Flaps and speed brakes are separate. You wouldn't be using regenerative braking for the same purposes as speed brakes/spoilers. You use spoilers specifically wh

Flaps and speed brakes are separate. You wouldn't be using regenerative braking for the same purposes as speed brakes/spoilers. You use spoilers specifically when you want to kill speed, or more often when you want to quickly lose altitude. Sucking potential (and kinetic) energy up and putting it in the battery would accomplish a lot of the same goals. You're not likely to have shock cooling issues in an electrically powered aircraft. Shock cooling is a piston aircraft thing, and is mostly an issue on turbocharged aircraft. You're not worried about shock-cooling the engine, you're worried about shock-cooling the hot side of the turbocharger. So in the use-case of spoilers being used to keep the engine spooled up, you're right that it wouldn't be necessary here. And as far as pulling the throttles to idle and more-or-less gliding during the descent, that's the ideal, but in the real world spoilers are used to drop more quickly all the time for non-emergency reasons. If you have favorable winds up high, you might choose to stay up high until absolutely necessary and then quickly descend to make better time. In trainer class aircraft you don't typically have spoilers to help this, so you end up cross controlling the aircraft to increase the sink rate. If I could have a big ol windmill in front of me in a 172 to do that, it'd be pretty darn nice.