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Fiberglass cloth

wirejock

Well Known Member
I epoxied 1/4" dowels in the wingtips for some added structure. It really helped.
Now I want to add a layer of glass over the dowel. The problem is the cloth won't conform. It just lifts off. I removed it and cleaned up the epoxy.
What cloth will stick? I tried the standard 8oz and bidirectional. Both are thick and won't stay put.
AS sells a really light cloth. I'm thinking it might stick better.
Thoughts or recommendations appreciated.
 
Are the wingtips made with epoxy or polyester??

Are you laying the bid at a 45* to the long axis of the dowel?

Are you doing a micro or flox fillet to smooth out the "ramp" up to the dowel?
 
Fiberglass

Are the wingtips made with epoxy or polyester??

Are you laying the bid at a 45* to the long axis of the dowel?

Are you doing a micro or flox fillet to smooth out the "ramp" up to the dowel?

Vans wing tips. I assume they are epoxy. Dunno.

I tried both. The cloth doesn't stay in place.

I could but flox is so brittle. I hesitate to use it for this.
 
You may end up having to vacuum bag the glass over the dowel. There's a limit to how tight even a very light cloth will conform to sharp curves or tight radius (radii?).
 
US composites in Florida has a ton or options for lightweight cloth. And vacuum bagging supplies. But something you could try first is sticking down a lightweight cloth dry with aerosol hairspray. Then brush on epoxy after. Epoxy will stick to either epoxy or poly, so it’s a good choice if you do t know what the wing tips are made from
 
Epoxy sticks to polyester but poly won’t stick to epoxy.

Radius. Light cloth bi-directional. You can use air cell to make lightweight but strong fillets.
 
I’ve never experienced a brittle nature with epoxy/flox, but my mixtures may have been a little bit “wetter” than yours. I know wetter means heavier, but you are dealing with a small fillet around a dowel to make the cloth transition easier. You could also try glass fibers. They may be a little stronger. Any time I’ve used flox (cotton) with epoxy, after it cures and you need to sand it, it’s like sanding concrete - I’m talking concrete with stones in it. If you don’t have any chopped glass, you can make your own, using a pizza cutter along the edges of any fiberglass cloth. Mix it up to a fairly dry consistency, like peanut butter (Jiff Creamy), and smother that dowel. You probably won’t need any glass cloth overlay. If you do, make sure you wet out the BID cloth first, then use peel ply (Dacron) to soak up the excess.
 
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Solution

I think I have a plan. Paint with neat epoxy. Mix up some flox or glass fibers and fill the tight area between the flat and dowel. Call it good. For some reason, I thought it had to have a layer of glass.
Thanks for all the tips.
 
Best laid plans and all, why not take a strip of pink rigid insulation and cut with a table saw in the cross section shape of a triangle. Sand the peak to round a little then stick it to the interior with a little micro mix, then overlay with some 2oz cloth? Practice on something else to ensure proper draping. It would be lighter and quite stiff, depending on the cross section.
 
Dowel

Best laid plans and all, why not take a strip of pink rigid insulation and cut with a table saw in the cross section shape of a triangle. Sand the peak to round a little then stick it to the interior with a little micro mix, then overlay with some 2oz cloth? Practice on something else to ensure proper draping. It would be lighter and quite stiff, depending on the cross section.

Yes. Best laid plans. Actually, dowels are light and really stiff after the epoxy set.
My mentor provided a neat idea. Roll the dowel in wet glass. Let it cure then epoxy in place. Best of both worlds and no need for any glass over the top.
 
Another method. Lay up the glass draped over the dowel on your bench, between a couple sheets of poly, than tuck it tight & weighed down with a couple pieces of wood. After it cures, you have dowels with flanges that you can easily attach to the skins with a flox slurry.
 
Use micro or flox to transition the edges, force the glass to conform to the shape as best you can then quickly place a sheet of Glad Wrap (I think you call it Saran Wrap in the USA) over the laid up fibreglass and “stipple” it down over the dowel with a dry brush/push down with fingers etc forcing any trapped air out to the edges then let it fully cure. This helps by preventing air getting back under the lay up if it tries to lift up. Provided the plastic wrap has not got folded into the top of the lay up it should peel off when cured.

For these type of lay ups I have always used Rutan Bi Directional cloth from Aircraft Spruce laid up at 45 degrees with good results although thinner cloth may conform better??

Fin. 9A, VariEze.
Australia.
 
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Larry,

A couple of questions:

1) Did you make a fillet for a smooth transition from the dowel to the wing tip?
2) Is the cloth "lifting" due to stiffness (memory)?
3) How wide is the strip of cloth you are using?

A) I used micro to make a transition/fillet from the dowel to the wingtip. My thought was that I wanted a "U" shape if it were viewed as a cross section. Without the fillet the cross section would be more like the Greek letter Omega. (wow, how dorky was that example?!!) I thought of the dowel as just a form to make this happen. The fillet kept the cloth from necking down at the point where the dowel attaches to the wingtip.

B) Yes, the cloth may/will try and lift due to memory. I found that making sure that I had a wide enough strip of cloth to get a good grip on the wingtip made it so that I could use the chip brush to fill the cloth at the fillet and "poke" the cloth into the fillet and make it adhere. The wetted cloth conforms better than the dry cloth.

C) I believe my strips were approximately 1 3/4" wide over a 1/4" dowel.

One other suggestion from my R/C days. Cyanoacrylate sticks to the cloth extremely well. You could use a single drop of medium thickness to hold the cloth in place while you work the epoxy into the cloth. The cyano acts as a clamp or "pin" and the epoxy will harden very well over it. I'd try a drop on the very top of the dowel to hold the cloth in place and use the chip brush to push the epoxy into the cloth and "tuck it in" to the fillet.



Hope that helps!

Fred
 
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Wondering what structural problem you are trying to solve in the first place - and how a round dowel is the lightest/best solution? Are you using the dowl as a tension, compression, shear, or beam element?

As long as you are fighting with fiberglass anyway, seems like a simple wet layup (make your own prepreg) "L" flange would be easier and lighter
 
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As long as you are fighting with fiberglass anyway, seems like a simple wet layup (make your own prepreg) "L" flange would be easier and lighter

Yes, even simpler, the "L" flange. Good suggestion for that type solution.

But I still favor the false rib pink/blue rigid foam insulation solution, it's worked successfully on many a wingtip for me.
 
Dowel

Ok. It's done. For those who come after, I will keep answering.

Larry,

A couple of questions: answers in line

1) Did you make a fillet for a smooth transition from the dowel to the wing tip? Not at first. That's why the fabric wouldn't stay. Fillet done.

2) Is the cloth "lifting" due to stiffness (memory)? Yes

3) How wide is the strip of cloth you are using? 2" but not using it now. No fabric over the dowels.
... <snip>
Fred

Wondering what structural problem you are trying to solve in the first place - and how a round dowel is the lightest/best solution? Are you using the dowl as a tension, compression, shear, or beam element?

No structural problem. The wingtips are so big, the open area has a lot of flex. Just trying to stiffen a little. I read a ton of logs and most used 1/4" dowels epoxied to the wingtip skin inside. Probably not the right method, but it's done and the surface is much stronger.
I have no idea if it's tension, compression, etc. Guess I should have called Vans first but Inread quite a few builders did the same so...

...<snip>
 
It appears to be to improve the local bending stiffness of the wingtip. Essentially these are stiffeners like most of our RVs have in the tail, using aluminum.

An alternative would be to use some 1/4" or thicker foam core and laminate a face ply layer on top of that. 1" or 2" wide strips might suffice, and you could significantly improve the stiffness by adding some unidirectional to the face layer. The uni would of course be oriented fore-aft.

Dave
 
Stiffeners

It appears to be to improve the local bending stiffness of the wingtip. Essentially these are stiffeners like most of our RVs have in the tail, using aluminum.

An alternative would be to use some 1/4" or thicker foam core and laminate a face ply layer on top of that. 1" or 2" wide strips might suffice, and you could significantly improve the stiffness by adding some unidirectional to the face layer. The uni would of course be oriented fore-aft.

Dave

That's exactly what they are. Imagine pressing on the top of an old car hood. It flexes and pops. Maybe it pops back out. Maybe not. Depends on how Murphy feels at the time. Probably wouldn't do it in flight, but it sure is soft. Feels like a big plate of jello! Just trying to add some structure so it doesn't go in and stay there.
 
I am at this point in my RV-7 project. I also feel that my wingtips as delivered had far too much flex in the fiberglass surface to be able to withstand any inadvertent pressure over the service life of the airplane, without risking damage. This may not be the case with all, but it certainly is with mine.

Thanks to all on VAF who have identified ways to stiffen them. Your suggestions have been helpful to me. They all offer a good solution in my opinion.

In my own case I applied a sandwich layer of 2mm Lantor Soric XL honeycomb core fabric under a single layer of 7781 8.9 oz fiberglass cloth to the underside of the weak areas, which was suggested in another VAF thread. I found that it solved the issue to my satisfaction. At approximately 0.5oz/sq ft, Soric fabric added stiffness without weight, although certainly the resin and single layer of fiberglass cloth added up.

Here is a photo.

DSCN0082.JPG
 

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No perfect method??

That's exactly what they are. Imagine pressing on the top of an old car hood. It flexes and pops. Maybe it pops back out. Maybe not. Depends on how Murphy feels at the time. Probably wouldn't do it in flight, but it sure is soft. Feels like a big plate of jello! Just trying to add some structure so it doesn't go in and stay there.

My paint shop guys really did not like the flexing. Concerns (and history) of paint cracking in handling and my issue of distortion of the originally intended shape. There are a lot of ways to stiffen, and I considered a 2 oz reinforcement layer over a Soric core material and have a lot of testing to support this design. But the tip will not flex to the wing any longer and making a buck to hold the correct airfoil shape was a bridge too far for me. My tips were the older white ones and stiffer (heavier) than the new big notch gray ones. My notches were expanded to the larger size and called it done.

Kudos for developing the dowel method and considerations for the weight.
 
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