MoGas STC Question

[RogerH]

Totally confused, I routinely fuel my cars with ethanol-free 91 octane unleaded at a local station. Small cost difference but that's it.

Been looking into the possibility of a Rotax powered aircraft and seeing mention on the Web of paying for an STC to have "permission" to do the same with aircraft????

I'm hoping someone can explain why an STC piece of paper is required, what benefits or protection's does one provide or is this just another bureaucratic FAA paper chase? Sorry if I'm letting my slip show.

Thanks for any explanations.

 

[Mike S]

STC is to the best of my knowledge, only for certified aircraft to burn auto fuel. Many various STC out there for certified planes, fuel is only one of them.

Supplemental Type Certificate. Our RVs are not type certificated but experimental.

More than just "permission" as the STC sometimes required changing "O" rings or other parts that were not compatible with auto fuel. Other STC sometimes had a long list of required changes/mods to keep stuff safe.

Pretty deep subject on some STC, others just paperwork only.

 

[RogerH]

STC is to the best of my knowledge, only for certified aircraft to burn auto fuel.

Supplemental Type Certificate. Our RVs are not type certificated but experimental.

May have been dated sites I was looking at but there was reference to sourcing the STC from EAA.

 

[BobTurner]

Yes, the EAA has for years sold STCs (paperwork) to legally allow certified aircraft run car gas. But it’s really more than paperwork. The EAA had to show each fuel system was compatible with car gas, which can have a higher vapor pressure than AvGas. And each engine was okay with the specified car gas. Remember, 91 octane car gas has a Motor Octane (AvGas spec) of about 87.

 

[RogerH]

Yes, the EAA has for years sold STCs (paperwork) to legally allow certified aircraft run car gas. But it’s really more than paperwork. The EAA had to show each fuel system was compatible with car gas, which can have a higher vapor pressure than AvGas. And each engine was okay with the specified car gas. Remember, 91 octane car gas has a Motor Octane (AvGas spec) of about 87.

Thanks for that clarification, I saw EAA as the source and hence my confusion. All clear now, glad to have moved to the dark side away from “certified” several years ago, definitely not looking back!

 

[BoydBirchler]

We ran 91 no ethanol in my wife's Rans S7/ Rotax 912ULS, until we sold it 700 or so hours later. No problems. I still run it in my RV7, PV Lycoming 180HP IO-360, 8.5 to 1 CR. I did retard the timing -2 degrees to 23, for cooler CHT's and better detonation margins. I have run it this way for over 900 hours. About 1/3 of the hours are on fill ups during trips with 100LL. I have friends who run the same engines at 25 degrees advance timing With no problems (I'm maybe a bit cautious).

I do not run winter blend and carry it into the warmer weather in the spring. It is ok to run summer blend into cooler fall and winter weather.

No STC needed for experimentals , and I doubt you need one on factory builts because Rotax; the engine manufacturer has documented recommendations saying Non ethanol, high octane is best, then E93 is next preferred and 100LL come in last.