Prop engines consuming fuel should generate electricity.

[Shaun]

Motors that consume liquid fuel like the R121 and R7000 should be able to generate electricity, depending on the torque output. Even the smallest torque settings like 1-2%, which can power a 2-4 blade type B prop should be able to generate enough electricity to power a cabin light or landing light at night. This became apparent because I don't use lights during the daytime making solar panels useless, and the RTG is often more expensive than the aircraft itself.

[XLjedi]

They could use some sound too...

If not the motor directly generating electricity, perhaps just an "alternator" part similar to the fuel cells that could convert LF to electricity maybe as a function of engine torque/power?

[Lisias]

Not necessarily.

Aviation engines like the Wasp Major and Duplex Cyclone don't do it. Airplane builders attach the alternator they think is adequate to the shaft to generate electricity. On multiple engine aircrafts, not all of them have alternators - sometimes, only one engine has one, and the pilot had to rely on the APU if that engine fails (to tell you the true, some commercial airlines are this way until nowadays).

Fuel cells are excellent APUs , but I agree that an alternator should be provided to be attached to the prop engines - or your idea should be implemented. It's probably easier to implement your idea, however.