Aviat Aircraft of Afton, Wyo., and Minneapolis-based Aviation Foundation of America introduced a dual fuel, piston-powered aircraft that operates on either compressed natural gas (CNG) or aviation gasoline (avgas) this week at EAA AirVenture Oshkosh. The proof-of-concept aircraft fuel system is installed on a standard Aviat Husky A1-C fitted with a CNG belly tank.
The pilot manually selects the fuel source at the flick of a switch, and the CNG fuel control system automatically compensates for density altitude, engine timing variations and other factors. With the exception of the fuel controls and belly tank, N15NG is a stock Husky, and the only modification to the Lycoming IO-360-A1 D6 engine was the installation of new pistons to increase the compression ratio from 8.50:1 to 10:1 to capture more of the fuel’s 138-octane power. The modified Husky is capable of operating entirely on CNG, but the current lack of refueling stations makes total reliance on CNG impractical.
AFA president Greg Herrick originated the idea for the CNG-powered aircraft, and approached Stu Horn, president and owner of Aviat, early this year about taking on the project. Horn concluded CNG represented a potential here-and-now solution to a variety of issues surrounding avgas, and assembled a team (eight from Aviat and half-a-dozen outside CNG experts) to develop a system, he told AIN, and in about six months Aviat conducted the first test flight of the system.
Among the advantages of CNG over avgas: it costs about 80 percent less; has higher octane (138 vs. 100); contains no lead; and it produces 90 percent less pollutants, according to program sponsors. Boosters note that CNG is distributed throughout North America by pipeline, and its already piped into many hangars for powering hot water heaters and other appliances.
The tank on N15NG holds the equivalent of nine gallons of CNG, and the installation weighs about 135 pounds, including its older generation 70-pound tank; a current generation tank would weight about 30 pounds less, and CNG tank technology is rapidly advancing, Herrick told AIN. In a production environment, Aviat estimates the dual fuel CNG option may add between $12,000 and $15,000 to the base price of a gasoline-powered aircraft. Herrick sees immediate application in flight training fleets, where he believes CNG’s cost advantage could significantly lower the cost of training.
