Mandan, an aerodynamic 6x10 foamie

[GPW]

Heat the foam to 190 F and you can tie it in a knot ... We’ve really not begun to investigate bending thicker sheets of foam with Heat ... BUT (the qualifier) , we Have bent the heck out of 1/4” -1/2” ” foam for RC planes ... Just need to bend/heat on a bigger scale for a Foamie’ Camper ... 190F is not a difficult figure to heat to ...

[GPW]

http://www.rcgroups.com/forums/showthre ... t=BendFoam Bending efforts on thin foam for planes... for those who’ve not yet seen this...

[Pmullen503]

Heat the foam to 190 F and you can tie it in a knot ... We’ve really not begun to investigate bending thicker sheets of foam with Heat ... BUT (the qualifier) , we Have bent the heck out of 1/4” -1/2” ” foam for RC planes ... Just need to bend/heat on a bigger scale for a Foamie’ Camper ... 190F is not a difficult figure to heat to ...

I've done a lot of heat forming of foam. The problem with heating thick foam is the time it takes for the heat "soak" in. Even with 1/4" foam it takes 10 to 15 minutes when heating with hot air to get the entire sheet warm enough that it will hold it shape when cool. Wet steam heats much faster but you are still trying to heat insulation and getting enough of the foam warm enough to bend and hold a shape would take a long time in an oven (I don't think you could do it without one.)

I'm in the process of moving my shop otherwise I could toss a piece of 2" foam in my oven and find out if it's possible. Here's a picture of the kind of thing I do for RC planes. Shown are a form with the foam taped to it (tape acts as the female mold), the male mold, and a finished molded shell. It takes about 20 minutes for the heating cycle; 10 minutes from RT to 212F and 10 minutes at 212F to soak.

[jgraham698]

I posted comments to to the discussion about kerfing concerning bending with a compression strap. Are
you interested in more info?

[skyl4rk]

I don't think I want to do kerfing. It is a lot of work and reduces the strength of the panel. I would rather change the design to fit the material.

[jgraham698]

Using a compression strap doesn't involve kerfing or heating. I didn't realise how confusing what I
posted was, sorry. Here's something simple to do that might give an idea of what I'm talking about.
Take a piece of foam 1/2 " - 1" thick and cover one side with masking tape and then try bending it.
Once it's bent and held in place cover the inside with tape or glue on paper. You can then remove the
tape from the outside and the foam will hold its new shape. You can bend 2" foam with a strap and
end blocks. Let me know if you want to hear more.

[GPW]

Of course we want to hear more ....

[jgraham698]

Hello

[jgraham698]

My posts don't work every time, don't know what I'm doing wrong. First I want to say using a compression
Strap isn't my idea or new. This is a technique used for bending wood and my understanding of why it works
comes from that. Foam breaks when you bend it because the out side of the bend is stretched. If you can
stop that from happening all of the bend results from compressing the foam. Taping or gluing something to
one side works up to a point. A compression strap uses blocking at the ends to keep the out side from stretching.

[skyl4rk]

So if one were to Titebond III glue kraft paper to the outside and let it dry, then try to bend it with a ratchet strap, you could get more bend out of it?

[GPW]

Why not just glue on something to absorb the tension loads that would become part of it anyway ... like the outer skin (fabric) ..
Still the inner surface under compression forces would still have to be dealt with , either by kerfs or heat ... My only problem with kerfing is it removes material from the structure and the bending part left is only a thin bit of foam ... Heat on the other hand just softens the foam and trapped air within, no structure is lost , just compressed ... theoretically making it Stronger.

[Pmullen503]

So if one were to Titebond III glue kraft paper to the outside and let it dry, then try to bend it with a ratchet strap, you could get more bend out of it?

The kraft paper is going to shrink as it dries which will put MORE tension on the side you are bending away from. On thin foam at least, the foam bends toward the side covered with paper if not supported by the structure.

How much bend do you need? A 2" sheet of R250 will bend 6" to 8" along it's length without excessive pressure. I still think that 2 layers of thinner foam will be easier and laminating them will hold the curve without depending on support structure.

[jgraham698]

If you think gluing Kraft paper to one side might work, you should do a small test sample first. The glue joint
will be subjected to shear force and while the glue will hold up the foam may tear away. If the paper is strong
enough to bend the foam without being torn you can easily make it into a compression strap. All you need to
do is attach blocks at the ends of the paper that will keep the out side of the bend from being stretched. So

what I'm suggesting you try is to lay your foam on the paper and glue or secure some other way 2" thick wood
along the ends of the foam. You can then start bending. A test sample would be best, but if you go slow and
see a problem you can just stop and start over. When things are working the way you want you can take the strap off and apply the glue and redo the clamping process. My children helped me post a YouTube video you
can see by googling the key words "bend styrofoam". They're going to help me post an updated version over
the holiday break.

[GPW]

Something we’ve not tried yet is compressing the inner surface of a curved sheet (compression side) ... that alone would “curve" a thick sheet ... Big HEAVY roller ...

[skyl4rk]

The reason I called my build the Mandan is in reference to earthen log homes built by the Mandan people. I admire the original Mandan dwellings because they could survive in the northern plains in very harsh cold weather.

My build has very little in common with the original dwellings, but has a general shape that might remind one of the originals. I am using different materials, building a much different size dwelling and the reason for the shape is aerodynamics, which the original builders probably did not take into consideration.

I do hope that the insulation properties of the foam would allow the trailer to be comfortably used in cold weather.

So my reference to the name Mandan is only because of a similar shape and out of respect to builders who were able to survive cold weather in houses of natural, found materials.