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!

On Apr 4, 4:24 pm, "dirigible designer"
wrote:
My dirigible design requires a few long spars curved into C-
shapes. They would be triangular cross-section with their three
faces being about 3 feet wide and 100 feet long. They need to be
light, strong and stiff. [what's new?]
If anyone's has experience building large spars or frame members, I
would like some advice as to how to make them cheap and easy.
My present thoughts favor a thin fiberglass skin around a bundle of
polypropylene tubes, which could get expensive.
I think that EPS blocks carved into the triangular shape and then
covered in glass would require the extra labor of building a glass
internal spar, yuch.
This design has to be a cheap and dirty way for the working guy to
get in the sky.
thanks from Allen