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Guest micgrace

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ahhhh corrosion, my sworn lifelong enemy! even 5 yr old Hawks are


riddled with it! in one place its 10mm deep in a lower wing plank thats


50mm thick! not nice if your looking to get into the high G area!


but all corrosion has a cause! and what would hav caused that? water trapped under the fabric?



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Guest micgrace



The cure for it is simple. 2 pack epoxy primer (careful using, potentially toxic)before


the fabric is attached unfortunately spray pack zinc chromate just


won't cut it. MEK dissolves it. Sadly this is not done regulary even in


production aircraft using fabric. Few fabric production aircraft




Unfortunately even with all the drain holes in the


world, some water is going to be trapped at some time in the structure.


Best to be prepared to block it coming into contact with the metal till


it can evaporate.


Some people seem to think aluminium is


invunerable to corrosion. As for steel parts? Well, only a fool


wouldn't do something about it. There's a whole industry devoted to


ways with overcoming it. Still no universal technique.


Put together moisture, dissimalar metals (not even that, a slight variation in base metal will do) and corrosion is the result.




real way to prevent is isolate metal from air/moistureand/or attach a


sacrificial anode/coating . I wonder if anyone has actually tried that


in an aircraft? Seaplane?


Micgrace :)



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Corrosion is a strange beast, to repair the above, first replace the


damaged part, treat the new part in a alochrome solution, then zinc


chromate primer, and a final epoxy finish coat. should stop it


re-occuring. I dont know much about fabric construction, but can fabric


coverings be bonded over epoxy painted and treated parts??




sever corrosion we are finding on hawks is caused by Rubber! the rubber


seals on the overwing fairings are causing a sever corrosive reaction,


to a point of total destruction of the part within a year! yet the


metal not in contact with the rubber is in new condition! the rubber


strip is solid riveted between a metal skin and metal backing strip,


and the corrosion only occurs where the rivets press the 3 components


together. all know treatemtns have been tried and all have failed to


stop it. (yet the RAAF wont allow us to chage the rubbertype)


3 aircraft in teh fleet were test flown before being painted! and as you would expext, all 3 are showing signs of corrosion (to damaging levels) in just 5 yrs of life, where the other aircraft are relativly corrosion free.


so be sure to have your aircraft primed and finish coated before any test flying!



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Guest micgrace



Unfortunaetly if using the zinc chromate primer, the MEK (methyl Ethyl Ketone) will attack it and dissolve even if under 2 pack expoxy primer topcoat.


Alodine treatment, 2 pack expoxy primer and topcoat of 2 pack paint with flexi agent (or buy the certified product $$$)




paint adhesive to surface, lay fabric, brush with MEK push into fabric,


heat tighten put on strengthening tapes, clips/screws/rivets/tie fabric


to ribs, finishing tapes, drains, inspections holes etc seal fabric,


more dope, silver dope, then epoxy primer (with flex agent) then top coat (flex agent) the last painting steps are NOT certified after the silver, but the standard coloured dopes look crook. (ceconite system, available locally) Other systems e.g. aeroflite exclusively use epoxy and urethane.




like a lot, it is, but the results can be stunning with modern paints.


Especially as you can actually wet sand the fabric coatsto absolute


flatness. And if done correctly, unlimited lifespan.


Micgrace :)



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