Sling Pilots Forum

Hi everyone,

This is a subject most of you are already familiar with, but I wanted to take a deeper dive and pull together everything that I could find from Rotax documentation, owner forums, and articles into one place. The result is a paper (and a summarized blog post) that looks at both the technical and practical sides of using MOGAS and 100LL in the Rotax iS-series engines.

It covers:

• Rotax’s official guidance from Service Instruction (SI) on Selection of suitable operating fluids for ROTAX® Engine Type 916 i (Series), 915 i (Series), 912 i (Series), 912 and 914 (Series)
• Maintenance differences (oil change intervals, plug life, gearbox service)
• How Decalin helps mitigate lead buildup when running avgas
• Ethanol and vapor-lock considerations when using auto fuel
• The pros and cons of mixing small amounts of 100LL with MOGAS to reduce vapor pressure
• Future unleaded options like Swift UL94, G100UL, and Swift 100R, and the FAA’s 2030 phase-out goal for leaded avgas

For example one interesting insight is that the Sling Pilot Academy itself routinely uses a blend of 100LL and MOGAS in their Rotax-powered aircraft, particularly in hot weather or when ethanol-free auto fuel isn’t readily available. That small percentage of avgas (typically 30%) lowers vapor pressure and helps prevent vapor lock while keeping most of the benefits of running unleaded fuel — a practice echoed by many experienced Rotax operators.

If you’re flying a 912iS, 915iS, or 916iS, you might find this a useful reference or at least a good conversation starter.

You can read the post and download the paper here.

Stathis