Calculations, models and trials have provided us with a more precise idea of "fuel" consumption in the case of a "dual-energy" engine:
A 40hp engine would need approx 1 liter of fuel (any fuel that is) for its external and permanent "air-heating" system.
In this configuration air is taken in from the athmosphere, compressed (via the compressor part of the pistons), heated (to obtain more volume = more energy), drives the engine side of the piston.
For a twin-engine installation 2 liters of fuel / hour will provide propulsion.
Not bad in times where the barrel of any fuel is rising without forseeable ceiling!
