is foam core fiberglass enough strength to be chassis?

[mickri]

You could stitch and glue flat carbon fiber sheets. One thing about carbon fiber is that because it is so strong you don't need very much for a given strength but then you have to add other materials to bulk it up to resist things like buckling. Like most things it all depends on the design and what you are trying to build.

[LoadOS]

I have wanted to make another monocoque for a long time. A Locost seems like the perfect use of that construction method.

Addressing the OP, yes, foam core and fiberglass are strong enough to make a monocoque. I made one (monocoque, not Locost) with CF and it was excessively stiff. Downgrading to S-glass or E-glass and using less layers would still create a massively stiff structure if you do it right.

My initial thought is to make a male buck for the seat and firewall area, cover it with peel ply and then lay the interior skin. Next apply fiberglass reinforcements and foam sheet to make the core, fill in all the gaps with good dense spray foam, then sand to get the exterior shape right and finally lay up the exterior skin. After it is cured and removed from the male buck, apply light weight filler anywhere the tub needs to be smoothed, sand it, body-work it and then paint.

The dash and front structure might have to be pieces laid up and bonded on later. I would probably make the rear fenders like aluminum "over fender flares" that bolt on because they probably wouldn't meaningfully add to the structure. The hood would be aluminum too but the nose would probably be off the shelf fiberglass.

Any way a Locost built like that would be plenty stiff, plenty strong and probably lighter than a space frame too.

It is a labor intensive and messy way to do it but the Locost layout is probably one of the simplest designs that can be turned in to a monocoque because the lines are mostly straight and without compound curves. So if I'm going to make a monocoque, this is probably it...