foam and glass construction

[Adam H]

I am attempting to fabricate a foam and fiberglass horizontal stabilizer for my honeybee gyro. I'm wondering if it is ok to use the standard pink polystyrene insulation available from the hardware store? I know you can't use poly resin with it, but is it ok if you use straight epoxy? Any tips would be much appreciated!

[banaari]

You can certainly use epoxy resin with polystyrene; many's the surfboard built that way. I'm in the process of doing my first ever fibreglass layup at the moment (instrument pod): It's a hell of a good fun. Go for it. :)

Now I think about it further: *Pink* polystyrene???
The wall insulation I bought for the pod was white... hopefully there's nothing nasty lurking in the pink. Maybe a fire retardant or something?


cheers,
John

[donshoebridge]

Adam,

To keep the weight down, make sure you seal the surface of the foam with micro balloons and epoxy (about 50/50). While it's still wet, lay your glass on then add straight epoxy, wet out the cloth and squeege off all of the extra epoxy. You'll be all set!

PS - if you don't seal the foam, the epoxy will soak into the foam and make the panel heavier than it needs to be.

[Brent_Brown]

If if could soak into the foam it would with balloons. I was told and read the balloons and epoxy base is to help stop the glass from peeling off or bubble up in the sun. you make it light by using just eoungh epoxy to to the job. But you may be right.

[Victor Duarte]

hi,
i think adam means to use extruded polystyrene (the hard blue ,yellow, pink, or grey)
instead of expanded polystyrene that produces those white sticking hips when you scratch it.
from my recent searhes, microspheres are used to gain lightless and sould be used where there will be lots of resin.
but if you're talking of filling, you can use "fluff" kind of fine cotton fibers that will fill the spaces.

Scott made a thread where he described how he did his rudder.

[Mayfield]

Good morning Adam,

I am certainly not a composite guru, but do have a couple of suggestions.

1. I am partial to one of the Urethane foams. For a horizontal, a mid density foam should do.

2. Just before skin layup, I would coat the foam with a mixture of epoxy and microspheres. You can mix it until it is (at 70 degrees or so) slightly thicker than honey. You just want to fill the irregular surface on the foam to give a good bonding surface for the cloth so don't paint it on thickly.

3. Then lay your glass and stipple/squeege the excess resin away.

4. If you have an inside corner that needs some structural reinfocement, you can use "Flox." This is made using chopped cotton fiber and resin. This mixture is quite a bit thicker. When you have finished mixing it, "peaks" in the mixture should hold their shape.

These are just my opinons Adam. Good luck with your project.

Jim

[Alan Coats]

Adam,

You might want to go to the GyroBee site at http://taggart.glg.msu.edu/gyro/gbee.htm and look at the documentation. At the very end of the documentaion you will find Doc Watson's instructions on making tail feathers using the method you are talking about.

Alan

[Adam H]

Thanks for the comments and suggestions! The polystyrene I'm using is extruded and pink, don't know if that matters. I already hot wire cut out the shape and sanded it the way I want it. If I'm going to invest in epoxy, fiberglass and labor I just want to make sure that I'm using the best kind of foam I can. I don't want to have a heavy or otherwise screwed up stabilizer because I was too cheap to spend the extra few bucks on the right kind of foam from Wicks when I already spent a bunch on epoxy and fiberglass.

[skyguynca]

The extruded pink is fine, it is the same type of foam the varieze and longeze wings are constructed from. It hates petrolum products and will desolve under the glass if oil residue from the engine's exhaust gets thru a pin hole in the glass creating a void. The foam is fine, alot of ultralight airplanes use it also, you just have to make sure it is sealed. Use flox to glue in your hard attachment points for the pivot hinges for a rudder and to mate the horizontal to the rudder. It can be very light but do not starve the glass for resin. I would purchase urethane foam to build from. True it can not be hot wired, you have to shape it with a knife or hacksaw blade then you can smooth it with just another piece of foam or a sanding block, if you try to hot wire it will create a very poisionous gas. It is lighter and stronger than polystyrene and you can usually get it locally from insulation distributors. It is also used in housing and building construction. IT is usually yellowish/orange if purchased this way and comes in thicknesses from 1/2 to 4 inches thick and runs from about $14 to $90 for a 4x8 piece.

[Mayfield]

Thanks David,

That is very good advice about the hot wiring.

When I use urethane, and want a repeatable shape, I usually make end caps the shape I want and then use a long board to sand it to shape.

If I am making something big I usually use one of the polystrenes and hot wire it with a nichrome wire.

Jim

[donshoebridge]

Having just glassed my seat components, I can tell with with confidence that the pink or blue foam from the hardware store will soak up straight epoxy. It may look like closed cell foam, but it's not. The Watson tail documentation says to do the same thing - 50/50 balloons and epoxy first, then glass with straight epoxy over that. This the same technique that the guys at Oshkosh perform/instruct/demo at the forums. I've done it with and without balloons and there is a difference in the "spunge" factor. Try it on a small piece of foam first just to see. The micro balloons do tend to fill the pours better than straight epoxy.

Also, the smooth mill finish on the foam, rough it up with 220 grit sand paper first. Also make sure all of the foam dust has been removed. Both of these steps will help prevent delamination. So will the balloons.

[Victor Duarte]

Don, i am curious to see your seat , particularly if it is strong .
I am actually working on a 1:1 model made from extruded foam (blue), and, once shaped, i plan to thermoplatic on it and smooth with a heater, so i get a perfect surface, then i will coat with polyester and fabric for the mold... did someone try this ? i don't know the behaviour of the plastic film under polyester.
Thanks

[donshoebridge]

Details of it can be found in my documentation package. I only put a coule layers of glass on it, and when you compare the strength of the seat to the amount of work required, it wasn't worth the effort, so I changed the design and made everything flat-simple pieces. I also added a couple of aluminum support pieces.

In the "Hornet Design" section of my site, near the bottom of the page is a rendering of the new seat design. I'm waiting for the weather to get better (warmer) before I build the new seat.

[Victor Duarte]

Don, i have seen it, yes you simplified a lot.
i saw a similar building and must say that i was impressed by the strenght of a simple epoxy-glass layer over foam. it's a wonderful material.
great job on the documentation..congratulations
thanks

[Goody34]

where do u buy the extruded polystyrene, im looking into building some rotors out of it

[donshoebridge]

Brad,

The foam I'm using I bought from Lowes. The same stuff can be found at any builder supply outlet. A 4'x8'x2" board will cost you around $10.

[Brent_Brown]

Wow I'm getting ripped off I paid over 20 bucks a 4' x8' x2". They must make it in your back yard.

[Adam H]

Don,

That is pretty cheap, I'll have to find a Lowes near me. At a local lumberyard they wanted $30 for a large 2" sheet of dow blueboard. You said earlier that you used pink foam, were you able to find it without the slits cut in it to make it easier to break? Once the glass is over it I don't know if those slits would matter much, but I would think it would be better to use foam without them.

[woodsher]

Adam
I am just about finished building my tall tail with pink foam. It cost me $17.00 for a 4x8x2" piece. I have alot of pictures of my progress of the build on my website. I am just like you. I had never done this before but what I had done is started with a small piece of foam board and made a test. to see how to mix and lay the fiberglass and epoxy. Then I found that it was really quite easy to do. I bought all my epoxy and fiberglass thru wicks aircraft and now that I am done with the laying of glass and epoxy I realize that I over bought on the fiberglass and just had enough epoxy resin and hardner to do the job.
So I also learned just how much of what materials that it takes to do a good size job.
Only thing now is I have to learn to get it ready for paint!
:eek:

[Doug Riley]

A popular brand name for the pink extruded board is Foamular. It is fine for tail surfaces and can safely be hot-wired. The use of micro slurry to prime the raw foam is a standard technique.

[Adam H]

Brian,

Thanks for sharing your website, very helpful! It looks like your using exactly the same foam as me. I see a green stripe running top to bottom on your rudder, is this where you filled in the slit in the foam with epoxy?

[skyguynca]

Oh, one thing I forgot about using polystyrene, make sure to sand off the shiny coating on the foam, if you don't the resin won't bond as well and you will get the glass pulling away.

[et3dotcom]

Adam, the green stripe is probably the rudder spar caps ??

[woodsher]

Adam
The green line is a 2"x2" piece of fiberglass tubing that I glued the foam to so I could use a aluminum plug in it to attach the tall tail to the airframe.
and I wrapped the vertical with fiberglass and epoxy.

[donshoebridge]

Don,
That is pretty cheap, I'll have to find a Lowes near me. At a local lumberyard they wanted $30 for a large 2" sheet of dow blueboard. You said earlier that you used pink foam, were you able to find it without the slits cut in it to make it easier to break? Once the glass is over it I don't know if those slits would matter much, but I would think it would be better to use foam without them.


Adam,

I have not found any foam insulation board WITHOUT slits. One thing you can do is use those slits to your advantage. I had considered snapping the board at the slit, sanding both edges flat, then wrap a layer of glass and epoxy over both edges, and mating the surface back together while they are still wet. This would create an I-beam shape instead of the slit. Then cut the board to size, sand to shape, and glass to finish. I've heard of people making wings in this manner with thicker pieces of polyurethane foam where the I-beam runs from the root to the tip. Sounds like a lot of work.

An easier approach would be to pour a 50/50 mix of epoxy and micro balloons into the slit and let that cure. It would fill the gap and add a little strength to the board, but I don't know how much.

[Doug Riley]

Pink Foamular brand lacks slits. It is cut to provide a tongue-and-groove joint along the long (8-foot) axis. This joint can be used when making up the blanks for parts that are more than 24" wide... such as the vertical surfaces of the Watson/Gyrobee tail. I use liquid urethane foam as a glue to join styro boards this way. Although joints so glued should not be hot-wired, the joints can easily be sanded to shape with 60-grit paper.

When buying foam boards, pick through the pile to get straight ones, just as you would when buying wooden lumber. The usual retail inventory contains a lot of badly warped pieces.