+++ #101 Subject: Re: Another hole method for tubes From: Bruce A. Frank BTW, regular zinc chrome primer is not a good corrosion preventive for steel, though it has been the traditional choice. On steel many of the quality automotive self-etching or conversion type primers will hold against rust just about forever. The best of them, will not allow rust to propagate beyond the area of damage, such as a scratch through to the steel. That scratch area will rust but galvanic action is sealed out of the areas still covered by the paint. +++ #107 Subject: Prime? Sure! Topcoat? Sometimes! Chemfilm? I wi From: bearhwk27- Here is some food for thought on the prime issue. My vote is chemfilm, light prime coating system, assemble and rivet. First a little background. I have a degree in engineering and am employed full time in the aerospace industry. Since 1978 I have been involved in the design and development ( thru qualification, environmental, endurance,and flight test ) of various aircraft systems and controls. My handy work can be found on Beech 1900, Starship,Saberliner,F-117,B1B, Airbus A319,A320,A330,Jas29, Darkstar, Apache AH-64, V-22, Boeing 717,HyperX, Bearhawk. No protection for our little aircraft is required, not even on our welded steel tubing! The question is how long do you want to keep your aircraft in airworthy condition? What environment will the aircraft be operating in? I have seen Beechcraft nose landing gear actuators rendered scrap from corrosion in one year of commercial commuter service. These actuators were anodized, primed and painted. The cause of corrosion was a specific brand of soap used by the line personnel to rinse down the aircraft. The soap got trapped in the units and was "reactivated" each flight by thermal condensation. The current industry procedures are in general: Chemfilm * (Conversion Coatings) These coatings cause a change in the chemical composition of the surface aluminum that creates an oxide and seals the surface without affecting the strength of the material. ( Anodize reduces the fatigue endurance properties of aluminum.) Many of the Mil Spec coatings work quite well and will withstand salt spray tests. Primers * Various primers, chromate, epoxy, urethane and Isocyanates are used in conjunction with the chemfilm for enhanced corrosion protection. Enhanced protection is indicated for structural elements exposed to moisture either thru direct contact or condensation. Primers are also used as additional protection when moisture can be trapped between laminations, (ie, Bearhawk wing spars ) or when surfaces in contact are either dissimilar metals or subject to fretting corrosion. Some primers are designed to work only with a topcoat system, if you will be priming only, use a primer that does not require a top coat. Most primers are designed to be applied only a few mills thick. Topcoats can be applied before or after assembly. Some aircraft areas are top coated before assembly for maximum protection. (ie, lavatory and galley, engine nacelles and flaps) ( Have you seen the plans sheet for the Bearhawk Lav?) Properly applied, paint and primer systems will not have any adverse affect on the type of structure we are dealing with on the Bearhawk. (Might even be good) The spar cap laminations on the main spar are sandwiched to the main spar web. Assuming positive g flight, the loading on the top cap strip is compression the bottom cap strip is tension.There is no shear to speak of in the capstrips, the shear is in the web. The web might fail in shear or the web might fail in bearing where the rivets pass thru the stackup, but that remains the same primed or not. The rivets going thru the spar laminations hold the laminations together so that the cap can take the column. (compressive loading) Without those rivets the spar laminations would act like wet spaghetti when pushed on. My guess is that there is more tensile stress in those rivets than shear stress. qThe wing skins attach to the ribs with dimpled flush rivets, the rivets hold the dimples together so they can't move, the dimple is very strong, normal primer in this area will have no effect on the joint, its the dimple not the rivet doing most of the work. Do not get lazy and use universal head rivets because strength will be sacrificed regardless of how much primer was not used. +++ #241 Subject: Blind Rivets and Prime Preparation From: bearhwk27- A while back you acknowledged about 100 hrs of spar detail and prep to prime and paint..... I thought that was a little steep ...... Well I have just about validated and duplicated that little feat. Metalprime seems to work as advertised just avoid spraying in no humidity or temps above high 80 deg f. +++ #288 Subject: Re: new member From: amsp- > I plan on anodizing all the spar parts,then stick them together,then > prime them.I would like some coments on this idea if you would please. i am still looking at the bearhawk to build.i havent bought the plans yet cause im still overseas.i will get them when i get home in a few months.you are talking about that you want to anodize the parts then prime and put togethor. i work on aircraft that are over 25 years old.the internal parts have no corrosion.the way this was stopped is the parts in the aircraft were alodined then zinc cromate primed all internal parts.zinc cromate works great to stop corrosion.there is a few problems with zinc cromate.1) it is can be hazardous to your health if you dont wear your protection.you should wear a tyvex suit and a resperator,and gloves.2) you cant paint over the top of the zinc cromate primer.so it should be used only on the internal parts of the wings.for the outer side of the spar that you want to paint i would use a 2 part epoxy primer.then put a light coat of finish paint. for the parts that get attached togethor. the zinc cromate will protect the parts very well.this is what i will use on mine when i start it.i fig if it is good enough for military aircraft that log on tens of thousands of hours and years, i fig it be good enough for my aircraft.i hope this helped you out some. +++ #289 Subject: Re: new member From: Tim Anderson I'm not a paint expert, but the only disadvantage to assembling first, then priming is that the small joints (spar - ribs) may not get primed. painting then assembling would prevent that. Just a thought. +++ #293 Subject: Metal Prime Primer From: Russ Erb > How much metal prime did you use on all the spars and spar related > kinck knacks? Did you ever measure thickness on a fully cured item to > determine film thickness? Good question. Who knows? I think I went through 4 gallons (lost count) to do everything except skins (spars for wings, flaps, ailerons, ribs for wings, flaps, and ailerons), however it might be significantly less if I was to do it over again (a scary thought). I had a lot of excessive overspray early on that I eventually learned to control. You might just want to start out with 2 gallons and see how it goes. You won't have a problem finding stuff later to use any leftovers on. I never measured the film thickness. It wasn't a problem except in a few holes where I just drilled the back out to the right size. It would depend on if you sanded it down or not. Note: If you plan to sand anything, I'd wait until it was fully cured (like a few weeks). If you try to sand it within a few hours or a day, you're likely to pull the whole film off. After it is fully cured it is not a problem. Won't see you at Copperstate--we have the Edwards Open House to take care of this weekend. +++ #296 Subject: Anodizing From: woodpre- my understanding of this anodizing process,is that you clean the oil and grease off the metal,dawn dish liquid can work.wash with clean water,then brush the anodizing on.let it sit for 2-3 minutes and rinse with clean water and dry.I have a small shop so can only do a limited # of parts at a time.if anyone thinks this is the wrong way to do this,let me know before I mess up a bunch of good parts. Thanks, Sonny +++ #297 Subject: Anodizing From: woodpre- another thought of mine on anodizing the spar parts is that if I do this,then stick all the parts together,prime after with Zinc Cromate,all the bases will be covered.If I were to prime first,then stick the spar together I think there will be around ten coats of paint between the rivets in places.this amount of paint bothers me.time and flexing could take its toll. Sonny +++ #300 Subject: Anodizing From: Russ Erb > my understanding of this anodizing process,is that you clean the oil > and grease off... What you have described is an alodining process, not anodizing. Anodizing involves electricity. Suggest you go to http://www.eaa1000.av.org/technicl/corrosion/corridx.htm for more info. +++ #303 Subject: Re: Anodizing From: Timothy Neil As far as priming goes: You really don't need more than a couple ( 3 at most) light coats.It should not make any difference in fitting.I used epoxy primer but the new primer by Poly fiber is supposed to be great.Russ did an excellent write up on the stuff a while back.I have always thought that priming between parts before assembly is the way to go.Its the corosion you don't see that will kill you! +++ #305 Subject: Re: Anodizing From: Russ Erb > I was under the impression that alodine was the absolute best > treatment before painting. I did not see any discussion of paint over > alodine in the articles. Am I incorrect? There are subtle references to it. Yes, primer sticks to an alodined surface better than to bare metal. +++ #307 Subject: Re: Metal Prime Primer From: bearhwk27- I spoke with Jon and Floyd and they say that 1.5 to 2.5 mils of buildup per surface is correct for metal prime. I found that at this application rate the primer had a slight transparency or mottled look to it. Applied 1 tack coat and 3 wet coats to achieve this film thickness. Ended up using almost one gallon for all wing spars. +++ #457 Subject: Metal Prime and 4130 steel parts From: Russ Erb This weekend I primed the first set of 4130 welded steel parts with Poly Fiber Metal Prime. I started by sandblasting the parts. I used my Sears sandblaster with 90 psi air pressure. For sand I used 60 grit silica sand. I did the blasting outside "open loop" with no attempt to recover the sand. I was impressed by how easily this removed the scale left from the welding. The blasting also removed the black oil surface that normally protects the tubing, leaving everything with a nice, uniform gray surface. I used a respirator and goggles, which were an absolute requirement. A noticeable amount of the sand bounced back in my face regardless of what direction I held the sandblaster. I had no trouble with sand in my eyes or breathing any sand. My hair, socks, and everything else was another story--like a day at the beach. I further cleaned each part with d-limonene cleaner, followed by a water rinse and compressed air drying. The parts were then strung up in the paint booth on the rotisserie. I used the same procedure to spray the parts that I had used on the aluminum parts. Ever mindful of the spirit of Bubba, I was conscious of not spraying it on too thick. However, I was surprised that the spray not only seemed to stick better to the steel parts (perhaps a rougher surface to cling to?), but also seemed to cover it quicker. That is, the same spray that gave aluminum the look of a dusting of white looked almost like a finish coat (completely white) on steel. At first I was worried that I had overdone it and would have runs galore, but these did not happen. I suspect this better adhesion is why the book says only 2 coats are required on steel compared to 3 coats on aluminum. It seems to work very well on steel. As always, one of the best parts was the ease of cleanup (water only, no solvents). +++ #461 Subject: manmade sandstorms From: Float-by Shooter > leaving everything with a nice, uniform gray surface. I used a > respirator and goggles, which were an absolute requirement. These should be regarded as minimum safety equipment for sandblasting. Far better than goggles, is a sandblasting hood which covers the entire head and shoulders (a respirator is still required). The safety instructions that came with my sandblaster says that for more than occasional use (which admittedly rules out most homebuilders) you should use a fresh air supplied hood. They went on to say that the air supplied hood is mandatory when using any abrasive containing silica, due to risk of silicosis (a bad thing). I'm fortunate to have access to one at work and after using it, would have real misgivings about blasting without it. For those of you closer to "civilization" you may be able to find one at a tool rental place or something. I've blasted using just goggles and respirator before with no ill effects, but do not care to repeat the experience. > the sand bounced back in my face regardless of what direction I held > the sandblaster. I had no trouble with sand in my eyes or breathing > any sand. My hair, socks, and everything else was another story--like > a day at the beach. I did some blasting about 3 weeks ago and was pretty successful for once at keeping the sand off. I had coveralls on, high top rubber boots, the hood, and heavy rubber sandblasting gloves. I didn't get any actual sand grains in my hair until I was cleaning up and went to close an overhead door that some had accumulated on (grr). Of course the dust always gets everywhere. I highly recommend making friends with somebody who owns a blast cabinet for doing the smaller parts. A good place to get sandblasting stuff is TIP Tools. They have a website at http://www.tiptools.com/ +++ #465 Subject: Re: Metal Prime From: Rodney Smith Russ do you plan on topcoating your steel parts or going with the Metal Prime alone? I'm still somewhat leary of using a water based primer by itself on steel parts. Many primers dont seal the metal and you eventually will have rust. When I rebuilt the Maule I followed sand blasting with two coats of epoxy chromate primer followed by two coats of polyurethane enamel on the frame. Admittedly probably overkill. I'm still struggling with the route I want to go this time. Thinking of powdercoating but I've heard some negatives about that also. May end up repeating what I did before as I wont ever have to worry about it. +++ #468 Subject: Re: Metal Prime From: T & E Yeomans I am Tom Yeomans building Bearhawk #75. For primer on the metal parts excluding the fabric areas and all the aluminum stuff, I used Dupont variprime self etching primer as a base coat then top coated with Dupont Prime n seal. The fuselage and tail surfaces were primed with the Poly fiber epoxy coating per their covering instructions. I used the Dupont products because they didn't require the acid conversion as did the old zinc chromate. The Dupont product do a great job of biting into the material and sealing. It is important to seal an automotive primer, it doesn't offer a vapor barrier. If the surface is painted for final color it will seal fine, I used the gray prime n seal to have a uniform color on nonfinished parts. +++ #474 Subject: Re: Metal Prime From: Russ Erb > Russ do you plan on topcoating your steel parts or going with the > Metal Prime alone? I was not planning on topcoating the primer. But since I didn't know the answer to all of your questions, I forwarded them to Jon Goldenbaum at Poly Fiber to find out what their research has shown. Here is his response: 1. Primers vary in porosity, some that are made only as a filler primer (like automotive products) . Aircraft products are generally made to protect metal and may or may not be good filler primers. But in all cases, aircraft primers (hopefully including our waterborne products) are made for the sole purpose of corrosion control. Having said that, , putting a coat of paint over a primer gives you the cadillac of corrosion control procedures. But is it necessary? 2. Your fellow builder lives in AK. That tells me something . If it were me, I would probably prime and paint 4130 in those conditions. He leans toward that position with good reason, there is no place tougher on airframes than the frozen North. 3. So other than in extreme conditions would I paint over Metal Prime? Probably not. Metal Prime tests well in moisture, in fact it tests the same as our Epoxy primer. Remember how we used to do it: zinc chromate (a lacquer based primer) with no paint over 4130. Did it work? Most of the time, but still, those planning for the worst probably painted the frame with something. 4. On the other hand, the majority of competent restoration mechanics do not paint over the new tougher two-part primers (in which I include Metal Prime). 5. So like everything else in aviation it is really your choice. Do you want belt and suspenders?, if so paint over primer. But in short, we don't think Metal Prime acts any differently from other polyurethane primers because it is a waterborne. Twenty years may prove us liars, but that is our best lab and field supported guess. +++ #475 Subject: Re: Metal Prime From: Russ Erb I am Tom Yeomans building Bearhawk #75. For primer on the metal parts excluding the fabric areas and all the aluminum stuff, I used Dupont variprime self etching primer as a base coat then top coated with Dupont Prime n seal. The fuselage and tail surfaces were primed with the Poly fiber epoxy coating per their covering instructions. I used the Dupont products because they didn't require the acid conversion as did the old zinc chromate. The Dupont product do a great job of biting into the material and sealing. It is important to seal an automotive primer, it doesn't offer a vapor barrier. If the surface is painted for final color it will seal fine, I used the gray prime n seal to have a uniform color on nonfinished parts. +++ #496 Subject: powder coat alternative From: amsp- i know of a product that works at sealing as good as powercoating.when i restored a spitfire i sandblasted all my steel parts then coated them with the product PUR15. it is a chemical that makes a bonds to metal and makes a rock hard coating on it. i accidently got some on places i didnt want it and it took almost forever to sand blast the stuff off.i know that it uses moisture to harden itself.this is what i am thinking of useing on my steel parts and fuselage.im not sure if it is dope proof so i would prob spray a light coat of primer that is dope proof to be on the safe side. +++ #501 Subject: Re: powder coat alternative From: Float-by Shooter > i know of a product that works at sealing as good as > powercoating. POR-15 is good stuff. It is generally used in automotive restoration applications where the metal is sound, but is impractical to remove all the rust. It stands for "paint over rust" and that is exactly what you do, wirebrush off the loose stuff, and glop it on. A sandblasted surface is acceptable as well. About the only things which will hurt it are UV light and application over an existing finish. If you don't topcoat it, or remove all the existing finish, it is only a matter of time before it starts to come off. Do not ask me how I know this. 8^( I'm not sure if it would be worth using on an airplane since you are going to have the frame very well prepared beforehand no matter what you prime it with, there isn't going to be any rust to seal off which is the main attraction of POR. And since it must be topcoated, you automatically have the extra weight of another coat of paint. +++ #515 Subject: Re: Corrosion Resistance From: Bruce A. Frank > With a plane parked outside, everytime the temperature drops through >the dewpoint, water will collect on the tubing. I know from sad >experience that eventually that will rust zinc chromate primed tubing. Since I am fairly new to this discussion group I do not know if this topic has been discussed to any depth. I am surprised that zinc cromate continues to be used on steel. Zinc chromate works well on aluminum but it will not hold steel against the normal contact with acid rain or costal salt air. There are several dozen primers developed for automotive use that will prevent rust almost as well as hot dipped galvanized. Rust preventative primers range from epoxy type, which seal the steel so well that nothing gets to it, to sacrificial types that contain elemental zinc that works like galvanized, to conversion types that change the surface layer of the steel itself so that it resists rust even if the paint over it is scratched. I was in a hangar when a builder began to shoot his steel fuselage (2+2 Sportsman) with a red engineering-spec structrual steel preservation conversion primer. When his fellow hangar mates saw red paint through the paint booth windows you'd think they'd found a rat in a bucket of chicken. They brow beat him mercilessly because of his disregard of "tradition". A fuselage is supposed to be yellow or green!! To keep the peace he switched to an epoxy primer product that had the "color" of zinc cromate. Everyone was happ(ier). The builder sold his special order red primer to me for what he paid for it, $130 a gallon. (I shot a piece of 4130 with this primer, let it cure, cure is the correct term, then overcoated it with Krylon spray paint from Home Depot. It has been submerged in a bottle of ocean water for 4 years now with no sign of rust). One last thing, real "zinc cromate" is a highly carcinogenic substance leading to lung cancer later in life if the painter is not well protected. Most of the readily available "zinc -----" type paints are a different compound that is safer but still meets the military spec for corrosion prevention on aluminum. THat all being said, when I finish my fuselage it will be powder coated. (yes, I have given away several gallons of primer and some top quality 2 part urethane topcoat paint----because the powder coat is better at the same cost) +++ #520 Subject: Re: Corrosion Resistance From: T & E Yeomans Bruce. I think the powder coat is a great way to avoid the politics of the paint. and makes the prep easier for you. How can they dispute the direction of a lot of kits. I used the stits product epoxy on my air frame and it sticks like crazy (thats a good thing). I used automotive primer on the aluminum parts i.e. flaps and ailerons. even being an epoxy the fabric glues softened it some, the stits stuff didn't move. Again once you start with a process stay with it for the fabric all the way to the final finish. Happy coating. +++ #522 Subject: Re: Corrosion Resistance From: Bruce A. Frank >I think the powder coat is a great way to avoid the politics of the >paint. and makes the prep easier for you. How can they dispute the >direction of a lot of kits. > > I used the stits product epoxy on my air frame and it sticks like >crazy (thats a good thing). I used automotive primer on the aluminum >parts i.e. flaps and ailerons. even being an epoxy the fabric glues >softened it some, the stits stuff didn't move. Again once you start >with a process stay with it for the fabric all the way to the final >finish. Happy coating. Yes, epoxy is not fully resistant to the solvents in dopes. Usually the exposure is short so it survives. Two part urethane is impervious to the solvents in both Randolph dope or Stits coatings. That is also a consideration in powder coating. The urethane powder coating is the most resistant to solvents. THere are some polyethylene powder coatings available. These are very durable but glues don't stick very well. +++ #524 Subject: Re: Corrosion Resistance From: Russ Erb Bruce--I agree that powder coating is a good way to go. Where will you get it done that has an oven big enough to do a Bearhawk fuselage? +++ #525 Subject: Re: Corrosion Resistance From: T & E Yeomans If you don't have a powder coating sorce. You may check with dune buggy builders in the area. some of them are powder coated... +++ #526 Subject: Re: Corrosion Resistance From: Bruce A. Frank What is the full length, firewall to tail post, of the Bearhawk fuselage? The two powder coaters I have discussed this with here in the San Jose area can handle 18 ft. Another I have talked to has a shorter oven but says he can swap ends of the fuselage to produce a perfect finished job. If you want the phone numbers I'll get them tomorrow. +++ #527 Subject: Length of Bearhawk Fuselage From: Rodney Smith The Bearhawk fuselage is 1" short of 17' from firewall to tailpost. +++ #539 Subject: Powder Coating From: Rodney Smith With all the talk this past week about powder coating, I decided to visit the local powder coat shop. They had a couple super cub fuselages they were working on. A local outfit gas welds new replacement cub fuselages. They do two coats here, the first is a grey primer coat. I couldn't get any details about it other than it is a hybrid powder. The finish coat is polyurethane and you can get it in any color you want. Each coat is baked for 40 minutes at 425 deg F in their 20' oven. They prep the fuselages by sand blasting with #60 garnet sand. Makes a smooth finish. The two coats are approximately 8 mil thick together and on a cub fuselage weight 4 1/2 pounds. This was determined by a before and after weighing. They said they commonly sprayed two coats anyways to get good edge coverage. They decided to make the first coat a primer for additional corrosion protection. They said contrary to popular belief the finish is not as thick as it looks and cracks in the tubing will crack through to the surface. I asked about pricing and they quoted $675 for the two coats. Sandblasting is charged by the hour, they just did a Maule for $360. That is a great price as I must have spent close to that in sand and sandblaster rental when I did mine several years ago. Now that I know about the primer coat, I feel better about going this route. The fuselages look absolutely beautiful. Of course a really great welding job helps. +++ #540 Subject: Powder Coating From: Tim I agree with Rod, Powdercoat is the way to go...I paid the extra $$$ To have my Kitfox Model 4 done....that Red Airframe made me Hard... For the price I was amazed at what was done and the absolute fine finish/detail....Can't beat this method, time or money wise....If you've been down this road, you quickly realize there is those who have Powdercoat and those who wish they did.....If you have already passed this stage....do yourself a favor... Don't check it out...... +++ #542 Subject: Powder Coating the other opinion From: gdanfor- I agree with everyone that thinks power coating is beautiful and durable etc, however, if you ever need to add a tab, repair a weld, modify a bracket etc you have to GRIND the stuff off. Grinding on a longeron or any part of the airframe structure isn't a good idea. The purests worrry about pencil marks on longerons think about what a grinder marks could do???? Primer and paint that can be taken off with solvent or paint remover is the way I would suggest. Powder Coating Certified Aircraft is a little different, you can't modify them without a 337 etc therefore you seldom modify, add, or change anything on them homebuilders are by nature tinkers and are constantly changing everything. +++ #544 Subject: Re: Powder Coating the other opinion From: Bruce A. Frank The easiest way to remove powder coat "paint" is with the torch with which you are going to weld it. Some tape off the section and use a small sand blast gun. +++ #546 Subject: Re: Powder Coating From: Tim Anderson The only disadvantage I found on my Powder coated Kitfox was removing the coating in places that It shouldn't have been. Fitting and bolt holes, ect. Some were in very tight places and getting a reamer in was tough. But other than that, it really saved effort from priming and painting. +++ #1785 From: Tony Dean Subject: [Bearhawk] Re: Tack welding The snippet below raised a question about preparation and setup. I plan to seal my tubes with line oil and that means that I have to drill holes for the oil to enter the uprights and diagonals. If you tack weld, do you drill all the holes for uprights and diagonal tubes before tacking (I presume you do)? Or, would you simply not oil treat the uprights and diagonals? The examples I have seen are ones where the oil holes are drilled and after the fuselage is completed you turn it up on end and pour hot oil in one end and let it flow throughout the tubes. Any ideas? +++ #1786 From: Russ Erb Subject: [Bearhawk] Re: Tack welding > If you tack weld, do you drill all the holes for uprights and diagonal > tubes before tacking (I presume you do)? Or, would you simply not oil > treat the uprights and diagonals? I plan to oil the tubes (another controversial topic if you talk to Richard Finch). The trick is remembering to drill the little hole before tacking the tubes in place. Poly-Fiber sells a good line oil for anyone looking for a source. +++ #1788 From: Bruce A. Frank Subject: [Bearhawk] Re: Tack welding I would drill holes allowing communication between all the tubes. I started with a salvaged fuselage which did not have holes between any of the existing tubes. For all of the new structure I added I first drilled an eighth inch hole to allow this free communication between longerons, diagonals and vertical tubes. For the tubes already in place I drilled through from the outside of the longerons, up through the clusters, into each of the tubes. I then welded up the remaining hole in the outside of the longeron. +++ #1797 From: Zippydogg Subject: [Bearhawk] Re: Tack welding I was thinking of interconnecting all the major tubes in the fuselage, and plug the ends. I would then install a shrader valve (tire stem) and pressure gage. After welding is complete, but before the first flight, the time required to "leak down" from some particular pressure would be measured. Then periodically, I could accomplish the same test. A shorter time to "lead down" may indicate a crack. This would also be a good way to get the tubes completely sealed. IMHO this would be the best rust prevention measure. This method was used on the Porsche race car frames in the distance past. +++ #1798 From: Russ Erb Subject: [Bearhawk] Re: Tack welding > I was thinking of interconnecting all the major tubes in the fuselage, > and plug the ends. I would then install a shrader valve (tire stem) > and pressure gage. After welding is complete, but before the first > flight, the time required to "leak down" from some particular pressure > would be measured. Then periodically, I could accomplish the same > test. A shorter time to "lead down" may indicate a crack. This would > also be a good way to get the tubes completely sealed. IMHO this would > be the best rust prevention measure. This method was used on the > Porsche race car frames in the distance past. I've heard of this method. In fact, it is mentioned on page 112 of the EAA "Aircraft Welding" book. What you didn't mention is that it involves filling the tubes with nitrogen--you have to get the oxygen out for it to work. Have fun finding those pin-hole leaks that always seem to exist. If you use line oil, the stuff has such incredible capillary action that it will work it's way out of pinhole leaks. Leaving the pin hole leaks in probably wouldn't be a problem from a corrosion standpoint, but it would be so ugly to have it come out on your fabric. Either way, you still have to remember to drill those holes! +++ #1800 From: Bruce A. Frank Subject: [Bearhawk] Re: Tack welding After the fabric is on what do you plan to do if the pressure gauge shows you have a leak? Cut off the fabric? How are you going to find that leak? Just put connecting holes in all the tubes and install line or linseed oil. The oil will clot and seal any pin holes. You may be loosing sight of what you're trying to accomplish. Oxygen inside the tube in a fully sealed system presents no rust problem. A little light haze rust forms on the inner surface of the tube and that is it. Once the small amount of oxygen has reacted with the surface of the steel no further rusting can take place. The object is to prevent "breathing" of the tube during barometric pressure and temperature changes. Such breathing carries in fresh oxygen (necessary for rusting) and moisture. With the system oiled, besides sealing any pin holes, the oil eats up any free oxygen. With no free oxygen, even with water present, no rusting takes place. If a small crack eventually forms (no single crack is going to cause catastrophic failure in these truss style tube frames) it is likely the internal coating of oil will continue to protect the tube. It is also likely that remaining liquid will seal that new crack to continue to protect the tubes. I have welded tube frames that showed absolutely no leak down over 4 weeks. But once the frame was put in service the pressure leaked out. No crack, just a pinhole unclogging from the bumps and flexing. Linseed oil prevents such a problem. I once cut apart a gear leg from a TriPacer that had been rebuilt 30 years in the past. It had been oiled when rebuild (though the original Piper leg was not). When I opened up the rear tube of the leg it contained about 8 oz of water and 4 to 5 oz of still liquid linseed oil. There was not one speck of rust in that tube(the plane had been in dry storage for 15 years). I actually sawed it full length to be sure that there was no rust present. Don't know how the water got there, but the oil still did its job. Use the oil and don't worry about all those "what ifs". +++ #1802 From: Tim Anderson Subject: [Bearhawk] Re: Tack welding General questions on the oiling process. Correct me if I'm wrong. 1. Drill all interconnecting holes at tube joint locations (prior to welding) Bruce your drawing is great. 2. weld the frame completely 3. poor in hot linseed oil to several locations? How much? 4. seal up the tubes 5. rotate the frame to prevent pooling? But how does one prevent oil pooling at the low spot in the frame when all the tubes have interconnected drain holes. On the taildrager, all the oil will end up in the lower tail (which is probably where any water or condensation will also pool). The top of the fuselage will never see oil after the initial application. +++ #1804 From: Russ Erb Subject: [Bearhawk] Re: Tack welding > But how does one prevent oil pooling at the low spot in the frame when > all the tubes have interconnected drain holes. On the taildrager, all > the oil will end up in the lower tail (which is probably where any > water or condensation will also pool). The top of the fuselage will > never see oil after the initial application. Line oil (Poly Fiber Tube Seal) has incredible capillary action such that it will climb up the inside of the tubes against gravity. I can't tell you why it does that but I've seen it happen. Thus the oil will stay in the top tubes. Oil pooling at the tail is not a problem (only a few ounces of weight), and a good place to have it if that's where the water collects. +++ #1806 From: budd davisson Subject: [Bearhawk] tube oiling Bruce brought up an important point about internal corrosion: it needs oxygen to happen. I don't know the percentage, but a major percentage of the old fuselages weren't oiled on the inside and many just oiled the longerons. Drilling and oiling all the diagonals is a great preventative measure but in cutting up and repairing dozens and dozens of old fuselages, I don't think I've run into internal corosion more than a couple of times and then it was the result of exterior rust pinholing the tube and letting air/moisture in. Sloshing line oil in there and making sure every tube is sealed will make it last into the next century. Sloshing the oil in and not welding everything as tightly closed as possible, may let oxygen do it's thing, dispite the oil. Another thing, is making certain the exterior of every cluster joint is completely clean before painting it. If a piece of scale flakes off after painting it, all the line oil in the world won't help, as it'll start rusting from the outside. We have a local powder coating outfit that does a terrific job of gently (repeat, gently) blasting a fuselage and then powder coats it any color you want for $300. I think it's worth the investment. Incidentally, safely sand blasting fuselages is an art: don't turn it loose with your local pool contractor. +++ #1808 From: Tim Anderson Subject: [Bearhawk] Re: tube oiling Do you powder coat just the fuselage, or do you coat other steel pieces also, such an landing gear, rudder, stabilizer, engine mount, control yoke, etc? My Kitfox came powercoated, any steel part was coated. When I assembled it, I has unclear as to whether to remove to coating for surfaces that where bonded (epoxy and rivets) to another. Removing the coating is a pain. Also, reaming out coating from bolt holes in tight places was challenge. But it sure beats blasting, priming, and painting by yours truly! +++ #1809 From: budd davisson Subject: [Bearhawk] Re: tube oiling On a Bearhawk, everything that's welded could be powdercoated, but the comment about the bolt holes, etc, is a good one. I've never tried it, but I'm certain the powder coaters have some sort of masking procedure to protect holes and certain areas. You could pound wooden dowls in holes you want kept clean and mask areas where tubes slide inside one another and just chromate those afterwards, as powder coating can be thicker than paint. Has anyone out there had this experience? +++ #1813 From: Lee H. Erb Subject: [Bearhawk] Oiling Tubes I am not yet familiar with "line oil" but I specify "raw linseed oil" inside the tube. "Raw" will stay gummy and gooey while it absorbs the oxygen (corroding element). "Boiled" linseed oil develops a hard surface that will crack and flake. "Bioled" is good for the outside of tubing while you are storing 4130 ( or any steel) and don't want it to rust. +++ #1814 From: Float-By Shooter Subject: [Bearhawk] powdercoating/control bearings > On a Bearhawk, everything that's welded could be powdercoated, but the > comment about the bolt holes, etc, is a good one. I've never tried it, > but I'm certain the powder coaters have some sort of masking procedure > to protect holes and certain areas. You could pound wooden dowls in > holes you want kept clean and mask areas where tubes slide inside one > another and just chromate those afterwards, as powder coating can be > thicker than paint. Has anyone out there had this experience? I use the Eastwood powder coating system made for home/small shop use ($150) and they sell heat resistant plugs for holes that you don't want coated. They also have a heat resistant masking tape which works very well. I really like the system and the finish it leaves, but I am not sure if it will be useful for a lot of the Bearhawk parts, especially those that have one tube moving inside another, as in the control system. On many of these parts they have to be welded together before any finish is applied, and I'd be afraid of the powdercoating immobilizing the moving parts. It's probably something that can be worked around, but I haven't experimented with it yet. +++ #1819 From: Bruce A. Frank Subject: [Bearhawk] Re: tube oiling >On a Bearhawk, everything that's welded could be powdercoated, but the >comment about the bolt holes, etc, is a good one. I've never tried it, >but I'm certain the powder coaters have some sort of masking procedure >to protect holes and certain areas. You could pound wooden dowls in >holes you want kept clean and mask areas where tubes slide inside one >another and just chromate those afterwards, as powder coating can be >thicker than paint. Has anyone out there had this experience? My powder coater plugs all holes as normal proceedure. +++ #1823 From: Russ Erb Subject: [Bearhawk] Oiling Tubes For those still wondering what line oil is, go to page 297 of your 1999-2000 Aircraft Spruce Catalog. You'll see it there. +++ #1825 From: Donald Schindler Subject: [Bearhawk] Re: tube oiling I agree with Budd on this issue, that internal corrosion, should'nt be a problem if it's properly welded then protected. If you go with sandblasting they need to use the finest grit and the lowest pressure needed to do the job. I went that way with my Kitfox and it really turned out nice. Then I gave them an engine mount from another airplane. I didnt realize it had been oiled, then the heat from powder coating boiled the oil out and what a mess. +++ #1826 From: Donald Schindler Subject: [Bearhawk] Re: tube oiling The one time I did it I had to go back and ream all the holes again, but it wasnt to bad, not as hard as reaming metal. Budd's idea about putting dowels in the holes might work if they would stand up to the heat, as the process cures in a giant hot oven. The biggest bonus to podercoating is not only rust prevention but it doesnt scratch off during the building process like Chromate and regular paint. Don 068 +++ #1827 From: Tim Anderson Subject: [Bearhawk] Re: tube oiling The only time I had problems removing the coating was in tight places like on stabilzer/elevator hinge fittings. They only had about 1/4 inch clearance with the frame. That made reaming very tough. I had my Kitfox power coated at the factory. Great stuff. +++ #1852 From: Rod Smith Subject: [Bearhawk] Powdercoating Ribs etc. I am wondering if 2024T3 components such as ribs and spars can safely be powdercoated. The local powdercoater takes the oven to 400F for nearly an hour. Does this get into a temp range that will change the properties of 2024? They powdercoat steel here with a primer, then a finish coat. I would just have the primer coat done. Would experiment with some test pieces first. Sure would save a bunch of time. +++ #1853 From: budd davisson Subject: [Bearhawk] Re: Powdercoating Ribs etc. I wouldn't take a chance running your aluminum parts up to 400 degrees, although someone out there may have more experience with powdercoating aluminum than I do. It'd be a real bummer to have your stuff come back completely annealed and shaped like pretzels. +++ #1860 From: Shelly Subject: [Bearhawk] Re: Powdercoating Ribs etc. Not only that, Rod, but parts won't fit, you'll need to clean out holes so the hardware will fit, skins wont fit, and most importantly, you will add a lot of weight to your airplane needlessly. Powdercoating is wonderful, but it is heavy and thick -- fine for steel fuselage. Just a light coat of primer is all that is necessary for aluminum wing structures - and I mean really light. +++ #1864 From: Lee H. Erb Subject: [Bearhawk] Re: Powdercoating Ribs etc. > aluminum parts up to 400 degrees, Using or designing with aluminum in temperature conditons is risky because it loses strength (and temper). 2024-T3 will lose the following yield strength in 1/2 hour: 200 deg F 3 percent 300 deg F 6 percent 400 deg F 13 percent 500 deg F 28 percent And time is accumulative ! (Hence the reason for steel firewalls) +++ #2361 Bruce A. Frank Subject: [Bearhawk] Rust Prevention > I was wondering the exact same thing! I always thought it made > more sense to leave the oil on the tubes (except for the weld > area, of course!). The humidity around here dictates the practice. > > You can clean it off if you want to, and polish everthing nice and > pretty, then sit back and watch it rust before your eyes. Not > fun. My guess is Bill's steel came that way (or close to it) and > he has a thin film of preservative on there you're not seeing in > the image. Discard all of this if you're in Arizona in August. Even here in CA after the tube is welded, if left as is, it will rust. It takes longer than it did in PA, but it still rusts. As soon as the weld cools I hit everything with WD-40. It prevents rust. Stops rust. And it is easily cleaned off to do additional welding if necessary. +++ #2587 William & Delinda Johnson Subject: 023 Update 2. Painting - All parts are cleaned with PPG DX330 wax and grease remover, etched with PPG DX 533 aluminum cleaner (I use aluminum cleaner even on the 4130), and cleaned again with PPGDX330. Aluminum parts are conditioned with DX503 and zinc cromated. 4130 parts are sprayed with PPG epoxy primer (see picture above). +++ RAH From: jjmaj@dow.com Subject: Re: tube fuse cleanup > What's the preferred way to clean up a steel tube fuse that's been > exposed for a little while? A few weeks in a chicken coop has left it > rusty and gummy, is sandblasting ok? And after it's clean is it best > to prime immediately or is there another way to keep it clean as I > still have some tabs and fittings to weld on. Go to www.tinmantech.com and check out a product called MP-7. Applying this liquid to steel (just wipe on with a rag) removes rust and puts down a very thin conversion coating of zinc phosphate that is a very effective rust inhibitor. You can weld through it or prime over it. I use it on all steel parts. +++ #2762 From: Bob Romanko Subject: Who's Using Poly-Fiber Metal Prime? On Erbman's recommendation I called Poly-Fiber and ordered the Flight Gloss book. I'm strongly considering going the Metal Prime route and bagging zinc chromate. Although I can get it no problem as "commercial" (as an A&P), zinc chromate is still not something I'm looking forward to swimming in for the next three to four years. I sent off for the Flight Gloss book today, and was wondering if anyone else has gone this route. If so, what are your thoughts on the system? Pro's/Con's? +++ #2763 From: Rod Smith Subject: Re: Who's Using Poly-Fiber Metal Prime? > On Erbman's recommendation I called Poly-Fiber and ordered the Flight > Gloss book. I'm strongly considering going the Metal Prime route and > bagging zinc chromate. Although I can get it no problem as > "commercial" (as an A&P), zinc chromate is still not something I'm > looking forward to swimming in for the next three to four years. I cant personally comment on metal prime because I haven't used it yet. I would strongly recommend not using zinc chromate, at least on steel. It is a porous finish, steel rusts real well under it if exposed to moisture. I plan on using metal prime on all my aluminum. The polyfiber epoxy chromate primer is great stuff but is highly toxic and I will be painting in my garage. I recovered and painted a plane using Polyfiber(Stits) products exclusively and was very happy with the results. I plan on powdercoating all my steel parts, otherwise I would top coat the primer with a good epoxy finish coat. I just had the c-frame tool I made powdercoated last month and it really came out nice. +++ #2765 From: Robert Hughes Subject: Re: [Bearhawk] Who's Using Poly-Fiber Metal Prime? At the risk of shamelessly promoting Montana industries, I would suggest you also check http://www.aircraftfinishing.com for a description of their AFS Two-Part Waterborne Epoxy Primer system. I have only used it on aluminum (over etch/ alodyne) so far, but I think I will try it over a prep/conversion coat on steel as well. I don't know how it compares to similar products from PolyFiber, but I have been very pleased with the AFS 2-Part (Although my experience is limited to applying it with a small airbrush). Local lore has it that one of the residents of Ennis MT has been drinking one pint a day as part of the EPA certification process. The web site has some interesting stuff on tubing prep and fabric covering that you might enjoy reading over. +++ #2770 From: Russ Erb Subject: Re: [Bearhawk] Who's Using Poly-Fiber Metal Prime? > Erb's got a giant size brain! Oh, great! If that's true, I'll have to stop building the Bearhawk and start a Private Explorer just to have room for my head... Semi-seriously, I've been shooting Metal Prime again this week on the wing skins. Hopefully will get the Tech Counselor inspection soon and then rivet the top skins on. I have reverified something I ran across a long time ago. When using Metal Prime, you must remember that the waterbased stuff is a totally different animal than solvent based primers. PATIENCE is the watch word. 1. It MUST be shot in very thin coats. Otherwise it will run just like rain down your parts. Alodined aluminum takes 3 thin coats for coverage, sandblasted 4130 steel takes two (this stuff LOVES sandblasted 4130). However, 30 minutes between coats is plenty. 2. This stuff is dry to the touch in 30 minutes, but it is far from done. The crosslinker continues to work for a long time (days, weeks, I'm not sure how long it takes). The result: It is very easy to scratch the finish off, even with a fingernail, shortly after shooting the primer. However, after a reasonably long time, the stuff is rock hard. I scratched as hard as I could with my fingernail on a rib that was primed a year or two ago with no visible change. Time to go shoot some more... +++ #2773 From: mailstuff Subject: Re: [Bearhawk] Who's Using Poly-Fiber Metal Prime? We tried that water-based s**t on the big airplanes and it doesn't hold up over time. After it has fully cured, put a piece of duct tape on it real good and rip it off. If your primer wont hold to the aluminum, throw it out. There are many epoxy based primers that are green. No, it is not zinc chromate in them. We haven't been able to use Zinc primers on airliners for about 5 years, and all of the replacement primers are epoxy based and dark green in color. You prep with etch and alodine as usual and they hold up great. If you could imagine the urine build up under lavatory floors and the spills under galley floors, you will respect these primers as pretty damn good. Dynol works good too, but avoid it like the plague. We have recently been forced to use water based primers and we can't get them to hold up. After 18 months in the aircraft, they have completely broken down. Maybe poly fiber has perfected something that the commercial paint business hasn't, but I will stick with what I know works. Even the tech reps couldn't get a good bond with the stuff. Epoxy based primers work on steel and aluminum equally well. Epoxy primers are easy to distinguish from poly primers by the mix ratio. Epoxy 1:1 and poly 2 or 3:1. That is my 2 cents worth. +++ #2775 From: Subject: Re: [Bearhawk] Thumbs up on Metal Prime? I have been using metal prime. It works just like Russ says. Keep the primer thin. Keep the applied coats thin. Allow to dry 30 min between coats. Etch and chemfilm is required for good bonding. After a few weeks cure it is tough. After a few months I can't remove it from my test coupons. (I will try my best to keep food and urine off my aircraft!) +++ #2777 From: budd davisson Subject: Re: [Bearhawk] Who's Using Poly-Fiber Metal Prime? Re: metal prime, etc. Why not just powder coat everything? Eastwood Automotive makes an at-home-kit that works really well. Otherwise, I'd stick with epoxy. just a thought. +++ #2778 From: Bob Romanko Subject: RE: [Bearhawk] Who's Using Poly-Fiber Metal Prime? Budd, are you talking about HotCoat? If so, that needs a dedicated oven. I think I'd have a rough time getting the spars in there! +++ #2992 Subject: Re: [Bearhawk] dwell time From: Ron Morrison > I'm alum-a-prepping and alodyning -- > > For the Ribs, I found a large under-the-bed sized cloths container > to let the ribs soak for a few minutes in inch-deep solution. The > spar's and cap strips are a bit large. I could simply sponge it on > but to get a good coating, one really needs to submerge for a few > minutes, (at least per the instruction). I thought of building a > narrow wooden box lined with plastic, but I hate to use that much > solution for only a few peices. One option is the cream-type > (wipe-on/wipe off). > > Any suggestions? Use a PVC pipe capped on one end and with a threaded cleanout plug on the other. Pour in solution, insert work, install plug and roll around on the ground for a few minutes. The work piece doesn't have to be submerged, just repeatedly wet. I've seen this technique recommended by several builders. Some builders just use a spray bottle and let the excess run down the piece into a container. Be careful to not breathe any of the spray. An appropriate respirator is recommended. Alodyne and other such products are carcinogenic. Use gloves as well. +++ #2993 Subject: Re: [Bearhawk] Prep Tank From: I made my "tray" from a framework of 3/4" dia PVC pipe in a rectangle covered with plastic. Framework was just a bit bigger than the rib.Filled it with about 1/2 " of solution. For the spars just add a few more linear feet. +++ #2994 Subject: Re: [Bearhawk] Prep Tank From: Bruce A. Frank > I made my "tray" from a framework of 3/4" dia PVC pipe in a > rectangle covered with plastic. Framework was just a bit bigger > than the rib. Filled it with about 1/2 " of solution. For the > spars just add a few more linear feet. I am setting up to start my wings assembly for my V-6 STOL. For the uninitiated these are aluminum spar with aluminum ribs that are fabric covered. When I salvaged parts from both a Colt and TriPacer neither had any obvious preservation application to the aluminum parts in the wings. The youngest parts were from the 1963 vintage Colt. None of these parts, spars, ribs, or leading edges, showed any evidence of corrosion. As I understand the built-up nature of the Bearhawk spar I see there is opportunity for trapped moisture that might lead to corrosion. I have used the alodyne process many times before painting. Is it an effective corrosion preventer if not painted? I am certainly a neophyte in this area (aluminum preservation), but I thought the primary use of alodyne was to create a bit of tooth on the aluminum's surface allowing the paint to get a good "bite." I do know that it is an etching process that creates a thin oxide layer on the surface. It also seems very fragile and easily wiped off in the normal handling process during assembly. That all said, is there value in alodyning the extruded spar(new A&E parts) and Piper OEM ribs for my type of wing construction? +++ #2995 Subject: Re: [Bearhawk] Prep Tank From: Float-By Shooter > covered. When I salvaged parts from both a Colt and TriPacer > neither had any obvious preservation application to the aluminum > parts in the wings. The youngest parts were from the 1963 vintage > Colt. None of these parts, spars, ribs, or leading edges, showed > any evidence of corrosion. Do you by any chance know what alloy the Piper parts are? The 2024t3 used in the Bearhawk wings is fairly susceptible to corrosion if unprotected, but other alloys (like 6061) don't corrode as easily. +++ #3006 Subject: Re: [Bearhawk] dwell time From: Ron Morrison Whether or not an a/c develops corrosion or not is largely dependent upon how it is stored and what part of the country it is located in. Even the FAA points out that a/c located in coastal areas are much more likely to develop a problem. Lucky guys live in AZ or NM. Alodine (yellow chem film) and other brand names form a coating that improves paint adhesion yet weigh almost nothing. In areas not subject to wear the alodine coating by itself is far superior to no protection at all. I remember reading that Cessna omitted the alodine on certain model years of the Cardinal and that those models are more likely to have corrosion problems. Good enough for me, especially since I live in Houston. I bought the concentrated powder form (10# for $200), but I think that I could alodine a 747 and have some left over. Buying the premixed (diluted) liquid form is very expensive on a per gallon basis. It is extremely important for the aluminum to be squeeky clean. For a uniform color it is best to do a final rinse in pure water prior to alodining and to keep the surfaces uniformly wet when spraying. Test the adhesion of samples after sufficient drying by scratching through the coating with a sharp point to form small squares and then trying to lift the coating off with tape. I spent a lot of time researching this subject. Anyone wanting to know more or where to find the Mil Spec just let me know. +++ #3015 Subject: Re: [Bearhawk] dwell time From: mailstuff Aircraft Spruce sells a marking pen with a big tip. The alodine in it is a one-step (etch and alodine) that you use like a marker and don't wipe off. We use them regularly on commercial aircraft and they do a good job. They aren't cheap, but one of them would do most of the wing parts. The skydraul resistant primer placed over it sticks really well - even in the wheel wells of skydraul leaking DC-9's. +++ #3187 Subject: Re: [Bearhawk] Cutting the goofy (lightening) holes From: Tim Anderson I just finished priming most of my wing parts. I used 2.5 qts, for all the ribs, spars, etc. The only thing left is one set of cap strips and the flap/aileron spars. I have been told that it takes a little over a gallon for all including the skins. I can't personnaly confirm that. A lot depends on how thick one applies it. I used stits epoxy primer and put a fairly thin coat on. +++ #3205 Subject: steel tube fuselage protection From: budd davisson Yet another opinion based on cutting up lots and lots of old fuselages. 1. Don't pressurize. That's a competition airplane thing and gross overkill. 2. Drill clusters only if you want to be positive. Factories almost never did that. 3. If you do a good weld, each piece is airtight inside and won't rust. Not once have I found a diagonal or vertical rusted that didn't have a pinhole in the weld or rusted through from the outside. Even those with pinholes only get light frost inside. 4. DO oil at least the longerons. All of the old fuselages we cut up and repair these days have set outin the elements for decades without the advantages of powder coating or epoxy primers and paint. We're not likely to treat our airplanes so poorly and, even if we did, judging from what we see on existing old airplanes, it must take 40- 50 years for the elements to cause serious problems. +++ #3207 Subject: Re: [Bearhawk] steel tube fuselage protection From: Bruce A. Frank I agree, with a bit of caution. When I lived in PA, many's the time I walked into the hangar when the planes were cold soaked from the night to find the morning's temperature rise causing heavy condensation to form on the fuselages. There were times when rivulets of water ran off the fuselages and formed pools on the concrete floor around the tail wheel. Pinholes in the wrong place, as the barometric pressure changed, would actually suck water into the tube. Almost like being submerged. Longerons with no linseed oil inside pulled water in and did rust through in as few as three years from new. I agree that the perfect solution is a completely airtight weld, but linseed oil is the insurance policy--the "just in case" safety net. I have welded pipe fuel-oil lines that showed no leaks during pressure test, but over a year later a pinhole opened up in a socket weld. If fuel oil hadn't stained the paint of the pipe it might not have been noticeable for years still. Powder coat if possible, but at least oil the longerons. (Yes, I know it is likely that fuselages in CA will probably never see moisture like this) +++ #3214 Subject: Re: [Bearhawk] steel tube fuselage protection From: Kent White The cloud chamber effect is exactly the problem, along with atmospheric pumping. The Alaskan FBO gents tell me all the time about rusted tailends on the taildraggers. Rusted from the inside out. I took a steel tube years ago, 1983, and put 8" of the end into a large can of boiled linseed oil and left it in the rain for 2 years. (We get 4' of precip a year, except for 1983, when we got 96".) The tube had rusted pretty scabby in that time, under the oil. Haven't figured yet how to coat the insides of the most rust-prone tubes for the most rust prone environments. Go to it, guys. Kent "still figurin" White On Thu, 24 Aug 2000 19:13:24 -0700, +++ #3215 Subject: Preserving Tubing From: dmccarroll1 One of the old time tricks I have learned in preserving tubing is to mix lead carbonate with the linseed oil before treating your tubing with it. You bring two quarts of the oil to a gentle boil, (about two thirds of a coffee can), in the meantime dissolving a teaspoon of the lead carbonate with a few ounces of vinegar. You slowly pour the lead carbonate into the boiling oil, (It will froth), when the frothing stops, you skim off the top. The vinegar will boil off so you don't have an acid problem. What you have is a boiled linseed varnish that is more resistant to moisture and will harden into a red chestnut colored coating. Or you could just treat the tubing with hammerite. Whatever you decide be sure and post it, I am interested in learning what works best. +++ #3217 Subject: Re: [Bearhawk] steel tube fuselage protection From: Bruce A. Frank I do favor linseed oil for two primary reasons, it plugs pinhole leaks and it eats up all the oxygen inside the tube. No oxygen, no rust. +++ #3218 Subject: From: Bion Rogers I just posted a document in the files section for anyone that is interested. It contains information on the dynamics of rust and my views of rust prevention and its effectiveness. When I started writing it, it took on a life of its own and got too big to post here. I thought that I could share some knowledge I have gained from my work and add some fuel to the fire. The document is in MS Word 97 format. +++ #3222 Subject: [Bearhawk] (unknown) From: Russ Erb I read this document, and thought it was well written and informative. I think I learned some useful facts. Good job, Bion! This is the type of information exchange that makes this list useful and, from some things I've heard about lists for other airplanes, unique. +++ #3227 Subject: Re: [Bearhawk] Re:RUST From: Thank's for the guidance to the files section and the writeup. Makes me wonder if the correct method is to NOT drill cross holes into the longerons keeping the volume down and minimizing pinholes. Mechanically clean the interior of the longerons from the front end then cap and paint the interior. Then for good measure throw in some of the Argon. +++ #3294 Subject: Flap and Aileron Building Tip From: Finally found a use for .032 lockwire. For those who will be priming structure the big nemesis is how to avoid all the tags identifying detail parts and their location. One answer is to thread the detail components on a long piece of lockwire, like beads on a string or trout on a stringer. One piece for the right flap, forward of the spar, thread all the parts on using the top angle to rib rivet hole. Then remove the clecos to the spar, ribs and angles now on stringer in correct order and orientation. Debur, clean, etch and prime. Repeat for aft of the spar etc. +++ #3461 Subject: Corrosion Inhibiting for Aluminum From: Montee, Dan L. I have watched the bearhawk debates on primers and coatings for aluminum and I didn't see a clear winner. They are either, 1. carcinogenic, or 2., marginally effective, or three difficult to use (two part epoxies). I thought I'd go off line from aircraft and see what was available elsewhere. The most interesting product I found is called NYALIC. I talked to their tech rep and it appears this product has been around for military use for some time. It was used on the X aircraft, B58 nose cones, Apollo's and other NASA projects. It is impervious to chemicals, sheds salt water, and has no nasty MSDS health warnings. The only down side appears to be it doesn't like glycol. I don't intend to de-ice with the big boys so I don't see that as a problem. As a novice aircraft builder my question is to those of you with military/commercial experience. Has anyone had any experience with NYALIC? +++ #3462 Subject: Re: [Bearhawk] Corrosion Inhibiting for Aluminum From: Float-By Shooter > As a novice aircraft builder my question is to those of you with > military/commercial experience. Has anyone had any experience with > NYALIC? No commercial or military experience, but the Eastwood company sells Nyalic as a non-yellowing clear coat to be applied over bare polished surfaces to keep them from discoloring due to the elements. I have some and it seems to work for that purpose. +++ #4338 From: budd davisson Subject: PS-primer > And have you got a favorite paint/epoxy for the fuselages? The first batch of airplanes is going out with primer that meets MIL-23377G (the latest revision). This meets spec with no top coat. If we find something we like better and works well in a production environment we'll use it. +++ #4339 From: "David McCarroll" Subject: Re: [Bearhawk] PS-primer We use DuPont Epoxy primer here at Kenmore. It seems to work very well against corrosion. It is recommended by Bombardier/DeHavilland and Boeing. You can get it in Zinc Chromate Green. Randolph also makes some very good primers. +++ #4345 From: Corky Scott charles.k.scott@d... Subject: Re: [Bearhawk] Digest Number 266 >> Are the tube joints drilled for oil, or doesn't anybody do >> that any more? And have you got a favorite paint/epoxy for >> the fuselages? > We haven't decided yet, but most production airplanes only oil > the longerons and we'll probably do the same. Call me a heretic but I haven't oiled any of the fuselage longerons or any other tubes of the fuselage. I just could not see the point in going through all that detail, to remember to pre drill every single tube for every single joint so that the oil would successfully travel from one end to the other, leaving a bunch in there. Think about the logistics here, you'd have to drill four holes at each joint to make sure the oil can travel properly while you tilt it one way and hang if from the nose then tilt it another way etc. etc. I can see that I'm closing the tubes off completely from the atmosphere with the welds and besides, it's going to get painted and covered with painted cloth. The airplane will outlive me by many many years. I also do not see the point of installing schrader valves and pressurizing the tubes with nitrogen or some such gas so that you can see if you have a leak. Well what do you do if you do discover that the pressure has leaked out? Do you ground your airplane and strip all the fabric off, and check for leaks, then sand blast the area(s) and re-weld, re-install the cables and re-cover? That sounds like a AWFUL lot of work for a pinhead leak that at worst is letting in a little bit of atmosphere. But of course, each to their own. My son's son might want to think about a re-cover and checking for rust but I won't need to. By the way, I've installed Tripacer nose gear on the airplane so it doesn't sit tail low, another heretical act. +++ #4347 From: Russ Erb Subject: Re: [Bearhawk] Digest Number 266 > I can see that I'm closing the tubes off completely from the > atmosphere with the welds and besides, it's going to get > painted and covered with painted cloth. You'd be surprised at how many pinhole leaks exist in those welds. Put a good line oil in a test peice and see where it leaks out. I've done that on some pieces and could never find the leak, but there was oil on the outside to show it was there. Of course, the good part about the oil is that it will congeal and seal the hole. Try welding a fuel tank and chase the leaks. It's very difficult to truely seal any tube by welding--the heated air expanding on the inside keeps blowing out the final weld. One nice benefit of all of those oil holes is it gives that air somewhere to go. My recommendation: try it, test it, THEN make your decision how you want to go. +++ #4474 From: "Float-By Shooter" Subject: Re: [Bearhawk] media blasters > Any guidance on the type of media blasting to use on 4130 > parts prior to painting? Getting the welding scale off parts > with nooks and cranies is a challenge. A blast cabinet is nice if you have one available, since it allows you to use a more aggressive media like silicon carbide economically because it is continuously recycled, and 2) you don't have to wear a bunch of uncomfortable safety equipment. Otherwise a good "bucket" siphon blaster with commercial sandblast sand is probably sufficient for most tasks. If you will be doing a lot of heavy blasting of large objects a nice pressure blaster is tough to beat, but more expensive. With a non cabinet blaster you will want to wear at minimum a respirator and goggles, and cover all exposed skin with clothing. Don't do it in your workshop because the sand will get everywhere, if possible a lighted sandblast shed is ideal. I don't bother trying to reuse the sand and instead save it to sprinkle on my driveway in the winter. +++ #4476 From: Bob Romanko Subject: RE: [Bearhawk] media blasters There are some things I prefer to let other people do. Exhaust work, for example. My local muffler (national shop) can buy the parts AND put them on cheaper than I can buy the parts at the auto parts store. In addition, I hate working on exhaust and brakes. Both jobs are dirty and nothing EVER comes apart like it's supposed to. Agreed? Now, blasting. It's not really worth the hassle, in my opinion (expect anything less?) to go out and buy the equipment, manage the media, dress yourself like something out of Star Wars, and clean up your own parts. Unless you're in a production environment, I'd just throw all my parts into a truck (yes, fuselage included) and take 'em all to a local shop that's already set up. Let THEM dig media out of their @#$$%! Blasting is nasty work if you're not working in a cabinet, and I doubt if you'll find a cabinet big enough to fit a fuselage. So now you're outside in the weather, dressed like some Martian in a chem suit, sucking air through a nasty respirator, and at the end of the day you'll STILL be wondering how sand ever got THERE, and THERE, and THERE? (insert name of any bodily crevice you can imagine). No, for this reporter I choose to just let someone else do the dirty work. That's my 2 cents, and about all it's worth. +++ #4477 From: budd davisson Subject: Re: Sand blasting Bob is right about blasting: let someone else do it but MAKE DAMN GOOD AND SURE THEY KNOW WHAT THEY ARE DOING!!!! Not just any sand blasting outfit can do airplane parts because they are used to cleaning swimming pools, dozer blades and old boilers. More than one fuselage has been ruined by over blasting. I used to do all my own blasting and had a tent that dropped from the ceiling (doubled as my paint booth) with an exhaust fan. I always used the black sand (Black Beauty??) which is expensive, but less dust and more effective. I had a plastic sheet on the floor and just picked up one corner and ran the sand to the other corner and through a screen to clean out the big stuff to re-use it. I bought a small pressure blaster which is miles ahead of any siphon system, but costs about $400. Another note about blasting: it REALLY likes dry air. As dry as you can get it to keep the sand from clumping and jamming the lines. A final note: I had a two story basement workshop (house was on a helluva hill!) and even though I did my blasting in a tent and the floor was caulked, the sand still managed to find its way into the lower level. Never did figure out how it got there. +++ #4479 From: "Tim Anderson" Subject: RE: [Bearhawk] media blasters I would agree with your approuch for an entire fuselage. My immediate concern is the small wing hardware peices. One'ies, two'ies... would like to get them painted before they start to rust. I made my wing compression tubes last summer, didn't finish the parts like with the flap drive torque tube fittings and so forth until my wing was at least clecoed together. those parts started to rust after a few months and I had a bugger of time getting the rust off in the tight spots so that I could paint them. The rust wasn't heavy, but still it was there. WD-40 probably would have worked. +++ #4481 From: budd davisson Subject: Re: [Bearhawk] media blasters Re: Small parts blasting Somewhere I saw the plans for a homemade blasting cabinet built around a siphon blaster. It seems to me they were being sold by TP, the same folks who make a wide range of blasters and cabinets. They have lots of neat, applicable stuff, www.tptools.com. +++ #4485 From: "Kent White" Subject: Re: [Bearhawk] media blasters Media blasters? Why, ferevinsakes? I have acid washed frames for years, and the acid locks on the primer or paint just as well as blasted surfaces, but good heavens---the time saved!!! +++ #4486 From: Ken Beanlands Subject: Re: [Bearhawk] media blasters Here in Calgary we have a do-it-yourself blasting outfit that is even open on Saturdays. You could easily blast an entire airframe in about 1-2 hours. The neat thing is that it's outside in a yard with a sand hopper holding several tons of sand. You just stand back and have at it. It is equipped with a hood style respirator and everything. Total cost is about $40 per hour. I understand that they recycle the sand, but they have all the right gear for it. I'd recommend finding a place nearby that does the same thing as I doubt it's unique to Calgary. +++ #4487 From: "DANFORD, GARY" Subject: RE: [Bearhawk] media blasters I have been working on cars, pickup's, lawnmowers and airplanes for years and don't see how you can get by without a sand blaster. Your welding immediately gets better because you don't have to weld thru slag. The sand blaster takes the surface tension from welds and the paint sticks. I would suggest[http://www.tptools.com]. They sell a sandblaster kit with plans for the cabinet for around $149.00. The cabinet requires 2 sheets of plywood and you're in business. Mine works great and wouldn't be without it. You can also call them at 1-800-321-9260. +++ #4489 From: "Rod Smith" Subject: Re: media blasters I'm guessing you have never sand blasted an aircraft frame Ken. Took me a day and a half to do my Maule. I ended up spending more for sand and blaster rental than I could have paid to have it done for me. Wont make that mistake again. The local powdercoater has a sand blast set up in a tractor trailer box. They routinely do new replacement super cub frames so I'm not worried about their work. At $40/hr I bet you will end up with at least $400 in the job and you could probably hire it done for not much more. Just my thoughts. +++ #4490 From: "Rod Smith" Subject: Re: media blasters > I have acid washed frames for years, and the acid locks on the > primer or paint just as well as blasted surfaces, but good > heavens---the time saved!!! What type of acid and at what strength? +++ #4492 From: "W. Shalm" Subject: Re: [Bearhawk] media blasters Respirators are a must. It's not just the "inconvenience" of digging out the sand but if ingested into the lungs can do more than make you cough. There's this little thing called silicosis - that tends to do serious things to your lungs. However there may be a good use for it. It might work as seed for those Pentiums in Sillycone Valley (re: Planter Bob's machine) +++ #4499 From: Del Rawlins Subject: RE: [Bearhawk] media blasters > environment, I'd just throw all my parts into a truck (yes, > fuselage included) and take 'em all to a local shop that's > already set up. Let THEM dig media out of their @#$$%! There are times when I wish I lived someplace where I didn't have to do everything myself. I bought the nice $400 pressure sandblaster (highly recommended unit BTW) from TP tools and I have to hide it when I am not using it or people coming by the shop try to rent it or hire me to do their blasting. +++ #4500 From: Jim Ash Subject: Sand blasting vs godzilla On the dry air note: I was surfing the web looking for the toilet paper oil filters that were sold for aftermarket automotive and industrial use 20 or 30 years ago. Apparently someone has adapted one of these for water filtering of compressor air. Franz still sells the kit. +++ #4505 From: Russ Erb Subject: Re: [Bearhawk] media blasters > Any guidance on the type of media blasting to use on 4130 > parts prior to painting? Getting the welding scale off parts > with nooks and cranies is a challenge. I picked up a simple 50 lb sand blaster at Sears and run it off of the compressor. Works good, lasts long time. Except for the rubber hose, which has dried out and cracked and needs replaced. Should be able to get at the local hardware store. As for using "really dry air", I do have a cooling plenum between the compressor and the water trap/drier, and have never had any problems. Then, of course, I do live in the high desert to begin with... +++ #4507 From: "Kent White" Subject: RE: [Bearhawk] media blasters > get them painted before they start to rust. I had a bugger of > time getting the rust off in the tight spots so that I could > paint them. The rust wasn't heavy, but still it was there. Oh foosh. Use Must For Rust. Wipe the metal parts with solvent or whatever to clean off the oil. Wipe down with MFR, keeping the surface wet for 20 sec or so. Then wipe dry, very leisurely. NO neutralizing needed. Prevents rust..for...a year...or more. And is ready for primer or paint AS IS. Sheesh. Quit working so hard. Been doing this method for years. +++ #4526 From: "Kent White" Subject: Re: [Bearhawk] media blasters >> Oh foosh. Use Must For Rust. > >I assume this isn't a magic bullet against weld scale? >For that, you still need to blast? Weldscale just happens. While there are products like sprays and coatings which are designed to reduce its occurrence during various welding operations, for the guy making parts like we do, nada. The MIG guys may find an anti-spatter coat helpful to limit the metal globule attachment around the welds, but they must still clean the metal prior to paint. MFR is a sort of magic bullet for post-weld cleanup, as it knocks down most of the scale and all of the discoloration. The little scale that is left is so tough that I either leave it on there, or if doubtful, I give it a kiss with the wire wheel and then re-wipe with the MFR. There are other similar products, like Ospho, but I know this chemistry and the long industrial history of the product. Like the painters, once I get onto a particular chemical system it's tough to change over to another. If the first (or only) coating is going to be the PPG black oxide primer (awesome stuff, I have tested it for years), then I am less apt to nitpick every bit of scale. The reason for this "less than sterile" method is that the restoration work I have done has routinely shown that the tenacious weld-scale remains fastened tightly for decades, with the paint surface showing no sign of its letting go. +++ #4527 From: "Kent White" Subject: RE: [Bearhawk] media blasters >Where do we find this "Must for Rust" product. Um...ah...well....there is this nice little site that helps the metalguy..... ahem...caught again? +++ #4528 From: "Kent White" Subject: Re: [Bearhawk] media blasters > Your experience with, Must for Rust sounds like the way to > go....Have you in the past used 'Glass Bead' like for Aluminum > heads etc...How would that be for removing scale & eb-geebees? "Media" for blasters... I have used glass beads, plastic beads, plastic particles, carbide, silica sand, glass etcher's sand, mortar sand, walnut shell, and mixtures of all of the above. I have watched Erickson Aircrane clean airframes with soda, (right next to I-5 as you leave Medford, OR heading North). I have discussed the CO2 ice crystal method with Douglas engineers, and think it is really neat. I know there are many closely-gaurded media compounds used in industry. I have blasted tattered and laced steel and aluminum, heavy iron, glass, and frameworks of many kinds, and have watched expen$ive parts ruined by heavy-handed people. I like my present system. +++ #4533 From: "Donald Schindler" Subject: Re: [Bearhawk] media blasters Tim, One cheap thing you can do to protect your metal parts is buy a couple gallons of oil, cut the top of the jugs off and submerge your parts and fish them out when your ready. When I did my Kitfox, their factory guidelines for media blasting was make sure they use the smallest grit and lowest possible pressure to get the job done, then powdercoat immediately. They say that rust can actually start to form within minutes under the right conditions. +++ #4536 From: "vic" <11acs@g...> Subject: Re: [Bearhawk] media blasters > Where do we find this "Must for Rust" product. Phosphoric acid. Under diferent trade names in most auto parts stores. +++ #4538 From: Bob Romanko Subject: RE: [Bearhawk] media blasters That's a great suggestion. Even better, just keep your old motor oil. I have a 55-gallon drum I pour all of mine into. Pump out when you need to and fill a 5-gallon bucket 1/2 full and drop in a colander from the kitchen full of parts with safety wire tied to it for a handle. Parts will stay rust-free until you need to finish 'em. +++ #4541 From: Pierce Terry M Civ 412 TW/TSI Subject: RE: [Bearhawk] media blasters Please keep in mind that used motor oil is carcinogenic. +++ #4543 From: Ken Beanlands Subject: Re: [Bearhawk] Re: media blasters The blasting outfit I was using has a nozzle about an inch in diameter. The effective area is about a 2 foot diameter. While I was waiting one morning I watched a guy blast a 6' x 30' vessel on one of the big blasters. It was taking off the paint, rust and weld slag in 3' wide swaths. Tank was done in about an hour. It is an industrial blaster so you have to stand about 4' - 6' back to get a nice light blasting. It really is quite amazing as you are not really standing close enough to get much sand blowing on you. +++ #4551 From: Del Rawlins "Float-By Shooter" Subject: RE: [Bearhawk] media blasters > That's a great suggestion. Even better, just keep your old > motor oil. I have a 55-gallon drum I pour all of mine into. Old motor oil is far too valuable as heating fuel to be used for pickling parts. The few steel parts which I've managed to produce were small enough to spray with WD-40 and stick in ziploc bags. It's been not quite a year since I put them there and they looked fine when I was showing them off the other day. I'm slowly but surely getting my other projects in order and am looking forward to the day when I can start back on the Bearhawk! Once I get some parts that are too large for the bag method, I'll probably just hit them with some hardware store rattle can primer. I'll be sandblasting them eventually anyway. +++ #4552 From: Del Rawlins "Float-By Shooter" Subject: Re: [Bearhawk] media blasters >> Cooling plenum? do tell! I've had a real problem with water >> while painting and I'm willing to try anything to fix it >> (short of hiring out the process > Therefore, my "cooling plenum" is about 40 feet of 1" Schedule > 40 PVC pipe zig-zagging downhill (to drain the water) before > getting to the filter dryer. Granted, now I live in the > desert, but I occasionally do pick up a little water in the > dryer, so I'm guessing it's working. I may have mentioned it in the earlier discussion we had, but I have a set of videos on auto restoration and one of the things shown is a very simple cooling plenum made of a long piece of copper tubing coiled into a big spiral so it doesn't take up much space. I'm envious of the dry desert air some of you enjoy. Between the steel pipes (which provide excellent cooling) in my shop and the coastal climate, I have to drain the tank/traps regularly. If I am using the blast cabinet for any length of time I often have to stop in the middle to drain the trap. If I fail to do so, the whole process comes to an abrupt halt. +++ #4576 From: "William & Delinda Johnson" Subject: 023 Update I have been lurking for the past 4 weeks without a post! So, here goes: 1. Media Blasting - I use walnut shells and glass beads. It works so I keep doing it. 2. Welding - don't weld more than is necessary. For instance, my washers which keep the spring on the support frame are just tacked in four places. The spring will break before those tacks come apart. Use some judgment; however, don't under weld in a effort to make it look nice either. 3. Window frames - Follow Bob's lead - he has found the easiest way to get things done. 4. In all cases, the Nike shoe slogan applies, 'Just do it!' +++ #6080 From: Ken Beanlands Subject: Re: [Bearhawk] Digest Number 420 You should be fine, Sonny. My family has had a Cessna 180 on floats since 1975 in Newfoundland, arguably one of the harshest salt-water environments on the continent with ever present salt in the air from the high winds and ocean spray. On top of that, they dump tonnes of salt on the roads every year. We've purposely avoided landing in salt water with the plane and so far there has been no corrosion problems to speak of. The only parts that needed rebuilding due to corrosion were the two watter rudder hinge assemblies but the floats have been in service since the mid 60's. Most of the interior aluminum bits were completely uncoated but due to accidents over the yuears, both wings now sport fully primed interiors. However, it was not done until 1994, 19 years after new. However, I'm sure that if we were flying out of salt water it would be a different story. The 185 that we share a hangar with has had to have the entire LG box replaced as well as several panels under the tail due to corrosion. It was occassionally used in salt water (half a dozen landings per year). Just my $0.02 CAD worth. Ken Beanlands B.Eng (Aerospace) +++ #6081 From: Russ and Penny Erb Subject: RE: [Bearhawk] Digest Number 420 Well, that's an improvement. The last Wicks catalog showed a picture of some completely different airplane as the Bearhawk. Alodining is better than leaving the aluminum bare. Priming over alodine is better, but that doesn't mean alodining isn't good. Alodining and priming both will add to your build time significantly--perhaps that's what has driven me out into the upper 3 sigma. It's the classic Fram commercial: You can take the time now, or you can take the time to rebuild later. Russ Erb +++ #6093 From: sonny cilley Subject: Re: [Bearhawk] Digest Number 421 Ken & Russ, thanks for the thoughts on the Alodineing. from what I gather from the Tech Councelors up here the alodineing will be fine also, but I guess that I'm just getting antzy to get this together and at this point in the project it is when it'll be the difference between a good aircraft and a great one.also there are alot of Cessnas and others out there that never had anything done to them for corrosion protection. I hadn't given much thought to the fact that it gets pretty cold in Vt. and the heating and cold does produce a condensation problem. THERE, I just answered my own ??? priming after alodineing it is. I'm a builder (houses and such) and I wouldn't consider leaving a customers house without the proper paint coverage .it wouldn't last 2yrs. off to the paint store, Sonny #234 +++ #6096 From: Russ and Penny Erb Subject: RE: [Bearhawk] Digest Number 421 One of the biggest non-sequitors in aviation is "Cessna didn't do anything for corrosion protection so I don't need to either". The part everyone forgets is that Cessna expected you would fly the airplane about 3 to 5 years, then trade it in for a new model, just like a car. No one expected that those airplanes would still be flying decades later. A friend is totally rebuilding a Cessna 310 that he totally deskinned because the corrosion was so bad. Had Cessna done some treatment, he might have spent these years flying. Another friend has a Cessna 180 that came with the "seaplane package" which included corrosion protection all over the inside of the structure. It's still in great shape as a result (never been on floats) Russ Erb +++ #6109 From: "Bruce A. Frank" Subject: Re: [Bearhawk] Aluminum wings > But, then there's the steel to worry about. Powder coat all those parts. Bruce A. Frank +++ #6111 From: Budd Davisson Subject: Re: [Bearhawk] Aluminum wings Aha! Powdercoating. Here's another subject for discussion that I think we started a long time ago, but needs revisiting. One of us had some info from a Boeing engineer who said that powder coating isn't a good protection against corrosion via moisture. I'd always thought it was bulletproof. Anyone have any input on that that we can track to the source and know it is accurate?? bd +++ #6112 From: "Derrick Howard" Subject: Re: [Bearhawk] Aluminum wings Too much weight to powder coat ALL the steel parts, perhaps a light zinc-chromate primer coat. Derrick Howard #192 +++ #6114 From: Russ and Penny Erb Subject: RE: [Bearhawk] Aluminum wings As of late I have been hearing that zinc chromate is not really effective as protection against moisture because the coating is porous, allowing the moisture to still get to the metal. I still recommend a good epoxy primer or my favorite, Poly-Fiber Metal Prime. Russ Erb +++ #6117 From: "Mark Goldberg" Subject: RE: [Bearhawk] Aluminum wings The latest Mil-spec primer is MIL-P-23377G. This is certified to provide excellent corrosion proofing without a topcoating. Primers that meet this spec are made by several manufacturers like Randolph, U.S. Paint, and Sterling. It is effective on aluminum (after alodining) or steel. Mark Goldberg Austin TX BH#444 +++ #6122 From: "Donald Schindler" Subject: RE: [Bearhawk] Aluminum wings The holy grail of corrosion protection is suppose to be Duralac. It's a mixtureof lanolin and zinc that was used on warbirds that kept them perfectly preserved after sixty years in salt water. I believe it was used along all rivet lines. I think it was of English origin and I have searched for it several times but to no avail. The web turns up nothing. Regarding Zinc chromate, the big problem with it is you will find that by the time you finish your airplane alot of it will get scratched off. That doesnt happen with powder coat. Soldier on...Don 068 +++ #6123 From: snort imer Subject: RE: [Bearhawk] Aluminum wings Try this link: http://www.bamar.it/duralac.htm or this: http://www.sanshin.co.uk/duralac.html there is http://www.duralac.com/ too but it isn't appearing when I try it. I use www.alltheweb.com. Works like a charm for most searches. Kind regards, John Walsh +++ #6124 From: rsmith@a... Subject: Powder Coat People talk about powder coat like it is all one uniform substance. Actually there are many formulations of varying quality available, just like there are many types of paint. The powder coat applicators in both Anchorage and Wasilla use two coats for aircraft fuselages and parts. First a prime coat containing zinc and then a top coat of your color choice. Just like any paint job, surface preparation is very important. A freshly sandblasted surface is hard to beat. At a minimum it needs to be clean and dry with no loose rust or scale and a solvent should be used to get any oil or grease off. If done properly with quality materials it will be every bit as good as a primed and painted job and has the advantage of being more durable and scratch resistant. Rod Smith #246 Wasilla, Alaska +++ #6126 From: Mike Subject: Duralac and other stuff The Duralac sounds like some very interesting stuff - like maybe for floats. I put in an e-mail to the company that makes the stuff to see if there is a U.S. supplier. I'll let you know what I find out. We might get Wicks to stock it if there is enough interest and the stuff isn't too expensive. It might be considered toxic in the U.S. let's see what the company has to say about it +++ #6181 From: "Kent White" Subject: RE: [Bearhawk] Powder Coat Is there still a hardness/brittleness factor which can lead to cracks when parts flex? Can the powdercoat still be repaired nicely with a urethane spray paint? best regards, Kent White +++ #6189 From: rsmith@a... Subject: Re: Powder Coat I have not heard anything about a problem with cracking, I will have to ask about that. The only airframe jobs I have examined have not been put in service yet. One builder I know added some tabs after powdercoating. He used a propane torch to melt the powdercoat and wipe it off at the locations, welded the tabs and then touched it up with an epoxy primer and top coat that was a pretty close match. Rod +++ #6213 From: Budd Davisson Subject: Re:Termites and corrossion > -- and Budd, good point about getting the corrosion coat up into > the 'cupped in' T-25 channels. I wonder if one could get the > rattle-can style zinc primer, then replace the nozzle with the > type that comes on WD-40 cans with the 6" straw tip? Use spray can chromate and the flexible hose and remote nozzle that comes with some termite spray cans. bd +++ #6224 From: Float-By Shooter Subject: Re: [Bearhawk] Re:Termites and corrossion > Use spray can chromate and the flexible hose and remote nozzle that comes > with some termite spray cans. The Eastwood Company sells an "undercoating system" which features a srayer with extension and flexible tips. Del Rawlins +++ #6319 From: sonny cilley Subject: Re: [Bearhawk] Digest Number 433 Hi guys, I have another ? about priming , . I just got done talking to a friend who has build a RV 6A and now a RV 4. and I asked him about priming and he uses Variprime. I think I'm gonna use it also , do any of you have any experience using this product. sorry to drag everyone down this road again,but this is my next step. Sonny # 234 +++ #6321 From: rsmith@a... Subject: Re: Priming Someone correct me if I am wrong but I believe that Variprime is an etching primer made by Dupont. I believe you would clean the aluminum well, then spray the variprime without needing to acid etch. It should be fine for aluminum with or without a top coat. I do not know about its use on steel. If used on steel it definitely would need a top coat because like most primers it is porous. Rod Smith #246 +++ #6322 From: n95mf@a... Subject: Re: [Bearhawk] Digest Number 433 Sonny, Veriprime is a good product, but I think (?) it is mainly for aluminum. This is what goes on all of Van's QB kits. However, as a corrosion preventer, it really requires a top coat to do much good, especially on steel. I think for steel you would want to use an epoxy zinc chromate. For aluminum, if you live on the coast you want to top coat the Veriprime for good corrosion prevention. My feelings: Veriprime is better than nothing, but not the best protection available. Mark Goldberg Bearhawk #444 +++ #6323 From: Benton Holzwarth Subject: Re: Priming From: rsmith@a... Subject: Re: Priming > If used on steel it definitely would need a top coat because > like most primers it is porous. A fabric guy talked at the last chapter meeting. He mentioned using a 'High Zinc Primer', don't remember whether he talked about it being any of the two-part products, but said to top it with, say, polyurethane, because the fabric cement will lift the bare primer off the steel. He liked the AirTech (sp?) process. It was interesting to me that it's STC'd for use with *any* of the PMA'd fabrics. AirTech's position was that there's already several prefectly good (perfectly identical) polyester fabrics on the market -- the last thing the world needs is another! That's a practical attitude I can identify with. Benton 2jun01 +++ #6325 From: Russ and Penny Erb Subject: RE: [Bearhawk] Re: Priming As I've said before, Ceconite was bought out by Poly-Fiber years ago. If anyone starts trying to tell you that one fabric is better than the other, try to suppress your laughter. The owner of the company tells me that they come off the same machine. The only difference is which stamp they use on the fabric. Don't forget Poly-Fiber Metal Prime, a waterborne primer that won't lift under fabric cement. As good as any epoxy primer, and no nasty solvents. Listed in the Spruce catalog in the composites section (p. 40 in 2000-2001 catalog), even though the primer is for aluminum and steel. Russ Erb +++ #6334 From: n95mf@a... Subject: Re: [Bearhawk] Digest Number 433 Jimmy, IMHO the best primer available is one that meets the new MIL-P-23377G certification. This gives very good protection without a top coat. However, on aluminum it does require Alodine treatment first, according to the spec sheets. Several manufacturers make a product that meets this mil spec. Among them are Randolph, Sterling, & U.S. Paints. Good luck. Mark +++ #6349 From: "Collin Campbell" Subject: Priming > Hi guys, I have another ? about priming , . I just got done > talking to a friend who has build a RV 6A and now a RV 4. and > I asked him about priming and he uses Variprime. I think I'm > gonna use it also , do any of you have any experience using > this product. sorry to drag everyone down this road again,but > this is my next step. As an ex-RV builder I am familiar with Dupont Variprime. Used it in the Bearhawk wings. I like it and highly recommend it. It is a two part "etching" primer, works good on aluminum and steel surfaces. However, I don't think it is the best primer to use under fabric. In this case it is best to use a durable two part epoxy type primer that will not "lift" due to the solvents in the fabric cement. Variprime should work well everywhere else though. It's easy to use and obtainable at most auto parts stores. One could primer everything with Variprime and second coat the surfaces where fabric contact will occur with a good epoxy primer. Collin Campbell #370 Bolivar, MO +++ #6351 From: "Kent White" Subject: RE: [Bearhawk] Priming > Hi guys, I have another ? about priming , . I used DuPont products exclusively for years in my high-end restoration business. VariPrime is reliable and of high quality on steel/aluminum structures, when used properly. The acid-etching characteristic is absolutely necessary when coating aluminum sheet, as any other method is protracted in application and generally unreliable. All, virtually all-- of our troubles with blistering and lifting disappeared when we changed over to the acid-etching system from the "wash-and-scuff-and-prime-quickly" system. PPG also offers similar reliable coatings, as well as impervious-to-weather black chromate coatings for steel. I have used their products, as well. I would also prefer a neutral grey base coat under most colors, unless a colored sealer is available, to prevent bleed-through with color combinations of excessive contrast. Black is best under white, though, contrary to what one might think. Kent White +++ #6355 From: yeomans@s... Subject: Re: Digest Number 433 I used Variprime on my inside wings and components. I topped it with another primer that will seal it . variprime doesn't give a vaper barrier but does bite in good into aluminum and steel for a good bottom coat. as for the tubing, I would use the product that goes with the fabric system you use. stits will soften the other primers. Tom Yeomans +++ #6363 From: "Kent White" Subject: RE: [Bearhawk] Digest Number 433 > Several manufacturers make a product that meets this mil spec. > Among them are Randolph, Sterling, & U.S. Paints. Good luck. > Mark I would be a trifle leery of Sterling just now. Apparently they have made chemistry changes recently which caused one unlucky painter to strip and repaint 5 King Airs...on his own nickel....And this peccadillo due solely to this (undisclosed by Sterling) change in their formulation. Kent White +++ #6594 From: Budd Davisson Date: Wed Jun 20, 2001 7:15 am Subject: Re: The Mexican Bearhawk > Budd- Is it too early to ask (and sorry if I missed earlier) > what sort of corrosion control steps you will be taking with > the kit spars/wings? Before the spars go together the individual parts are primed using Randolph's Mil Spec primer, the name of which has escaped me. We'll be primering all of the wing parts with the same stuff. bd +++ #6597 From: "Montee, Dan L." Date: Wed Jun 20, 2001 11:18 am Subject: Fuel Tank Interior Coatings I'm about to close up my fuel tanks. I've assumed up till now that the interior of the tanks did not receive corrosion protection of any kind, but when I thought about the tanks sitting in storage so to speak for the next few years I began to wonder if there is something I should do to protect the interior, like purge and oil mist some how? Is there a common practice for protecting tank interiors? Dan Montee # 415 +++ #6615 Date: Fri, 22 Jun 2001 09:15:51 -0700 From: "Kent White" kent@ Subject: RE: Fuel Tank Interior Coatings > I'm about to close up my fuel tanks. PRC??? Kent White +++ #7539 Date: Tue, 04 Sep 2001 08:12:34 -0400 From: "Chris Vuxton" Subject: Annodizing Aluminum and Maple flooring for form blocks Looks like my last message about using maple flooring for form blocks got lost. Try www.huskyfloors.com. They advertise in the back of Fine Homebuilding. Their last ad listed 2 3/4" maple for $2.95 per square foot. On another topic. Has anyone talked about annodizing the aluminum parts in the 'hawk? Seems from posts from some EAA chapter site that it can be done by electrolysis or by dipping in a lye solution. After both you dye it with Rit fabric dye. The prospect of gold wings on the inside is appealing along with almost zero buildup between the parts. Thoughts here? I was in the UDLP plant recently where they build Bradley Fighting vehicles. They had large open tanks that seem to be bubbling. They do chemical anodizing. Chris +++ #7540 Date: Tue, 4 Sep 2001 07:08:32 -0700 From: Russ and Penny Erb erbman@ Subject: RE: Annodizing Aluminum and Maple flooring for form blocks As for chemical anodizing, that may have been alodining (iridite). Different process, same basic purpose. If you do anodize, realize that the anodized layer is electrically an insulator. Not a problem unless you wanted to use the structure as an electrical ground (not recommended for corrosion and other issues) or as a ground plane for your antennas. Russ Erb +++ #7603 Date: Thu, 6 Sep 2001 13:30:59 -0500 From: "Tony Chisum" tonychisum@ Subject: Rust Prevention Budd -- What are you doing to prevent rust on the inside of the BearHawk airframe. Tony +++ #7604 Date: Thu, 06 Sep 2001 12:43:30 -0700 From: Budd Davisson buddairbum@ Subject: Re: Rust Prevention This is a subject we've gone over and the FAQ section probably has most of it. If anything, we'll oil the longerons, but nothing else. As we've pointed out, very few manufactures in aviation have ever oiled their fuselages and we've all told stories of those we've cut open and found perfect inside as well as those which have rusted out. Most of the time the rust starts on the outside, perforates the tubing and continues inside. To my knowledge of the people currently building rag and tube airplanes, only WACO Classic oils theirs. I'm quite certain Aviat, Maule and American Champion don't. The fear of rust starting inside a tube that has been properly welded is largely theoretical. Yes, it can happen. No, it doesn't happen often. bd +++ #7615 Date: 07 Sep 2001 08:15:36 EDT From: charles.k.scott@ Subject: Re: Digest Number 541 > The fear of rust starting inside a tube that has been properly > welded is largely theoretical. Yes, it can happen. No, it > doesn't happen often. I second with this. How long do you guys plan on living? Just careful welding and painting will protect the fuselage for as long as you will be flying it. Corky Scott >>> 2mar02 #7686-9153 +++ #7698 From: rsmith@a... Subject: Progress (lack thereof) I was supposed to go to work last Weds but got delayed until Saturday due to flight restrictions, so got in a couple quality days of building. I am still working on the fuselage frame. I am getting close to putting the top and bottom together. Russ you mentioned you were looking into a method of bending the lower frame without heating it. Did you find one or resort to using the torch? Strangely enough, all my steel parts rusted this summer. Where I live normally the humidity is quite low. This was the wettest July on record however and very humid. I have steel that has sat in the garage ten years and never gotten a spot of rust before this summer. Fortunately nothing was to the point of pitting, and I used Ospho to convert it. I already had a bottle. Rod Smith #246 >>> 4sep02 #9154-11297 +++ #9598 From: "Chris Vuxton" Subject: Corrosioin Control While reading an old issue of Fine Homebuilding I found a letter from a guy who said he treated the inside of his air compressor with some stuff called "Corrosion Block" (http://www.corrosion-control.com/index.html). He said he has never had any water drain from his compressor that wasn't crystal clear, no rust. I went to their site and besides this looking like a neat way to keep your compressor well they have a few other things. The Navy treats the inside of their airframes with another one of their products called ACF-50 http://www.corrosion-control.com/MilitaryTesting.html While I don't think we want to get the whole sprayer unit why not dispense with oil and pressurized fuselages and use this stuff. I have emailed for pricing. +++ #9600 From: Tim Subject: Re: Corrosioin Control ACF 50 good stuff......In the past I used it on my rusty 1974 C-150L it spent about 10 yrs close to the ocean and showed it 'internally'.....ACF-50 goes right into the rivet line displaces water/stops electrolysis and inhibits corrosion for 1yr. When you treat an aircraft try on collecting it a the low point for re-use, if it's still reasonably clean. The stuff penetrates like penetrating oil/a-bullet ;-)...Think it's made in Canada & Aircraft Spruce carries it. +++ #9601 From: Ben McCain Subject: Re: Corrosioin Control Wag-Aero has it for $89 a gallon. The information says the treatment is good for 18 months. +++ #9602 From: "Bruce A. Frank" Subject: Re: Corrosioin Control I may be wrong, but isn't ACF 50 designed for aluminum? +++ #9606 From: Russ and Penny Erb Subject: RE: Corrosion Control The write-up in the Spruce catalog talks about using it on Piper lift struts, which I think were/are steel. That's the limit of my knowledge. +++ #10205 From: John Thompson Subject: Powdercoating > Has anybody priced powder coating the fuselage and is that a good > idea? I've never had anything powdercoated before, but a lots of pros and cons have been discussed about this. It looks pretty, and helps prevent corrosion... BUT, it does hide welded joints (hard to inspect for cracks) and adds weight. Someone on the Zenith list was just telling how he found a crack on his powder coated engine mount. He was looking only because he found the alternator bracket had cracked (not PC'ed). >>> 20may03 #11298-18250 +++ #12069 From: Budd Davisson Subject: Re: Priming, was (Re: Weight of Wing Panel) What's the general opinion about priming the insides of wings? It's obviously a good idea but what are you float plane types seeing in Cessna wings up north? Is it really worth the effort or is it a peace of mind thing? bd +++ #12070 From: Russ and Penny Erb Subject: RE: Priming, was (Re: Weight of Wing Panel) Many people forget that the corrosion doesn't occur on the large open spaces. It happens between parts (faying surfaces) where the water gets in and doesn't get out. To answer the question if it is worth it, you have to answer several questions first: 1. What environment will the airplane live in? 2. How long do you want spend building? and most importantly 3. How long do you want the airplane to last? If the answer to #3 is "not very long" then don't waste your time. If you plan to pass the airplane on to your children, then you'd better take the time. Erbman's theory on why Cessna didn't prime the insides of their wings (note--they did if you ordered the seaplane kit): You were supposed to buy one, use it for a few years (3 to 5), then come back and buy another one. Much like people do with cars. Cessna didn't expect airplanes to last for 50 years. Russ Erb +++ #12072 From: Budd Davisson Subject: Re: Priming, corrosion. It has always amazed me how little corrosion we find, considering how many of the airplanes we're restoring these days spent most of their lives sitting out side as derelicts without ever being moved, so the water just pooled in them. I used to rebuilt 195's for fun (definitely not profit, although that wasn't on purpose), a number of which had been on floats and I didn't' find much corrosion at all. I've also done the C-140/Luscombe thing and you can predict where you'll find corrosion, if there is any and that's where the spar trapped the water running down hill. Even there, however, the airplane had to have spent some time on the coasts for corrosion to develop. On the other hand, I was looking at a derelict square tail 150 on my home airport with an eye towards doing a 150/150 tailwheel conversion, but you could look in any inspection panel and see nothing but white power. It was amazing! Then I found a Long Beach Airport fee stamp on it which explained the corrosion. Theoretically, fresh water won't corrode aluminum. It takes salt or acid rain to do it. Or mice. Still... bd +++ #12077 From: Ken Beanlands Subject: RE: Priming, was (Re: Weight of Wing Panel) I have to disagree with you on how the Cessna's were delivered, at least in 1975. Our plane was shipped from the factory with Edo 2960's installed and a factory float kit. An easy way to tell if a C-180 prior between '65 (?) and '78 has a factory float kit is to look for the larger C-185 vertical fin (forward part that extends up the fuselage is quite a bit larger). This prevented the need for a ventral fin to be added under the fuselage. All later model C-180's were equipped with 185 gear and fins. Earlier 180's sported the smaller fin in the float kit. Anyway, I digress. Our 180 definitely did not include interior priming. One wing has since been primed during a rebuild in '94 but the other is bare. We also primed the inner interior panels in the tailcone during the rebuild. What has been thoroughly primed and painted were the interiors of the floats. I have yet to see a pair that was not primed and painted inside. Ken Beanlands B.Eng (Aerospace) +++ #12078 From: Budd Davisson Subject: Re: Priming, was (Re: Weight of Wing Panel) What kind of corrosion of deterioration are you seeing in the parts that aren't primed? I would never build a spar like the BH's without priming every part first. However, if I ever get to build a Desert Hawk (or BH, for that matter), it's not going to be interior primed. For an airplane in normal use or one that only sees fresh water, I'm not convinced it's worth the effort. Yeah, I know. This'll start a bunch of guys wailing, but those are my thoughts. bd +++ #12079 From: Ken Beanlands Subject: Re: Priming, was (Re: Weight of Wing Panel) When we were doing the rebuild in 93/94, I took a good look at the old materials as they were scrapped. None of them showed any signs of corrosion except in a couple of places where steel and aluminum came into contact. There was some corrosion around the tail of the floats, specifically in the area around the water rudders. There was wuite a bit of pitting on the water rudder along the retracted waterline. I can only guess that it was caused by something on the surface of the lake. Ken Beanlands B.Eng (Aerospace) +++ #12101 From: Tony Dean Subject: Re: Priming, was (Re: Weight of Wing Panel) Russ, Are you the one responsible for the http://www.eaa1000.av.org/technicl/corrosion/faysurf.htm and related pages? This is some great stuff about corrosion. In Kent Poser's "Speed With Economy", he specifically talks about using a MIL Spec corrosion inhibitor in the faying spaces on his Mustang II. This was because he was being encouraged to move to Houston and he had seen the results of an unprotected Cessna 150 where corrosion started in the faying areas. The real problem with this kind of corrosion is the insideous characteristic of "when you see it, its already too late". Once it is visible there is little to be done to salvage the aircraft part where this appears. I plan to use something but have not decided exactly which product yet. Regards Tony Dean +++ #12121 From: "Fred Spain" Subject: corrosion proofing and struts???? I've run out of excuses for the hot and humid weather of the summer and am again working steady on #402. I'm working on the spars and planning what to do for corrosion proofing. I want to do a little more than "The Bob" did but not as much as Russ did. Right now I plan to dip or brush all the spar and rib parts using the alodine process and then treat the rivet holes with Poly Fiber Metal Prime just before riveting. Russ, What stock # prep and alodine did you use? How much of each did you buy? Those look like 35 gallon barrels in your CD and the thought of the cost of filling them deep enough to cover the center ribs scares me. How long should the parts soak in each solution? +++ #12129 From: "gmgdls" Subject: Re: corrosion proofing and struts???? Be careful here with the alodine/chem. film process - this is chromic acid you are dealing with. Also please keep in mind what are you are going to do with left over's, including the acid pre-cleaner. This is the type of stuff if your nosey tree hugging neighbor ever saw you dispose of it illegaly would - lets just say there will be a really cheap BH for sale in Cleveland Ms. to help cover your legal bills. Oh yeah one more positive thing about alodine your skin and system absorb it like a sponge. Don't get me wrong now, I'm no chemist, just a QE with a vast and varied background who has worked all types of job shops for the last 25 yrs. including plating shops. Alodine comes in many types - of particular importance is the Hexavalent Chromium types (HC) nasty, nasty. U.S. Military is now starting to require a substitute where ever possible for HC, it is difficult to find an acceptable substitute because alodine is the best for what it is designed to do. There are a number of smaller plating shops out there who run chem. film lines. I can give you the names of some really good shops in the Southeast U.S who we have used at various times. I'm here in N.E. Bama. Send me a private email: gemsilica@aol.com and I can get you started in the right direction. I know 3 or 4 shops now who can do it. You will be surprised it's not that expensive, plus they can do all your parts say 168 BH wing pieces in about 2 hrs depending on tank size, and they will all be uniform in appearance and coating coverage. Now that I think about it I did a Quality system survey and special process survey on a plating shop in Macon Ga.a couple of years back called Aerospace and Defense Coatings - they did all types of special processes. And the guy who owned the shop was an avid pilot flew something like a WACO or Stinston Reliant, bet he would be interested in helping some homebuilder. Drop me a line heck I may have to drive over some weekend and take a look at your progress. Still wishing and looking skyward in N.E. Bama. +++ #12130 From: Russ and Penny Erb Subject: RE: corrosion proofing and struts???? Fred, go to http://www.eaa1000.av.org/technicl/corrosion/alodine.htm This was written by the guy who taught me how to alodine. I bought the same stuff that he did in the same quantities. When I bought the stuff the company was MacDermid. As I recall, be prepared to supply a company name, since as I recall, they only sell to businesses, not to individuals. Don't know what that accomplishes. I didn't use the liners discussed in the article. The barrels you see are 55 gallon plastic barrels. Don't try to use trash cans or similar ideas because they aren't built to hold the pressure of that much water for long periods of time. The barrels are significantly thicker than plastic trash cans. Find a business that has supplies delivered in plastic barrels and buy there castoffs. The process is described in the article. Russ Erb +++ #12131 From: Russ and Penny Erb Subject: RE: Re: corrosion proofing and struts???? The accepted method of disposal seems to be to find yourself a good concrete project and use the "chemicals" to mix the concrete. The concrete traps the chemicals and the sources I've talked to say it doesn't leech out. I didn't tell you, and your tree-hugging neighbor would never believe it, but the rinse water will be such a diluted solution that normal sewage treatment will handle it (you put worse things down your kitchen sink). The rinse water doesn't need to be changed very often. Also you're not producing anywhere near the amount of waste products that a business would. Don't confuse laws that apply to commercial firms with those that apply to individuals. Of course, don't do nothin' dumb either. Of course, this is only an issue if you need to dispose of the stuff. My barrels sit over by the wall out of the way happily and quietly, serving double duty as extra tables. Just because you're done with the stuff (which I'm not yet--more aluminum parts in the fuselage to come yet) doesn't mean your friends and neighbors don't have aluminum parts to treat. Your friends building composite airplanes will love you because they will have aluminum parts to treat but not nearly enough to justify tooling up a whole alodining site. Alternative way to get rid of the stuff--when you're done, convince someone building an RV that they need the stuff. Also, as a rule I keep my hands and other skin out of the chemicals. Russ Erb +++ #12132 From: "Bruce A. Frank" Subject: Etchant Tanks The way I have done it is to nail together a 2 X 4 frame 18 ft long and 1 ft wide. Lay the frame on the level table or floor then drape with two layers of 6 mill plastic from Home Depot. Gave me a trough 4 inches deep by 12 inches wide by 18 ft long. Was able to immerse spars and ribs. Same method for the rinse tank. Pumped it down the drain with additional water dilution. +++ #12395 From: "Bruce A. Frank" Subject: Re: Removing oil from 4130 > I'm sure this has been discussed before, but through searching I > couldn't find it. What is the best way to remove the oil/grease > from 4130 prior to priming? Sand or bead blasting. The second best and by far more hazardous method is wiping down with solvent, such as MEK. A solvent or any other "wash down" method cannot get into all those nooks and crannies to make your fuselage absolutely oil free nearly as well as blasting can. I'll put that another way, the solvent gets into those places but you cannot wash with enough of it to remove all residue. The blasting method removes all oil and welding scale and leaves a surface rough enough to readily hold any paint you want to use. Bruce A. Frank +++ #12397 From: Bob Romanko Subject: RE: Removing oil from 4130 Sam, if you haven't done any blasting before, don't be afraid to pay someone else to do it. Nasty, dirty, yeach. @#$% sand gets in places you didn't even know you had, and takes a lot longer gettin' out than it did gettin' in! If you have done some blasting before, I'm just giving my opinion from my experiences blasting heavy equipment for my dad when I was a kid. For this camper, it ain't my bag. There are two jobs I can do, but would rather pay someone else to do: exhaust work and sand blasting (big stuff that is). Both are nasty jobs no matter how you slice 'em. For what it's worth, Planter Bob +++ #12398 From: "Steve Eldredge" Subject: RE: Removing oil from 4130 Funny this should come up. I'm sand blasting my Stinson fuselage right now and it it's a pain. This is the second fuselage I have done, and probably not the last. I'm using the harbor Freight pressure blaster. It will hold about 15 minutes worth of sand. A 5 hp 30 gallon compressor is barely adequate (read not really, but it's the best I have) So far I'm about 2/3rds done and have spent 1.5 days so far doing the job. If your going to tackle it, Start with some a 1 piece jumpsuit, hearing protection, and good gloves. Sand goes everywhere. I used a roll of plastic sheeting to contain 80% of the sand for reuse. I've used 700lbs of abrasive so far, and will probably have enough. I can post some pictures of my fixtures and more on the procedures if anyone would like. Finally have something to contribute! Steve E. +++ #12401 From: Ken Beanlands Subject: RE: Removing oil from 4130 I found a self service sand-blasting service here in Calgary that I've used with good success. They use a commercial blaster set up outside with a large (15' high) sand hopper. It doesn't run out of air or sand. A whole fuselage can be done in about 1-1.5 hours at about $30 per hour. It is also equipped with a full hood and respirator. Works really well. Look for one in your community and go for it! Ken Beanlands B.Eng (Aerospace) +++ #12407 From: Del Rawlins Subject: RE: Removing oil from 4130 If you can get your hands on a fresh air supplied hood, sand blasting is no big deal. Between the sandblasting, and all of the paintwork on the airplane it might be worth considering since the price on some of the hobbyist type units is fairly reasonable. The only disadvantage is the fact that they are a pain in the butt to work in. -- Del Rawlins +++ #12409 From: charles.k.scott@d...> Subject: Re: Digest Number 973 > What is the best way to remove the oil/grease from 4130 prior to > priming? I haven't gotten there yet but I know what I'm going to do. I'll first build the paint booth using either fitted together plastic tubing or wooden 2x2's. Only when the paint booth is ready will I blast the fuselage because I know how quickly the freshly blasted tubing begins rusting if you don't prime it immediately. Then I'll be renting an engine powered compressor/blasting rig, something that can keep up with the demands of constantly sandblasting. That way I won't be standing around waiting for my compressor to catch up. I used one of these rigs before and it definately had the power to stay with me, no waiting. I also bought a touchup paint sprayer to use specifically to paint the tubing. It is small so it can be easily held inside the fuselage and can be adjusted for a narrow cone of spray. Bruce's HVLP that he gave me works fine, but it cannot be adjusted for anything other than a wide fan pattern which allows most of the paint to waft on by the tube. Corky Scott +++ #13147 From: sonny cilley Subject: Re: Digest Number 1031 Hi guys, I have ? about alodineing again. yesterday I finally alodined all my spar plates and web stiffeners for both wings and you can see that the alodine did something but it didn't turn them brown. the process I did was to wash all the parts with dawn dish liquid, use metal prep and then alodine . I rinsed the parts in clean water in between the different applications. I can see that the alodine did something to the aluminum but it just didn't turn brown like I expect. I did wait the aloted time for the brine to work too. I am going to go ahead and put the spars together anyway , but I was just wondering. boy to listen to you guys as to your progress is amazing. Pat F. has run up his engine and is 2 number ahead of me on the plans. Oh well , one piece at a time , and I don't have alot of it to spare. thanks, Sonny # 234 +++ #13154 From: Russ and Penny Erb Subject: RE: Digest Number 1031 Don't worry about it. One of the odd things about the alodining process is that color is NOT a good measure of the effectiveness of the film. Many times I have identically prepped two pieces from the same original stock, ran them through the solutions together (i.e. the same exact time) and they come out different colors. If you look at an airplane assembled from alodined (unprimed) parts, it looks like a patchwork quilt. If you can tell that something occurred, then your parts will be fine. Mine rarely turned a dark color. Most were very light. Russ Erb +++ #13679 From: "egenz" Subject: Zinc Cromate I need a little education about metal prep and finishing. Zinc Chromate has been the standard for years and seems to have stood the test of time. Other than being highly toxic, it seems to be a simple process. How does Alodine and other primers compare to Zinc Cromate? Did anyone use anything other than zinc chromate on the interior of their wing? Eric Genzlinger #595 +++ #13684 From: "rodsmith52" Subject: Re: Zinc Cromate Alodine is not a primer, it is a surface preparation chemical ( the chemical details escape me at the moment). By itself it offers some protection but should be the last step before using a primer on aluminum. Zinc chromate like most traditional primers is porous. I would not hesitate to use it on aluminum although I think there are better products available. When used on steel parts without a topcoat, they will eventually rust unless you live in the desert. My 1977 Maule had a seriously rusted frame by 1989, but it spent its life in humid areas like South Carolina and Alaska. Check out the steel frame of an airplane tied outside on a morning with dew on the grass. There will be drops of water on the frame or at least moisture that you can wipe off with a rag. I believe the epoxy chromate primers are non porous but I would still be tempted to top coat them with a finish coat on steel parts. Russ Erb used the Polyfiber water based primer with good results. I would use that on aluminum but not steel. It's not toxic like zinc chromate or any of the epoxy primers. Rod Smith #246 +++ #13890 From: "Shawn Burns" Subject: Re: Zinc Cromate On a related topic, I have read through Russ's CD info on alodine and priming processes. Does anyone know of a current source for Iridite 14-2 powder and can John Q Public get his hands on it? I don't want to give up any more cash than absolutely neccessary to Aircraft Spruce, Wick's, etc. I have another question- would PVC sheet react with any of the chemicals and/or products of the chromic acid conversion process. I have tenative plans to set up a alodining line in my hangar. I will set up four 8.5 ft X 2.5 inch X 12 inch deep tanks made up of 3/4 plywood and 2X4's, double lined with PVC (so I can get the spars in the tank) end to end with a clothes-line wire overhead extending outside to the drip-drying area. I had originally decided to build the tanks of 12 inch PVC pipe, cpped at both ends and sawed in half but the volume of those tanks was near 50 gallons (lots of $$$ for alodine #1201, $900.00 from Aircraft Spruce). Plus you would need a similar volume of etching/prep solution, along with the 100 gallons of really nasty waste generated to dispose of afterwards. The box tanks have a lower volume and will still allow submersion of the largest parts (spars). I soppose you could make some similar but large and shallow tanks to do the skins, too. The tanks will then be set up in the acid etch-rinse-chromic acid-rinse sequence, each part being dipped for the appropriate time prior to hanging to drip then slid down the line to the next station. This will allow me to dip all of the parts except the skins ( A 2inch diameter, longer tube will be used to alodine the capstrips). The tanks will be set up allow draining into a sealed storage container when not in use. Any comments regarding this proposed setup would be appreciated. +++ #13897 From: bearhwk272@a... Subject: Re: Re: Zinc Cromate Alodine - Chemfilm is available from local suppliers Just have to find a friendly one. When I did my chemfilm I made up just one basin from PVC tube for the frame and the tub from sheet polyethelyne drop cloth. About 12 in wide by .75 deep X 8 feet long. Used a pump from a fish tank to circulate and wash over the parts. Cheap, used little fluid and kept the parts wet which is all you need. Rinse well with clean water. Prior to my etching I washed all parts with a soapy water wash and rubbed with