I was under the (perhaps mistaken) impression that Rotax engines had no problem with ethanol in the fuel and that they didn’t suffer from any vapor lock when running on Mogas.
So I was a bit surprised when I noticed this advert on planecheck
planecheck_PH_REH_52659_pdf
On closer inspection I see a placard on the fuel tank stating no ethanol
On the panel I notice a placard stating no flight above 6K when flying on mogas.
I suppose the “no ethanol” restriction could be because of something else in the fuel system (eg tanks, fuel lines, fuel pump) can’t handle it rather then the Rotax engine.
But that would still leave the curious altitude restriction? I thought Rotax engines didn’t suffer from vapor lock which is what I think the altitude restriction is trying to avoid.
Have I got this wrong and these restrictions are common with Rotax? Or is someone being over cautious?
dublinpilot wrote:
I thought Rotax engines didn’t suffer from vapor lock which is what I think the altitude restriction is trying to avoid.
I don’t think engines suffer from vapour lock. Fuel systems do.
Since I was reading this only yesterday and still have that smell on my fingers: Yes you can use normal car petrol (E5 and E10 it’s called over here) for a Rotax engine.
If the fuel system can cope with Ethanol is another story. Also that particular plane doesn’t have an altitude restriction for petrol with Ethanol. It only has a rather high temperature limit which I believe is not caused by the engine but by the composite airframe.
dublinpilot wrote:
On the panel I notice a placard stating no flight above 6K when flying on mogas.
Could it have been on G-reg at some point? UK CAA has got that wonderful rule, that if you have ethanon in the fuel, it has to be up to 6K.
As far as I know the Dutch also have the same altitude limit for mogas.
Peter_Mundy wrote:
As far as I know the Dutch also have the same altitude limit for mogas.
There was a period in the 1980s when MOGAS was extensively used in Sweden for tax reasons. The same 6000 ft limitation was applied. It could be waived after a flight test at higher altitudes with high temperatures. (At that time, of course, there was no ethanol in pump MOGAS.)
I used to fly in Aquila A210 in Switzerland mostly fueled with MOGAS. Definitely don’t remember any limitations like that, 6000ft would have prevented almost all alpine crossings.
Bristell B23 (certified), Rotax 912S. AFM: ceiling is 14.000 ft and Mogas with upto 5% ethanol allowed.
As said above, the airframe, including its fuel system, may impose limits. The Bristell has an aux fuel pump.
An anekdote: I actually had to use the aux pump once ‘in anger’. Landed at a hot and high airport in the middle of Spain. Refueled and took off again within 30 minutes. OAT 35 degrees C. At start up it was impossible to keep the engine running without the aux pump on, so the engine was clearly heat soaked. I decided to keep the pump on until at cruising alt of 6.000 ft, at which the OAT was still 30 degrees C.. Then risked my life and tried without. All fine.
I had the same, SF25C Rotax912 solo filled with UL91 Avgas on +35C hot day, the checklist require to switch OFF fuel pump on start & taxi to check that mechanical pump is working, I end up asking for “start up” 3 times: twice on apron and once in the middle of taxiway while on idl
So I put pump ON all the time and stayed on high power, then asked for extra time for power checks (20min) until I was dead sure it’s vapor lock rather than dead mechanical pump, water or sediments
I did not feel risking that much on TMG: the sky was full of cumulus and plenty of land out options for takeoff & along the route (I flew engine OFF once passing Brize airspace) but Glocs ATC was seriously worried 
the same week LAA and BMAA issued a warning letter mostly for Mogas flyers…
In SEP, it would have been different, I would have a heart attack if the engine ever blips in cruise (will jump on the fuel pump/switch), before takeoff, forgot about it !
“I used to fly in Aquila A210 in Switzerland mostly fueled with MOGAS. Definitely don’t remember any limitations like that, 6000ft would have prevented almost all alpine crossings.”
Auto fuel is said to have different characteristics depending on season, etc. Hence CAA reference to " fresh .mogas". Swiss fuel will be formulated for. high altitude motoring.
