Cool Andrew! Seems I am onto the right track then..

subbed

I haven't had much time or motivation for building lately (and it's so damn hot there's not a lot of attraction for being in my steel un-insulated shed) but I do hope to have another go at this soon. The light PU winged Scratcho, with the tips cut off, is amazingly good and I've been flying it a lot! I want to make another wing using a mylar splitter plate between the mould halves while the PU expands, then crack it open, scrape out the PU around the edges and put some expanding epoxy in there, then close the mould again.

And I'd like to take some bits of video of the steps to (hopefully) show that it's not rocket science ... definitely back shed stuff, but capable of making a brilliantly light, very tough wing in a very short time.

Originally Posted by AvB

I haven't had much time or motivation for building lately (and it's so damn hot there's not a lot of attraction for being in my steel un-insulated shed) but I do hope to have another go at this soon. The light PU winged Scratcho, with the tips cut off, is amazingly good and I've been flying it a lot! I want to make another wing using a mylar splitter plate between the mould halves while the PU expands, then crack it open, scrape out the PU around the edges and put some expanding epoxy in there, then close the mould again.

And I'd like to take some bits of video of the steps to (hopefully) show that it's not rocket science ... definitely back shed stuff, but capable of making a brilliantly light, very tough wing in a very short time.

Cool, what was the 3ft lbs of the foam that you used for the wing?

I was thinking of using 5 - 8lbs foam it since it has a longer work time but use them to make foam blocks out of for CNCing

Sounds like moisture is a big issue in the foams expansion

Hi! my name is kelvin im from Caracas, Venezuela.

Im doing test of polyurethane to make a core for my wing like AvB did in the video. But i got some doubts for the skin in fibreglass in foam core.

1- Which resin (epoxy or polyester) do you recommend to work in polyurethane core?

2- if i make my foam core, and i put a fibreglass skin, it gonna be trouble with a vacuum bag? its necessary make a vacuum to a foam core, fibreglass wing?

Originally Posted by KASL

Hi! my name is kelvin im from Caracas, Venezuela.

Im doing test of polyurethane to make a core for my wing like AvB did in the video. But i got some doubts for the skin in fibreglass in foam core.

1- Which resin (epoxy or polyester) do you recommend to work in polyurethane core?

2- if i make my foam core, and i put a fibreglass skin, it gonna be trouble with a vacuum bag? its necessary make a vacuum to a foam core, fibreglass wing?

Can you make your own molds?

If so PM me

Regards

Originally Posted by erh7771

Can you make your own molds?

If so PM me

Regards

you have a mail.

The foam I used was about 30kg/m3, and I'm not sure how that compares with cubic foot! But it's about the lightest version available and expands to about 33x at maximum. However I used it at about 1/12th of the cavity volume, so it gets lots of back pressure and forms a nice even dense foam.

I don't think it matters if you use epoxy or polyester for the skin. I use epoxy. The foam is so fragile that the bond between the foam and the skin isn't strong anyway. The foam in the core is mainly performing the function of keeping the skins rigidly held in shape. The main thing is to find a way to make sure that the wing seams are solidly joined.

Originally Posted by AvB

The foam I used was about 30kg/m3, and I'm not sure how that compares with cubic foot! But it's about the lightest version available and expands to about 33x at maximum. However I used it at about 1/12th of the cavity volume, so it gets lots of back pressure and forms a nice even dense foam.

I don't think it matters if you use epoxy or polyester for the skin. I use epoxy. The foam is so fragile that the bond between the foam and the skin isn't strong anyway. The foam in the core is mainly performing the function of keeping the skins rigidly held in shape. The main thing is to find a way to make sure that the wing seams are solidly joined.

ok, but my doubt is if i use polyester resin in the PU core, it gonna bring troubles? like disintegrate of some way the PU core?

Originally Posted by AvB

The foam I used was about 30kg/m3, and I'm not sure how that compares with cubic foot! But it's about the lightest version available and expands to about 33x at maximum. However I used it at about 1/12th of the cavity volume, so it gets lots of back pressure and forms a nice even dense foam.

Converts to 2lb/cu. ft., definitely on the lower end of PU foam density in the hand-castable systems. Spray foam goes lower density but has lower physical properties fyi.

Originally Posted by AvB

The foam I used was about 30kg/m3, and I'm not sure how that compares with cubic foot! But it's about the lightest version available and expands to about 33x at maximum. However I used it at about 1/12th of the cavity volume, so it gets lots of back pressure and forms a nice even dense foam.

I don't think it matters if you use epoxy or polyester for the skin. I use epoxy. The foam is so fragile that the bond between the foam and the skin isn't strong anyway. The foam in the core is mainly performing the function of keeping the skins rigidly held in shape. The main thing is to find a way to make sure that the wing seams are solidly joined.

Greetings AvB. I did a test with a sadwich fiberglass, polyurethane and fiberglass, polyester resin used to bond the piece, but I had a problem. Part of the fiber is not acceded to Polyurethane possibly because it absorbed. My question is, how you solved that problem by putting on layers of fiberglass Polyurethane? I imagine that you also get the same problem as me.

Discussed via PM's! KASL was misunderstanding this method. He moulded a PU foam core, and was then laying up glass over it.

Originally Posted by AvB

Discussed via PM's! KASL was misunderstanding this method. He moulded a PU foam core, and was then laying up glass over it.

Hmmm sounds doable ...like glass a foam wing but with PU all at one time?

I would think the PU would absorb the glass but still come out smooth and strong...

What were the side effects?

regards

Originally Posted by erh7771

Hmmm sounds doable ...like glass a foam wing but with PU all at one time?

I would think the PU would absorb the glass but still come out smooth and strong...

What were the side effects?

regards

Yes, in fact the PU absorb the resin making it so much heavier, so i try to make a lil wing of fiberglass a put in some PU to expanded and adapted to the for of my wing, but it change the for of my wing.

So i think a good process to make a core PU wing is:
1- you must do you wing (skin) in a mould.
2- when its cured, put inside of the skin the PU, while you have the skin inside the mould for no change in the geometry

If I had a wing mold, I'd try this, so I learned some 3D blender and am having some wing tips printed. Those tips will be used to help make the plug.

Here's how I'd do it though, I'd paint the mold for the finish and lay up with glass and polyurethane glue. Then, I'd pour the 2 part foam. I plan to have an open ended wing mold for each wing half and that should allow uniform expansion and overflow. The PU glue and the foam will get along nice.