Pardon the strange design. This was built off a crappy old top speed project of mine. Ignore the stupid intake.

This is an experiment I tried because I'd never seen it before. It allows you to fit large prop blades close to each other by spacing them and using counterrotating props. To use it, barely activate the inner engine with the throttle so that the "shared" props (in between the two engines on a wing) are parallel. Then activate group one, and you're ready to go. Video demonstration here: https://everyplay.com/videos/42217363

NOTE: unfortunately it seems to take badly to rolling (read: explosions). This is likely because rolling the plane creates counter-rotation or additional rotation on a given prop, leading to a desynchronization of position, meaning the props collide. I haven't been able to alleviate this, but let me know in the comments if you have success!