We previously had a discussion about epoxy types and where/how to use them. I found most of my older epoxies (including an ancient set of HobbyPoxy Formula II that is at least 45 year old) were over the the hill, so when I needed a slow-set version - that is, slower than 5-minute but faster than the various laminating epoxies - I got some Devcon "2-Ton" 30-minute epoxy, which I had lots of good luck with back in the good old days before I found all these modeling types.

    Swell, I mix it up in a cup, pour it into a syringe, start putting on the ribs of my Nobler wing, did it many times before. Before I get to the end of the first panel, I notice it getting stringy, by the end it was still flowing but clearly clotting up on me. I started moving faster, got it applied, then went to get a bit more for the center section - and the stuff left in the cup had boiled, hot as hades, and was 90% set up.

    I never had this issue before with this epoxy, I used to use it to sheet foam wings. It had no problem with pot life at room temperature. Now, it's way faster and self-heats at a prodigious rate. Now that I know what it will do, I can use the old "pour it out on foil" scheme to keep it cool, but still, you might get caught out if you are not expecting it.

     Brett

Brett,
Good information to know, I like the spread it out on the foil tip. I have used the LHS brand (I think it is Bob Smith that they product for LHS label?) 30 min epoxy and 20 min finshing resin. The 30 min takes several hours to cure the finishing resin only a couple. Their 15 min epoxy is brittle, I don't use this. I have not found anything like the old hobby epoxy 2hr stuff in small quantities.

Best,   DennisT

   EZ-Lam 30-minute is better for almost anything I would have used Hobbypoxy Formula 2, and has much more pot life since the self-heating it negligible. The reason I did not use this instead of the Devcon was that the "30 minutes" is a very conservative pot life, at the temperatures I am going to have, the solid cure is more like 36 hours.

     I would have (and did) use the supposedly same Devcon 30-minute instead of Hobbypoxy Formula II for putting the LE sheeting on my Noblers. It's just that this batch is much faster than the older batches of supposedly the same thing.

    As a meta-comment, I suppose everyone knows not to follow Aldrich's directions from the plans to build the wing "in the air", leaving the glue off the spar, until you are almost done, then twisting it straight and gluing it to the ribs and sheeting. The idea was to not let the glue holding the ribs to the spars shrink and pull in a twist, but you also can't sand it properly for the ribs to fit - and some of them are die-cut slightly oversize. I forget which ones, I knew back in the day.

   When I was building them on a semi-production line back in the 70's, I had a saddle jig that held each rib. That is long gone, but I did have some cores I cut for it back in the early 80s, so I used the cradles as a jig, and the core as a mold for the LE sheeting. Gluing the sheeting on more-or-less determines the shape you will have, straight or crooked, and after you do that, it is extremely stiff and nearly impossible to straighten out without cutting something. So you have to hold it straight when applying the sheeting. And don't use Ambroid, that guarantees a "starved horse" effect.

     Brett

p.s. I would also point out that I am building this more-or-less straight from the kit - actually, parts from at least 4 different kits, including a fin/rudder from my last build effort in 1979. I picked out the best individual sheets of die-cut parts from the kits I had, but have subbed most of the sheeting from some that I won in a contest that Walt Ghio ran, giving out good balsa as a prize.  I am also amazed that I used to be able to throw one of these things together in less than a week. My standards may not have been as high, then, perhaps.

.You sure you got the mixture correct.  I know I used to cut the amount of activator when I would need more time.  Even then it was still a 24 hour for full cure.  But really I settled on Elmers White glue for sheeting as some areas seemed not to adhere were put down with heat on balsa no thicker than 1/16 inch thick..Also worked on cap strips.

  Good idea, Doc,  I have used the heat-activated PVA for other things. But I wanted something that would give me enough working time to apply it, and then enough time to "creep" until is set up hard, to make sure that it took the shape of the cradles - just like a foam wing.

   I would add that I have built about 10-15 of these wings and most of them were with pins and Ambroid, and always had a problem with glue shrinking and "starved horse" and warps a few days after I finished. And the bonds were far from solid since the glue was practically dry at one end by the time I got to the other end. So this time I am dedicated to use only low-shrink materials and to build in minimum stress.

     Of course, this is partially because I want to fly classic the way I used to fly when I started, but also - because I am working up to doing my first built-up wing on a regular airplane in about 40 years, all my serious airplanes have been sheeted foam.

     Brett

Epoxy for ribs? I just used Hot Stuff and then a dab of Tight Bond.  The rib would fail in a crash but never the joint.  Besides, epoxy is kinda heavy.

   It's not about strength, it's about working time - which in this case was a bit shorter than I expected.

     This idea in this case is that the leading edge sheeting and D-tube, once glued solid, set the shape of the wing. To avoid setting up with a warp, in this case, it's a blind joint, because I am using foam wing cradles to hold it straight until the glue sets. So I need something without "grab", so Hot Stuff or Titebond isn't a good choice. That leaves Ambroid and epoxy. Ambroid is out because is shrinks tremendously, causing warps and "starved horse" effects later. So, epoxy.

    Scoff if you want, but the result is *straight as a die", as good as any sheeted foam I have done, on a wing design  that is notoriously prone to warps that are difficult to remove. The whole thing, with the controls, hardware and flaps, is about 6.5 ounces.

     Brett

I am awed by the number of 1x2x3 blocks, Brett. There are only 3 pairs in my tool box. Some have cutter notches/dings, but that doesn't hurt anything.  Steve

   These are Hecho En Chine, not Starrett. Cheap but very useful, hardened, and as far as I can measure, about 1000x as accurate as needed for model airplane purposes. I think I got 10 of them for $84.

       Brett