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Fiberglassing Pu foam

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Old 05-29-2004, 01:25 PM
  #1  
Radil
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Default Fiberglassing Pu foam

Hello guys,

I am building a wing completely with Poly urethane foam. I am not using any molds, just sanding to required shape of wing. Now

1. Can i directly fiberglass to Pu foam with some epoxy-hardener or polyester resin - hardener.PU foam what i have chosen is hard enough(35 kg/m3), i mean its not easily dented when handling.

2. What is that u are referring to Balsa sheeting on foam, then sealing it, then fiberglassing it , then sanding, primer, painting, etccc Why is that balsa sheeting done , is it indespensable to achieve a good smooth wing and is there any simple substitute like paper etc...[sm=confused.gif] . Please give me the complete picture of how fiberglass cloth is laid on foam and epoxy (matrix) bonded to foam ????

3. Would i be having same smooth wing if i directly fiberglass !! AND please let me know the complete procedure of how to paint the fiberglassed foam .
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Old 05-30-2004, 07:31 AM
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Ed Smith
 
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Default RE: Fiberglassing Pu foam

I d not know of anybody who uses Polyurethane foam for wing construction. I am not being sarcastic here, it's most common use is by flower arrangers for sticking the stalks into to hold the arrangement in place. Some modelers carve it to shape to produce temporary forms for glass cowlings etc. I have never used the material for wings so I cannot comment on it's suitability. I would have to guess though that it does not posses the required qualities for wing construction.

Now my arithmetic might be wrong here so check it and correct it if you wish. 35kg/m3 comes out to 2.2lbs/cu.ft. The foam that is used most of all is 5lb/cu.ft. This material is the white expanded bead foam usually used for building insulation, it has other uses as well. A slightly heavier blue or pink foam is also used. These materials are readily available from building supply stores.

I build a lot of foam core wings, and apply the glassing process. I am reluctant to describe the process if using your chosen material. I would be advising you to do what to me seems like a potential disaster. I would be very interested to know the reasons for your choice of wing material.

Ed S
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Old 05-30-2004, 01:14 PM
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Radil
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Default RE: Fiberglassing Pu foam

Hello, Mr Ed Smith

Thank u. Ya it comes to 2.2 lbs/ft3.

There is no big reason, basically what happens is, the procurement of materials in INDIA is really difficult. What we have to do is search for available materials around my place, then try to figure out what would be the combination of all these materials. We have here 0.3 to 0.4 mm of fiberglass cloth available at my place ( whole city ) , that is lot thicker of what i think u normally use.

WE only have PU foam available here , but a vauge guess to say, its nice, absolutely rigid and its good at what we call compression.

Choice obviously comes from the weight factor as far as our wing is concerned , as light as possible. So what we decided is , this .3 to .4mm thick fiberglass cloth is heavy , any way foam is just going to take compressive loads as well as to just increse the rigidity of cross section, so this density PU foam is ok (compromise) , as u even know this
.4mm cloth we giving us a lot of strength, i mean if we really use good binder(matrix).

SO , experimenting with lot of problems, gettin materials is difficult and imagine building.[].
Now Is there any serious problem with the composition what we have taken.Please suggest me , i am already drenched in lot of troubles.

Thank you.
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Old 05-31-2004, 12:46 PM
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Default RE: Fiberglassing Pu foam

I can't speak for the aircraft and/or rc aircraft industry but I do use a lot of polyurethane foam for model construction as well as core material. It's light and very strong once covered with glass or carbon graphite. 2lb density is about the lightest material avaiable. Then it goes up to 6-8-10-15-20-30 and so forth.

Evan
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Old 05-31-2004, 02:10 PM
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Radil
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Default RE: Fiberglassing Pu foam

Thanks a lot

I ll get you back after my construction ; and with pics of my Todbee 1.1.
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Old 05-31-2004, 06:15 PM
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Default RE: Fiberglassing Pu foam

Two problems I see with using polyurethane foams for models... it tends to be very brittle (moreso than polystyrene) and you can't cut it with a hotwire.

-David
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Old 05-31-2004, 06:51 PM
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Default RE: Fiberglassing Pu foam

After the composite shell has cured, go back and melt the foam out with gasoline. It'll reduce weight, without taking away much strength.

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Old 06-01-2004, 03:03 AM
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Default RE: Fiberglassing Pu foam

Polyurethane foam won't melt out with acetone... and I would not use gasoline, either. Regardless... what a mess that would make!

-David
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Old 06-03-2004, 09:04 PM
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Default RE: Fiberglassing Pu foam

David:

I used to make rough shapes to model boat hulls with P.U. foam. I do not remember having problems shrinking the foam when using Methyl Ethyl Ketone. I could take some which had been used for spray gun cleaning and apply it to the foam. It used to really compact up. Never used Acetone as had an endless supply of M.E.K. from a painting father who got it in 5 gallon cans.

I think your other experiences match what I experienced back then too. It was pretty crummy, but cheap stuff.


Wm.
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Old 06-04-2004, 02:19 AM
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Default RE: Fiberglassing Pu foam

I never tried MEK... acetone works fine for dissolving EPS, so that's what I tried.

If ever I need to melt some polyurethane foam, now I'll know how. Thanks!

-David
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Old 06-04-2004, 12:37 PM
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Radil
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Default RE: Fiberglassing Pu foam

Hey guys,

It just got cured , and it is pretty tough but the thing is its filled up first with

microbaloonsand it just got finished well. But the thing is , do u really need to use

microbaloons for laying this fiberglass laminate or is there is any simple substitute , please let

me know . If its not required ,it just helps us economically.

Awaitin .......
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