[M Wreford]

Hi all, i have just pulled my left wing spar and ribs down off the shed ceiling to start the skinning process only to find little spider webs of corrosion around some of the rivets and even in the areas that aren't in contact with anything else . I bought the wings from another guy and he'd etch primed them before assembly but in spite of this corrosion is forming. Can it be cleaned by some sort of blasting (baking soda ) or would acid etching and alodine work better. I am concerned that acid in between the spar plates with be difficult to nuetralize and may keep eating away at the spar. If it can't be halted then scrapping the wing seems the next ( although expensive option), cheers Mat

 

[HEGASIS]

can you post some pics?

 

[penguin]

The spar strips will corrode in a heartbeat if not properly protected. Can you rub the etch primer off, and then rub the corrosion away with a 1" scotchbrite wheel in a die grinder? Van's will allow you to rub away a few thou - I can't remember how much. You may have to remove a rivet or two if the corrosion goes under the rivet heads, but be careful to drill out straight as its real easy to enlarge the hole and make setting the new rivet difficult.

Pete

 

[apkp777]

Yikes,

I would be EXTREMELY careful with removing corrosion from the spar. What you are seeing is simple surface oxidation. It is not something that I would use ANY power tools to remove. I can tell you that I have removed a truck load of corrosion from commercial aircraft. It's never a fun job and often can lead to serious structural repairs.

Don't use any acid or "baking soda". It's not going to work. The best defense for corrosion is to keep it away from Oxygen and moisture. A corrosion inhibitor works best.

At most, I would use a sheet of green scotchbrite and hand polish the corrosion away. Don't take out any rivets. There is nothing under them.

If it was me, I would just leave it. Maybe treat the spar with LPS 3 or CorrosionX. Both do a great job and I am planning on using LPS 3.

http://www.aircraftspruce.com/catalog/cspages/lps_rust.php

 

[chaskuss]

Hi all, i have just pulled my left wing spar and ribs down off the shed ceiling to start the skinning process only to find little spider webs of corrosion around some of the rivets and even in the areas that aren't in contact with anything else . I bought the wings from another guy and he'd etch primed them before assembly but in spite of this corrosion is forming. Can it be cleaned by some sort of blasting (baking soda ) or would acid etching and alodine work better. I am concerned that acid in between the spar plates with be difficult to neutralize and may keep eating away at the spar. If it can't be halted then scrapping the wing seems the next ( although expensive option), cheers Mat

Matt,
It is still possible to etch and Alodine your spars. It will require a lot of Alodine though. The only way to safely do this would be to fabricate 3 tanks large enough to completely submerge one spar into. The issue is being able to COMPLETELY rinse the etch and Alodine off of the parts. You need to make sure that the rinse water has time to get into all those small spaces between the laminations.
After etching a spar, you would need to submerge that spar into a rinse water tank for at least 30 minutes [longer would be better] to ensure that the phosphoric acid in the etching solution was rinsed off. I would use some sort of method to "stir" the rinse water while the spar is in the rinse tank.
This same extended rinse method would have to be used after the Alodine step, as well. You can NOT let the metal dry between etching, rinsing, Alodining and rinsing again. That is why you need 3 tanks. Each step MUST rapidly follow the prior step.
I would suggest diluting the etch acid 6 to 1, to minimize the amount of etch required and to lengthen the time that the spars may remain in the etch bath. I would also purchase the Alodine [or Iridite 14-2 or DoradoKote] in powder form. Purchasing powder reduces the cost from $26-$32 per gallon to $2 per.
The other solution would be to use a product like Corrosion X on both spar assemblies.
Charlie Kuss