In the thirties a steam powered plane was built. video
Could a hybrid electric steam plane be viable?
Perhaps there are three advantages to going hybrid.
- The steam engine can be down sized to cruise power levels.
- The radiator is being cooled by frigid stratospheric air < -40 deg so can be smaller.
- The efficiency may be improved if a kalina or lower temperature condensing fluid is used that can exploit the frigid heat sink.
The electric engine is used to reach altitude, but the steam (or other rankine cycle) is used at altitude.