Theres No Fuel Like An Old Fuel

By:      Norm Goyer

Fueling an airplane may become quite different if 100LL is dropped in favor of 94UL.

“Wichita, we’ve got a problem.” You should also add Vero Beach and Duluth, Michigan. The problem is not new, and everyone in the aviation industry knew it was coming, but very little has been done to resolve the problem. Many believe that a huge fuel availability change is coming and an even larger financial burden. The problem, leaded aviation fuel; the feds don’t want it, the EPA doesn’t want it and our Air Force and the airline industry don’t need it. The military switched to diesel/Jet fuel years ago as did the airlines. The auto industry solved their own problem by building their engines to be able to run efficiently on unleaded gasoline blends. Not so in the aviation industry, the anti-detonation qualities of lead are still needed in a large number of the engines that power most of the light business fleet. The minimum octane remains at 100LL (low lead.) The number of aircraft using 285 and 300 hp range of six cylinder air cooled engines demand 100 LL to prevent damage to the engines. Fortunately the large number of sport aircraft with smaller four cylinder Lycoming and Continental engines can run on auto gas, with some modifications. But it is the larger airplanes that wealthy, often influential pilots prefer. They are the Bonanzas and Barons, Cessna 206s, Cessna Golden Eagles, Piper  Piper Malibu, Mooneys, Cirrus and the Cessna 400 Columbia. All of these brands have pilots and owner associations who are fighting the bureaucracy demanding the end to 100 LL fuel. This group rightfully believes that the 94 octane UL (essentially 100LL without the lead) will damage their engines.  The aviation press has been reporting these problems for the past year or so and it appears that it might be coming to a head. What if anything can be done? Problem number one is that auto engines are liquid cooled and run very slowly. My 1500 Suburban will cruise at 60 mph at 1200 rpm. Airplane engines bang away at 2400 rpm, hours at a time, and depend on air flowing over the cylinders for cooling. According to recent findings, the problems seem to be pre detonation which can cause failure of engine components. Hot spots in the cylinder, mostly around the exhaust valves, cause pre detonation when using no lead fuel which can cause valve failure, often taking the whole engine with it.

Cirrus just announced a new low- compression engine with a powerful turbo charger which should be able to use a lower octane fuel.

Diesel engines seem like a very good idea, but acceptance by the flying public has not been good. Several of the new diesel engines that have been brought out have developed problems and they have been withdrawn from service. These problems are not fuel related, but related to the extreme stress that diesel engine components suffer from the high compressions needed and the explosive nature of the fuel. One of the recent diesel engines that had been installed in several certified aircraft was not re-buildable, the whole engine had to be replaced, and this was expensive. The latest diesel aircraft engine that is making the news is a rotary (Wankel). This type of engine is not technically a reciprocating engine, components don’t move up and down rotating a crankshaft, instead it is more like a jet engine in that the main section of the engine rotates and wipers control the opening and closing of the heads and the valves which are non moving. Mazda has been successful for years marketing a Wankel type engine in their sport model cars. This new engine, which is still under certification testing, has the possibility of operating with diesel fuel. At this time it is being tested with no lead auto fuel. Many years ago, I flew an experimental aircraft that used a two bank Norton liquid cooled modified motorcycle engine that was a Wankel. It put out about 100 hp and was very smooth in operation. Again it simply faded into oblivion.

This Piper PA-46 has an engine which will need modifications to run properly with any fuel less than 100 octane low lead.

It is obvious to anyone  dealing in reality that the true solution is about 70 years old, a small turbine that is in the 200 to 300 shp range. Remote control aircraft have been using miniature jet engines for many years and they are outstanding, reliable and fast. Pratt & Whitney built some of the best large radial engines ever at their huge plant near Hartford, Connecticut, for many decades now, they only build turbines. I refuse to believe that Continental and Lycoming do not have the capability to build small turbines for general aviation, but, they just keep on building a dying breed of engines that are soon to become paperweights. I have flown Bonanzas and large Pipers with retrofitted prop jet engines, no comparison, they do everything better. I have flown all of the Experimental Aero Comp aircraft with prop jet engines, outstanding power and quietness and they simply don’t need 80, 100, 100LL or auto fuel, they run on jet A. As my farmer ancestors often reminded me, “Why kick a dead horse?”

The owner of this Beechcraft A-36 Bonanza installed a Tradewind propjet engine conversion.

Lurking in the wings is the lure of electric motors powering aircraft. As the battery industry progresses, so will the use of outrunner type of electric motors using Li-Ion cells arranged in batteries of high voltage. Electric cars are a reality, testing is underway using motors in aircraft and the motorcycle drag racing record is held by an electric motor powered motorcycle. About three years ago I switched from large gasoline and methanol powered engines to even more powerful lighter, very reliable, outrunner electric motors for my fleet of giant remote control aircraft. Electric power is fantastic, and, it’s on its way for general aviation aircraft.

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