My character crashed his plane. Whoops, what an idiot! He needs to get a small flywheel. I figure there should be some part of the engine that can be used to make a flywheel. Any heavy disk with a hole in the center will do, preferably between 3 and 6 inches. Thoughts? Edit: small single engine propeller plane, is as specific as I've gotten so far.
There’s quite often a flywheel in the starter mechanism of propeller engines. Older ones were hand cranked and their momentum would be used for, effectively, a jump start. I’d be confident with the newer ones that the hand cranking is just replaced by a motor... so, yes, they exist. eta...but not 3”. 6” might be rare too. They tend to have their weight over a bigger diameter. Plane would need to be a small one.
Electrician on F18s. I don't know props. BUT, planes that small should have disk brakes. Just disassemble a wheel and strut to pry it out.
The rotor on a disk brake may be a little larger than you wanted, at about a foot in diameter, but if you were able to get it out, the circular central cover plate on the disk brake housing may work in the five to six inch range. Getting it apart may be a little tricky though.
I have an observation... your pilot has the ability to pull apart his engine, but not make a flywheel? What kind of tools and resources are around? Is there some reason the flywheel needs to be machine precision or toughness? What's it for? Also, does it have to be round? For example, if you're making a gyrocompass, the flywheel in no way has to be round, it just has to be balanced, a long bar would work just as well as a disc.