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  #1  
Old 01-02-2007, 01:06 PM
Glos Glos is offline
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Default Corrosion under the skin

Late in the year I removed both ailerons to inspect for hinge corrosion. To my surprise I found a lot of corrosion in completley different areas. Normally I never removed or dismantled the ailerons during a condition inspection.

The first thing I noticed was the corrosion at the ends of the torque tubes.
I could have just cleaned it off and put it back in but I elected to replace them with stainless steel.

Then I noticed rust protuding from the paint around the counterbalance weight.

I sanded down arround the affected areas with the idea of patching it up but it kept eating at me so I removed the entire counter weight. In the photos you can see dark areas on the aileron just behind the counterweight. This is where the rust extended a full 360 around the rod. They have been in the garage for over a month and there was still moist areas.

The plane has been outside since 1986. Oddly enough there was no evidence of rust on the wing attach bolts.

The found rust was hidden from view. I assume that it just wicked in from the ends over time.

I just ordered new SS counterbalance rods from Wicks. they weigh the same as the steel rods.

This is just a FYI for whatever it's worth.

Oh by the way the area where the hinges attach to the torque tube in the aileron showed no evidence of corrosion
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  #2  
Old 01-02-2007, 02:03 PM
Wayne Hicks Wayne Hicks is offline
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Default

Oddly enough there was no evidence of rust on the wing attach bolts.

----> Why should there be? The iron rods we use as counterweights for the ailerons are untreated. The wing bolts are treated.
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  #3  
Old 01-02-2007, 03:38 PM
Buly Buly is offline
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When I received my counter ballance rods, they were rusted bad already. Trew them in the garbage, went to Home Depot and bought galvanized rod.
Using stainless inserts inside aluminum tube is not a good idea. They react galvanicly and can cause even more corrosion than steel tubes.
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  #4  
Old 01-02-2007, 04:10 PM
SteveWrightNZ SteveWrightNZ is offline
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why not go 100% stainless ? (other than the weight, brittleness, cost, difficulty machining it, etc)

S
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  #5  
Old 01-02-2007, 04:40 PM
Hugo1962 Hugo1962 is offline
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Default sealant

I just did a yahoo search on

install bracket sealant faying surface

I invite you all to read some of the suggested URL's and form your own opinion on how sealants maybe useful as corrosion stopper/prevention aid).
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  #6  
Old 01-02-2007, 07:38 PM
Lynn Erickson Lynn Erickson is offline
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Quote:
Originally Posted by Buly View Post
When I received my counter ballance rods, they were rusted bad already. Trew them in the garbage, went to Home Depot and bought galvanized rod.
Using stainless inserts inside aluminum tube is not a good idea. They react galvanicly and can cause even more corrosion than steel tubes.
There is a slight galvanic reaction between aluminum and stainless but the steel parts will be rusted to destruction long before the alum. will be affected by the stainless. if galvanived steel parts are used in contact with alum. there will be a reaction and the ( Zinc ) galvinizing will be corroded way only to leave the steel to rust. ask anyone that knows boats, the zinc installed on the alum hull is there to corrode away first so the alum hull does not and it is held on with stainless screws. the screws are not even corroded and can be easily remove to replace the old zinc with a new one. sail boat masts are aluminum and the perfered fasteners are stainless and you would never use galvanized fasteners as it will destory the mast in no time. on float planes with aluminum floats the fasteners are all stainless and the FAA and the manufacturer recommend stainless and tell you to never use galvanized fasteners.
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  #7  
Old 01-02-2007, 08:02 PM
Glos Glos is offline
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Good to know Lynn.

I will stay with the SS inserts in the torque tubes.
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  #8  
Old 01-02-2007, 11:07 PM
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crashdog crashdog is offline
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This is all very true, Lynn. The only thing that would be worse than zinc would be bronze. With that kind of battery, you wouldn't have to have the good old gelcel in the fuselage!

Buly, you're a boat builder aren't you?

Of course, there's always plain pure nickel! Or tantalum.

cheers

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  #9  
Old 01-03-2007, 09:25 AM
Buly Buly is offline
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I was not advocating zink plating anything. Just that galvanized steel rod may be corrosion free for much longer time than one already rusted.
I think there is something in the epoxy resins that reacts with aluminum. I have seen aluminum parts that were bonded with epoxy after removal. They had white crust of aluminum oxyde and were pitted. It does not happen every time for some reason?
I used to build small boats as a hobby and worked maintaining and repairing yachts for many years. Including diesel repairs, fiberglass etc. So I have seen first hand that aluminum and stainless do not like each other
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  #10  
Old 01-03-2007, 12:59 PM
SteveWrightNZ SteveWrightNZ is offline
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Quote:
Originally Posted by Lynn Erickson View Post
if galvanived steel parts are used in contact with alum. there will be a reaction and the ( Zinc ) galvinizing will be corroded way only to leave the steel to rust.
this is true, but while this is occurring, this process will protect all the other metals local to the reaction. You can be sure that your aluminum brackets and other metal parts will maintain their integrity. This sacrificial anode action may be a benefit here. It will also take quite some time to eat all the galv off.

disclaimer: not a chemist

S
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  #11  
Old 01-03-2007, 01:59 PM
chasingmars chasingmars is offline
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Quote:
Originally Posted by crashdog View Post
Of course, there's always plain pure nickel! Or tantalum.
heh... if you want the ultimate in counterweights, go Tungsten!

Craig.

Last edited by chasingmars : 01-03-2007 at 06:50 PM.
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  #12  
Old 01-03-2007, 02:42 PM
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Clutch Cargo Clutch Cargo is offline
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Default Rusty...

Here is a few extra facts for those not having a complete understanding of the wonderful world of corrosion. There is also the introduction of other chemicals ending in the letters: INE such as chlorine, bromine, etc which accelerate the corrosive process. ALL metals oxidize and with some, the oxidation forms a protective coating.
Boats and airplanes can share one similarity, exposure to the elements. A lake boat will not be as prone to have corrosion as a salt water boat. Salt water with salt and water (Na sodium + Cl Chlorine + H20, water) exposed to a little electric current, makes hypochlorous acid which besides being a good anti-bacterial, also promotes corrosion.
An airplane or a boat not exposed directly to water or rain will develope some condensation from cool down periods, especially in high humidity areas where temp changes can have the same effect. High mass materials that resist temp changes are prime for condensation, or areas that hold humidity because there is no way for air to dry them out.
Most stainless likes to stick to steel, so putting a stainless bolt in a carbon steel nut and tightening it, may marry them for life.
Metals rubbing against metal will corrode or wear faster without a protective coating, even stainless. Stainless mating parts or aluminum do well with teflon coatings or even spray lube with teflon. Phenolic bearings swell using it though.

That's why I'm using a lot more stainless in exposed parts of good ol' # 618. Interestingly enough, not all stainless is good at resisting corrosion either, it depends on the alloy.

Zinc is just a soft metal that is resistive to corrosion, but it likes to "go with the flow" of electrons, that is. It then exposes the protected metal to the elements. It is very effective in protecting ferrous metal as in "Galvanization". The Brooklyn Bridge cables were coated decades ago when they built it. After an inspection a few years ago, they found the underlying cables quite protected still after all these years. It also inhibits the growth of mold and mildew.

That's all for now....gotta end the holiday break!
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  #13  
Old 01-03-2007, 03:03 PM
Buly Buly is offline
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On my control system, I replaced the steel tube inserts with solid Delrin rod after noticing another FL builder's controls seized even before he flew. And instead of phenolic I used Nylon plate. My controls are smooth and corrosion free (for now).
Did all of the above since I'm stationed in a year around humid and salty environment. My car's window is covered with salty film every morning,
and I have to run my car's AC year around. It is very hard on us here in the Deep South!
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  #14  
Old 01-03-2007, 03:17 PM
Marc Zeitlin Marc Zeitlin is offline
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Quote:
Originally Posted by Buly View Post
On my control system, I replaced the steel tube inserts with solid Delrin rod .....
To which inserts are you referring? Not the tube end inserts into which the rod ends screw, I hope?
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  #15  
Old 01-03-2007, 03:27 PM
Buly Buly is offline
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Quote:
Originally Posted by Marc Zeitlin View Post
To which inserts are you referring? Not the tube end inserts into which the rod ends screw, I hope?
You hope right Marc Just inside the fuselage and NOT the rod end inserts.
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