Author Topic: Foam core fibreglass blades (Read 3724 times)

BadNIMBY · « **on:** April 28, 2007, 06:55:49 PM »

Hi all

Have posted a couple of posts recently, both went a bit wayward and disappeared, not sure whether this is a common occurance or what, but thats beside the point, hopefully this one will stay.

What Im wanting to ask the collective, is that I have been playing around with constructing some small, experimental fibreglass blades. Found some nice art material which comes in boards and is a foam sandwich between plastic/paper.

It works well and i shaped a very nice twisted 1 1/2 ft blade from it.

However I foolishly got carried away and forgot about the chemical reaction between the polyester resin and the foam. Fondue springs to mind.

Anyway, I would like to ask if there is any commonly used barrier coats I could put onto the foam before laying the fibreglass.

Would a simple coat of paint suffice or do I need something specific, how have people on this board done things?

Thanks in advance

I wish you all a successful morning, afternoon, evening or night.

Will

vawtman · « **Reply #1 on:** April 28, 2007, 01:31:15 PM »

Why not use epoxy resin?

etownlax · « **Reply #2 on:** April 28, 2007, 03:15:46 PM »

I know spray paint doesn't work. I've tried what you are trying but I didn't think to use some "scrap" foam. :-(

-Randy

paradigmdesign · « **Reply #3 on:** April 28, 2007, 04:21:49 PM »

I would strongly recommend using a polyester foam instead.

willib · « **Reply #4 on:** April 28, 2007, 08:53:41 PM »

the clear epoxy resin is what ya want to use , like has been suggested ,assuming you are using regular foam

in my diaries is a history of my escapades with foam

the best epoxy to use on blades IMHO is West System epoxy , like all epoxy ,it does not eat the foam at all,

dont waste your time trying to coat the foam , i tried everything imaginable(sp).

and ended up using epoxy

a source for regular foam is Home Depot or Lowes , sold as insulation..

wdyasq · « **Reply #5 on:** April 28, 2007, 09:06:56 PM »

I'll agree on epoxy but just say there are many formulations of epoxy better for composite over Styrofoam than Gougeon/WEST 105/205 system. Be sure and choose the proper system for the property you are looking for.

Ron

coldspot · « **Reply #6 on:** April 29, 2007, 02:18:42 AM »

Way back-

(RC 10th scale combat airplanes)

What ever foam gotten that was sized right-

Hot wire cut to wing shape then,

wrapped with brown paper bag, skinned so to say, regular white paper glue thinned down with water sprayed on with old hair bottle pump type, to glue down both sides, (foam side and outside).

After dry time an extra outer coat then sanded smooth.

After that a couple of coats of spray can clear coat

made for a pretty tuff wing skin.

white glue made seal coat to not let clearcoat solvents melt glue if done carefully and slowly letting coats flash off before adding more.

Of course they had spars and even extra strength from strips of plastic like from a banding machine but cut down to a smaller width but still inserted into a simple razor blade cut down the wing leading edge and pushed inside to be flush with edge. One more was glued to spar side to be 90 to the wing width before spar was inserted, used plastic same size as spar.

This plastic does not like to bend edge wise.

$0.02

BadNIMBY · « **Reply #7 on:** April 29, 2007, 05:24:10 AM »

Thanks all

Are we sure that epoxy resin wont do the same?

Im just trying to remember if 2 part araldite epoxy glue didnt start doing the same.

The other alternative Ive heard of is vinyl ester resin.

Could I (presuming there is no reaction between foam and epoxy, put a coat of epoxy glue over the blade then polyester resin the fiberglass over that?

Shall pop off to do a quick experiment, pics soon

Thanks all

Will

DanB · « **Reply #8 on:** April 29, 2007, 06:52:08 AM »

Im sure the results may be different with different formulations.

In my experience you don't want to put polyester over epoxy (there will be a gooey layer in between the two that never dries). That may be true with vinyl ester over epoxy too - never tried that. You can put epoxy over hardened poly or vinyl ester though.

wdyasq · « **Reply #9 on:** April 29, 2007, 08:05:03 AM »

Will,

You can't be sure about anything said on this board. It costs nothing to contribute and many replies are worth less than the membership fee. A few posters are very knowledgeable and their advice is as good as one could purchase with an unlimited budget. Other posters occasionally stumble on the truth and step around it. Another group complains when an editor pulls stupid posts and tries to keep truth as an objective.

In a glass/epoxy matrix - the part that gives the strength to a 'foam/fiberglass blade', the epoxy is the weak part. The same is true for polyester resin/fiberglass or vinyl ester resin/fiberglass. There are different types of 'fiberglass' cloth also. One can actually get 100% or more strength gain for the weight by using an "Engineered system" rather than just going down to the local hardware store and buying 'what they have'.

I run on a very tight budget. I don't have much free time either. I damn sure can't afford to use the wrong materials, get to do the project a second time and waste money. It is difficult enough to work in a 'prototype' industry. All these wind machines are, essentially, prototypes and 'beta' machines.

Do yourself a favor, do some of your own research. You will soon figure out which side of the boots the manure is on for many of those who post.

Ron

BadNIMBY · « **Reply #10 on:** April 29, 2007, 02:31:42 PM »

Thanks for the info Ron.

I always check numerous sources of info, (be that here, the internet or people I know) as well as doing some research for myself before deciding. Not to mention the hours spent 'experimenting' successfully or not.

The posts here are great because often something is brought up that you hadn't thought of and off you toddle, exploring a new avenue of research.

At the moment I have applied a thin 'veneer' of 2 part epoxy glue, letting it harden. this seems to work well so far and it stays pliable, no fondu'ing occurred, the next test is to apply some good quality fine fibreglass cloth and see if it adheres nicely and gives the bmade the rigidity i need.

So far so good

Thanks all for replying

Will

twombo · « **Reply #11 on:** April 29, 2007, 08:32:19 PM »

NIMBY

Try this post:

http://www.fieldlines.com/comments/2006/7/11/193843/311/15#15

A good collection of study materials regarding building aero parts using foam and glass. Study all the references and you will be ready to start designing your dream. This is a short compilation of 30 years of homebuilt aircraft composite technique.

As a general rule, use epoxy on polystyrene foam. Always consider closed cell polystyrene foam over "bead" foam for hot wired cores.

Your glass layups MUST to be integrated into the the cellular surface matrix of the foam core to be a a successful composite structure. Where the different materials are not fully bonded, the part is considered delaminated and maximum strength and longevity are fatally compromised.

Polyester resin is cheap but has short pot life as well as many other liabilities. I have posted some conceptual designs for blades tht would likely result in strog, light and with the right airfoils, spans, TSRs were properly considered.

As much as I like composites, you can't argue with successes of DanB and crew using wood blades. Bottom line, they make power every day with pretty modes outlays on materials.

Thanks for the inspiration DanB

Mike

coldspot · « **Reply #12 on:** April 30, 2007, 04:39:50 AM »

Well

"replies are worth less"

Don't

take my word for anything but,

Brown paper bags

are wood, thin and light weight.

easy barrier coat.

Google for model airplane sites,

RC combat sites go thru a lot of wings and have learned how to made them cheap and fast with strength being highest goal!

PS: The plastic banding trick is very good!

$0.02

And NOT worth that!

BadNIMBY · « **Reply #13 on:** April 30, 2007, 07:14:47 AM »

Your worth every cent, nickel and dime my friend

RogerAS · « **Reply #14 on:** April 30, 2007, 09:20:37 AM »

Hi,

In areonautical composite situations poyurethane foam, and other types, and compatable epoxies are used (in conjunction with other materials). This foam comes in many densities and stronger foams are used in the high loading areas of the airframe. This foam-epoxy-glass system is not cheap but is tested and proven in life or death situations. Google aircraft composites and check it out.

Hope this helps, and like another poster said this is just an opinion. Having been involved in aircraft related employment I have some experience in this area.

Those big turbines in Texas use blades with a balsa wood core and fiberglass coating. I saw a TV show this weekend talking about those turbines and the blades are 100' plus each!

check out:

http://www.professionalplastics.com

and:

http://www.sportair.org/articles/Building%20A%20Composite%20Aircraft.html

Mary B · « **Reply #15 on:** April 30, 2007, 09:50:09 AM »

Aren't surfboards made from foam cores with a fiberglass overlay? Might be a spot to check into.

willib · « **Reply #16 on:** April 30, 2007, 11:19:49 PM »

as a matter of fact they are

i should have taken an edge on shot, to show how thin the top of the board is..

i dont have to tell ya how difficult it would be to engineer a spar on a blade with a taper and twist ...

not impossible just very difficult IMO..

this spar is about 5/16 thick , been looking into what they use ,i think this board uses a milky white epoxy , its not crystal clear anyway..

going out on a limb here by saying the a spar may not be needed on a composite windmill blade.

the camera could not show the finish on this board , its beautiful.

if it wasnt busted in half i would never had found out that they start wraping it on the underside edge , then go round the top and then finish the underside , as far as i can see there is not one airbubble in the board , and it is super strong ...and hard as a rock ,

what i dont understand is HOW they started the laminate , i mean did they start it with a thick bead of epoxy , let it cure , then finsh it off?

a blade is different obviously because of the sharp trailing edge

anyway it has some really nice foam inside cant wait to try it out..

twombo · « **Reply #17 on:** May 01, 2007, 08:50:17 AM »

In most cases resin mixed with micro-balloons is squeegeed on the bare foam to "size" the finished foam surface. This increases the structural bond between the foam and the glass layups. This will dramatically reduce delamination which is on of the cheif enemies of composite structures,that, and dry (resin starved)layups.

I never made a surf board but the idea is pretty simple. If one uses Bi-directional (BID) cloth laid on a 45 degree bias to the long axis of the board, the cloth will readily conform to the boards surface contour, rounded edges and all. The BID stuff is super easy to conform without wrinkles.

In a nut shell, layup one side and as the epoxy resin reaches the semicured (rubber) state, do a razor trim and cleanup of the draped excess and let the layup cure. Flip and repeat. Overlap the layups enough that the up and lower surfaces are fully bonded together.

The Quickie construction manual is a REALLY well written primer on moldless composite construction. I'm sure you have heard of Burt Rutan and his fabulous flying thingies. Burt and team did much of the prototyping of the Quickie aircraft and construction manual development. This manual is in the public domain and is on of the references in my previous post. Even a rank novice like me found the procedures very easy to duplicate.

Willib, check the Quickie manual out, it will be a very revealing experience.

Mike

twombo · « **Reply #18 on:** May 01, 2007, 09:09:09 AM »

Couldn't agree more Ron!! Talk is cheap!

Check out the reference materials in the link I posted. Having built and flown composite aircraft with my pink little ass in them, these are reference materials that I have trusted with my life.

Wasted Resources - Again, Ron, you are on the mark, good composite materials are not cheap and ARE NOT available at Lowes. One of the time tested sources is Aircraft Spruce and Specialties.

Mike

willib · « **Reply #19 on:** May 01, 2007, 09:45:37 AM »

ya mean the quickie builders pdf?

twombo · « **Reply #20 on:** May 01, 2007, 02:00:52 PM »

Yes, willib, that one, really good introduction to moldless composite construction.

Check out the section on airfoils for some interesting details on trailing edges and leading edges.

Also some good guidance on setting up inboard outboard airfoil templates to set wash-out/wash-in during hotwire cutting of cores.

Cheers

mike

BadNIMBY · « **Reply #21 on:** May 02, 2007, 08:20:16 AM »

Do you have a link to that file?

Will

willib · « **Reply #22 on:** May 03, 2007, 01:57:12 PM »

http://quickiebuilders.org/QBA05/q1plans.pdf

3rd Charm · « **Reply #23 on:** May 04, 2007, 02:42:50 AM »

Long ago in my model airplane days, we just used 2 part 10 min epoxy glue and just brushed it straight onto the glass matting over foam cores. There was this other stuff that kinda dried and looked like baking soda that was used to fill the foam and make it smooth prior to laying on the glass matting. I can't remember the name of it.

Go shopping online at hobby lobby, You'll find it.

twombo · « **Reply #24 on:** May 04, 2007, 01:50:49 PM »

That "nice" foam has become somewhat difficult to obtain since the Clark foam people went out of business a year or so ago. The foam is a 2 lb density per cu.ft. polyurethane, that was well known for its even consistency and ease of hand shaping or carving. I'm sure something else has taken up the slack, but Clark foam was really prime stuff to work with.

Being polyurethane, you CAN NOT hot wire cut it!!! The hot wire will crate phosgene gas. Hotwire cutting is only applicable to polystyrene foam!

Cheers

Mike

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Author Topic: Foam core fibreglass blades (Read 3724 times)