On Radio Three this morning, "London Transport Suite" by Sidney Torch (great name!) full of themes evoking/mimicking steam locomotives. Made me wonder; how the blazes would you represent a diesel, or electric, loco in a musical piece without recourse to recordings of the real thing?
Carrying on with the thought I also wondered about jet propelled aeroplanes. A multi-engine propeller aircraft, even a turbine engined one, has a beat frequency that could be used though even that's not so marked in modern aeroplanes as older ones, but a jet?