http://seanlinnane.blogspot.co...ler-steam-plane.html
A Travel Air 2000 biplane made the world's first piloted flight under steam power over Oakland, California, on 12 April 1933. The strangest feature of the flight was its relative silence; spectators on the ground could hear the pilot when he called to them from mid-air. The aircraft, piloted by William Besler, had been fitted with a two-cylinder, 150 hp reciprocating engine

Didn't Bill Lear experiment with a 'closed-loop steam' engine for such a use - one that did not exhaust the spent steam but re-heated and recirculated it? I think he even developed a fluid called "Learium" for the application?