Back to the general topic, does anyone have any insight on what is really going on? These Rotax engines have been installed, often very crudely, into 100 different types of microlights in the past 30 years, and they always ran more or less ok, if the carbs were ok.
What happened? Is it really just the numbers of certified and non-certified aircraft with these engines have slowly grown more and more, thus uncovering a problem that has always existed to some degree?
Why does BRM write such a nonsensical service bulletin? Is it that they have no clue why the engines installed in their aircraft random start surging and losing power? Or do they know and don‘t want people to know, and therefore write this stuff so that stupid people have something to cling onto?
Airborne_Again wrote:
I believe that’s exactly what I wrote that I’ve learned
How is that exactly what you wrote ?
Like Bosco, I’m also quite surprised by all of this. To start with, one would expect Rotax to communicate first.
I don’t think this is a problem caused by BRM’s implementation of the Rotax 912, i.e. lack of cooling, and I live in a hot climate. It is true that BRM has an ‘improved cooling’ cowling option available, but that’s really meant for the 915 engine and particularly relevant if towing gliders.
LeSving wrote:
How is that exactly what you wrote ?
You can express the same thing with different words. ’nuff said.
Airborne_Again wrote:
You can express the same thing with different words.
OK, like a “yes” is the new “no” 
boscomantico wrote:
Is it really just the numbers of certified and non-certified aircraft with these engines have slowly grown more and more, thus uncovering a problem that has always existed to some degree?
In Norway the NLF set up a committee (of all things) some years back to investigate why so many, obviously pilot induced mishaps, happened to certified Rotax installations. I don’t know any more details, or whatever happened to that committee, but it looks a bit like this Swiss case.
IME a Rotax don’t suddenly stop producing power unless something is seriously wrong. Usually it is fuel or over heating. Whatever these problems are, it’s a combination of poor installation, poor engine management and probably fuel (MOGAS, could be ethanol related). I have also heard of several problems when using unleaded AVGAS: Detonation at certain engine parameters, which will eventually ruin the engine over time, and I imagine it would cause a similar symptoms when the damage first is noticed ?
The best fuel is ethanol free 98. Then 100LL. 100LL is probably the safest (lower risk of “vapor lock”, read: fuel boiling in the carburetors due to heat soaking on the ground), but it’s not good for the engine. Ethanol free 98 is best for the engine. We have switched entire to ethanol free 98. 95 E10, throw it away. The same goes for the unleaded AVGAS in existence, it will eventually ruin the engine, except perhaps the original 80HP 912.
I’ve noticed there are two kinds of people (with apologies to Clint Eastwood):
As is well known in GA, a lot of negative stuff doesn’t get posted to protect business interests and marketing (a school, for example) or to protect a dealer relationship (most owners with a warranty for sure). But it can also be that there is some as yet not well known factor which is in play.
The best fuel is ethanol free 98.
Where will you get that??
Then 100LL. 100LL is probably the safest (lower risk of “vapor lock”, read: fuel boiling in the carburetors due to heat soaking on the ground), but it’s not good for the engine.
Lots of people say the lead is what does the damage and they use 91UL.
Ethanol free 98 is best for the engine. We have switched entire to ethanol free 98. 95 E10, throw it away.
But that is most car petrol in Europe – by orders of Brussels. Some remains at 5%. But probably not for much longer. 10% fuel dissolves a lot of materials – totally dissolved the fuel gauges in my generators.
The same goes for the unleaded AVGAS in existence, it will eventually ruin the engine, except perhaps the original 80HP 912.
How does that square up with what lots and lots of people have been saying for many years? Like 91UL being great. Or 96UL in the 1 or 2 places where it exists.
One day 100LL will vanish and there will be 100UL (effect on Rotax engines??), 91UL in a few places but getting rapidly fewer, and 96UL in the very few places.
This stuff doesn’t really add up.
@lesving maybe you can elaborate a bit on your opinion to “throw away 95 E10 Mogas”. Rotax says it’s fine to use up to 10% Ethanol and most aircraft manufacturers endorse that.
In my ‘community’ here, about 40 Rotax users, maintained by one guy, there have been zero engine stoppages or other extraordinary engine wear issues. All use 95 E10. Of course this is still a small sample. So I read the Rotax owner forum where there is a ton of experience. From some recent chats:
I can go on but this is far too much as it is so let me summarize what I believe is important.
First, AVGAS is not a bad thing if you address the lead with something like TCP and frequent oil changes. Try to be sure that your cylinder head temperatures are normal and not running excessively cold.
Second, MOGAS without ethanol and at the right octane for your engine is great but personally I would want to use it up within 3 months, ½ the time the fuel supplier says. Don’t use winter fuels in hot environments. (don’t ever save winter fuel)
Third, MOGAS that has ethanol is fine but not over 10% by volume. Storage time should be ½ of the claims it will last so no more than say 6 weeks. Personally I like to see it gone it 4. Never use winter fuel in summer.
Lastly, RVP is critical to prevent vapor lock. (as well as a good fuel system with boost pump, return line, etc.) If you are unsure of the blend you purchased and concerned about winter fuel or having stored it longer than you want…do what Paul and Sean recommend. Blend it with some AVGAS. if it is a small amount just burn it up in your car in small amounts. (don’t dump it on the grass)
and:
I agree with what you have observed with MOGAS. In general as long as the water is kept in suspension in the fuel corrosion is not a problem. Most issues are from extremely long storage issues where phase separations occurs from saturation of the fuel with water. In the old days of certified aircraft we were all told to fuel the aircraft directly after flight. The metal tanks then had only a small space for condensation to accumulate. With AVGAS given there is nothing to absorb water from condensation it will drop right away to the bottom of the tank. Always sump the fuel before flight, especially important with AVGAS . Todays LSA type aircraft see a lot of variables in fuel tanks. if you have metal tanks the condensation issues are still there. The differences are in what fuel you might be using. MOGAS, even even in the european standards have alcohols that absorb water to some extent. In the USA ethanol is blended into some 90% of the normal automotive fuel supply.
European EN228 * For gasoline with max. 3.7 m% of oxygen, allowed oxygenate contents are methanol 3 v%, ethanol 10 v%, iso-propanol 12 v%, iso-butanol 15 v%, tert-butanol 15 v%, ethers with five or more carbon atoms 22 v%, and other oxygenates 15 v%. For gasoline with max. 2.7 m% of oxygen, allowed oxygenate contents are methanol 3 v% and ethanol 5 v%.
On a side note. When Rotax was asked to allow the use of ethanol in their aircraft engines it was done after a lot of consideration. The test engine in the field was an aircraft in Brazil that ran some 25% ethanol all its operational life in a flight school. The engine was some 8 years old and was overhauled and the components analyzed by representatives from Rotax at the time. The results were that it was pretty normal. The issue however is they could not allow 25% as the emissions from that level of ethanol are very bad for the environment. Benefits from high levels of ethanol emission wise do not begin until over 30% by volume. NOx emissions and other emissions were a major concern. The engine in question, a carburator 912ULS, has no way to allow for changes in the fuel density and ratio of the burn. The timing is fixed and we can’t use a knock sensor or full electronic, auto adjusting, system to compensate for the different fuel mix. This is also true of the iS, it is a Map system, it is not auto sensing in that it does not change timing on its own. That all said the safe bet was that 10% would be a safe compromise to allow. The issue is then up to the OEM, builder, to be sure that the fuel system is suitable. (fuel tank, lines, filters, etc) to use ethanol.
LeSving wrote:
OK, like a “yes” is the new “no”
What’s your problem, LeSving?
We lost an MCR-4 yesterday at Grenchen with 2 fatalities. They crashed on short final. I think it is also Rotax powered? The SUST will investigate.
What bugs me in this is the careful wording. It’s very unusual for the SUST and FOCA to communicate like that. It indicates to me that they are seriously concerned and want to make sure they get more data on which to base future action on.
Peter wrote:
Where will you get that??
In Norway I guess also elsewhere, but you have to investigate/ask. This “E” marking is simply a play for the gallery, and in every sense of the words. “E5” means “up to” 5% ethanol for instance. This is all EU regulations. The fuel resellers themselves are bound by other (EU) regulations. They are bound by selling X% of the fuel as biofuel, any biofuel. I don’t remember what this X is, but the important part is this X% relates to the total of all fuel they sell. They typically sell lots of diesel with biodiesel for instance. Shell includes biogasoline. Biogasoline is a drop in replacement for gasoline (chemically identical). It’s not ethanol, but counts as biofuel (obviously) for the resellers.
Another thing is that 98 octane counts for less than 5% of all the fuel a typical reseller sells. They mostly sell diesel and 95 octane. This means that 98 octane must be stored on average for a much longer time, and its’ very stupid to mix it with ethanol if you don’t need to, for storage reasons. 98 is also marketed as “premium” fuel, and is more expensive. The result is that mixing ethanol into 98 octane is an expense (and a risk) they don’t need to pay, so they don’t do it. Both Esso and Shell in Norway has made it clear they don’t mix ethanol into 98 octane, and have no plans doing so. It would be surprising to me if they did this elsewhere.
Peter wrote:
Lots of people say the lead is what does the damage and they use 91UL.
Yes, lead is not good for the engine. But, in the US they have used 100LL on Rotax engines for years. If you replace the oil more often, according to the Rotax manual" to protect the gears, then based on the US experience, any additional problems are highly exaggerated (non existent or freak occurrences). You probably also have to replace spark plugs more often. The Rotax manual does not specify how much 100LL on average you can use before “100 LL maintenance” has to be introduced. It’s only some vague “mainly/mostly” nonsense. But, the US importer and usually the aircraft POH specifies this as 30%. If you use up to 30% 100LL on average, then it doesn’t matter. 91UL is a much higher risk IMO due to detonation. On the low compression 80HP, probably not. On carbureted 100 HP, probably yes, but it depends how the engine is run, and the quality of the fuel. On the EFI/FADEC variants, I have no clue. These EFI variants seems to just run, except when something goes wrong with the FADEC, then nobody seems to be able to fix it
Peter wrote:
How does that square up with what lots and lots of people have been saying for many years? Like 91UL being great. Or 96UL in the 1 or 2 places where it exists.
Which people have been saying that for years regarding Rotax? What I have heard for years is 91UL/96UL is NOT good for Rotaxes. I have previously just dismissed it at nonsense, mainly because Rotax themselves say this fuel is OK. However, this also depends on what the octane rating actually is in the fuel you fill the tank with. According to ULPower, they have measured this, and found the octane rating way below specs. 100LL and MOGAS 98 (as well as fresh 95) is always on spec.
Peter wrote:
One day 100LL will vanish and there will be 100UL
Will it? 100UL will probably be just fine, but who is willing to pay double price on fuel when MOGAS 98 is readily available at half the price of 100UL. The day we actually can get 100UL, we will find out. That day may never come.
IMO, as of today, there are only two fuels I would use: 100LL and 98 MOGAS.
aart, I agree with basically everything you say. Winter fuel/summer fuel is in itself a factor that can explain 80% of those Swiss problems (I’m not saying it is the explanation, but it could be). This is essentially a user problem (pilot problem). To be ignorant to how stuff works, is stupid, especially if your life depends on it.
aart wrote:
maybe you can elaborate a bit on your opinion to “throw away 95 E10 Mogas”
The main thing is that in Norway they started selling E10 last February. Then all kind of stuff happened. This was mostly snowmobiles, ATVs, outboard motors, snow blowers and so on. They wouldn’t start, they would develop faults. The fuel, when stored would go sour very fast, create particles. How much was true? probably a lot. On all my garden stuff I have since years back used alkylate fuel, mostly to prevent the problems with storage of MOGAS (alkylate can be stored for years). From 5 to 10% ethanol, these problems do not follow a linear relation, it’s more like exponential. 100% ethanol (96%) would also be no problem.
This summer, there also started coming SBs from aircraft manufacturers prohibiting 10% ethanol. The club has a Atec Faeta which got such an SB in June. This is mostly due to delamination of fuel tanks, which is particularly nasty if the tank is an integral part of the wing structure, as it often is on carbon fiber planes. The Danish UL association issued a nation wide warning about this, which was resent to all Norwegian owners also.
At the club we have a fueling facility that others also can use. Obviously 95 E10 is poison for many aircraft. In itself it is as bad as it gets regarding storage and degradation. 98 octane has none of these problems, so the choice is obvious. 98 octane does not store as well as alkylate or AVGAS, but the problems are minor. Winter/summer fuel is obviously a problem, but the only issues I have seen is the pilot letting the engine getting heat soaked on the ground. Flying very high with MOGAS in (very) warm temperatures is also not a good idea regardless of summer/winter grade. But I mean, a P2008 with two people on board barely makes it to 6000 feet anyway. I cannot see this as a real problem except for Turbo Rotaxes.
As I said, if you want to play it safe, 100LL is the way to go IMO. More maintenance will be required however. If you know of, and can handle the potential issues with ethanol free 98, this is a better option. It’s much better for the engine. 91UL and 95 E10 is asking for problems of some kind or the other somewhere down the line.
