You might find this interesting.  A rotary engine at 30,000ft
http://www.bmaa.org/upload/flo/fo1007.pdf  scroll down for full story

Marc
Montreal, Canada

It was that flight that inspired me on the overall idea and the rotary
engine in particular. The TAS was over 100 mph if I recall at 28,000 ft -
quite something when you consider it's a draggy parachute even if
streamlined. Bear still had a climb rate and could have gone over 30,000 ft.

One of the key elements in the engine prop combination is a much larger prop
than one would normally carry for a regular airplane. Lots of thrust with
drag but top speed is not your objective.

We would look at putting something in the 8 to 12 ft diameter range on a 300
Hp engine to increase overall thrust. Additional gearing down would be
necessary, but this has been done already in high altitude applications.

Cheers,
Brian
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Brian Feeney
DreamSpace and The da Vinci Project
bfeeney@davinciproject.com
http://www.davinciproject.com