In my last column, Unleaded avgas: You’d have to be insane to try to develop it (June 22 issue), I discussed the downside to the proposed lead phase out for aircraft piston engine fuels. But, like most things in life, there’s also a positive side to the issue.
In my last column, Unleaded avgas: You’d have to be insane to try to develop it (June 22 issue), I discussed the downside to the proposed lead phase out for aircraft piston engine fuels. But, like most things in life, there’s also a positive side to the issue.
The biggest plus is that it forced the industry to actually look at some new technology. If one compares a 1950 car to a 2007 vehicle, the only similarities are the four wheels and the fact that most are still powered by an internal combustion engine. If one compares a 1950s aircraft to a 2007 aircraft, they are mechanically almost identical. We have some changes in the electronics, but the design and engine and prop assembly are basically unchanged. It is difficult to understand that, in this age of electronic ignition and fuel injection systems, aviation still uses a carburetor and magneto.
I know that there are other justifications for many of the new developments in aviation, but the possible lead phase out is probably the biggest. Two of the biggest advancements are the development of aircraft diesel engines and Fully Automatic Digital Engine Controls (FADEC).
Diesel engines have two big advantages over conventional avgas engines. First, they operate on Jet A, which is available at almost every airport worldwide. Second, they offer a significant fuel economy benefit over comparable spark ignition engines.
The first advantage is significant in the United States, but it is a huge advantage in many Third World countries where “”on-spec”” 100LL is difficult to impossible to find. In many areas of the world, the demand for 100LL is so small that people have to ship it in drums or cans. This results in some marginal handling procedures and possible mix-up with other products. By comparison, Jet A is used worldwide, and clean on-spec product can be found just about everywhere. A major concern if 100LL is off-spec with insufficient octane is that many engines can be damaged ? usually on takeoff and climb out. When Jet A is off-spec, if the diesel engine will start, it will probably run fine, especially at lower altitudes and in warmer weather.
The second major advancement has been in the area of electronic engine controls. With a FADEC system, an electronic box will adjust the timing, mixture strength, etc. The first electronic controls on cars were not that reliable. However, now reliability is significantly better than with a magneto. Electronic controls allow for things such as knock sensors, altitude compensations and ? the most amazing of all ? air/fuel ratios across all of the cylinders. This has a significant effect on knock control and fuel economy.
There are other advancements in the piston aviation market, such as several new engine designs that will allow general aviation to continue even if 100LL goes away.
So there was a good part to the lead scare: It got the industry moving toward newer technology. But was it worth the cost and worry that it caused?
We’ll examine that in the next issue.
Ben Visser is an aviation fuels and lubricants expert who spent 33 years with Shell Oil. He has been a private pilot since 1985. You can contact him at [email protected].
