To any new guys starting out, and to all ARF fanciers likely to purchase a ready built: After 25 years in this hobby, you tend to learn a few things, and the first one I was taught in building technique, is to always, and I repeat always, fiberglass the center section of any wing panel you join. NO EXCEPTIONS AND I DONT CARE WHAT ELSE YOU ARE THINKING OF!!!! No joiner no matter what the material is made out of, will prevent wing fold over during a high "G" maneuver, without a good and proper fiberglass job![X(] If you already own an ARF, and you assembled the wing halves just with epoxy, fiberglass your center section NOW!!!. Put on some Nitrile or latex gloves and apply plenty of 30 minute epoxy for joining the root rib ends and associated joiners, (wipe off any excess with denatured alcohol) check and re-check then fixture the dihedral with end spacer shims and weights, let set. Failure to "set in place" the dihedral during curing can ruin your wing! Remove at least a 3 inch wide strip of original covering in the case of an ARF, top and bottom of the center section, (use a brand new #11 blade and press very very lightly not to cut into the sheeting!!!!!) Now we do the bottom first: Apply a low tack painters type masking tape just at the very end of the recently removed covering, staying on the covering, not the wood, its ok if a little epoxy wicks the end of the covering by maybe 1/16 of an inch. Remember all this fiberglass work will soon be covered again with Iron on! We now are controlling where the extra epoxy will be going! Sparingly brush some well mixed 10-15% thinned out 30 minute epoxy over the newly exposed center section, (use denatured alcohol and an acid brush. Dont over thin the glue! Mix the epoxy first very well before thinning), apply the fiberglass strip (cut it an extra 4 to 6 inches long) onto the thinly applied epoxy and position it centered and parallel to the joined center seam. (Don’t ever try this with medium "CA" as some instructions say to do, its way too brittle after it cures, and the fumes will lock your heart right up!!![:'(] ) Tape the ends of the fiberglass CLOTH STRIP, to the opposite sides of the wing, (the top of the wing where you are not fiberglassing) with regular masking tape, wrapping over towards the top, and pulling it as tightly as possible. (Use a three-inch wide strip of glass on planes weighing over 12 lbs.) Continue to now wet and cover the top of the glass sparingly with the thinned out epoxy, until the white changes to translucent. Push the glue into the weave with the brush, or try your gloved finger tips, as just a little epoxy goes a long way here. Keep the gloves cleaned off with alcohol, so you won’t mess up the rest of your covering. Allow adhesion and purchase, to extend a 1/2-inch onto the end area, past the center line of the leading and trailing edge, onto the opposite side of the wing. When we do the other side, this gives us eventually a one inch over lap, and its strong as steel. You may decide to follow up with another layer while still wet, but cut it an inch wider on both sides. I personally think it's over kill at that point, and adds unwanted weight. Only a big quarter scale or third scale project demands the second layer. Get your fiberglass wing joiner cloth at an automotive body repair supply house, it's usually a heavy grade like 5 to 6 ounce cloth, and a single strip is plenty. If you purchase cloth from your LHS, specify 5 or 6 ounce cloth. Dont bother with finer weaves, they're way too weak. Now here's the big secret to a glass smooth perfect fiberglassed joint: Cover the wet glass with a 6 to 8 inch wide strip of plan protector or even better, some old discarded mono-cote plastic backing. (You can consider taking off the gloves at this point too) Spread and work the glue in and across the joint area, but don't push too hard allowing it to migrate past our low tack masking tape borders. Two separate paper towels to smooth it with in both hands, makes it nicer. Continue to smooth it down for a while, and In about 20 to 25 minutes, try lifting one end in a quick jerk. If its still tacky at this point, rub the plastic back down, and wait 5 more minutes. (It makes a distinctive ripping sound when its ready to remove) When you can shear a corner of the plastic sheet off the epoxy without any stringy adhesion, continue to remove all the smoothing plastic, and after 45 minutes, slowly and at a sharp angle, remove the low tack masking tape. Let set overnight and do the same again for the other side. Do not allow the epoxy to cure completely with the smoothing plastic on top, you might not be able to remove it at that point! Sand off any raised fiberglass before you start the top, and repeat all the steps again. If you do a good job, you will be able to stand on the center section and it will hold a 200 lb. guy without collapsing. (But dont try it though! Duh[sm=bananahead.gif])
"What goes up, will surely come down"
And: "Haste Makes Waste, so fiberglass your wings religiously!
Dave the Rave...
P.S.: Let me know if you liked this method......
HERES ONE OF MY 3 GP LEARJETS I BUILT

just wondering, what high G manuevers are you speaking of

Thanks for taking the time to give us all your instructions for fiberglassing the wing center. I have learned to do that (the hard way). Your explanation of the task is great.

I've NEVER glassed the center of a wing and I've never had one "fold over". I know I've abused my planes and have subjected them to plenty of high "G" manuevers. Please help me understand what I'm doing wrong so I too can experience this dreaded wing fold up that you seem to think I should have experienced by now.

I have had a wing fold up before--during a high speed dive and pull-out. It was on a trainer that was already too heavy due to balancing issues. Anyway, I still don't fiberglass. I know it strenghtens to some degree, but I don't know if it's as strong as everyone says. Afterall, all you're doing is mating the sheeting together. That's (at the most) 1/16 inch balsa? Not a lot of strength there--when compared to the G forces that can be produced. I know, I know, now everyone will chime in and say "ever since I've been fiberglassing my wings, I've never lost one." Well, some have never glassed their wings, and have never lost one. I'm not one of those guys, but I'm not completely sold that fiberglassing would have saved my trainer. Also, I'm not satisified that I wouldn't do more damage cutting the covering off of the wing in order to do the glass work--any scoring at all will weaken the already highly stressed joint.

Again, I'm not advocating that it's a bad thing, I'm just saying that not everyone does it, and not everyone feels as though it is "necessary." Take the advice as it is--one man's opinion.

Not everyone.
So true.

I lost an LT40 a few weeks back in some "wind gust induced" high G maneuvers. All 10 rubber bands snapped and the wing came off. The wing came down in one piece, and is as strong today as the day I epoxied it together, WITHOUT a glassed center section. I'm not saying that glassing the center section is not a good idea, and your explanation of the procedure is outstanding, BUT, to insinuate that anyone who doesnt glass their center sections will undoubtedly have a catastrophic failure is a bit over the top. Out of all the planes I've seen go in for whatever reason, only one of them had the wing fold, and it was on a trainer that was about 10 years old that had been sitting up in a garage unused for several years. Thanks for the great info, and I will probably use it at some point, but dont make it sound like anyone who doesnt do it will surely crash their plane due to structural failure.

lol - this thread is about 48 hours too late for TGViper (who just lost his H9 arrow to an in-flight wing failure!)

I have to admit I don't understand the fascination people seem to have with glassing the wing. Look at it this way. Fiberglass only has strength in it fibers. This means it will only have strength in the direction of the fibers for as long as the fibers are. So any fibers running chord wise are providing no strength to these "high G manuevers". Also The extra strength stops as soon as the fibers stop. Someone suggested putting a 3 inch wide strip on the centre of the wing. Well that helps the first inch and a half of each wing but what about the rest?? The wing is only as strong as its weakest point. My GP bipe's fuse is more than 3 inches wide so the glass would not extend past the fuse edges. I am willing to be that if I stressed the wing to overload it would break outboard of the fuse so in this case glassing the wing would do nothing other than add weight. I don't know about you guys but I have never seen a wing fail right in the centre. All failures I have seen have been from the edge of the fuse outboard. Adding glass to the edge of the fuse would actually be worse because of the load transfer from the glass is focused when the glass stops.
If you feel better glassing your wing go ahead but I would rather save the weight.
P.S I have a GP RV-4 a GP ultimate bipe a seagull Edge 540 and a UCD 3D. None of which are glassed and I abuse all of them.

I have only seen 2 wing failure incidents in a modern (since ~1990) ARF & they were both VMAR models -- the wings failed at the mid-point not at the root. While I certainly don't discourage anyone from glassing wings, based upon my own experience I'm not convinced of its necessity, as long as the model is constructed or assembled correctly in the first place.

I have a couple of 10-yr old Superstars that have been brutally mistreated all of their lives. Both were simply put together as the manufacturer recommend, but they were both powered by TT .46 Pros & both had their necks wrung as hard as possible -- snap rolls following hard pull-outs from terminal velocity dives. They have subsequently been modified extensively, including conversion to no-dihedral wings using hardwood joiners, without glassing. The engines have been hopped up & they both exceed 75 mph in level flight (still with full-span wings). The high-G abuse was greatly intensified following the mods & not a hint of wing failure.

I think that some models probably do need extra strengthening, but certainly not all. I also think that good work practice in construction & assembly is essential -- but that should always be the case.

I don't glass my wings & I haven't had a wing failure since the early 1960's (it took me a quite a few years to finally admit that lightness is a virtue, but strength is a necessity).

I had 1 wing come apart on a Cessna 182. My son was flyin it at the time and he wan't even doing anything radical. He just completed a slow loop and then we watched the wing come apart leaving the fuselage screaming for the ground whle the 2 wing halves were slowly looping to the gound. The plane was given to me. The entire plane was one color, white. My wide added some colors to make it easier to see. It was kind of bashed up and the control rods weren't even working properly. The fuselage was made of foam sides and the wings were made of foam. I don't know if the wing halves wern't glued together properly or if foam wings are just weaker. Any way it was a fast plane and fun while it lasted.

Whether or not a wing absolutely needs to be glassed depends upon the structure. In a properly-designed wing, plywood joiners will do as good a job supporting the wing as will a glassed joint. Some models, such as many Joe Bridi designs had no plywood center joiner, but used wide fiberglass tape that was epoxied down. That's how they were designed, and it was an easy job to join the wing panels.

I've had large models with foam wings that had spars added and heavy plywood across the center section.

Whether glass or wood, a properly-designed and properly-constructed model will not come apart when it's flown within its intended flight envelope.

If you feel more secure by glassing a wing that has a plywood joiner, then do so. Your confidence in your model goes a long way towards having fun with it.

As has been mentioned, a properly glued toghether wing is very strong. If the interal structure of the wing is not glued well, then all the epoxy and fiberglass in the world over the center joint is going to do no good.

I have only built two kits as I am more of the ARF type, but one thing I did when building these 2 kits (SSE's, both of them) was to add carbon fiber tape to the top and bottom of both spars in both wings. After the wings were built and before they were covered you could not twist or bend them. Fold, spindle and otherwise mutilate would probably have been a different story.

The only ARF I ever glassed was a 4*40 and only because of some of the stories I was hearing about wing centers on planes on high stress manuvers were snapping. I now know that this was not really needed. I now have a 4*60 that has not been glassed and I fling this thing around as hard as I did the 40 size and probably harder as this plane is my "grab and beat the heck out of" plane. I have several other more aerobatic and 3D capable planes and I do not through them around as bad a I do the 4*.

As an example, a high speed snap roll on a Funtana90 may very well rip the plane apart, I do them on the 4* and that is with an OS91FS turning a 15X6 prop so it's not that slow.

As a matter of fact, go over to the Funtana90 thread and you will find that the early models had wing problems and they were blowing apart in the air at slow to moderator speeds flying straight and level. Now some of the was due to flutter but there were issues. Mine had right wing ribs broken right out of the box. I am sure this would have lead to the planes destruction if I would not have checked.

I find glassing is particularly useful if there is very little structurally holding two wings together. I am refering to to flat rib pieces and a small plywood joiner. There is not a lot of interconnection between the two halves and if a small piece of the structure at this weak point in the assembly fails then there is not a lot of backup holding them together. if the two halves are built together or have long plywood joiners that connect tightly to the spars then glassing is not as necessary in my opinion. Wing halves should always be expoxied together with 30 minute epoxy unlike some instructions that say slide wings together and secure with a strap and screws. I have seen a few of those screws come out and wings separate. Another good use for glassing a wing is that if the wing is mounted by rubber bands the glassing keeps the bands from digging into the wood. On bolt on wings I always glass a small area around where the bolt holes or drilled through to give the wind more ability to resist the bolt being torn through. I know the wing bolt holes don't normally see a lot of stress but the stress sure mounts up when the wing decides to shear the bolts by saying hello to the ground. This has allowed me to be flying the same day on a slightly bad landing or cornstalk engine out landings.

"slow to moderator speeds", bubbagates??

I've owned/built somewhere in the vicinity of 30 to 40 planes in the past nine years, the majority ARF's, but many built from kits. Not one of them had the center of the wing glassed, and I've NEVER had a wing failure. I've been known to abuse them every once in a while too.

And this has included ARF's where there was only a simply dihedral brace, and the root ribs were epoxied together. No additional bracing to the spars, no carbon fiber, simply built per the instructions.

Maybe that's the key?
Dennis-

Why, that's TTTOOO slow for me

The only glassed wing I have is from a Sig Kougar. I can see it adding strength. One of the problems however is if you do the top part of the wing and then the bottom, and the plane is a top mounted wing like on an Ultra Stick, and you trim the covering to do the job, how are you gonna re-cover the part that will show in that the re-cover job looks good without any humps from the cured fiberglas? You can sand but once you get to a point, you've sanded away all the strength that you wanted in the first place.
When I join wing halves together, I epoxy all the spars and the whole length of the root. Only had one wing come apart on a Cessna Skylane but it was due from a crash.

Dave...

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....

I glass all my wing joints in a much simpler fashion. I just cut the covering back and inch on both sides the length of the seam. Brush on some epoxy, then a strip of cloth, smooth it all down and get rid of the excess and thats the end of it. Have not had one fold on me.

Dave, that missive was a considerable effort on your part (at least it would be for me) -- thanks from all for the very usefull tips.

Some wings , like a Stafford kit, use a stressed skin design. There is no internal hardwood structure. The strength of the wing is from the skin in tension on the bottom and in compression on the top. To insure continuity the center must be glassed.

Some wings, like the Goldberg Chipmunk for example, are built like a Loiusville Slugger, lots of hardwood and a reinforced center section. Glassing adds very little strength because the wing skin is not being used to carry the load.

ARF's are another animal. The kit must be designed to fit in a box for shipping. The builder usually slides in a plywood brace and glues the wing halves together. Lord only knows what is in that wing. Are you gluing plywood to plywood or are you gluing plywood to balsa ? The ARF may indeed be designed as a stressed skin wing. When in doubt, glassing certainly can't hurt. And if there is a foam core, then you know it is a stressed skin design and must be glassed.

Glassing the center can't hurt. It may or may not be necessary.