I suppose I should just let the subject drop.  However, on February 3rd
I spent quite a bit of time photographing an uncovered section of an
air motor in its various stages of open and close and, along with some
explanatory material, I submitted it for inclusion in the MMD Archives.
To date, I haven't heard whether it will be posted.

 [ We are working with Dave to find a mutually compatible public
 [ (non-proprietary) file format for his article.  -- Robbie

One point about the air motor that I haven't seen mentioned in the
discussion is the fact that the action of the eccentric crank shaft
limits the pneumatic to being open a maximum of 2-3/4 inches and closed
to a minimum of 1-1/2 inches.  Therefore, the cloth is never stretched
fully open or cramped fully closed when covered to open 3 inches.
I believe that this has the effect of greatly extending the life of
a pneumatic that has to flex thousands of times during its intended life
span.

I would also like to point out that I have at this time two Aeolian air
motors of 1925-1928 and that both of them were originally covered to
open 3 inches.

Dave Geissinger