The Nelson H-63, known in the US military designation system as the YO-65, is an American dual ignition, four-cylinder, horizontally opposed, two-stroke aircraft engine that was developed by the Nelson Engine Company for use in helicopters and light aircraft.
[1] The H-63 was designed in the late 1950s specifically to power the sort of very light single-man helicopters that the US Army was investigating at the time.
Application for certification was made on 15 March 1958, and the engine was certified under the CAR 13 standard on 8 February 1960.
Ownership of the type certificate was transferred to the present owner, Charles R. Rhoades of Naples, Florida, on 14 February 1996.
[1] The four-cylinder engine runs on a 16:1 mixture of 80/87 avgas and SAE 30 outboard motor oil.