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The continued availability of leaded specialty aviation gasolines remains as an item of crucial importance in the near-term future of general aviation; however, the development of new piston engines capable of operation with other transportation fuels available in large pools is considered an indispensable element in the long-range survival of the industry. This paper offers a road map that while allowing the continued utilization of the current fleet of piston aircraft, sets the stage for a transition to new piston powerplants and associated aircraft, compatible with widely available transportation fuels such as motor gasoline based aviation fuels for the lower and some medium performance aircraft, and aviation turbine fuels for the balance of medium and high performance airplanes.

Since 1980, the Cessna Aircraft Company has explored new piston engine and related fuels technologies for future general aviation products, with extensive studies and supportive research activities. This paper describes the development of a piston engine multi-fuel hybrid combustion system, capable of burning all types of transportation fuels at specific power outputs typical of current aircraft engines, specific fuel consumptions lower than current aviation engines, optimum medium compression ratios capable of limiting peak combustion pressures and associated engine structural weights, altitude performance comparable to current turbocharged engines, starting characteristics virtually insensitive to ambient or fuel temperatures, and particulates or smoke emissions in tune with current ground transportation engines. This paper also reflects on the factors and conditions that prompted the Cessna Advanced Piston Powerplants Program.

The American Society for Testing and Materials (ASTM) sponsored a Symposium entitled Future Fuels for General Aviation Intermittent Combustion Engines[1] held on 29 June 1988, in Baltimore, Maryland. This event prompted the formation of an ASTM D02 Subcommittee J Section 2 Future Fuels For General Aviation Task Group [2], that successfully capped a ten year effort with the recent publication of ASTM D 6227-98 Standard Specification for Grade 82 Unleaded Aviation Gasoline [3]. This paper reflects on the Grade 82 UL Aviation Gasoline Specification development program[4,5], beginning with fundamental questions related to the quality of available feed stocks. It includes results of studies and tests undertaken by the Cessna Aircraft Company to demonstrate the feasibility of using the fuel described by the Specification in aircraft designed for its use.

The development of unleaded high octane aviation gasolines is being pursued in a cooperative effort by fuel producers, user organizations, regulatory agencies, and The General Aviation industry. The evaluation of abnormal combustion characteristics of new unleaded candidate fuels under actual flight conditions, pose unique instrumentation and equipment requirements. On-board detonation indication and test fuels blender systems have been developed, to evaluate the abnormal combustion behavior of unleaded candidate fuels against reference fuels of known characteristics. These systems have proven capable of delivering precise and reproducible results during validation tests performed on the ground and in flight under significant time and space limitations.

It is considered a matter of vital international interest to assure the survival of general aviation and to consolidate its important role in the overall transportation picture around the globe. However, in spite of plentiful supplies of crude, the general aviation industry has suffered severe set-backs in recent years due in part to increased costs and decreasing availability of aviation gasolines. The vulnerability of these fuel supplies is now well substantiated and a concerted effort involving fuel producers, general aviation manufacturers, specifications and standards writers such as The American Society for Testing and Materials (ASTM) and The Society of Automotive Engineers (SAE), and the user groups is required to establish long-range strategies in this area.