Date: Sat, 11 Jan 1997 19:57:32 -0500 From: Mahan Subject: Re: COZY: Aluminum/Composite Corrosion About a month ago there was a lot of discussion in this forum about aluminum-to-composite corrosion in general, and elevator mounting bracket corrosion in particular. To recap, a builder found corrosion on the bracket where it was buried in the canard, and speculated that moisture had wicked in between flox and the bracket. Surprise, concern, and anxiety were registered, ideas were exchanged on how to detect or prevent this corrosion, and some writers were considering changing bracket material to steel. I'd like to add some additional information to tell, as Paul Harvey says, "the rest of the story." The canard in question is a flown canard. It was removed by A, a resident of Tampa, sold to B, a resident on Florida's east coast, then eventually sold to C. What is not known by most people is that the project sat on B's screened-in back porch for about two years. B lived on waterfront property, on East Florida's Indian River, a long, salt-water lagoon. People who live on saltwater-front property here in Florida fight constant battles with rust and corrosion. For instance, like everyone else, B had problems with aluminum window corrosion on his house. The project fuselage also sat on the porch, and the canopy hinges corroded to the extent that white powder and tiny pieces of aluminum flaked off of them. In view of where the project was stored, it's really not surprising that the brackets were corroded. My source for this information is another canard aircraft builder/flyer who knew B for many years. So, by all means alodine the canard brackets and lift tabs, and any other hard-to-inspect aluminum pieces on your project. However, you may want to consider the history of this canard before you start changing the materials specified in the plans. I hope this helps. Fred in Florida Long-EZ N86LE Date: Thu, 15 May 1997 12:47:42 -0400 From: bil kleb Organization: NASA Langley Research Center Subject: Re: COZY: Chap 4 Alum Inserts Ron Lee wrote: > > Supposedly epoxy sticks well to alodine so sanding after > alodine would not be needed. my logic goes like this: o sand (220 grit) the aluminum to get a rough surface so that the epoxy can make a decent _mechanical_ bond. o alumiprep (or similar) to remove the original, unknown quality, oxide layer and create a `new and improved' oxide layer with alodine so that the surface the epoxy _adhesively_ bonds to (the oxide layer) is reliably bonded to the aluminum. o epoxy part in place. sanding the part after alodining would just remove the stable oxide layer you had just worked so hard to create with the alumiprep/alodine process. note that the oxide layer is very thin, so the sanding beforehand still serves its purpose of giving the epoxy something to `grip' when the interface is loaded in shear. not alondining just means you will be bonding to an unreliable oxide layer---even with sanding, since aluminum starts oxidizing the instant is can find a single molecule of oxygen, i.e., instantaneously. it seems to me that in cases where you don't think moisture will be a problem and you aren't relying on an epoxy-to-aluminum bond, the alodining process is not necessary? -- bil Date: Thu, 15 May 1997 11:35:32 -0600 (MDT) From: Ron Lee Subject: COZY: Alodining Aluminum (was Chapter 4 AL parts) SNIP >it seems to me that in cases where you don't think moisture >will be a problem and you aren't relying on an epoxy-to-aluminum >bond, the alodining process is not necessary? > >-- >bil > I would disagree with the last statement. There have been a few reports (maybe only one) of corrosion in the aluminum parts that hold the elevator into the canard. Seems to me that taking a little extra time to alodine those "exposed" parts would be beneficial. Note that this may not apply to parts that are totally embedded in foam and fiberglass. But even there, a few minutes work may not be wasted. IN this case, all of the CS-3 (long-ez designation) parts would be alodined, even the part embedded in Foam/flox. This is the route I will take even if it is not that critical. Ron Lee Posted-Date: Thu, 15 May 1997 15:34:23 -0500 (CDT) Date: Thu, 15 May 1997 15:34:07 -0500 From: Darren DeLoach Subject: Re: COZY: Chap 4 Alum Inserts >my logic goes like this: > < ... ... ... EXACTLY what I was looking for! Thanks! >it seems to me that in cases where you don't think moisture >will be a problem and you aren't relying on an epoxy-to-aluminum >bond, the alodining process is not necessary? > My inclination was to take a little extra time and prep every embedded aluminum part, particularly ones I won't have visual access to later (like ones covered with glass), since I might have moisture seepage I didn't know about. The chemicals are relatively cheap, the extra time required negligible, and it seems it can can't do any harm but might do considerable good. Weight is not an issue in this case, since the prepping of the few alum components won't add any! -- Darren DeLoach http://www.deloach.com Garage is clean, jigging table finished, epoxy warming box done, ready to start! Date: Fri, 23 May 1997 18:04:45 -0400 (EDT) From: Gunrider@aol.com Subject: COZY: Alodining Someone want to give me a quick lesson on how & when to alodine instead of zinc chromate? Never seen it done. Thanks. Hugh Farrior - finishing ch. 9 Date: Fri, 23 May 1997 20:46:32 -0400 From: Jim Hocut Subject: Re: COZY: Alodining When to alodine - Pretty much anytime an aluminum part has a chance to corrode due to moisture. I haven't been worrying about it with stuff like the firewall inserts, but was careful to do elevator hinges, torque tube inserts, etc. How to alodine - Not very hard if you remember that the secret word is CLEAN. Parts must be scrupulously CLEAN for alodining to be succesful. If there's any oil or greas present remove it first with soap and warm water and rinse thoroughly. Then use a mild etching cleaner like Alumiprep as per package instructions. (Swish the part around and scrub it with a soft brush while in the alumiprep). Rinse thoroughly (any drag-out from the alumiprep will contaminate the alodine). What I like to do is set up 3 one gallon milk jugs cut open and filled with fresh water, rinsing in each one (dunking the part up & down several times). The final rinse before the alodine I'll pour a small amount of the alodine into to neutralize any remaining cleaner. If the part is really really clean the water film will stay on the part, if it's still dirty you'll see right away where the water film breaks away and beads up (like from a fingerprint). Make sure that the part doesn't get a chance to dry between any of the steps. Shake off excess water then put in the alodine with mild agitation for the length of time the instructions call for. Rinse very carefully after the alodine in 3 more separate rinses, then hang to dry. One of the secrets of doing several small parts at once is hanging them on a piece of wire so that they don't touch each other (and only touch the wire in inconspicuous places). Wherever the parts touch will end up with a miscolored blob, not very professional looking. I remember an idea I heard once upon a time (can't remember who to give credit to though), about alodining tubing (i.e. torque tubes etc.). Get several pieces of PVC pipe of a diameter just large enough to hold the tubing, cut it to length, cap one end and put the alumiprep, rinse water, and alodine in separte pieces of pipe. If you wear rubber gloves you can simply cover the open end with your hand while you agitate the pipe, and just move your workpiece from one pipe to the next. Hope this helps. It's really quite easy if you take your time and are careful about cleaning the part. Jim Hocut jhocut@mindspring.com Date: Mon, 10 Nov 1997 21:21:10 +0200 From: Rego and Noleen Burger Organization: R.N.B. Enterprises Subject: COZY: Corrosion! Sorry but I feel I should address this one! Help? A fellow coastal Vari-eze owner has sold his craft after 15 years ownership but with only about 550hrs on it. The new owner has found corrosion on the wing attachment mounting area's. ie. the 2024 has gone white and fluffy. 1.)He feels he must rebuild the wings...does anyone have some advice? 2.)How can we builders prevent this. Mine's in already! Rego Burger CZ4#139 RSA From: "norm & monda" Subject: Re: COZY: Corrosion! Date: Mon, 10 Nov 1997 15:01:15 -0500 the best bet is to alodine or anodize the parts before installing. they should be able to remove the metal and replace it alone instead of building an entire wing norm Date: Mon, 10 Nov 1997 15:43:20 -0500 (EST) via SMTP by admin, id smtpdAAAa001Vm; Mon Nov 10 15:43:06 1997 From: Nigel Field Subject: Re: COZY: Corrosion! At 09:21 PM 11/10/97 +0200, you wrote: >Sorry but I feel I should address this one! >Help? >A fellow coastal Vari-eze owner has sold his craft after 15 years >ownership but with only about 550hrs on it. > >The new owner has found corrosion on the wing attachment mounting >area's. ie. the 2024 has gone white and fluffy. >1.)He feels he must rebuild the wings...does anyone have some advice? >2.)How can we builders prevent this. > >Mine's in already! > >Rego Burger >CZ4#139 >RSA > The Wing attach for the VE consists of double "tonge and slot" type plates with the spar caps sandwiched in between the 2, 1/8 2024 plates on both the wing and carry through spar, spar caps. Corrosion on these plates is a serious issue as they carry the full cantelivered wing loads. My VE has flown since 1985 and has 1150 hours with no corrosion on the wing attach fittings. Being of somewhat modest means (meaning no hangar), it lives at a tie down in the rain with only a canopy cover. I bring it home every winter and in the spring I coat the fittings, taper pins, and bolts with a liberal coat of GE silicon grease, the kind used as a heat sink conductor in electonics. This lasts out the season quite well and has kept it completely corrosion free. The LE, Cozy and similar types, employ the overlapped spar type of attachment, a very different design, so the problem is not as critical. But I would suggest the same treatment be used on the attach fittings and bolts every 1 to 3 years depending on your climate to keep corrosion at bay. A good coat of chromate primer on these parts would not hurt either. Nigel Field