Actually these electronics are real sophisticated and while a tad expensive and weight is a challenge the can mimic Don Garlits AA gasser very realistically...or a Roll Royce Merlin, or a super Giant Locomotive coal fired engine including the noises of the drive wheels and steam spews....
There is an ever growing library of sound files to play on these amplified sound systems
BUT loud sound demand a decent SPEAKER and enough drive (WATTS) to amplify the sound so we can enjoy it...miniaturization is about state of the art but a good LOUD system is HEAVY
I know guys who fly RC WWII birds that actually have sound sequencer to simulate start, run up, back to idle, taxi to run way, Lock brakes and run up,,,unlock and take off, round the pattern, Fast low pass... climb to altitude, bleed off, back to idle, flop over the top, dive with accelerating growling and screaming engine.... truly impressive air show out of a 100" wing span Foam ARF P51....
BUT I know the pilot...the snazzy electronics cost way more than the simple Hobby king ARF/RTF Mustang