On Oct 3, 1:29*am, The Natural Philosopher wrote:

Indeed, and the 100% efficient prop is of course the infinitely large
one turning infinitely slowly, for generating STATIC thrust.

Yup - we were going to go with one of those on the Blackbird, but JB
brought up all these silly problems about the height of the pylons,
cost of fiberglass - blah, blah, blah.... : )