I don't see any circuit breakers that reset after cooling down and toggling the master switch.
But I do see some "not FAA approved" electronic circuit breakers in the Aircraft Spruce (2016) catalog.
They shut down with over or under voltage and reset by toggling the master.
Might be what...
That is a bit too simple. In his test he has the fan blowing the flat backside of the prop. In flight the wind hits the curved frontside. I did it with my fan and my prop, big difference. It barely rotates in the correct orientation and doesn't hurt when sticking my finger in it.
One guy on the yahoo small engine forum flew his vertical shaft Briggs with the 90° belt drive on his powered parachute. I would think three feet of straight belt should twist ok.
I wouldn't call it a twin engine airplane because if one engine seized it would stop the other engine same as any...
Long V belts can be a shaft alternative. The engine would be vertical shaft like a Briggs 810 or two- stroke mounted vertical. The belt is turned 90° around rollers to the horizontal prop shaft pulley sheave.
Two Briggs 810 could power one prop for about 60hp.