keep in mind that the flywheel also acts as a cooling fan for the cylinder head, which in a stationary application is necessary, in a plane where a propeller is placed directly in front of the cooling fins, this is not an issue at all...

at most you might loose a couple ounces using electric ignition, a flywheel and magneto weigh about a pound, if you add up the weight of an ignition module and battery needed to run it (a standard reciever type battery is supposed to last around an hour of run time), you're 3/4 or so of the weight of the flywheel and coil... the magneto is kind of like free ignition, and if you had to custom make some kind of cooling fan, that's a lot more trouble than it's worth...