On Thu, 26 Jul 2018 12:21:52 +0100, "Bert Coules"
wrote:

Many thanks for the new responses; much appreciated.

GB, a deflationary bang might actually add to the effect. The possibility
of an inappropriate slowly-collapsing-balloon sound is a little off-putting
(though I appreciate that it would be more likely to be a drawn-out hiss, as
you say). Also I do need a near-instant vanish rather than a slow collapse.

If the 'opening' was large enough and the volume of the frame small
enough it should deflate pretty quickly, especially if assisted by
some other means (elastic etc).

For the opening it could be a neck of a container (pringles can?)
bonded to the skeleton that has it's lid removed by a spring loaded
mech.

If it was positioned in the middle (vertically) the wind resistance
over the length would be minimised?

FWIW, the air pressure in my Zodiac inflatable dinghy is ~3.6 PSI and
that makes it stiff enough to support 4 people, an outboard motor and
all bouncing about on the sea. ;-)

Cheers, T i m