ROAN Rotax Engine tips

[Roger Lee]

Hi All,

 

Here is a link to the ROAN website to watch a fairly new Rotax engine tips video. It covers things like start up, carb sync, prop balance, shut down and proper engine rpm, ect. This video gives proper idle speed. This video is in conjunction with "Service Letter" 0912-016.

For those who have argued about idle speed for the 912ULS 100 HP I hope this will clear up any low rpm idle issues. It not only talks about it, but you can see it on the instrument panel. The 912UL with only a 9.0:1 compression can do 1500 idle rpm, but the 912ULS at 10.5:1 compression has too much compression and beats up the engine/gearbox, not to mention the chance of loosing an engine at a 1500 idle approach. Be kind to your engine, it's the only thing that keeps you off the ground and out of the tress.

The video will tell you to keep rpms at 1800 + rpm and higher depending on the phase of the engine run. Running a 9121ULS at rpms of 1500-1700 is not good for your engine as we have discussed here before. This is in writing now and I hope alleviates some of the confusion from other sources.

 

 

http://rotax-owner.com/index.php?option=com_content&view=article&id=207:tips&catid=15:training&Itemid=174

[airhound]

Does anyone have a strong opinion, either way, about decalin fuel addative. Is it authorized by

ROTAX?

[Roger Lee]

Yes Decalin is fine. There is an SB out on TCP to not use it (too many harsh chemicals, that's yesteryears lead scavenger). You absolutely should be using Decalin if you burn 100LL.

[airhound]

Hi Roger,

 

I posed the same question to a competitor's official and got similar response regarding TCP, except he was referring to Decalin. I guess he might be confused. But the reason I brought this old subject up was due to an eye opener at a local home improvement store about the effects of 90day old gas/ethonol sitting in lawn mower systems. YIKES! The picture supporting adds along side the product was a marketing attention getter. An to a ROTAX owner, it was alarming on how it can gum up the works and destroy components. I know, if we flew more, then whats the point...

 

So, is there any Mogas additives which ROTAX supports like Stabil etc that may help stave off the bad effects that E-stuff can cause?

 

Is there a happy medium to be achieved with part mogas and part 100LL that one can mix and avoid potential damage due to prolonged unuse?

 

Would there be any positive or negative effects on the engine if one were to shut it down by turn the fuel off and letting it starve? The idea is to leave the firewall forward fuel less..Just an idea?

 

Thanks!

 

This above acft mfg also suggests that ROTAX proper, doesn't view the use of in-line fuel filters as necessary in systems design, just a gascolator with screen is all that is warranted. Any thoughts?

[Jim Meade]

...an eye opener at a local home improvement store about the effects of 90day old gas/ethonol sitting in lawn mower systems. YIKES! The picture supporting adds along side the product was a marketing attention getter.

I'm a farmer who typically buys gasohol (10% ethanol) 1,000 gallons at a time when it's cheapest each winter and lets it sit in my farm tank nearly all year. I burn this in my cars and trucks and usually take about 9 months to use a tank. In all the 15 or more years I've done this, I have had one incident of a 5 hp lawn mower lawn mower engine carburetor gummed up from fuel sitting in it from one year to the next. This was a trim mower that I used once or twice after I bought it, so the fuel sat without being refreshed for at least 6 months. Other than that, I've used this gasohol in my 30 hp zero-turn lawnmower (which sits all winter), 5 hp gas pressure washer, cars, truck, and when I had gas tractors in them with no incidents. Now, I grant that old gasoline gets skunky and the varnish will settle out. Sitting for a long time in a carburetor is probably not good for the engine. I don't use Stabil, although I have nothing against it.

 

But - why would the ethanol component of gasohol be an issue? The alcohol would seem to me to cut the varnish in the gasoline so that ethanol would likely last better if it sat for a long time than pure gasoline would. One of the raps on ethanol is that it "cleans everything out" so that gunk that sat in a gas tank and didn't go anywhere was dissolved by the alcohol and carried into the jets and floats of the finer parts of the fuel system. Cars have been engineered so that fuel system components have not been a problem for 30 years or more. Old airplane systems have not been changed. New airplane systems have seemed to be fixed in many regards but I've heard people say the composit tanks themselves are suspect. The engine doesn't care - we know that. Jabiru and Rotax both approve 10% ethanol in their engines.

 

Just what did the provocative ads showed that were so persuasive? And, I find it hard to believe that anything sitting for 30 days is going to be an issue. One sees all kinds of scary "so many days" statements but one sees very few definitive studies with actual experiments. Some of the "so many days" statements I've heard have been 6 months and 90 days.

[Roger Lee]

Several things here. It is TCP that has the harsh chemicals, Decalin is ok. Jabiru pulled their permission to use 91 Oct with ethanol in an SB. The 91 Oct sitting too long is a decrease in octane issue not so much gumming up. As the 91 Oct. sits for long periods octane diminishes along with some of the additives and there is nothing you can do about it. Stabil along with Seafoam claims they help, but usually it only helps the drying and gumming effect. In cars and most all other of our home engines you can use a fuel with a little less octane so it isn't an issue allowing it to sit for a while. Yes adding 100LL to your 91 Oct. will definitely help its longevity. Rotax would like any 91 Oct used within 4 weeks. Will it work after that, yes it will, but if you know you are going to be down for a long time 8 weeks or more add some 100LL or drain the 91. I would never personally let auto fuel set for the winter in my plane. That loss of octane with our 10.5:1 compression may cause serious issues. Yes it may work, but if for that one time it doesn't then you better get a loan ready to replace the engine top end. Leaving fuel set a long time has another hazard. trapped water or moisture. It will corode everything if it just sets. Where as using that engine more frequently helps keep that stuff flushed out. As far as the fuel filter. It was a requirement from Dynon and Floscan for use with the Floscan fuel flow sensor and must be mounted upstream of the Floscan which ours is. The gascolator is downstream of the Floscan. So FD started to put it in all of the CT's. It's not a bad idea and can only help. How many of our gasoline engines don't have some type of filter.

[Jim Meade]

Roger,

Interesting points. Can you tell me how the autofuel loses octane through sitting? How much does it lose and how fast, and what does that loss of octane do that might necessitate a top overhaul?

BTW, I have no disagreement at all with any of the comments that it's best to keep fuel fresh.

 

What is the fuel filter like? Does it trap water at all, as the gascolator might? What size is the mesh? Are there replacement, inspection, etc. guidelines on it?

[airhound]

I vaguely remember back from my GA Cert days there are Special Type Certificates (STCs) for older low compression Lyc and Cont engines to run MOGAS, but that was before Ethanol I think. Back when MOGAS was MOGAS. I wonder if those STCs allow for the 10%. My unschooled memory is most folk just bought the STC, which was primarily paperwork/certificate/instructions, but hesitated to use MOGAS, unless as a temp backup. There is a stigma out there probably created by folks that never checked for fuel contamination during preflight and blamed a sudden injection of water on MOGAS which 100LL will do too....probably folks that don't fly often enough to cycle through their fuel. I was looking at that special site for no ethanol MOGAS locations and noted they are really few and far between How do they even survive! One good thing in our little bug smashers is we have solid tanks. Some GA acft have rubber bladders and if installed improperly, wrinkle on the bottom, potential trapping large amounts of water. As the story goes, at a certain attitude the water would let loose and engine ingest it, or not....so, during preflight inspection one was to rock the wings to try to make any trapped water flow towards the sumps....blah blah blah....

[Tom Baker]

The STC's foe type certified aircraft do not allow any ethanol.

[Roger Lee]

When you let fuel set it will evaporate. leaving it in a can won't stop it and auto can degrade slightly just over time. For most engines that isn't an issue, but if you have a high performance high compression engine the lower octane will cause detonation. That will cause you to rebuild the top end and pay big big bucks. For me that's to big a roll of the dice since you never know when it might happen. The OAT can affect it i.e. cold dry air verses warm humid air (cold dry air can cause a fuel air mixture to become leaner), loss of octane hard climb with a hight CHT/EGT temps, ect....

As Tom stated an STC for auto fuel does not cover ethanol laced auto fuel. Our engines can burn water in the ethanol without any issues under normal circumstances.

[airhound]

Hello fellow ROTAX Engine Operators!

 

Any comments regarding the benefit of adding an Oil Cooler Thermostat Kit? Any growing pains associated with installation and impact on D120 function?

 

Thanks Doug in IL

[Roger Lee]

Read this thread, it may help some. You may want to move your post discussion over there.

 

 

http://ctflier.com/index.php?/topic/657-acheving-proper-oil-temperature/