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Urethane coated pack cloth would indeed make a durable membrane.  I've used
it to make drum heads for cardboard (concrete form) drums and it holds up
very well to getting "whomped" quite energetically.  One supplier is Seattle
Fabrics http://www.seattlefabrics.com/nylons.html  I have no idea if their
pricing is competitive, as I'm ordering small quantities and went for the
convenience of a known source.

We did large air cannons out of trash cans and used vinyl shower curtain
secured by bungie cords.  I don't think this material would be durable
enough for exhibit use, but it does suggest that the nature of the material
is not critical to the effective generation of vortexes, at least not in the
whomping version.

Dave Smith


On Thu, Sep 17, 2009 at 11:50 AM, David Savory <[log in to unmask]>wrote:

> ISEN-ASTC-L is a service of the Association of Science-Technology Centers
> Incorporated, a worldwide network of science museums and related
> institutions.
>
> *****************************************************************************
>
> After some experimentation, we went a different direction with our air
> cannon. We put a sheet of non-elastic material across the bottom for
> visitors to whomp. It's loosely attached and moves a decent volume of air
> when it's struck. Because the cannon is angled upward 45 degrees or so, it
> tends to fall downward again after the blow has been delivered. The material
> is a rubberized cordura (whose trade name, manufacturer and supplier are
> known only to a colleague who is on vacation) which is kinda like backpack
> fabric. Works just fine.
>
> David Savory
> Community Extensions Program Developer and Exhibit Curator
> Science World British Columbia
> TELUS World of Science
> 1455 Quebec Street
> Vancouver, BC
> Canada V6A 3Z7
>
> t: 604.443.7561
> f: 604.443.7434
> e: [log in to unmask]
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> -----Original Message-----
> From: Informal Science Education Network [mailto:
> [log in to unmask]] On Behalf Of Erich Rose
> Sent: Thursday, September 17, 2009 7:41 AM
> To: [log in to unmask]
> Subject: Air Cannons
>
> ISEN-ASTC-L is a service of the Association of Science-Technology Centers
> Incorporated, a worldwide network of science museums and related
> institutions.
>
> *****************************************************************************
>
> Hey folks,
>
> I am running into a bit of a problem specifying the correct elastic
> material for an air cannon. I have worked on several of these and we always
> used black neoprene rubber sheet. We used material already laying about the
> shop so I had to guess at the proper durometer. We used material 1/16" thk
> but it would tear fairly easily.  For the one I did recently I specified an
> elastic natural Gum rubber with a durometer of about 40A. It proved way too
> stiff.  The folks at McMaster-Carr have suggested an Ultra-elastic Natural
> Latex rubber with a durometer of 35A.
>
> The cannon is smaller than most at 8" diameter versus the usual 12-18"
> diameter ones most of us have built. But it is shooting a shorter distance
> and the mock up worked well with a plastic bag as diaphragm.
>
> Can anyone offer a specification for a good elastic diaphragm?
>
> --
> Erich Rose
> Exhibit, Environmental and Industrial Design
> 807 The Living End
> Austin, TX 78746
> 512-626-9930; [log in to unmask]
>
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-- 
David L. Smith
Da Vinci Science Center
Allentown, PA
http://www.davinci-center.org

Please consider the environment before printing this email.

Everything that needs to be said has already been said. But since no one was
listening, everything must be said again.  -- Andre Gide

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