How did they start up aircraft engines during WWII? This is from 20 years of RL flying and aviation experience.
It was roughly three different ways:
1) The ground crew inserts a crank into the cowling and they then wind up something that sounds like a flywheel to get it spinning as fast as they can. Then the pilot hits a start up switch and starts the engine. I'm guessing that that start up switch engages a clutch which connects the spinning flywheel to the engine, transferring the power stored up in the spinning flywheel to the engine, turning it over.
2) The pilot hits a switch which ignites a gas cartridge (a cartridge with gun powder in it?) generating pressurized gas, and this in turn (through a turbine?) gets a flywheel spinning. The pilot then, when he hears the flywheel spinning at top speed, hits another switch, which engages a clutch connecting the spinning flywheel to the engine, turning it over.
3) A ground crew member plugs into the cowling what looks like an electric cable connected to a small portable generator or a large battery(?). The electrical power from this generator or battery then provides power to an electric motor which gets a flywheel spinning, as described above, or provides power to a regular electric starter, as on a car, which then turns over the engine getting it started. I know that on the B-29, a small so called "put put" generator was installed right on the plane, powering what looks/sounds like an electric engine starter.
The start up process for radial engines vs. water-cooled engines was basically the same. (Besides the normal process of clearing out any accumulated oil in the lower cylinders by manually turning the engine over.)
These old engines could not just turn off and on in flight. The re-start process in almost all aircraft in WW2 is a 3 minute or longer procedure, and required the pilots complete attention. That being said, the aircraft would lose power and would need to glided for some distance before re-firing. In flight power lose would be an emergency situation very fast. Then again here in AH, we have are cartoon pilots that think this was an ACM tactic. It wasn't.
Aco 1/58 Avn H.A.A.F 18th Airborne.