Could a hybrid electric steam plane be more efficient at altitude than at sea-level, and how to optimise it to frigid air?

Question

In the thirties a steam powered plane was built. video

Could a hybrid electric steam plane be more efficient at altitude than at sea-level, and how could such a steam engine be optimised to benefit from frigid air at altitude?

Perhaps there are two advantages to going hybrid.

1. The steam engine can be down sized to cruise power levels.
2. The radiator is being cooled by frigid stratospheric air < -40 deg so can be smaller.

This is a parallel hybrid, the electric motor drives the propeller until the plane is at altitude. Once at altitude the electric motor is disengaged and the small steam engine starts up and engages with the propeller.

[edit]

There is a replica of the Besler engine at the Smithsonian. It has more specs than the video. It had a condenser

Steam Car Developments and Steam Aviation, VOL. III. JUNE, 1934 NO. 28., The Besler Steam-Driven Aeroplane

'Under the fuselage nose is the condenser, which is simply a section of an ordinary petrol car radiator, and this is said to be sufficient to recover more than ninety per cent. of the water from the exhaust steam.'

'The tests have shown that ten gallons of water is sufficient for a flight of 400 miles.'

Answer 1

Forget the electric stage - when using steam, you will most likely already have mechanical energy and when ducting that steam through a turbine, even rotational energy to turn your propellers. What advantage do you expect from converting that rotational to electrical and directly again to rotational energy?

That design could be simplified even more: Instead of heating water, the fuel could heat compressed air and let that run through a turbine. That is how any modern jet engine works.

In order to keep mass down, the steam would need to be condensed in a cooling circuit. While the wing surface could be used for this, the required piping would add a substantial weight penalty. In an open circuit where the relaxed steam is simply dumped overboard (like on the Besler biplane or most steam engines), range would be rather limited.

There was to my knowledge a single attempt at building a steam-powered airplane with steam condensation. This was a version of the Messerschmitt 264 bomber which was supposed to run on a mixture of coal powder and heavy oil instead of gasoline. It was never completed.

Answer 2

Possible? Yes. Viable? No.

A steam airplane is possible to build and fly, as a novelty hobby project. Modern technology will even allow a steam-powered airplane to have performance comparable to a very low-end homebuilt.

The term "airliner", however, implies regular passenger service for the purpose of getting from A to B. A steam-powered passenger plane is going to be completely useless for that purpose, as long as internal combustion engines exist. ICE have better efficiency, better power/weight ratio, and better reliability, sealing the deal.

The only advantage steam engines retain in the ICE era is the ability to run on solid fuel, like coal or deadwood picked up along the way. This kind of fuel produces much less power than oil and can sustain trucks hauling supplies to a besieged city, but not an aircraft that means to do more than short hops a few feet above the ground.

While the exhaust of hydrogen-powered turbines is mostly steam, so is the exhaust of kerosene-powered turbines, so both still count as gas turbines, not steam ones.

One possible modern attempt at a steam-powered airplane (not airliner) was the Tupolev Tu-95LAL, a flying lab for prototyping a nuclear-powered airplane. The Convair X-6 was another attempt that also stopped well short of any nuclear-powered operation. The only reason they'd count as steam-powered (had they actually used their reactors for power) is that steam is required to extract mechanical power out of operational nuclear reactor designs.

With liquid hydrocarbon fuel, gas turbines or at least piston ICE give you more power and more range for the same amount of weight, so steam will not return in this form. The advances in compact nuclear reactors might see more use of mobile steam power, but aircraft are more likely to go outright electric than nuclear.

Answer 3

With modern materials and modelling this should certainly be possible. The efficiency is likely to be VERY low though. If I was inclined to try, I would use the steam engine to create electricity to power the electric motors that you have for take-off - that would probably save a bit of weight. On the other hand, a sterling engine would probably be a bit better again - they use air or some other gas as the working fluid, rather than having to carry water or some other heavy liquid.

Answer 4

Look at contrails. In a way we are already doing it as combustion produces water, as well as CO2.

This concept is actually very similar to a small motor charging a battery to run an electric motor (diesel-electric). There is a significant weight savings here, which partially offsets the extra weight of the battery or pressurized steam tank. The motor only needs to produce the AVERAGE amount of power required, peak loads are handled by energy stored in the battery or steam tank. And the music wasn't that bad either.

So efforts to make it practical would be recovery of the steam, reducing the amount of water required to operate.

But if you used pure hydrogen as fuel, it may be possible to recover water from the exhaust by condensing it, and then re-extract heat energy from the engine to make steam.

The hydrogen (or natural gas) would power conventional propulsion, with water/steam utilized for (total loss) cooling and/or extra thrust.

But weight and complexity factors would have to be considered.