Conference vmszoo::rc

    The only place I have seen a piece of Rohacell that small used was
    glued to the inside of a VS sailplanes XICA fin, to provide additional
    stiffness to the fiberglass.  
    
    It sounds like what you got is a sample of the material.
    
                                            
                                                        Regards,
    
                                                        Jim

I've read articles (and heard from Terry T) that they've made hollow spars by 
starting with a box structure of this stuff and adding CF and fiberglass to 
make a very rigid, light structure. I was somewhat surprised when I saw the 
small size of your piece.

Bob Kaplow used to use it and actually took the CST coupons I had for it last 
year. There was a discussion about it's uses in here (somewhere). Alas, he's 
moved on.

    As I understand it, Rohacell isn't used for strengen as much as it's
    used for light weight filler.  Let me explain...

    If you have a foam wing with no sheeting, it's pretty flexible and
    usually isn't strong enough.  (Gremlin's excepted :-)  But, when you
    add balsa or fiberglass (or carbon or Kevlar or Spectra or ...) then
    the COMPOSITE structure is very strong.  The strength actually comes
    from the sheeting material, NOT the foam.  The foam is there simply
    to act as a filler to keep the sheeting in the proper place.

    Thus, Rohacell is just filler to keep the "strong" materials in a
    composite structure the correct distance from each other.  Since
    Rohacell only comes in thin sheets (and is not hot wire cuttable as
    far as I know), it is used for areas that it isn't desirable to have
    foam filling the entire area and it is possible to put fiberglass on
    both sides of the Rohacell.

    In other words, a piece of Rohacell with a layer of 3 oz. cloth on
    both sides will be stronger than 2 (or 3 or maybe 4 or 5) layers of
    just 3 oz. glass cloth.

    For a clearer explaination of this, get Jack Lambie's (sp?) book on
    composite construction from Zenith Aviation Books.

                                - Dan

How is this material used?  Sounds like it might be laid up like FG
cloth using resin or epoxy.  Interesting.

I think SIG makes some material that you soften with lacquer thinner
or dope then form around an object like a cowling blank.  Its sort of
cardboard looking and when it dries its the shape of the blank and can
be removed.  You would have to give it a little structure with FG
cloth or something, but it sounds like the Rohacell (sp) of this
topic.  

    We used Rohacell (Dow Corning makes the stuff) very much like styropor.
    That means cuting it with a hot wire. Additionally it can be sanded
    grinded and drilled, which styropor can't. Finaly Rohacell can be
    coated directly with fiberglass (epoxy) without having to have a layer
    of (abachi)wood inbetween, because styropor would melt. Make the whole
    plane (you should get blocks of it, it's used for isolation in buildings) 
    out of this material.

Rohacell is widely used in Europe for making wings, especially for them hi-tech
gliders.

The basic technique requires that you make a mold for the wing.
You them make a sandwich of carbon fiber or FG, then the rohacell, then an other 
layer of Carbon fider or FG. vacumm bagging is then used to form the wing.

The result is tough, light, expensive and very precise.

Marc Dufresne

Hi Mark,
I did a double take when I saw your name. With so many of the old timers leaving
in the past year or so its a pleasure to see you back.

Dan Eaton