Stefan Gasparin, of Czech Republic, began building CO2 engines in 1972. He designed and built over 60 variations from 1 through 18 cylinders including single-cylinder, inline, opposed flat, “V,” rotary, and radial configurations. He was registered in the Guinness Book of World Records in 1989 for producing the world’s smallest CO2 engine.
Mr. Gasparin’s 9-cylinder G24NR is a rotary rather than a radial engine. That means that the crankshaft is fixed to the airplane’s firewall and the entire engine rotates around the crankshaft, with the cylinders spinning at the same rate as the propeller. This was a common design for early aircraft in WWI. The bore on each cylinder of this engine is 3.175mm and stroke is 3mm. It weighs just 34.5 grams.