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Future demand for unleaded motor gasoline in general aviation

In the general aviation sector, the USA has led the field in aircraft and engine technology over the past five decades, with American manufacturers controlling the market for both aircraft frames and engines. Until recently, Cessna, Piper, Continental and Lycoming were the largest suppliers of piston-engined aircraft on the world market. The majority of these aircraft presently still fly with engines based on technology dating back to the 1950's. From the manufacturers' point of view there was never any pressing reason to make any fundamental changes to their construction. Aircraft frames and their licensed engines more or less formed a unit which seemed hard to break apart without a great deal of technical and financial effort. However, two crucial developments have helped overcome this anti-progressive status quo in the last few years.

Ban on lead in aviation gasoline

Traditional Continental and Lycoming engines run on highly leaded standard gasoline which is prepared for the general aviation sector in the form of special and quality-tested aviation gasoline (abbreviated to "avgas"). However, leaded fuel has since been globally shunned for conservation reasons. Moreover, the Clean Air Act prescribes a general ban on lead in aviation gasoline in the USA from the year 2005 onwards - i.e. by that date, engines must be able to operate on unleaded fuel. This has opened up the opportunity for aircraft manufacturers, together with engine designers with the necessary experience in developing gasoline engines for unleaded fuel, to enter the market for aircraft engines which had previously been dominated by the USA.

Upgrading options and new concepts

Meanwhile, apart from the option of upgrading leaded "avgas"-run engines to motor gasoline ("mogas") ones, interesting new types of engines have been developed which are intended for unleaded operation from the start. These new engines have been accompanied by steps to modernise airframe design. One example of this is the "Katana", an ultra-light (UL) aircraft fitted with a Rotax engine that may only be operated with unleaded "mogas".

Quality guarantee

Nowadays, regional airports are increasingly obliged to provide the general aviation sector with "mogas" as pilots would otherwise divert to other airports already equipped with "mogas" fuelling stations. Along with the growing demand for "mogas", i.e. standard "super plus" gasoline with an octane number of at least 98, regional airports and airfields are facing new requirements concerning the guaranteed quality of fuel delivery and refuelling. Whenever fuel produced primarily for road vehicles is to be used in aviation, the following factors regarding transportation and logistics must be guaranteed:

  • The same quality control procedures must apply as for "avgas";
  • It must be guaranteed that the gasoline will not be mixed with other types of fuel upon delivery;
  • The alcohol content must be less than 1% vol. corresponding to the EN 228 norm;
  • Quality control clauses must stipulate the shorter storage periods necessary for "mogas";
  • If possible, fuel is to be stored in underground tanks.

Compliance with these stipulations is essential for safety and liability reasons, in order to prevent the use of "mogas" leading to functional faults or operational power failures. In any case, safety (in other words: guarantees of consistent quality) must be the top priority. Even for small amounts, there must be proof that - subsequent to its delivery - the fuel has suffered no loss of quality due to negligence in storage or dispensation. Logically, the notion of refuelling of an aircraft with car petrol from a canister must be ruled out as this contravenes the basic principles of consistent quality control.

Trends in general aviation

The drop in the number of licenses for aircraft running on leaded "avgas" is comparable with the increasing number of licenses granted to newly developed aircraft running on "mogas" (UL aircraft and most power gliders, plus the licensed retrofitting process for E-class aircraft). This trend permits the following forecasts to be made for the general aviation sector:

  • "Avgas" - which will also be available with a reduced lead content in future - is currently still indispensable to a large proportion of aircraft with piston engines;
  • "Mogas" will become the only alternative for the constantly growing number of newly developed or upgraded aircraft. The appeal of "mogas" lies in its considerably lower price (some 30% cheaper than "avgas");
  • A forward-looking trend can be perceived in the recent efforts to develop a diesel engine for future use in aircraft. Among others, the Thielert engine (based on the Mercedes Benz A-class engine) and the new diesel aircraft engine recently developed by Volkswagen (based on a two-litre engine) are two concepts which promise future success. Using diesel fuel for aircraft engines ultimately means sanctioning these aggregates for jet A1 fuel (kerosene) as they are virtually identical from a technical point of view.

Future prospects

It seems possible that fuel-dispensing channels for aircraft supplies can be merged again in the future and that there will only be unleaded aviation gasoline and diesel fuel/jet A1 (kerosene) on offer. Airfields could therefore then return to a refuelling infrastructure of reasonable and economically sound proportions.