My son and I fly model airplanes. Electric powered models started to become practical about 10 years ago and are now as common as the methanol-fueled 2 and 4 stroke internal combustion engine models (commonly called glow engines per their platinum-element glow plug which reacts with the methanol fuel and provides a continuous source of ignition when we remove the starter batter leads.)
I'm sold on electric flight. We use lithium-polymer batteries, a very efficient brushless multi-pole electric motor and a solid-state speed controller.
The motors themselves do produce an audible noise depending on the particular configuration. Biggest noise is the prop but spin this up as high as 15k-16k rpm.
Biggest advantage of electric flight is the performance. We get instant torque when we hit the throttle. Some even describe it as "gut-wrenching." While they do produce some noise they are markedly quieter than their glow engine cousins but, because of the oil mixed in with the fuel tend to cover the entire model with an oily slime after a typical flight. This usually requires the finish of the model is totally fuel proof, requiring specialized paints and coverings. The electric powered models remain clean.
