[Ernie Martin]

Good information in the May and July issues of AOPA Pilot Magazine on 100LL fuel, which leads me to this question: does anyone know the compression ratio on our engines?

To get your attention, one of those issues has a statement I had never seen before, saying that 100LL will "certainly" not be available 1n 10 years. I had seen "probably" but not "certainly".

The issues report on considerable work being done to come up wih a solution, including the possibility of alternative fuels.

What most intrigued me was that most aircraft piston engones (~ 70%) can operate satisfactorily on avfuel without lead -- essentially 100LL but without the lead additive. These engines are those with compression ratios of 7.5 to 1 and below, where the lower octane (much less than 100) would be adequate. Only higher performance engines -- including turbos -- need the higher octane.

So the fix is easy for 70% of the engines (just remove the lead) but much tougher for the remaining 30% with higher compression (here, an alternative high-octane fuel and modified ignition systems with variable timing based on sensor data are some of the solutions being studied).

I'm starting this thread, not just with the compression ratio inquiry, but also as a catalyst for more discussions and views on the subject.

Ernie