Dave,

Your on the right track Dave.
I hold patents on inner tube joining machinery and as you say there is a
difficulty in using a regular joining machine at the smaller sizes.
Butyl inner tubes have been around since 1970.
An inner tube is made from a straight length of "tube" and then joined end
to end in a "joining machine"
Semperit Tyres produced and licensed the first joining machines that were
successful on butyl.
Goodyear Tire [licensed by Semperit] was supplying "airstop" tubes through
the 1970's.
Butyl is a oil product and significantly lower in cost than natural rubber.
However, natural rubber "joins" much more easily than butyl and therefore
remained the tube to use for the aviation industry.

And of course being for aviation, butyl tires are now sold at a premium, but
are most definitely lower cost to make because of lower raw material cost.

Roy
Piper Archer - N5804F






"Dave Butler" wrote in message
...
Mike Murdock wrote:
Where else but in aviation do you have to pay extra to get inner tubes
that don't leak? You gotta love it.

My understanding is that there is an actual technical issue. The kind of
rubber (butyl?) tubes that don't leak are difficult to make in small tire
sizes with small radius of curvature.

Dave

-Mike

"Kyle Boatright" wrote:
...
And they are not cheap. I believe Goodyear has come out with a version
too.

Desser carries both brands.

IIRC, my 5" x 5" airstop tubes were $30+ each. New tires were $50/ea.
It hurt paying almost as much for the tubes as the tires. Still, only
having to air the tires 3 or 4 times a year is nice.

KB