Date: Tue, 03 Dec 1996 21:53:06 -0500 From: Jim Hocut Subject: Re: COZY: Aluminum/Composite >Had an incident over the weekend that serves as a reminder to all of us who, >while in the process of building composite airplanes, bury aluminum in the >structure for mounting tabs, nutplates, wing mounts, etc. > Which brings up a question. I'm nearing completion of my canard, and have been wondering if steel wouldn't be a better choice for the lift tabs (not being a materials expert I used Al as per plans, but am still curious). Jim Hocut jhocut@mindspring.com Date: Wed, 04 Dec 1996 12:55:17 -0500 From: Mahan Subject: Re: COZY: Aluminum/Composite Just got my Rutan "Canard Pusher" newsletter today. A Long-EZ owner (not the builder) found (I can't figure out how) corrosion on the part of the elevator hinge brackets buried in the canard. He dug them all out and potted in new ones. Newsletter editor Mike Melvill recommended Alodineing the hinge brackets, then dipping in epoxy the part of the bracket that will be buried in the canard, letting it cure, then potting it into the canard. Fred in Florida Date: Wed, 4 Dec 1996 19:42:45 -0500 From: AllegroAvi@aol.com Subject: Re: COZY: Aluminum/Composite In a message dated 12/3/96 8:03:14 PM, you wrote: << Which brings up a question. I'm nearing completion of my canard, and have been wondering if steel wouldn't be a better choice for the lift tabs (not being a materials expert I used Al as per plans, but am still curious). Jim Hocut jhocut@mind>> Jim, I just took the canard off of Sid Stibers long, and that is a very old airplane... the Canard tabs were fine. Now if you want to get fancy, stainless steel! Robin du Bois cozy 22AZ From: "Krasa, Paul" Subject: RE: COZY: Aluminum/Composite Date: Thu, 5 Dec 1996 07:57:43 -0500 > >Jim Hocut writes: > >Which brings up a question. I'm nearing completion of my canard, and have >been wondering if steel wouldn't be a better choice for the lift tabs (not >being >a materials expert I used Al as per plans, but am still curious). I have a GU canard which has flown for 172 hours, and was built in the early eighties. Last year I replaced all the AL elevator hangers due to corrosion. There was very little surface indication on the hangers and except for a little bit of corrosion where one hanger entered the fiberglass, I didn't think I had a problem. When I removed the hanger with corrosion on it what I found was scary. The embedded part of the hanger was severely corroded. More than 50% of the AL had corroded away. I subsequently removed all the other hangers. All the hangers were severely corroded, and the worst one which had 60-70% of the material eaten away showed no sign of corrosion at the surface. I have taken two of the hangers to the Material Science Lab at Kennedy Space Center and shown them to the corrosion experts there. They said the corrosion was caused by micro cracking in the flox which allowed water to wick up into the porous flox material when flying through rain. Thus the corrosion is a design problem, IMHO. To replace the hangers, I heated the hangers with a propane torch being carful not to damage the fiberglass skin. The heat causes the cured epoxy to soften enough that the hanger can be removed easily with a pair of pliers. Any remaining flox and burnt high density foam is removed with a Dremel Tool. I replace the high densiy foam by floxing in a new piece then drilled out a cavity for the new hanger. I only replaced one hager for each elevator at a time so that I could keep the elevator hangers properly aligned. I have contacted Burt Rutan about this problem, and told him about the same thing I have written hear. Burt told me he will be putting something in an upcoming canard pusher. Paul Krasa Long EZ 214LP !---*---! > > > > From: garfield@pilgrimhouse.com (Garfield) Subject: Re: COZY: Aluminum/Composite Date: Thu, 05 Dec 1996 18:34:00 GMT Organization: Pilgrim House On Thu, 5 Dec 1996 07:57:43 -0500, "Krasa, Paul" wrote: >When I removed the hanger >with corrosion on it what I found was scary. The embedded part of the >hanger was severely corroded. More than 50% of the AL had corroded >away. I subsequently removed all the other hangers. All the hangers >were severely corroded, and the worst one which had 60-70% of the >material eaten away showed no sign of corrosion at the surface. > >I have taken two of the hangers to the Material Science Lab at Kennedy >Space Center and shown them to the corrosion experts there. They said >the corrosion was caused by micro cracking in the flox which allowed >water to wick up into the porous flox material when flying through rain. > Thus the corrosion is a design problem, IMHO. =20 Me personal thanks for this vital (and very scary) information. Especially following it up with the Lab at KSC. Knowing the cause is very illuminating, and effects most ANY hardpoint mount, since we almost always use floxed-in Alum in these places. Gives one pause, don't it? A very significant find. I will be nominating you for the Nobel Prize in Composite Design, heh. And we all thought we could get away from most corrosion problems going from spam cans to glass. Guess I'm gonna rethink any mounts that call for alum and see if I can't use G-board pieces or carbon fiber plates instead. Both are readily available, albeit a pain to machine. Also points out the absolute need for inspectability of any Alum pieces, (especially embedded ones? argh... double argh). Garfield From: garfield@pilgrimhouse.com (Garfield) Subject: Re: COZY: Aluminum/Composite Date: Thu, 05 Dec 1996 19:37:44 GMT Organization: Pilgrim House On Thu, 05 Dec 1996 18:34:00 GMT, garfield@pilgrimhouse.com (Garfield) wrote: >Knowing the cause is >very illuminating, and effects most ANY hardpoint mount, since we >almost always use floxed-in Alum in these places. Gives one pause, >don't it? A very significant find. Argh, ya know I forgot to ask one very important question about your elevator hanger pieces, Paul. Did you Alumiprep and Alodine these pieces before you embedded them? Or were they bare aluminum? Just want to make sure. TIA Garfield From: garfield@pilgrimhouse.com (Garfield) Subject: COZY: Aluminum/Composite Date: Thu, 05 Dec 1996 20:09:50 GMT Organization: Pilgrim House On Thu, 5 Dec 1996 07:57:43 -0500, "Krasa, Paul" wrote: >When I removed the hanger >with corrosion on it what I found was scary. The embedded part of the >hanger was severely corroded. More than 50% of the AL had corroded >away. I subsequently removed all the other hangers. All the hangers >were severely corroded, and the worst one which had 60-70% of the >material eaten away showed no sign of corrosion at the surface. > >I have taken two of the hangers to the Material Science Lab at Kennedy >Space Center and shown them to the corrosion experts there. They said >the corrosion was caused by micro cracking in the flox which allowed >water to wick up into the porous flox material when flying through rain. > Thus the corrosion is a design problem, IMHO. Me personal thanks for this vital (and very scary) information. Especially following it up with the Lab at KSC. Knowing the cause is very illuminating, and effects most ANY hardpoint mount, since we almost always use floxed-in Alum in these places. Gives one pause, don't it? A very significant find. I will be nominating you for the Nobel Prize in Composite Design, heh. And we all thought we could get away from most corrosion problems going from spam cans to glass. Guess I'm gonna rethink any mounts that call for alum and see if I can't use G-board pieces or carbon fiber plates instead. Both are readily available, albeit a pain to machine. Also points out the absolute need for inspectability of any Alum pieces, (especially embedded ones? argh... double argh). Garfield =20 From: "Krasa, Paul" Subject: RE: COZY: Aluminum/Composite Date: Fri, 6 Dec 1996 07:31:04 -0500 >Garfield asks: > >Argh, ya know I forgot to ask one very important question about your >elevator hanger pieces, Paul. Did you Alumiprep and Alodine these pieces before you embedded them? Or were they bare aluminum? They are bare metal installed per plans. I'm not real worried about corrosion because the long term plan is to replace the canard with a Ronsz Canard. Paul Krasa Long EZ 214LP !---*---! > From: "Krasa, Paul" Subject: RE: COZY: Aluminum/Composite Date: Fri, 6 Dec 1996 07:43:17 -0500 >Garfield writes: Guess I'm gonna rethink any mounts that call for alum and see if I >can't use G-board pieces or carbon fiber plates instead. Both are readily >available, albeit a pain to machine. The same problem will occur with any composite since micro cracking is present in all composite materials. There is a additional corrosion problem with Graphite. Graphite and AL have a galvanic potential, thus using the two together sets up a corrosive environment. What that means is that Graphite and AL with any type of water will create a battery. I can't comment on G-board since I don't know what it is. Paul Krasa Long EZ 214LP !---*---! > > From: "Krasa, Paul" Subject: RE: COZY: Aluminum/Composite Date: Fri, 6 Dec 1996 08:06:31 -0500 hrogers@SLAC.Stanford.EDU writes: >I am even considering substituting stainless hangars, since I >will probably need a little nose-ballast anyway. At the very least, I will >alodine and dip the hangars into epoxy and let cure, before installing them >into the canard. Come to think of it, I wonder how good this is, also, since water could conceivable wick up between the epoxy and the >aluminum, also, in time. I just talked to anouther builder who powder coated his critical AL pieces prior to installation because he was concerned about the same thing. This could be a possible solution but I don't know how well the epoxy will adhere to the powder coat. Paul Krasa Long EZ 214LP !---*---! Date: Fri, 06 Dec 1996 08:54:36 -0500 From: william l kleb Organization: NASA Langley Research Center Subject: Re: COZY: Aluminum/Composite Curt Smith wrote: > The culprit here was that the aluminum anchor sheet had > corroded and the "bond" between it and the glass was gone. > It looked like a crack in the glass had allowed moisture > to get to the aluminum and... Krasa, Paul wrote: > [ksc corrosion experts] said the corrosion was caused by > micro cracking in the flox which allowed water to wick up > into the porous flox material when flying through rain. > Thus the corrosion is a design problem, IMHO. appendix 4 in marshall's "composite basics" book has a reprint of an article by otis holt which appeared in the jan '84 issue of "homebuilt aircraft" magazine. mr. holt was primarily concerned with Al-to-Al bonds; but upon reviewing it, it is entirely applicable to proper Al preparation... just to wet your appetite, if you haven't purchased the book yet: "Although vibration and other stresses can accelerate deterioration, it is primarily dependent upon the presence of moisture, even in minute amounts, high humidity is the worst culprit." ... "It has been found that, to varying degrees, all epoxy adhesives absorb some moisture and are somewhat vapor-permeable, providing another potential means to deliver moisture to the bond interface. This tendency is most pronounced with epoxies that cure at low temperature, i.e., those most likely to be used in homebuilt applications." ... the conclusion of his article was that a single homebuilder couldn't afford to sufficiently prepare Al; but a group of homebuilders, or, better still, the original parts supplier would have a large enough batch to make it affordable to send the parts to a commercial phosphoric acid anodize installation. however, maybe in the 90's there is now a way (e.g., Alumiprep and Alodine) that a homebuilder can affordably and reliably create a stable oxide layer on aluminum? the underlying problem appears to be that after cleaning, Al begins to oxidize _immediately_; and without special techniques, this oxide layer is of very poor quality. --- bil kleb (w.l.kleb@larc.nasa.gov) 72 bellanca 7gcbc 9? cz4 -> aerocanard From: Marc J. Zeitlin Subject: RE: COZY: Aluminum/Composite (fwd) Date: Fri, 6 Dec 96 13:21:22 EST Paul Krasa writes: >>Garfield writes: > Guess I'm gonna rethink any mounts that call for alum and see if I >>can't use G-board pieces or carbon fiber plates instead. Both are readily >>available, albeit a pain to machine. > >The same problem will occur with any composite since micro cracking is >present in all composite materials. There is a additional corrosion >problem with Graphite. Graphite and AL have a galvanic potential, thus >using the two together sets up a corrosive environment. What that means >is that Graphite and AL with any type of water will create a battery. I think what Garfield meant was to replace the Aluminum with some form of composite that isn't suceptible to moisture/corrosion. Then, you wouldn't have any aluminum to corrode or to have galvanic action with. Since fiberglass layups can have approximately the same mechanical characteristics as Aluminum (stiffness, strength), this is not an unreasonable line of inquiry. G-10 is a readily available glass composite material which comes in varying thicknesses. It's either what PC boards are made of, or something very close to it. For parts that need to have bushings or bearings, the same ones that were used with the Aluminum could be used with the G-10. -- Marc J. Zeitlin Email: marcz@an.hp.com by SERV05.SLAC.STANFORD.EDU (PMDF V5.1-4 #16063) with SMTP id <01ICOVN8GQ540000J3@SERV05.SLAC.STANFORD.EDU> for cozy_builders@hpwarhw.an.hp.com; Fri, 6 Dec 1996 13:05:55 PST Date: Fri, 06 Dec 1996 13:07:41 -0700 From: hrogers@SLAC.Stanford.EDU (Howard Rogers) Subject: RE: COZY: Aluminum/Composite >hrogers@SLAC.Stanford.EDU writes: > > >>I am even considering substituting stainless hangars, since I >>will probably need a little nose-ballast anyway. At the very least, I will >>alodine and dip the hangars into epoxy and let cure, before installing them >>into the canard. Come to think of it, I wonder how good this is, also, >since water could conceivable wick up between the epoxy and the >>aluminum, also, in time. > >I just talked to anouther builder who powder coated his critical AL >pieces prior to installation because he was concerned about the same >thing. This could be a possible solution but I don't know how well the >epoxy will adhere to the powder coat. > >Paul Krasa >Long EZ 214LP !---*---! Paul, On the surface (no pun intended), this sounds like a good idea. I don't believe I would do it with any structural part, however, as powder coating involves a fairly high temperature, and the folks who do it certainly aren't qualified to make aircraft materials decisions. I have heard about a couple of fatalities that have occured, as a result of powder coating aluminum SCUBA tanks. The tanks exploded when they were being filled, after exposure to the heat. New Aluminum tanks (3000 psi) are coated with a clear coat that will discolor brown, if exposed to too high a temperature, and hopefully warn you if the strength has been compromised. I got a bunch of my handles, levers, etc. black anodized, and I believe they all fit in the minimum charge of around 50 bucks or so. I'm sorry I didn't think of doing the hinges at the time. I dealt with a shop that is certified for aircraft plating, and I believe it makes little or no difference on the price. Be sure to ask. As for the epoxy's adhesion characteristics to powder coated parts, I don't believe that is much of an issue with the hinge hangers. They are designed to be mechanically "held" by the flox that surrounds them, including the holes that are in them. I believe that this arrangement would hold them very securely, even if they were coated with mold release. Howard Rogers, A&P 2005148 by InfoAve.Net (PMDF V5.0-6 #4800) id <01ICP44V2NBO8YD1WH@InfoAve.Net> for cozy_builders@hpwarhw.an.hp.com; Fri, 06 Dec 1996 17:08:23 -0500 (EST) Date: Fri, 06 Dec 1996 17:08:23 -0500 (EST) Date-Warning: Date header was inserted by InfoAve.Net From: Nick Ugolini Subject: RE: COZY: Aluminum/Composite Marc wrote: I think what Garfield meant was to replace the Aluminum with some form of composite that isn't suceptible to moisture/corrosion. Then, you wouldn't have any aluminum to corrode or to have galvanic action with. Since fiberglass layups can have approximately the same mechanical characteristics as Aluminum (stiffness, strength), this is not an unreasonable line of inquiry.> After seeing the stength of the landing gear hardpoints (I broke my carbide router bit on them), I wonder if anyone has considered replacing the Al with a builder fabricated sheet (vice a purchased carbon fiber sheet)? The builder could do a wet layup of 15 or so layers of glass, on a flat surface, let it cure, then cut the necessary elevator parts out. You could even place a piece of teflon or stainless steel tubing at the pivot point to reduce wear. Nick Ugolini unick@mail.charleston.net Varieze N89RS Cozy Mark IV #0264 Date: Thu, 12 Dec 1996 23:41:19 +0200 From: edegov@aztec.co.za (ernie de goveia) Subject: COZY: Aluminium/Composite Corrosion Some thoughts on aluminium/composite corrosion problem. Sealing area of the flox on cannard where it is exposed to moisture and oxygen with a sealant such as RTV silicon or a PRC product would prevent much of the corrosion on new unflown canards. It may be possible to expose some 'in use' canards to a gentle heat source to drive any moisture out of the flox, and then seal. I dont think this will work on older cannards as I suspect corrosion on these may be quite advanced. My 0.02cents, may it help Ernie, Cozy 3 in Cape Town Date: Sun, 22 Dec 96 12:23:22 +0000 From: cac%exo.com@exo.com Subject: COZY: Flox wicking water into the structure I was reading about the problems with flox wicking water into aluminum hardpoints and started wondering if there was any concern for it wicking water into other areas. Obviously there could be added weight (enough to worry about?) is there anything else that would break down chemicaly in the presence of moisture? ////////////////////////////////////////////////////////////////////////////// // // // Cliff A. Carpenter // // // //////////////////////////////////////////////////////////////////////////////