Bill Lear was working on a steam turbine for a bus. I have not heard of any work on a steam powered airplane by Lear.
Also, the most efficient steam engine I can find is still way below gasoline engines in performance and that's a very heavy and complicated device.
If you want a steam engine aircraft, these would probably be the people you should talk to...
Cyclone Power Technologies - How It Works
To compare some numbers, a Rotax 912S is about 100HP at 136lbs.
Cyclone Power Mark V is 100HP at 336lbs. (Probably not weight optomized for aviation, but it was designed for use in a car)
I seem to recall the Besler engine being 40HP at 150lbs?
If you really want to add a turbine, how about turbo-compounding? It's already been shown to work on aircraft engines.
Turbo-compound engine - Wikipedia, the free encyclopedia
Here is a more in depth article on the Besler aircraft and engine system. The boiler is a flash type that operates at ~1200PSI and 800*F. The engine is a double acting cylinder, pressure compounded 90* V twin. 150HP @1625RPM.
William & George BESLER --- Steam-Powered Airplane -- 2 Articles & 2 US Patents
Last edited by Dieselav8tor; February 1st, 2010 at 12:19 AM. Reason: clarification and punctuation