912 ULS Unleaded Fuel Question

My RV-12 with Rotax 912 ULS has 830 TT running 93E10 I purchase at Costco.  I keep containers tightly sealed and use STA-BILL when airplane is laid-up over winter months.  See following VAF post for fuel transport system...  https://vansairforce.net/community/showpost.php?p=1643909&postcount=7

Hi Brett

The use of fuel with Ethanol up to 10% is permitted.  The real problem with auto fuels is the issue of winter blended fuels used in hot conditions.  This is an issue with the fluctuating Reid Vapor pressure of the fuels.  Simply speaking do not store any fuel that you get from mid September to April, the RVP is too low for high altitude or hot conditions. (this is a condition found in the USA and Canada, not so much in Latin America)  If you are worried about any stored fuel mix it with 50% Avgas to boost RVP and you should be fine.  For many this is tribal knowledge and nothing that Rotax would put in print. 

I 100% agree with any stored fuel in very tight sealed containers.  Metal is better than plastic in my view.  Try to have them full and not partial.  Keep them as cool as possible and out of the sun.  In general it will survive well if you follow that.  Do not open them until you intend to use it.  Never store fuel you buy between September to April as it normally will be the wrong vapor pressure for hot conditions. 

If you have any fuel in your aircraft, this would be in your vented tanks, I would suggest you not store them with any high volume.  Best to mix that with Avgas before you try to fly with it as the light ends of the fuel will evaporate and leave you with some risk of problems of vapor lock and even detonation. Remember that fuels are blended regionally.  In the countries where there are multi level RVP fuels used during the year be aware of what you are getting. 

You might consider a fuel like Swift  UL94 if it is available in your area.  It has a fixed RVP and enough octane to work well in the 9 series iS or ULS engines.  Check with Vans to see if they have any issues in their fuel system.

Cheers

Swift Fuel is from Lafayette, IN that is where I get my fuel.  

I disagree with Rotax Wizard's statement that gas bought from September to April has too low a Reid Vapor Pressure(RPV). It is more likely too high a vapor pressure, since in cold weather vapor pressures of gas reduce as it get colder. So, the gasoline companies increase the light components in winter to have enough vapor to get the gas to ignite when it is cold.  This raises the Reid Vapor Pressure of the gas, it doesn't lower it. When this winter gasoline is used in hot conditions, the Reid Vapor Pressure will increase a lot due to the temperature rise, and can get high enough to vaporize in the lines, causing vapor lock. 

If you can get Swift 94UL, I highly recommend it. It's a great fuel for the Rotax. I was recently reminded of this while helping some friends with a new build Rotax-powered that was fueled with mogas, and initially had a few leaks in the fuel system. When mogas leaks and evaporates, you will be left with an oily mess (after all the lighter components evaporate.) If you spill Swift and let it evaporate, there's nothing left.