172driver wrote:
Btw, there is an alternative method for the ‘burping’: run the engines at idle for one minute, then check. As per Tecnam POH.
Sounds a bit like using a match to see if there’s fuel in the tank 
It’s in the Tecnam POH. Like it or not.
Antonio wrote:
On Rotax the idea is to not use high RPM at low power (ie too low torque)
It’s rather the opposite, Antonio. You can rev any Rotax with 5500 RPM (5800 RPM limited to 5 minutes) all day long, no matter what MAP. All Rotax specialists will tell you “just let it rev…” and no WOT below at least 5200 RPM (a Service Instruction does exist for the latter). Rotaxes die because of running them too much with too low RPM, not because of too high RPM.
LeSving wrote:
What I have heard for years is 91UL/96UL is NOT good for Rotaxes.
That’s the first time I hear that. And as Rotax has approved it for all of their engines, I have no doubts, that they’ve thorougly tested it.
europaxs wrote:
That’s the first time I hear that
Then, under which stone have you lived? I don’t think they have tested it at all. What they have tested is “a” fuel, and found if the specs are according to what’s in the Rotax manual, then it’s OK. What the Rotax manual say is (for S/ULS):
UL91 has (per spec) RON 95 and MON 91. Which means RON 95 and AKI 93. What ULPower found actually testing various 91UL fuels was that the RON value was lower than 95. AKI is only relevant for US MOGAS I would think (ASTM D4814 according to the manual).
98 MOGAS has RON 98, while MON may vary a bit. It’s typically 89-91 in Europe. Meaning RON 98 AKI 94
Hjelmco 91/96 UL is (I guess) RON 96 MON 91 ? This means RON 96 AKI 93.5
In the newest Service Information, SI-912-016, they clearly specify minimum RON of min 95.
AFAIK traditional aircraft engines specifies a min MON, not RON. MON being the same as “aviation lean” according to Wikipedia.
Another thing with 95 E10 is that ethanol enhances octane rating (RON). The specification is RON 95 with 10% ethanol. Ethanol is hygroscopic. Ethanol and water will enter solution and fall to the buttom of the tank. It can be drained. Draining this slush, you will also drain out the octane rating. The original gasoline without the ethanol is way below RON 95.
YMMW is certainly true however. According to my own mileage, I would only use 98 mogas (ethanol free) or 100LL. They are not optimal fuel, but there are no uncertainties there. The problems are known, and can be handled.
LeSving wrote:
Hjelmco 91/96 UL is (I guess) RON 96 MON 91 ?
According to Hjelmco 91/96UL has RON 98 MON 91. On their website they provide a “representative quality certificate”. Make of it what you will.
The Super Guépard POH recommends SP95. SP is sans plomb or without lead.
It then says 100LL can be used with more regular oil changes. It seems in Norway choosing a fuel is a bit complicated by comparison.🙂
Airborne_Again wrote:
According to Hjelmco 91/96UL has RON 98 MON 91.
It’s substantially better than UL91 then. More or less equal to MOGAS 98, but with aviation vapor pressure and storage specs. The perfect fuel for any Rotax aircraft engine. Seriosly, that is what that spec sheet tells.
gallois wrote:
It then says 100LL can be used with more regular oil changes. It seems in Norway choosing a fuel is a bit complicated by comparison.
I am not Norway 
I may be complicated, but “Norway” is not, or perhaps it is ?
The issue was the Swiss findings. All of them, or the majority can be explained by fuel alone. This is nothing new. Taking off with a heat soaked engine is specifically mentioned in the Rotax manual as a danger when using MOGAS. It does not matter where that engine is installed. The manual is equally valid for certified engines as non-certified engines. The engine will run fine on 95 as the Rotax manual states. It will also run fine with 10% ethanol. That’s not the issue. The issue is if the PIC is aware of all the issues associated with the different fuels. I don’t think so. The PIC just read the POH and thinks “SP95” is Gods gift. Just because the certification say that MOGAS can be used, this doesn’t mean the problems with MOGAS magically and suddenly disappears. SP95 can be many different things spec wise.
I think perhaps a thing here is that for non-certified aircraft, the owners are more in line with what the reality actually is. Regarding the engine, Rotax is the authority, not the aircraft manufacturer. Thus, they tend to read the Rotax manual. There is no way to maintain the engine correctly without reading the manual. Likewise, there is no way to operate the engine without reading the manual.
Regarding “SP95” and similar nonchalant expressions. The SI-912-016 is rather interesting:
It’s a bit interesting that Rotax has to remind the manufacturers that it’s the aircraft manufacturer’s responsibility to make sure the installation is OK in all circumstances for all the fuels they approve for the aircraft.
Perhaps even more interesting is this:
First they urges the owners (of certified aircraft) to contact the manufacturers about compatibility of E10. Then they make it clear (again) that this is the responsibility of the manufacturer (of certified aircraft). Lastly a reminder that it’s a good idea that owners of non-certified aircraft also confirm to the documents by the FAA and EASA.
The wordings here are interesting. It’s like: “Listen all owners of certified aircraft with Rotax engines. Please help us wake up those aircraft manufacturers. And by the way, owners of non-certified aircraft, please do the same, or check yourselves”.
Bristell wrote:
common cause, or at least contributing factor, identified is engine mismanagement resulting in unnecessary thermal stress […] High thermal loading […] is associated with a combination of high RPM and moderate MP
And then goes on to quote instances of low power-high rpm to be avoided
europaxs wrote:
Antonio: “On Rotax the idea is to not use high RPM at low power (ie too low torque)”
It’s rather the opposite, Antonio.
I don’t get it. How is it the opposite?
I don’t know if you’ve noticed but there have been some very high temperatures in this area over this summer. The POH of the SG says SP95 the Rotax certified mechanics on the field say use SP95. The glider club in the C41 Ikarus have been towing old wooden two seat gliders, Discus and aerobatic machines into the ait all day every day only on SP95.
And another 20 ot 30 private ULMs and several certified Elixirs have all been buzzing around fuelled by SP95.
Many have been doing this for several years, and some have clocked up several thousand hours all without fuel issues or engine damage.
Do you think perhaps you are overthinking this?
