To all those who have responded to my "PLEASE FIBERGLASS YOUR CENTER SECTION!" post: Firstly, I appreciate you guys writing back....
I'll be the first builder to agree that, many successful models have lasted years and years without a fiberglassed center section, and while these planes were sometimes also put through the ringer during abrupt aerobatics, the best and time tested wing construction, can fail without warning... I've seen it happen many times, and in every case, where the CENTER JOINT OF THE WING failed, it was discovered there was no glassing done. Age, sympathetic vibrations from the engine, woods drying out, fuel and oil creep, hard landings, abrupt high "G"maneuvers, will eventually cause a failure of something. High wing designs, are most susceptible to this failure it seems. I fly at the East Coasts most supreme flying field, "FLOYD BENNETT FIELD" On a good Sunday we have about sixty or more guys flying their brains out, and I've seen it all, over the last 25 years or so....
Mid wing panel failures are a completely different type of defect, and usually mean two things upon careful examination of the wreckage:[] Cheap grade quality balsa sheeting, (BUY BETTER GRADE FOR YOUR MODEL, SOME KITS COME WITH POOR QUALITY SHEETING) or failure to obtain purchase and adhesion, to the ribs and spars during the sheeting process. If you want to TRY and ELIMINATE a possible MID WING FAILURE during building, Add the sheeting as usual with medium "CA", remember to have your little fan running so you don't die from the fumes. Please allow all the CA to harden first. [:'(] Then, run a fine bead of an aliphatic type glue, (white wood glue) on at least one side of the sheeting from the inside, against any adjoining structures that will hold it on better. Rib top sides, spar edges, leading and trailing edge joints, etc. It adds very little weight if your not the sloppy type, and adds considerable more strength, and helps stop warping later on. It will be necessary to jig up the wing panel half, as you need at this point to start to develop your wash out. Sheet one side at a time, and give the white glue plenty of time to cure. Once the glue cures, any warps will be almost impossible to correct! You might be wondering how to do this to the other side of the sheeting as it might be somewhat un-accessable when the second side sheeting is now in place. Well, you cant sometimes, especially if the wing has "Full Center Sheeting" (If your wing design doesn't include shear webs, you can work the reinforcement glue in through the upper and lower spars towards the leading edge) But once one side is done, again first with the "CA", then the white glue gussets, just get your self a lot of the small qauge T-Pins, and do the second side with slow epoxy or the white glue. Building everything with "CA" is expensive, very unhealthy if your huffing the fumes, and most importantly, the medium 'CA's" dont penetrate as well as aliphatics or epoxies do. The rule of thumb with adhesives are: the slower the cure, the stronger the bond! Slightly moistening an adjoining surface also helps speed up the set with "CA's", use the water sparingly, and see how much faster the work grabs when one side is slightly dampened! Oh, has anyone tried Gorilla Glue? I think its just jim dandy... It foams a bit during its cure, but man does it stick....Try it....
As far as sheeted foam wings go: if you have the original foam saddle (The negative side of the foam core from which the wing was electrically cut from) and have a good assortment of heavy weights, and you are not glassing the top of the sheeting in preparation for paint, (this will add too much weight eventually), Instead of using the old water based contact cement trick to apply the sheeting, use 2 hour epoxy. This method will give you an indestructible wing, with just a little extra weight. Epoxy the skins on, and that wing will never fail. Use a very thin coat straight up, "NO THINNING". A squeegee works well to spread the mix... Put the the whole set up on a super flat work bench and put some 1/4 ply on the top of the foam saddle, about sixty pounds of weight all around should start to squeeze out any extra glue, and let cure for 24 hours. If all goes well, you can use that wing as a diving board after wards![sm=lol.gif] Please note to observe "Wash Out" instructions that comes with your kit. Again, doing the glass work to secure the center section, is very cheap insurance against panel separation, keeping safety in mind as always. Do the little extra work, its well worth it. Remember: Loosing complete control of your hastily assembled model, equals money in the trash, not to mention you might god-forbid, "KNOCK SOMEONES BLOCK OFF!"!!!!! []
DAVE.....
Heres both my Lears at a static show....Won third place for the "Rainbow Lear....