Primarily for general aviation discussion, but other aviation topics are also welcome.
Please excuse this if it has been discussed previously, but I had a poke around and couldn't find anything, so...

I saw this rear its ugly head also in the press and decided to check it out and wondered what the implications are going to be for the future of older aircraft operating with MOGAS (I'm getting mine converted over to operate on both AVGAS/MOGAS) . It states that the ingredients of E5/10 can corrode fuel systems and engine components, I am aware (from an aviator perspective) that ethanol is not our friend, but looks this will become the 'new normal' from September in all petrol based fuel and in the future. I know which fuel at service stations near me are ethanol free, for now, but as the disappearance of leaded AVGAS over time will necessitate us to use these E rated biofuels and the consequences to our aged Lycoming/Continental engines and ancillaries are likely to be bad. If we see the disappearance of ethanol free MOGAS and AVGAS takes a dive, where are we? :shock:
Not just the engines but also the fuel tanks, the sealants, pumps and fuel pipes used in many aircraft.

Rotax are documented as able to take up E10 assuming the rest of the aircraft is so designed.

Bottom line - unless an AVGAS alternative is in the pipeline then another change in the future of light aviation is forthcoming.
From what I have seen following long groundings for other reasons than Covid, but with the same outcomes, I would drain all Mogas from the aircraft’s fuel system, check all filters, and replenish with fresh fuel.

Use the drained fuel in the mower or the old banger...

Most likely all will be well, but I have seen Mogas deposit unwanted gum and scum after long periods of ‘storage’.

The school I operated with Katanas used Mogas, Shell V Power, or Chevron 94 octane with absolutely no trouble at all, even hot summer’s days and high altitudes.
But being school aeroplanes the fuel was always fresh, and the filters were checked every fifty hours.

Ethanol is a problem if you can’t obtain fuel without it.
I saw a DA40 with a fuel leak in one of its rubber pipes that had perished, probably due to ethanol. It made a real stainful mess underneath.
The engine had to be rebuilt as well, and the engineer blamed this on the use of Mogas.
I think that, though the owner used premium petrol, I am not sure the suppliers were always ethical enough to be actually supplying it... You need to trust the petrol station... There’s always an easy test for ethanol.
The biggest issue is for high-compression engines, as they can't use MOGAS at all and UL91 is also not compatible - no way to change an engine or ancillaries to work. So you need a new, different type of engine.
For me, the 200hp AEIO-360 appears to only have one MOGAS compatible replacement (200hp, aero): UL Power UL520isa but it doesn't support a CSU (and electric ones don't move fast enough for aeros), new panel required for monitoring requirements, new mounts, fuel system (with non-return valves) needing modified; cowls needing modified; new prop. I've also not heard of anyone in UK with one, so I'd be worried about support / longevity.

For low-compression, generally all the ancillaries, pipes and installations need certified for MOGAS as well as the engine. Generally a bit more possible, but not necessarily easy, and requires manufacturer support for certified aircraft.
From memory the Rotax 912S has a 10.5:1 compression ratio which is higher than many Lycoming ‘high compression’ engines.

The 160bhp O 320 has to run on Avgas, but its compression ratio is 8.5:1 so there’s something odd about this argument.

Googling the RR Merlin which I believe was the excuse for 100 leaded fuel, it’s only 6:1!

In the olde days 71 Octane was the norm for Gipsy engines.
For high performance aerobatic in the Bucker Jungmann with the Hirth HM504 engine, a special cocktail was added to raise 71 Octane motor spirit to high Octane performance fuel.... 80 Octane!
MichaelP wrote: I am not sure the suppliers were always ethical enough to be actually supplying it... You need to trust the petrol station... There’s always an easy test for ethanol.

You need to trust the petrol station...


If you think the tanker is washed out after every delivery - it's not .

Tanker deliveries with mixed product and of course they always go down the right hole :salut:

Delivery drivers don't like taking product back , so a little diesel left over goes wherever it will fit.

Not many small filling stations left, so rapid turnover and even if trading standards turn up , it won't be the same as a week earlier .
Nick liked this
I've spent the last 20-odd years dealing with fuel contaminations. Far more problems arise with Jet A-1 and Diesel than ever do with Mogas. Happily, Avgas issues are rarer still

As for E10 Mogas (which will be here from September) - the UK is sticking with 5% max ethanol for Super Unleaded for the time being, so that will remain an option for the Mogas fleet.