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Nelson Engine Co H-63 / YO-65


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.

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.
Engines were produced for Nelson by the Franklin Engine Company of Syracuse, New York under a production certificate. Originally the type certificate was held by the Nelson Specialty Corporation of San Leandro, California, but it was transferred to Nelson Aircraft of Irwin, Pennsylvania on 15 July 1966. Ownership of the type certificate was transferred to the present owner, Charles R. Rhoades of Naples, Florida, on 14 February 1996.

The four-cylinder engine runs on a 16:1 mixture of 80/87 avgas and SAE 30 outboard motor oil. It is equipped with a single Nelson E-500 carburetor.


Vertically mounted version for use in helicopters, producing 43 hp (32 kW) at 4000 rpm.
Horizontally mounted version for use in light aircraft, producing 48 hp (36 kW) at 4400 rpm for take-off.

Hiller YROE

Lobet/Shafor Ganagobie


Type: Four-cylinder, two-stroke, dual ignition, vertically mounted helicopter engine
Bore: 2.6875 in (68 mm)
Stroke: 2.75 in (70 mm)
Displacement: 63 cubic inches
Dry weight: 76 lb (34 kg) including the cooling fan, cooling shroud and clutch
Fuel system: Nelson E-500 carburetor
Fuel type: 80/87 avgas
Oil system: premixed oil in fuel, SAE 30 outboard motor oil mixed at 16:1 fuel to oil
Cooling system: fan forced air
Reduction gear: none
Power output: 43 hp (32 kW) at 4000 rpm
Compression ratio: 8:1





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