[Spaceships] Non-TL^ Power Plants and air propulsion below TL7?

[vicky_molokh]

Greetings, all!

I noticed there's a shortage of power plants below TL7. Boilers are TL7 for some reason. Fuel Cell has no RAW analogues below TL7 . . . how much endurance would a power plant based on some sort of combustible fuel have at TLs 6 and below?

Likewise, what stats should I use for the equivalent of WWI planes' propulsion, those barely exceeding a hundred mph? Would Ether Screws be a close enough fit? (They seem to provide more speed than the planes of the age had).

Thanks in advance!