Building a composite spar?

On Apr 4, 5:45 pm, "SkyDaddy" wrote:
No offense, but I'm not sure a 100-foot airship will qualify as
"cheap" when you consider what it will take to fill it with helium and
store it securely. There's also the matter of getting dirigible
licenses from the FAA for the ship and its "working guy" pilot.

But practicality aside (this IS experimental aviation, after all), why
not use extruded aluminum bolted up into triangular trusses? It
worked for Count Zeppelin!

I've got this idea that a bunch of plastics and fiberglass is cheaper
than buying aluminum extrusions and rivets. Could be wrong, especially
if labor time is figured, [which it isn/t ;-]
Actually, there's not much way the ship could be 100' long and
"economical." The spar might be approaching 100' linear length but it
is curved into a C-shape and forms the circumference of the airship.
If you looked down on the design, it is a D-shape, with the flat edge
being the stern with the control surfaces. The length of the ship
would be only about 32'. It's a saucer with airfoil. That size doesn't
hold a lot of lift gas, and it needs to lift two persons and an
electric motor with PV cells, so the framework must be of minimal
weight and complexity.
The main challenge is the big strong lightweight frame spar around
the middle. It perhaps should be no bigger than ~ 3' wide. It has a
triangular cross section and is maybe stiffened with EPS foam or with
a bundle of polyethylene tubes, [which might get too expensive], and
covered in thin fiberglass skin.
Any alternatives which might work? How strong is a simple double-
walled f'glass tube with sheet EPS between walls?
thanks from Allen
P.s. Oh, yes, storage costs. The framework must be foldable after
deflation. I am maintaining, as second priority, the folding feature
as the design evolves.
As far as aircraft and pilot license fees, I think that this ship
design could be downsized to end up as an ultralight. It's an easier
process to design and consider a larger study prototype and get all
the aerodynamics and mechanics figured out before tackling the rigors
of extreme weight- trimming. [to my thinking, anyway]