Fuel Question

10% ethanol is no big deal. Plus many places that say they have 10% ethanol is not  really 10%. Here in Arizona they say 10%, but there are two guys at my field that have tested every batch for the last 10 years and it is always 6% - 7% and only a few time at 8%. Some places in the world use up to 18% - 23%. with no ill affects. I was always taught to use a minimum 50 / 50 blend of 89 auto to 100LL to get 91 oct.  Maybe the admin will weigh in here on the blend percentage.

If 10% was a big deal all our cars would be sitting on the side of the road.

You can mix 50/50 100LL and 89 Auto to get a lower lead content and higher octane, however, Rotax provides no documentation supporting this.

If my math is correct (might not be) 20% 100 LL should be sufficient to get 91.  As far as ethanol my understanding is that one issue is impact on rubber parts.  The auto fuel STC I had for my C182 specified only use gas without ethanol I am not sure about all the reasons why.  

Dagfinn Gangsaas wrote:

If my math is correct (might not be) 20% 100 LL should be sufficient to get 91.  As far as ethanol my understanding is that one issue is impact on rubber parts.  The auto fuel STC I had for my C182 specified only use gas without ethanol I am not sure about all the reasons why.  

My understanding;

Rotax have approved the use of up to  10% Ethanol in their engines - they are not suggesting that other components of the fuel system (tank, fuel lines, auxiliary pumps, etc) are compatible. These areas are the up to the aircraft manufacturer to determine compatibility.

Dagfinn Gangsaas wrote:

Right but better than straight 100 LL.  Maybe Rotax has some guidance on 20% 100 LL vs 10 % ethanol 

Sure its an improvement (reduced lead) on strait AvGas BUT why use leaded fuel at all?

Its not good for the engine, you, children & the environment.

If you have no other way (last resort) of accessing the correct grade of fuel, then go for it. 

I have used AvGas, as a top up (may be twice in 10 years) but only on an "away trip"  when access to ULP impractical.