Building a composite spar?

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

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

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]

"dirigible designer" wrote in message : 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]
:


Interesting question...what is an ultralight airship?

Use wire and posts to build the truss, like a box kite...

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


Have you considered using 1/2" foam with a layer of glass on each side.
3 pieces, each 3' wide, to form the spar.

Have you considered using 1/2" foam with a layer of glass on each side.
3 pieces, each 3' wide, to form the spar.

Thanks, Ernest, I think this will probably end up being the way I go
to hold the costs down to a minimum while giving me the strength I
need. Since EPS foam is used in house construction for insulating
roofs, it is locally available and cheap.
If 1/2" foam leaves the spar too flexible, I can then easily go up
to 3/4 or 1 1/2" or more.
Now I just have to figger out how to get those layers of
fiberglass, (matt and cloth), on the inside of the hollow triangular
spar 8-]
best regards, Allen

"dirigible designer" wrote in message

Now I just have to figger out how to get those layers of
fiberglass, (matt and cloth), on the inside of the hollow triangular
spar 8-]

Use the opposite of vacuum bagging; pressure bag it.

Make up glass cloth with epoxy squeegee into it, then lay it on the foam,
lay on the release cloth, make up the pressure bag, fold it all up, bind it
on the outside with tape or something, then put the pressure to the bag and
let it cure.

You will have to cut an inspection panel every so often, to get the release
cloth and bag out, but they are easily closed later.
--
Jim in NC

Morgans wrote:
"dirigible designer" wrote in message

Now I just have to figger out how to get those layers of
fiberglass, (matt and cloth), on the inside of the hollow triangular
spar 8-]

Use the opposite of vacuum bagging; pressure bag it.

Make up glass cloth with epoxy squeegee into it, then lay it on the foam,
lay on the release cloth, make up the pressure bag, fold it all up, bind it
on the outside with tape or something, then put the pressure to the bag and
let it cure.

You will have to cut an inspection panel every so often, to get the release
cloth and bag out, but they are easily closed later.

Good one.

Or just lay up one side, with the edges cut at a proper angle. Fabric
flow from the table, uphill, across the inside and downhill back to the
table. Peel-ply the hillsides. Once it cures, trim the excess fabric,
flox the 3 pieces together, and glass the outside.

The inside would look like this with * representing the fabric:

**********
*----------*
****/ \****
----------------

Earlier, "dirigible designer" wrote:
My dirigible design requires a few long spars curved into C-
shapes....

...They need to be light, strong and stiff. [what's new?]...
My present thoughts favor a thin fiberglass skin around
a bundle of polypropylene tubes...

In earlier posts, you were writing about aluminum skins. Be aware that
composite structure plus aluminum skin is often an unhappy mix. The
modulii of elasticity for the two types of materials are very
different. It's easy to have a structure with plenty of strength, but
with a stiffness so much lower than that of the skin that the skin
kinks or tears at stress levels well under what you thought was the
design load, and nowhere near the ultimate load.

Bob K.

On Apr 8, 10:58 pm, Ernest Christley wrote:
Morgans wrote:
"dirigible designer" wrote in message

Now I just have to figger out how to get those layers of
fiberglass, (matt and cloth), on the inside of the hollow triangular
spar 8-]

Use the opposite of vacuum bagging; pressure bag it.

Make up glass cloth with epoxy squeegee into it, then lay it on the foam,
lay on the release cloth, make up the pressure bag, fold it all up, bind it
on the outside with tape or something, then put the pressure to the bag and
let it cure.

You will have to cut an inspection panel every so often, to get the release
cloth and bag out, but they are easily closed later.

Good one.

Or just lay up one side, with the edges cut at a proper angle. Fabric
flow from the table, uphill, across the inside and downhill back to the
table. Peel-ply the hillsides. Once it cures, trim the excess fabric,
flox the 3 pieces together, and glass the outside.

The inside would look like this with * representing the fabric:

**********
*----------*
****/ \****
----------------- Hide quoted text -

- Show quoted text -

That would work, but you still have the issue of making up a curved
spar from a bunch of flat panels. Lots of very careful angle-cutting
required. The beauty of composites is the ability to do smooth
curves. Why not a tubular spar? You could use a swimming "noodle" to
do a mockup or an R/C proof-of-concept ship.