Leaded/Unleaded gas?

[David Pavlich]

I have a video playing in the background with AOPA's Craig Fuller. Part of the discussion is the continued work toward unleaded Avgas. Being a carguy, I remember the angst when the change came for cars, especially high performance types. Are the same problems that faced car owners of leaded gas engines pretty much the same problems that GA faces with their aircraft? I've read a couple of articles dealing with research going on to find the proper "mix" to get GA aircraft off leaded gas and onto unleaded. Lead does a lot of good things for an engine, but not so much for air quaility. Any comments or added information?

Thanks!

David

[rwanttaja]

The old 80 octane fuel (which most of our engines were designed for) had about a quarter of the lead as "modern" 100LL fuel. So, when I'm running unleaded car gas in my Fly Baby, I make every 4th fill-up with 100LL. This time of year, I'm 100% 100LL anyway, since the plane sits so much and car fuel isn't great for long-term stability.

The exception is a newly-overhauled engine...better to run it 50 or 100 hours on 100LL during the break-in.

This is, of course, for engines designed to run on 80 octane.

I, too, recall the sturm und drang when the automotive world went lead-free. However, they had a long transition period with both types of fuels. The average car is about eight years old, but the average GA airplane is about 40. So it'd have to be a very long transition....

Ron Wanttaja

[CarlOrton]

Unfortunately, there are far more variables involved than were experienced with the transition for autos. UL was mandated for air quality reasons. The main reason for the rapid transition was that in 1975 catalytic converters became standard on all (?) cars, and lead would have killed them. Remember how performance went from somewhere decent to downright sucky? A Corvette with 190 hp? It wasn't until the mid 80's when microprocessors became prevalent enough to allow continual monitoring and adjustment of the fuel/air mixture that we started regaining some of the lost power.

Unfortunately, even with injected engines (those without FADEC), the mixture control is still manually operated. Engines of any power more than around 180 hp need more octane than is currently available except in small quantities. Removing the lead also leads to stuff like combustion chamber quench factors and more that I have no business discussing.

Bottom line: It's not coming up with an UL fuel that's the issue. It's finding one that is as happy in a 150 as it is in a turbo Bonanza at 18,000 feet. Without having to add engine controllers.