[sokoloff]

1. The cost of the STC rounds to $0. I think when I started flying it used to be $1 per horsepower; it looks like it’s still under $1000, which represents no barrier.

#2 and the low availability of mogas at airports is the reason for a lack of adoption fleet wide.

[iamtheworstdev]

re: #2... because... ? Because they aren't going to stock a fuel that only applies to a handful of airplanes. The demand for it is near nil.

[sokoloff]

Exactly. You can barely sustain a fuel farm on the fuel that services 100% of the piston GA fleet. It's incredibly difficult to make the economics work to add a second fuel farm that serves only 30% of the gasoline sold, cannibalizing sales from your other fuel farm.

That's the premise/promise of G100UL: it can serve all the spark-ignition piston aircraft.

[mcronce]

Demand would be a lot higher if the leaded alternative weren't allowed.

[sokoloff]

No, it wouldn't be that much higher for mogas (typically a 91-ish octane unleaded, E0 (ethanol-free) gasoline).

If there were an unleaded 100-ish octane fuel legally available as a substitute, that would have demand if 100LL were banned. Over 70% of the avgas burned is burned in airplanes that are not eligible for the STC* to allow them to burn mogas (typically as a result of having lower worst-case detonation margins as a result of being turbo-charged, super-charged, high-compression, or some combination).

* - Supplemental Type Certificate - an airplane modification, in this case a mostly [entirely for most airframes] paperwork modification, to their original type certificate.