is a chemical treatment, made from chromate crystal,
http://www.aircraftspruce.com/menus/cs/metalprepsupplies.html

And the Zink chromate is a paint
http://www.aircraftspruce.com/menus/cm/primer.html

It's not "Zink", it's zinc. Look at a periodic chart, they usually spell out the element names, or look at the link you provided.

 

[Tom-D]

Hydroxide film? Nope. Hydroxide refers to an OH group. A chromium/aluminum complex isn't a hydroxyl group. Look it up in a chemistry book.



It's not "Zink", it's zinc. Look at a periodic chart, they usually spell out the element names, or look at the link you provided.

You should look it up on the bottle, WE refilled the 100 gallon Alodine tank at Fleet repair station Northwest every 6 months, and the directions on the 55 gallon drum says Hydroxide film formed to a light golden hue in color.

the rest of your protest is a simple typo.

 

[Tom-D]

Well I had a good look at my spar ct today... ugly, looks very bad. Scott, yours looked pristine compared to mine even before you did any work, if that photo is any basis to judge. My mechanic showed me blistered spots where you can remove tiny aluminum shavings with your thumbnail. It's all on the "web" part that connects the upper and lower flanges. The Cessna minimum spec for that section is 0.22", and he's not sure what it was originally but he suspects that it is (was) quarter-inch aluminum. He doesn't think that any of the blisters go more than .015" into the metal. He's mainly concerned that underneath the blistering, the corrosion has gone intergranular and he only knows of tests that can prove a positive, not how to rule it out.

He's taken some pictures that he will forward to a Cessna tech rep for a second opinion. He's asked mechanics from PTK to come over and look at it but everyone has refused. Despite being a Cessna authorized repair station, no one there has experience with Cardinal spars.

Know and understand what you are dealing with, read AC 43,13 chapter #6

http://rgl.faa.gov/regulatory_and_guidance_library/rgadvisorycircular.nsf/0/99c827db9baac81b86256b4500596c4e/$FILE/Chapter%2006.pdf

and keep in mind that Cessna has a detailed corrosion limits on that spar. And they must be followed to the letter.

normally to find out how deep corrosion is, it must be machined out, tested with dye penetrant, until a depth is obtained that shows no more defects.

then measured by depth mapping and the distance differing from the original is the number allowed in the criteria given in the Structural repair manual for the C-177.

If I had any doubts I'd get a new one, and have it replaced.

 

[Tom-D]

Got it, thanks.

As it turns out, this is all probably academic. I sent him the Cessna minimum serviceable limits for the spar CT from the CFO website. The corrosion is on the center "web" part of the spar, the part where the limit is strictest. I'm waiting now to hear the bad news, but I don't expect the spar to be serviceable.

That's really bad news, because the wings must come off for it to be replaced.