The rotary engines were certainly a challenge to the pilot. They had a total loss oiling system & the lubricant of choice was CASTOR OIL. Flying with your mouth open would certainly keep you regular!
Another strange one that is in use today in the British 432 APC is the RR K60; 6 cylinders, 2 crank shafts, 2 sets of pistons (12 total) meeting in the middle to form the combustion chamber. These are a multi-fuel engine. This looks like the result of the Detroit Diesel designers taking LSD, but it actually works!