Ernest Christley wrote:
Most of the fabric covered aiplanes I've seen didn't seem that hard.
That is, you could walk up to them and push the fabric in with your
hand. The way I understand the fabric process, it is basically a
composite structure. You have a nylon cloth with a paint "epoxy".

You have a cloth material coated with a doping silver compound to
reinforce the material and make it taut, on top of which paint is
applied. The former does not penatrate the material but is on one side.

Could a much stronger and lighter covering be made by wetting out some
2.5oz glass cloth on plastic, waiting till it's tacky and then wrapping
it around the airframe? The epoxy would be much lighter than paint, and
fiberglass cloth is MUCH stronger than nylon.

Keep in mind that fabric covered structures are not Load-bearing in
the structural sense of the term. The fabric is there to keep the
aerodynamic shape and provide an area for the pressure to act on. It
is not a stressed skin structure in that the fabric takes pressure
loading, especially on the wings, but does not contribute to the
strength of the underlying framework as in metal skined designs. As
such, the extra strength is not really required on existing fabric
covered structures. You could maybe argue for a weight saving factor
in the days of lead based paints, but now... There is the advantage of
better UV resistance and not cracking or pealing over the lifetime.

I've seen some places where builders used composites in place of fabric,
and it seemed that they all aimed for a multlayer, stiff panel, putting
the weight far above the original. I just don't understand why?

This is where there is some skin loading required. Stressed skin
designs can make the use of very thin aerofoil sections possible by
taking some of the load off the spars and ribs making for lighter and
stronger structures.