Fiberglassing foam wing - RC Groups
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Feb 13, 2011, 10:16 AM
Registered User

Fiberglassing foam wing

I have a 10 x 80 inch foam wing cut from 1.5 # white foam that I would like to cover with glass cloth. It is for a trainer type plane, so no extreme loads. I am using a carbon tube wing joiner. I wasn't planning on any type of spar, just using the glass covering for strength.
So my question is what weight cloth?
I don't have the equipment for vacuum bagging, so just was planning on hand laying the cloth.
Any help would be appreciated.
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Feb 13, 2011, 12:02 PM
I would sheet the wing with 1/16" balsa then use 3/4oz cloth. Plain glassed foam is not very ding proof and the sheeting with the glass will be a lot stronger than just the glass for not much more weight. I would think a plane with an 80" wing would not notice the extra weight from the sheeting. With no spar I think you will need the extra strength.
Feb 13, 2011, 02:04 PM
Red Merle ALES VI
Curtis Suter's Avatar
fiberglassing the foam without vacuum bagging will not give very good results.

the balsa suggestion is very good and can easily be applied with heavy weights.

ae you aware of the instructional DVD's at

Feb 13, 2011, 04:01 PM
Registered User
Thanks for the suggestion. I guess I could vacuum bag the wings, I do have a HVAC vacuum pump that probally would work. So if i bagged them using mylars, I am guessing you wouldn't need the balsa sheeting. What cloth would you use then.?
I have balsa sheeted wings then glassed with 3/4 oz. I was just trying so find an easier method with a decent finish.
Feb 14, 2011, 03:52 PM
B for Bruce
BMatthews's Avatar
You'd use a set of layers to get the best strength combined with minimum weight.

I did up this sketch to show how I did some foam control line combat foam wings covered in newsprint to provide the finish and strength. You'd want to use much the same sort of idea for glassing. And what I show isn't far off what I've seen on some vac bag website "howto's".

The big problem is that the epoxy you need to use as the resin isn't cheap and it isn't light. The vac bag process aids in reducing the amount of resin used and provides a much better finish. A "poor man's vac bag" process could be done using the mylar sheets a layer of soft foam rubber and a few hundred lbs of magazines or news papers. For this method you lay up the cloth on the mylar covers then apply the wet mylars to the wing and use the foam and magazines or newspapers to apply lots of pressure. The sandwhich for this layup would be the lower bed or a flat table depending on the airfoil shape. A layer of 1/2 inch soft foam rubber, the lower mylar with wet glass and epoxy, the core, the upper mylar layup, another layer of 1/2 inch foam rubber then about a hundred pounds of newspapers or magazines laid over top to weight the layups for a closer bond to the core. The mylars should be longer and wider than the wing to guide any squeezeout resin away.

For the layup you need to get some laminating epoxy resin and not the regular glue type. Brands such as West and others are much thinner and better for this than the regular glue style epoxies. For the layup I'd suggest a layer of 4 oz cloth overall with long spar diamonds of 4 oz cloth. I'd use two such diamonds in staggered sizes as shown on both top and bottom in addtion to the overall top layer. And don't forget some reinforcements at the leading and trailing edges at the center if you're using wing screws or rubber bands. A leading or trailing edge wrap around patch would need to be applied before the bottom and top layers.

Another option would be to do what I did and use newsprint. Back then I used thinned PVA glue as the adhesive. But these days I'd use water based polyurethane thinned with some additional water to aid in soaking into the paper better. With the newsprint method I'd suggest using more layers such as I show instead of just two layers and a top layer as you would with the fiberglass. The sort of layup using glue and newsprint proved itself to be extremely durable. Combat is not a style of flying that is easy on the model. My newspaper foamies powered by .15 glow engines survived quite a few full power "ground events". All three of them met their ends due to mid air collisions of some form. One in particular was a full on "bellcranker" and the pieces of the other guy's model were smaller and more numerous than my Newspaper Special...

A few tricks if you opt for the newspaper composite method, otherwise known as papier mache Once you start do all the work in one session. And use a water mister if you have to in order to keep the entire workup wet. There will be a fair degree of shrink in the paper as it dries and you don't want one side drying while working on the other. So keep it misted if needed to maintain a wet layup from beginning to end. For the same shrinking reasons you want the wing to dry evenly on both sides. So rack it up where it can get a good airflow to both sides evenly. And it wouldn't hurt to rotate it to various attitudes for that first couple of hours. Due to the thickness of the layup in the multiple layer areas it may take a few days to fully dry before you apply any top coating paint. So be patient. I found that all I needed for a tough easily handled wing was a single layer over all the spar layup and a bit of an over wrap where the leading and trailing edges met. Despite the many "ground events" I don't recall much, if any, leading edge dings. And the single layer over the light white foam stood up well to handling. I'd likely still be using this method for quick and dirty model building if I liked using foam. But frankly I hate the stuff so I haven't had the opportunity to use the method since those long ago combat days. If you try it out let me know how well it works for you. If you want to try out this newsprint idea and are doubtful about how many layers and how big to make it for the spars and such then post up the wing span, chord and %thickness and I'll do up a quicky sketch for what I'd recomend.
Feb 14, 2011, 04:31 PM
Registered User
we'll I have a couple gallons of laminating resin and various weights of cloth already and it appears the bagging supplies are reasonably priced, so I just might try bagging the wings. Just haven't tried it yet. I guest some testing is instore for a attempt the good cores.

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