View Full Version : Smith Cubs: Why no corrosion protection on wings?
02-04-2005, 06:18 PM
I was looking at several photos of Smith Cub wings and didn't notice any additional corrosion protection on aluminum. Is that correct? I was just curious. I am doing some protection on my aluminum D&E wings, not going crazy like some people do though.
02-04-2005, 06:36 PM
We had all our parts individually primed before assembly ,on two sets Smith's wings. We live next to the ocean and felt it should be done.
02-04-2005, 07:07 PM
I've got a '46 PA-11 that had no protection on any of the wing parts, as far as I can tell. It still has a date wax-penciled on the front spar.
....no worse for wear, corrosion-wise, even though it ag-sprayed for a stint.
It'd be nice, though, if Smith epoxy-primed all their beautiful parts.
02-04-2005, 08:38 PM
Smith will prime your wings if you like, belive they said about $1000.
They do not list it as and option on your order slip,you have to ask.
I primed my wings with a light coat of epoxy, but if I had known,
I would have had Smith do it. They prime all parts before assembly.
Most aluminum used in aircraft is Alclad aluminum. A thin layer of pure aluminum (no alloys) is bonded to the part as the last process. If it is not scrarched through the Alclad to expose the alloy, it will not corrode as readily as the alloy. Thats how it was explained to me.
02-05-2005, 07:09 AM
Many of you all ready know that the Piper comanche line was one of only a few production aircraft that every individual part was zinc chromated before assembley. This single step is why very few if any comanches have ever been retired because of corrosion. Painting your interior parts prior to assembley would be fairly simple and insure that your airplane will fly for many years, especially in a seaplane application.
02-05-2005, 08:16 AM
Seems to me that you hear of very few Cubs being full of corrosion in the wings, fuselage... yes, wings.... no.
Smith will prime em for you, if you want, 1000 bucks, and it is VERY nice.
Just depends on what you want.
02-05-2005, 12:00 PM
Sikkens makes a chromate acid wash primer called CR. With the acid it bites into the aluminum and steel. They also tell me that it will creep under rivets and seams. It goes on VERY thin and will not add much weight. To spray a wing after it was assembed I would try this stuff.
02-05-2005, 12:20 PM
I was talking to a Cessna rebuilder in MN a couple of weeks ago and asked if a 180 they were putting together had been stripped, acid etched and alodined before paint. He said they no longer acid etch their planes because he knew some Northwest Airline mechanics that said NW had stopped acid etching because they found a lot of corrosion between the aluminum sheet overlaps when they took the planes (767's and the like) apart later on. They felt the acid got between the sheets and under rivet heads and was impossible to get entirely washed out. It (acid) then continued to promote corrosion. They now just scuff the metal and use a self etching primer that stays out from between the sheet overlaps. He said that is what they had gone to on their Cessna rebuilds. Crash
02-05-2005, 02:49 PM
... They now just scuff the metal and use a self etching primer that stays out from between the sheet overlaps...
That's what I am using - Sherwin Williams GBP-988 self etching primer. A lot of RV builders are turning to this stuff.
02-06-2005, 12:54 PM
Acid wash primer IS self etching primer. THAT is what SELF ETCHING means!
02-07-2005, 10:28 PM
All the sheet metal rebuilds and repairs and re-skinning that I do get etch, alodine, and epoxy primer on all the surfaces.....that includes under skin laps and under rivet heads. Of course, I'm talking about new parts and parts that are completely unriveted from the airframe.
I can understand the idea that etch not getting rinsed out from under skin laps could be a problem, stripper could also be part of the problem. Good old zinc-chromate in the rattle can has done a fine job for alot of years on many of the aircraft in service, and when appplied to a clean surface (not necessarily an etched surface) will stay on for, what, 40 years?.
I believe that the zinc orthophosphate in the DP series of epoxy primers from PPG provides the "sacrificial' element that makes the DP series the choice of many industry professionals these days, myself included.
Some of the guys around here that once utilized so-called "self-etching" primers have ceased to apply them. I can't give any concrete reasons why.
02-07-2005, 11:26 PM
Smith will prime every piece on both wings for a $1,000 prior to assembly, I think that is a hell of a buy. Cub wings do corrode and I wound not consider going without primer. I have had to repair/replace Cub wings before due to corrosion. If you ever think of going on floats (salt water) priming is not an option in my book. Good thing we are all different and have different requirements.
I have heard people say that Dakota will prime their wings after assembly prior to leading edge skin installation. I don't think this is going to give the effect they are after. The bad stuff usually happens in places you can't see between layers. Pay a little now or a lot later.
02-08-2005, 01:01 PM
My comment about the -11 not having primer was not meant to convey that I wouldn't bother doing it. I do! (bother)
Also, what could be worse than salt water mixed with airplanes? If your steel parts are staying rustfree through salt-water ops....good on 'ya! If your aluminum is corroding...shame on 'ya!
I agree with ksecub that getting every part of a Smith wing-set primed for a thousand bucks is a bargain. I also agree about each and every part being primed BEFORE assembly, when possible.
Any of you potential Husky buyers out there BEWARE. I have several customers flying late model Husky's. These nearly new airplanes (built since Y2K) are exhibiting corrosion coming through the finish on the steel parts. Wing struts, jury struts, hor. stab. struts, etc. etc. These are new airplanes!!!!!
I repainted a jury strut where a previous owner had applied duct tape to "protect" the strut from his rifle boot. The new owner pulled off the duct tape and took the paint with it. THE MILL LETTERING AND BLACK MILL FINISH WERE STILL ON THE JURY STRUT, under the paint. This seems to be a huge problem. I can't imagine Aviat NOT bead blasting the steel pieces before primer and paint, but that's what's happening.
This is one good reason that 130K-Plus Cub or Husky buyers should go for a Cub built by a reputable builder.
'nuff said! Are you listening AVIAT?????
02-08-2005, 01:04 PM
These have been wheelplane Huskys until this past summer. Never any salt, according to the owners!!!!
02-08-2005, 06:06 PM
Our new struts from Univair came with red primer. Are you suggesting to blast these also before painting or are these different?
02-08-2005, 06:55 PM
Ron, It depends on your risk-exposure willingness.
Better yet, call up Univair and find out what they do before they put that red-oxide looking stuff on there. Also, might be nice to know EXACTLY what product the Univair red stuff is.
The Cub I did the winter before last had some new struts with red-oxide on them. I epoxy-primed over the red stuff, then painted them, per the owners request.
The Cub I did last winter got new front struts from Airframes, Inc. ordered specifically without any finish whatsoever. The local powdercoater sandblasted them, then I put epoxy primer and polyurethane on them.
Sorry Ron, it's hard for me to simply say "...I dont' know..".
02-08-2005, 09:05 PM
My experience with the red oxide primer that Univair uses hasn't been good. I epoxy prime over te red oxide. Has worked for me. In fact I epoxied a set yesterday.
My experience. If you paint over the red oxide, they will rust in a couple years. What ever it is, it ain't very good.
02-09-2005, 06:20 PM
I'll have to ask Univair, I've already white epoxy primes mine as yellow is the finish color I've painted them. They are not installed yet and the second set is untouched.
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