idafly

Are there any examples of aircraft made from molded polyurethane foam?
I see a lot of planes made from EPP, styrofoam, and polystyrene, bu
not PU

-
idafl
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bob adkins

It's too weak and crumbly AFAIK.

Bob

idafly

Thanks for the feedback. I am trying to see if any work has been don
with it. I would like to design an airplane around it.

I am planning on making a plane using molds. This would give me a
integral skin I could paint. I would also like to use it to stabiliz
a balsawood framework (shear and buckling resistance).

PU has some advantages:
1. It is highly customizeable (I have a couple patents) to make i
heavy or light, rigid or rubbery, closed cell or open, thermoset o
thermoplastic, etc.
2. It accepts most paints or glue.
3. In a rigid form, it works well for making plugs.
4. Molding would produce a more optimal structure and form. Composit
homebuilt aircraft have a similar advantage. Otherwise composites us
a safety factor of 2 while more traditional methods of construction us
1.5 because they are better understood and generally do not fai
instantaneously like composites.
5. PU is very chemical resistant and also make an excellent glue. I
is also the chemistry used on high-end cars and aircraft.

As was mentioned, if it is sanded, then there will be a big weigh
penalty trying to fill in the holes. And I agree that hot wire cuttin
is definately a bad idea.

There are three other disadvantages:
1. It sticks to most everything (exceptions=silicone, teflon
polyethylene, wax).
2. Fumes from isocyanates (one of the components that reacts to for
polyurethanes) is harmful. Sensitisation can result in alergi
reactions.
3. Certain types of PUs degrade fairly rapidly from UV light an
therefore would need to be painted and sun exposure should be kept to
minimum. Carbon black helps to a certain extent.

It is an interesting challenge to me, but I don't want to reinvent th
wheel if someone has already done it

-
idafl
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the natural philosopher

What you need in aircaft foam is light weight and high compression
strength, and a stressed skin applied over that. Some foams (epp,
depron) have enough tensile strength to be useable without skinning.
Most polystyrene foans do not.

I would, before you build a plane, buy a coule of foamie models say a
multiplex for example, take moulds off the wings etc, and duplicate in
polyurethane, and see if you can come close to similar strength to
weight using a standard load cell type setup.

You might also be able to incorporate e.g. glass cloth as part of

teh skin in teh moulding process. This may help a lot.

I was cutting up some polyisocyanurate board today - just tidying up
house insulation - and it is remarkably strong and light, especially
with its foil skin. Very sandable too. But the dust is evil.

If you can get the foam density right, and mould in a stressed skin, you
may be on to something.

john alt

That's possible, or a sock of stretchable fabric could be fitted to the
inside of the mold and then filled with the polyurethane. Another option
is to mold spars into the foam. I'm not up on all the types of foam
available right now. When I was working with it daily in the mid to late
80's, there was nothing cost effective for what you want to do. Maybe
things have changed. I still don't see an advantage to using it over the
more commonly used materials. I don't know of a cheap foam that is light
enough and at the same time strong enough for what you want to do.