joining aluminum sheets techniques

I'm making an eight-foot study model of a personal lifting body
dirigible design of mine. I believe the ribs will be made of
fiberglass and widely-spaced for lightness. I want the skin to be
aluminum sheet.
It would be desirable to avoid installing a rib for every seam
between sheets of aluminum. So, I would like some advice on what is
the state of the art with infallible glue joints between hard aluminum
sheets.
I imagine there is no alternative to crimping the meeting edges as
is done when sewing two sheets of cloth together.
No way am I interested in rivets.

"dirigible designer" wrote in message
oups.com...
I'm making an eight-foot study model of a personal lifting body
dirigible design of mine. I believe the ribs will be made of
fiberglass and widely-spaced for lightness. I want the skin to be
aluminum sheet.
It would be desirable to avoid installing a rib for every seam
between sheets of aluminum. So, I would like some advice on what is
the state of the art with infallible glue joints between hard aluminum
sheets.
I imagine there is no alternative to crimping the meeting edges as
is done when sewing two sheets of cloth together.
No way am I interested in rivets.

How about using sheets that are half as thick as you need and then glue them
on top of eachother with full overlap? I've used some 3M aluminum glue that
is stronger than the metal itself..

Rob

"dirigible designer" wrote in message
oups.com...
I'm making an eight-foot study model of a personal lifting body
dirigible design of mine. I believe the ribs will be made of
fiberglass and widely-spaced for lightness. I want the skin to be
aluminum sheet.
It would be desirable to avoid installing a rib for every seam
between sheets of aluminum. So, I would like some advice on what is
the state of the art with infallible glue joints between hard aluminum
sheets.
I imagine there is no alternative to crimping the meeting edges as
is done when sewing two sheets of cloth together.
No way am I interested in rivets.

Wow, where to start.

First, I would think you need to do a reality check, here.

How big will your full sized lifting body be? Figure the surface area of the
full sized design, and then figure how much weight the aluminum to cover
that area would weigh.

Next, figure what the volume of the full sized model is, and how much
buoyancy the helium in that volume would provide.

I think you will find that the volume of helium in the full size model would
not come close to lifting even half of the weight of the aluminum sheeting.

Once you do this, and run the numbers, I think you will not even need to
mess with the study model. The numbers will not work.

There is a reason that balloons and dirigibles are not covered with
aluminum. The areas and volumes are huge, and the only way to make it work
is with ultra lightweight and strong "fabrics."

As for not even considering rivets, I doubt you have any idea of the costs
and technology of what it takes to join aluminum without rivets. You have
friction stir welding, or glues. Friction stir is high tec and expensive to
set up. Glues are temperamental, and takes many complex steps and chemicals
to prep and bond the surface, and is also expensive, if you can even reach
the reliability needed for such an application. I won't go into the idea of
having ribs so far apart that there is not even a rib for the length of an
aluminum panel. It will not have enough support to hold its shape under
flight conditions.

I don't want to rain on your parade, but it looks to me (from how you
described your concept) that the whole idea is unworkable. If you have
further explanations that could convince me (and others) differently, go
ahead.
--
Jim in NC

"Rob Turk" wrote in message .. .
snip

I've used some 3M aluminum glue that
: is stronger than the metal itself..
:
: Rob
:
:

I would like to see what 3M product you are talking about...

Dan D.

Reminds me of the time when I was working on a ship, and somebody
started a kitebuilding contest. One of the engineers built one like
the proverbial brick s##thouse - then put a long tail of rags on it
(which got wet in a puddle on the deck), No, it didn't fly, even in a
stiff breeze. He didn't have a clue - and soon got frustrated and
threw the kite over the side.

On 13 Mar 2007 14:47:13 -0700, "dirigible designer"
wrote:

I'm making an eight-foot study model of a personal lifting body
dirigible design of mine. I believe the ribs will be made of
fiberglass and widely-spaced for lightness. I want the skin to be
aluminum sheet.
It would be desirable to avoid installing a rib for every seam
between sheets of aluminum. So, I would like some advice on what is
the state of the art with infallible glue joints between hard aluminum
sheets.
I imagine there is no alternative to crimping the meeting edges as
is done when sewing two sheets of cloth together.
No way am I interested in rivets.

Marine sealants like sikaflex or 3M 5200. would probably work but you
would have to come up with some very fancy clamping fixtures to let
it cure. blind rivets would be way easier. But like Jim said it will
be too heavy to fly.

Thanks for the suggestions to my question of how to join aluminum
sheets [without rivets] for making a dirigible.
The advice that an aluminum dirigible won't fly is not borne out by
reality. Do a websearch for Schwarz airship. It was aluminum and flew
in 1897. That's right, eighteen ninety seven. Then there was the Navy
ZMC airship which flew for ten years back in the forties.
One "advantage" of an aluminum skin is that the skin holds the lift
gas, saving the weight of internal separate bags. Also, aluminum,
being stiff, can add some monocoque strength to the frame.
I'm thinking of employing some corrugated alum. for added stiffness
and reduced drumming. It doesn't look nice but might work well.
Any ideas? [negatives not needed ;-]

dirigible designer wrote:
Thanks for the suggestions to my question of how to join aluminum
sheets [without rivets] for making a dirigible.
The advice that an aluminum dirigible won't fly is not borne out by
reality. Do a websearch for Schwarz airship. It was aluminum and flew
in 1897. That's right, eighteen ninety seven. Then there was the Navy
ZMC airship which flew for ten years back in the forties.
One "advantage" of an aluminum skin is that the skin holds the lift
gas, saving the weight of internal separate bags. Also, aluminum,
being stiff, can add some monocoque strength to the frame.
I'm thinking of employing some corrugated alum. for added stiffness
and reduced drumming. It doesn't look nice but might work well.
Any ideas? [negatives not needed ;-]




He didn't say it wouldn't work.

Just that at this scale it would ne too heavy to fly.

double - square - cube relationship...

Richard

"dirigible designer" wrote:
Thanks for the suggestions to my question of how to join aluminum
sheets [without rivets] for making a dirigible.

Hi "dd" (Allen?). I am familiar with the history of aluminum airships.

One remote possibility it to look into/experiment with aluminum
soldering. Once upon a time I did not think it was possible to solder
aluminum, but if you do a Google search on the subject you should find
some information on the subject. It's not impossible, merely difficult.

As to glues, I would suggest going to McMaster-Carr's website
(http://www.mcmaster.com/) and browse some of the categories under
"Fastening and Sealing". Perhaps a mix of some blind or solid rivets (to
provide structural strength) combined with a construction adhesive (to
provide a seal and some shear strength) might work?

Anyway, I'd suggest you try buying some likely candidates and try some
small-scale experiments.

Also, I believe there is a patent for the rivet machine that was invented
in order to build the ZMC airships, but I don't have the patent number
handy. But check patent 1,706,830. It is the main patent related to the
ZMC airship design. It should also hopefully provide a starting point for
finding the other patents related to the work done on the ZMC airships.

I'm thinking of employing some corrugated alum. for added stiffness
and reduced drumming. It doesn't look nice but might work well.

Well, the ZMC-2 used something like 0.006 inch thick aluminum. You can
now get hard-temper aluminum foil from MacMaster-Carr that is 0.002 inch
thick. But wider rolls (less joining needed for the same surface area)
are available down to 0.003 inch thick. Soft-temper of course can be had
down to 0.0007 inch thick. About the temper of house-hold aluminum foil,
though.

Corrugated is going to drive your raw material cost up (unless you build
equipment to corrugate the raw sheets or foil yourself). And I would
expect it would impose a large drag penalty, too.

Lastly, it is really hard to build working reduced-scale prototype
airship designs. They don't scale down well.

Good luck!

Jim Logajan wrote:
"dirigible designer" wrote:
Thanks for the suggestions to my question of how to join aluminum
sheets [without rivets] for making a dirigible.

Hi "dd" (Allen?). I am familiar with the history of aluminum airships.

One remote possibility it to look into/experiment with aluminum
soldering. Once upon a time I did not think it was possible to solder
aluminum, but if you do a Google search on the subject you should find
some information on the subject. It's not impossible, merely
difficult.


What about welding it?