Original Posted By: "dgaldrich"
Hello Axel,Wow, thank for the kind words. We've met you a few times over the years, and Iam very glad you will be there again this year, in one piece (give or take a fewpins) . Hope your new project is coming along!Regards,Steve--------Stevewww.mypiet.comRead this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Glue and Varnish Test
Original Posted By: "John Francis"
Several days ago, I revealed that I had "dunked" my ribs in varnish. Someone pointedout that the varnish might pose a problem with future glue. In order todetermine whether I'd have to sand all the nose portions of the ribs, I didan experiment, or rather two.I had some turtle deck stringers that were varnished and almost 1/4 inch thick-- .220-.245 inch -- that were laying around so I ripped them into 1/2 inch pseudocap strips and glued 6 inches of them to a piece of 1/4 okoume plywood. That length was chosen to approximate the amount of rib that would be glued tothe plywood leading edge. Since I had some mixed up, I used West System epoxyas well as T-88. Glued 3 each for a total of 6. Also had some douglas firthat was approximately .285 thick so I ripped some of that into 1/2 inch stripsand also glued them to the same piece of 1/4. After the glue had cured for24 hours, I marked the sticks at 6 inches out from the plywood, put the plywoodin a vice and hung a water bucket at the 6 inch mark.I chose this particular test, rather than a tension or compression arrangementwith the thought that the primary strain on the glue joint would be a side loadon the nose part of the rib where it's nominally glued to the leading edge plywood.After hanging the water bucket on the cap strip, I added water to it until thewood or joint failed and then weighed the bucket on a bathroom scale. Did itfor the twelve samples and the results are pictured below. ALL of the test piecesfailed in the same manner. They all broke at the "hinge" point where thecap strip met the plywood. NONE of the glue joints failed.Conclusion: Since this was more of a qualitative experiment than a serious quantitativeone, the primary one that I reached is that a T-88/West System gluejoint with varnished wood is strong enough for the intended purpose and I don'thave to sand off my ribs.Observations: The Douglas fir pieces were approximately 25 percent thicker thanthe Sitka and yet failed at an average of 70 percent higher load. This lendscredence to the AC 43-13 note that Douglas is stronger and those that use itcould probably use slightly thinner longerons and diagonals in the fuselage.Notes: This test was for ONE failure mode and the data samples were not tightlygrouped so the quantitative reliability is not very accurate and any calculationsshould be based on much more rigorous testing. Since the glue joints didnot fail, this is confirmation that West System is suitable for at least thissort of application.Pictures: Glue 1 is the board before testing. Glue 2 is the varnished piecesafter failure. Glue 3 is the Douglas fir pieces after failure. The numbers arethe weights at failure.Read this topic online here:http://forums.matronics.com/viewtopic.p ... ttachments: http://forums.matronics.com//files/glue ... ___Subject: Pietenpol-List: Re: Glue and Varnish Test
Original Posted By: "biplan53"
I believe it would be a mistake to proceed with your project based on these results.My understanding is that although a strong bond may appear to have beenmade, the epoxy has adhered to the varnish and not the wood. Varnish will eventuallybreak down as the moisture content of your wood changes seasonally andthe wood expands and contracts because of it. Time will weaken the joint. Have you checked with the manufacturer about these tests? John--------John FrancisRead this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Re: Glue and Varnish Test
Original Posted By: "tools"
I just read in the Bible(Tony's books) not to get ahead of game and varnish anythingto be glued later. I am not trying to be a rain cloud but I trust someonewho has been there and done that.--------Building steel fuselage aircamper.Read this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Re: Glue and Varnish Test
Original Posted By: "dgaldrich"
What needs to be glued to the ribs after you have varnished them? The leadingedge sheeting or the leading edge itself?I can't see any reason why you would have a problem. I'd sand any portion of therib that needs glued for some key, and then wouldn't worry about it.My dad dipped all his ribs just like you did on his Hatz, no problems. It's asimilar wing.Read this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Re: Glue and Varnish Test
Original Posted By: "tools"
I forgot to mention that the varnish on the wood was 12 years old and was takenfrom a previously flying airplane. With a great deal of difficulty, I priedoff the pieces that remained on the plywood. None exhibited the failure modeyou're describing. I've redone some 90 year old varnished furniture (I grantyou not SPAR varnish) that was not giving up without a serious fight. The pointis properly applied varnish of most any kind is a b++++ to get off.I think for use on the leading edge plywood, this is not an unreasonable test.This ends up being a low stress joint in any event due to: 1) the fact that allthe ribs will be held parallel by a combination of the drag/antidrag wiresand the fabric rib lacing and 2) there is very little, if any, "side load" fromaerodynamic forces.As a reference to the amount of stress on leading edge fairing, take a look atAeronca Chiefs and Champs. Their leading edges are .016 or .020 aluminum heldon by a relatively small number of short wood screws.Please note that I am NOT recommending using varnish under glue for anything structural.What I am suggesting is that the dunking technique DOES insure thatthe entire rib, even the nooks and crannies behind the gussets, is varnishedand protected from moisture. The "conventional wisdom" that you can't or shouldn'tuse glue on varnished surfaces may NOT apply to this specific kind of stresswith these specific epoxies. That's what experimentation is for and why I offered this data.DaveRead this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Re: Glue and Varnish Test
Original Posted By: John Woods
I agree with you. Epoxy is recommended to glue all sorts of non porous thingstogether, don't know why wood with the grain sealed would be any different. Keyis the key, needs to be sanded some is all.I've never seen varnish release due to seasonal movement. I do believe some veryold varnishes eventually oxidize to the point they flake off, just like thepaint on old machines. Varnish being spar or not shouldn't have anything to do with it's ability to holdeither, spar varnish means that it's got UV inhibitors is all. I like the idea of dipping the ribs because of the difficulty of ensuring you'vepainted all the surfaces. It's EASY to miss places.Read this topic online here:http://forums.matronics.com/viewtopic.p ... ______Date: Wed, 27 Mar 2013 12:08:28 +0800 (WST)
Original Posted By: "Jim and Grace Malley"
I Like the dipping idea too. But if the desire tohave bare wood for gluing is there then simplycover those areas with a bit of masking tape.Remove that after taking the rib from the tank.Spar varnish is more than UVinhibitors. That'sa modern idea. Traditionaly this varnish wasformulated to be highly reflective. You brushedit on and left it bright. Until it dulled and beganto lose the shine, it deflected the rays away.ClifLife is uncertain. Eat dessert first I do believe some very old varnishes eventually oxidize to the point they flake off, just like the paint on old machines.>> Varnish being spar or not shouldn't have anything to do with it's ability > to hold either, spar varnish means that it's got UV inhibitors is all.>> I like the idea of dipping the ribs because of the difficulty of ensuring > you've painted all the surfaces. It's EASY to miss places.________________________________________________________________________________
Original Posted By: Clif Dawson
No apologies. I remembered that you were going to your parents and would be busy. Hope the trip wasn't too bad.Yes, let's talk at Easter. Give your family my love. Hope things slow down a bit so you get some rest.Grace-----Original Message-----
. Hope your new project is coming along!Regards,Steve--------Stevewww.mypiet.comRead this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: Glue and Varnish Test