Rotax engine questions

[Nomore767]

I've got limited experience with Rotax 912 series engines, and that is as a renter, not an owner:-

1) Fuel - exactly what kind of auto gas can I use? Can I literally go to the gas station and pick up 93 Premium and use that?
My local shell doesn't say what level of ethanol is in it. Can I use gas with ethanol?
If I fly locally and bring my own auto gas, what happens on an x-country if I have to mix with 100LL? Do I need a lead
cleaning additive like Decalin? My school uses 100LL without any additive but then has 100 hour inspections.

2) Engine model- I have only got experience with the 912US engine. If I were to buy a Rotax LSA and there was a choice would
the newer 912iS injected model be better long term? The Remos I flew had some issues with balancing the carbs,
or so the CFI said. The engine was quite noisy throttled back, and although CFI didn't say to, another pilot told me
keeping it above 4000rpm in descent and 5000 in cruise was better for the engine, especially if using 100LL.
I must say after flying the 0-200D in the C162, the Rotax , to me, seemed loud, sensitive and more fiddling with
turning the prop to burp the oil, getting access to the oil in the Remos, and the issues with carbs and idle speed.
The engine in the Remos, quit on me twice, fortunately on the ground!

3) Propeller- I've flown both two blade and three blade. To me the three blade looks better although I didn't see much difference
otherwise. The three blade was a nice composite Nu-form. If you had a choice which would you pick?

4) Rubber replacement- what is this and why does it need replacing periodically? How much?

Thanks for any answers, Howard.

[Helen]

Yes, you can go you the gas station and get 93 Octane with up to 10% ethanol so long as the airframe manufacturer authorizes it (which general depends on what the fuel tank is made of). Your engine will last a lot longer and will require less routine mx if you do this rather than buying 100LL for twice as much at the airport. (For example, with the correct oil your oil changes go from 25 hours to 100 hours by using 93 rather than 100LL.) Running 100LL causes a lot of valve problems and it has been my experience that you will likely not make it to TBO doing so.

Mixing 100LL occasionally is not a big deal. You can mitigate the effect by using Decalin, although strictly speaking, Rotax does not authorize any additives. You may need to change the oil more frequently if you are doing this a lot.

The RPM issue is more of an issue for pilots using 100LL. Neither the Rotax nor the O200 were designed for use of 100LL. (The O200 was designed to use much lower lead 80 which is no longer in production.) Running the engines hot will help mitigate the effects of lead on the valves.

Rotax engines are much quieter than O200's IMHO but noise you hear is more dependent on the airframe design than anything else.

If the engine was stopping on the Remos you were flying your mechanic likely was either not balancing the carbs regularly and/or not setting the idle correctly with seasonal changes in temperature. It is important to have a trained and certified Rotax mechanic to maintain a 912. 912s will have more routine mx but less surprises, like a top over haul (from running 100LL) or mag failure, than an O200.

I would personally not want to own a 912iS. It is much heavier that a 912ULS, much more expensive, and there are very few people in the country trained and qualified to maintain them at this time. The fuel savings is minimal at low altitudes and you can buy an awful lot of fuel for the cost difference. I like also really enjoy useful load. Carburetor 912ULS's are tried and true, reasonably priced, and simple to maintain by a Rotax trained mechanic.

Helen

[Nomore767]

Yes, you can go you the gas station and get 93 Octane with up to 10% ethanol so long as the airframe manufacturer authorizes it (which general depends on what the fuel tank is made of). Your engine will last a lot longer and will require less routine mx if you do this rather than buying 100LL for twice as much at the airport. (For example, with the correct oil your oil changes go from 25 hours to 100 hours by using 93 rather than 100LL.) Running 100LL causes a lot of valve problems and it has been my experience that you will likely not make it to TBO doing so.

Mixing 100LL occasionally is not a big deal. You can mitigate the effect by using Decalin, although strictly speaking, Rotax does not authorize any additives. You may need to change the oil more frequently if you are doing this a lot.

The RPM issue is more of an issue for pilots using 100LL. Neither the Rotax nor the O200 were designed for use of 100LL. (The O200 was designed to use much lower lead 80 which is no longer in production.) Running the engines hot will help mitigate the effects of lead on the valves.

Rotax engines are much quieter than O200's IMHO but noise you hear is more dependent on the airframe design than anything else.

If the engine was stopping on the Remos you were flying your mechanic likely was either not balancing the carbs regularly and/or not setting the idle correctly with seasonal changes in temperature. It is important to have a trained and certified Rotax mechanic to maintain a 912. 912s will have more routine mx but less surprises, like a top over haul (from running 100LL) or mag failure, than an O200.

I would personally not want to own a 912iS. It is much heavier that a 912ULS, much more expensive, and there are very few people in the country trained and qualified to maintain them at this time. The fuel savings is minimal at low altitudes and you can buy an awful lot of fuel for the cost difference. I like also really enjoy useful load. Carburetor 912ULS's are tried and true, reasonably priced, and simple to maintain by a Rotax trained mechanic.

Helen

Helen,

Thanks so much for the response!

Right now, my list has the RV-12 SLSA, the Bristell, Astore and the Phoenix motor-glider on it, all using the 912US engine.

My 'mission' would mostly be local flying (up to 1-2 hours each way) and I could fill up myself with local 93 octane. From what you say if I did a longer cross-country I could fuel with 100LL at a pinch and not need any additive? The thought crossed my mind about how I would buy auto gas on the road, short of bringing along empty gas cans which probably isn't a good idea.

Indeed, the low idle was an issue that needed to be fixed, according to my CFI. Not sure about the carbs. There is a Rotax shop about 90 minutes drive from me, so not far by air. How often would you schedule the 'routine' maintenance on the carbs etc? Every season change?

Do you have any opinion on a 2 blade versus 3 blade propellor?

What plane are you flying with a Rotax?

Again, thanks for the response and cheers! Howard.

[ct4me]

+1 on the above.... except I'd LOVE to have an IS. The 9 lbs extra weight is easily offset by the 25% better mileage. No more carb balancing, smoother starts, no carb ice issues, & no choke. Even the payload issue is improved by the more efficient engine: a CT with the fuel injected engine should be able to go the same distance on 26 gallons, as a non-IS CT would go with 34 gallons. Even giving 1.5 to offset the extra weight, that 36 pounds of extra useful load.

The redundancies built into the 912IS are comforting.

The mechanics are being trained as we speak... as long as I've had my Rotax, pretty much the only reason I've needed a mechanic was for carb balancing. I'm guessing the price of an annual will go down $100.

[roger lee]

Hi Helen,

Nice answer. Now I can go take an early nap.

Tim,
The weight increase is more like 20-22 lbs total. It is not just the engine alone, but other supporting mechanical and electrical components.

That' the only reason you come to see me is a carb balance.
My poor little feelings.

[drseti]

Since the other Rotax gurus on this list have already answered your engine questions, I'll discuss the prop.

In order to produce equal thrust, three blades can be shorter than two. Shorter blades means quiter operation, as well as better ground clearance, leading to less abrasion of the props from dirt, dust, and debris on the runway or taxiway. However, more blades means more drag, which gives you a speed penalty. Prop drag increases with speed. With LSAs limited to a Vh of 120 kcas , drag is not much of an issue, and the speed loss will be negligible. (A high speed aircraft is another matter altogether.) Also, the more blades you have to turn, the more fuel you burn, so your best fuel economy would occur with a one-bladed prop (don't laugh; there WAS such a thing in the 1930s!)

Since all propeller blades have finite lifetime, and cost $, a three-bladed prop will end up costing you more. But, three blades are better for STOL operations, because they tend to shorten the takeoff roll (again, at a slight penalty in cruise speed). Thus, I tend to favor the three bladed prop. (Notice that I'm not even mentioning the cool factor, which is only evident when the prop is stopped!)

[drseti]

A word about ethanol: I won't use it. (OK, that was four words.) Ethanol is a solvent. It dissolves things. Like airplane parts.

Yes, Rotax says up to 10% is OK. Yes, some airframes have ethanol-impervious fuel tanks (mine doesn't). But there are other things that the ethanol can destroy, and those things are not supplied by Rotax. Things like the fuel selector valve, fuel cap o-rings, fuel filters, and even the behind-the-firewall fuel lines. Some manufacturers say "no problem, the tank is fiberglass." That doesn't address the whole issue.

To determine whether a particular airplane is really compatible with ethanol, the manufacturer should really take all components that come into contact with fuel, drop them in a tank with ethanol, and let them soak for a month or two. Then, do microscopic and structural analysis of all the parts, to see if there's any damage. Few manufacturers of SLSAs have chosen to do this. I figure it's best to err on the side of caution.

Another consideration is shelf life. Avgas can safely sit in a tank (or in the float bowls of the carbs) all winter, while the plane isn't flying. Then, come spring, charging and re-installing the battery (which should have spent the winter indoors, in a warm closet) will let you fire up and fly. with mogas, you'd best drain the tanks, hoses, carbs, etc. if the plane sits idle for more than a week or two, or you'll find things gummed up when you try to return the plane to service. So, if you do decide to use auto gas (with or without ethanol), it's a good idea to run the tanks nearly dry before putting the plane away for the winter, and filling up with nice, stable 100LL for the duration.

(Note: you can tell from the above that I live in the snow belt...)

[Nomore767]

So, what is the 'rubber replacement' that folks mention, which needs doing at a certain number of hours? How expensive is it?

Also, for planning, what do most Rotax 912us owners use for planned fuel burn per hour?

I read a piece today where the reviewer mentioned 5.5 gph. I thought this was high as I remember 4.7gph from my Remos training. I would have thought in cruise you could beat that. The 0-200D is about 5.6gph.

I would have thought (and I'll do some digging) that 4.5gph is better for the 912US which means the RV-12 is about a 3.5-4.0 hour plane with a conservative 45-60minute reserve.

[drseti]

A comment or two about maintenance of Rotax engines seems in order.

I drive an antique MG (a 1950 TD). It uses dual side-draft SU carburetors (not too different from the Bings on a Rotax 912). If I were to bring my MG to a Ford or Chevy garage for a tune-up, it would have to come home on the back of a rollback towtruck. The mechanics just aren't trained to maintain an XPAG engine. So, I don't bring my MG to the Ford or Chevy shop. Period.

Unfortunately, all too many SLSA drivers bring their Rotax to a shop that specializes in Continental or Lycoming engines. But, those mechanics are just not trained to work on an MG -- er, Rotax, even though their A&P license says they are legal to screw them up. That's probably why rental LSAs often have engines that run rough, or make noise, or quit.

The solution? Find yourself a mechanic who took the Rotax factory courses (there are four of them). Better still, if you are a gearhead, take the courses yourself. They're not that expensive (well, not compared to the cost of an engine). You may be able to educate your mechanic, or do your own routine engine service and light maintenance. You may even grow to love the Rotax engine -- it's quirky, but very efficient, and a fine piece of Austrian engineering. It's also very economical to own and operate (but only if you keep it away from the Lycoming and Continental shops!)

[CharlieTango]

Chevron Premium in Mammoth Lakes = $4.79
Avgas @ Mammoth Yosemite = $7.70

And I believe it is far better for my Rotax and tolerated by my CTSW

[drseti]

So, what is the 'rubber replacement' that folks mention, which needs doing at a certain number of hours? How expensive is it?

Ah, I was getting to that!

I owned a Lycoming IO-360-powered Beechcraft for 30 years. At every annual inspection, the IA examined (and tested) all the rubber fuel, brake fluid, and oil hoses. And, every year, we had to replace one or two. Or three. They were replaced on condition, not on a schedule, and to determine condition required the mechanic to spend time inspecting them (which cost money). So, my plane was in a constant state of rubber-replacement.

Rotax has decreed that, every five years, every bit of rubber in the engine has to be replaced. By declaring a five-year service life for hoses, they are being conservative. They are also recognizing that "on condition" is an inconsistent standard, and that some owners would be inclined to say "good enough is good enough," and run a hose until it breaks. In flight. So, I think the five year interval is a good thing.

But, it's costly. The exact rubber kit varies between LSA manufacturers, but mine ran around $1500. The labor (depending upon the hourly rate of the shop you use) could be $1000 to $2000. So, it's probably a good idea to budget a kilobuck per year toward your rubber replacement.

BTW, the rubber replacement is calendar-based, independent of the number of flight hours. If you only fly 20 hours a year, your rubber, on a per flight hour basis, is expensive! The more you fly, the cheaper it becomes. And, if you fly 400 hours a year (as some flight schools do), your rubber will take you up to TBO, at which time your new engine will come with new hoses anyway, if you buy one fresh in the crate.

Also, for planning, what do most Rotax 912us owners use for planned fuel burn per hour?

In training, I average 4 GPH. On trips, I flight plan for 5 GPH. If I push the engine right up to the bottom of the yellow arc, that goes up to 6 GPH (and only buys me an extra 5 knots -- hardly worth it!)

[Nomore767]

A word about ethanol: I won't use it. (OK, that was four words.) Ethanol is a solvent. It dissolves things. Like airplane parts.

Yes, Rotax says up to 10% is OK. Yes, some airframes have ethanol-impervious fuel tanks (mine doesn't). But there are other things that the ethanol can destroy, and those things are not supplied by Rotax. Things like the fuel selector valve, fuel cap o-rings, fuel filters, and even the behind-the-firewall fuel lines. Some manufacturers say "no problem, the tank is fiberglass." That doesn't address the whole issue.

To determine whether a particular airplane is really compatible with ethanol, the manufacturer should really take all components that come into contact with fuel, drop them in a tank with ethanol, and let them soak for a month or two. Then, do microscopic and structural analysis of all the parts, to see if there's any damage. Few manufacturers of SLSAs have chosen to do this. I figure it's best to err on the side of caution.

Another consideration is shelf life. Avgas can safely sit in a tank (or in the float bowls of the carbs) all winter, while the plane isn't flying. Then, come spring, charging and re-installing the battery (which should have spent the winter indoors, in a warm closet) will let you fire up and fly. with mogas, you'd best drain the tanks, hoses, carbs, etc. if the plane sits idle for more than a week or two, or you'll find things gummed up when you try to return the plane to service. So, if you do decide to use auto gas (with or without ethanol), it's a good idea to run the tanks nearly dry before putting the plane away for the winter, and filling up with nice, stable 100LL for the duration.

(Note: you can tell from the above that I live in the snow belt...)

So, Paul...this is what I find SO confusing about Rotax. One view says use auto gas and ethanol is fine; avoid 100LL as the lead damages the engine. Another says the opposite, (my school did this). Use 100LL, use Decalin if you want, just change the oil more often and expect more maintenance. You say don't use Ethanol at all, even though you said that Rotax allows for 10%. How can you get auto gas that doesn't have Ethanol? Aaah...which is it?

I wouldn't put the plane away for the winter, but draining the tanks to avoid stale auto gas seems to me another hassle.

Lastly, if you say use 'nice, stable 100LL' then maybe using the 0-200D Continental is the better way? I mean it uses 100LL (albeit it was designed for lower octane)....period. It's at every airport pump, doesn't damage the components, I don't have extra maintenance for lead date like the Rotax, and the extra cost sounds like it outweighs the cost and hassle of Rotax operation. Just about every shop in America can work on it!
The 912iS sounds like an improvement with no carbs to maintain and adjust, no choke, better fuel burn despite the extra weight, but then some say there's minimal advantage. Then I've heard from a few sources about contamination in the carb bowls. In the case of Rotax, two carb bowls

All this, and then I have to locate a Rotax shop who still may be in training? Hmm....

Appreciate the answers!

Cheers, Howard.

[Helen]

We've moved almost our entire fleet over to E10. Prior to that very few of the engines were making it all the way to the 2000 hour TBO because of lead related issues. We expect to see nearly all of them do so now. Rotaxes should not be run on 100LL if you can avoid it. Ethanol is fine so long as you don't let it sit and routinely inspect rubber parts.

Now bare in mind, one thing most people don't talk about is that O200's don't like 100LL either. They were designed for 80 which you can't get any more. You'll have many of the same problems running an O200 on mogas but you don't have the option of running E10 on them.

The biggest disadvantage of an O200 though is weight. I have yet to see any LSA with an O200 that can legally carry two grown men and gas all at the same time.

Helen

[drseti]

So, Paul...this is what I find SO confusing about Rotax. One view says use auto gas and ethanol is fine; avoid 100LL as the lead damages the engine. Another says the opposite, (my school did this). Use 100LL, use Decalin if you want, just change the oil more often and expect more maintenance. You say don't use Ethanol at all, even though you said that Rotax allows for 10%. How can you get auto gas that doesn't have Ethanol? Aaah...which is it?

Believe me, Howard, I understand your confusion. I'm four years ahead of you on the learning curve, so I can assure you that the confusion will dissipate.

Yes, Rotax authorizes up to 10% ethanol - in their engines. That doesn't say they approve it for any given airframe (they can't; only the aircraft manufacturer can do so). In the case of my Evektor SportStar, the manufacturer does not approve ethanol, so I don't use it. (Some do anyway. Since I'm running a flight school, and my plane is available for rental, you can imagine the lawsuits if I operated against the airframe manufacturer's instructions, and somebody had a problem...)

Ethanol free mogas used to be available. When the Rotax 912 (and, in fact, the Evektor SportStar) were designed, that's what was used. It worked great! For the first year I owned my SportStar, that's what I used. It worked great! Then, the elected legislators in my state mandated that no auto fuel could be sold without ethanol. That was probably a politically wise decision (for those wanting to get re-elected). It didn't make much sense economically, or from an engineering perspective).

When the ethanol mandate kicked in, I switched to avgas. That has cost more for fuel, but had only a very small impact on maintenance costs. Yes, I do 50 hour oil changes now (used to be 100). And, I change spark plugs every 100 hours now (used to be 200). But oil and plugs are relatively cheap.

maybe using the 0-200D Continental is the better way? I mean it uses 100LL (albeit it was designed for lower octane)....period. It's at every airport pump, doesn't damage the components, I don't have extra maintenance for lead date like the Rotax, and the extra cost sounds like it outweighs the cost and hassle of Rotax operation. Just about every shop in America can work on it!

All this is true; I've flown many an O200 powered aircraft over the years, and it's a good engine. However, it is heavy (at least, compared to the Rotax) -- this matters in an LSA more than you can imagine), and typically requires a top overhaul midway to TBO. The Rotax easily runs 2000+ without the jugs or heads ever having to come off. And, the Rotax, new in the crate, is only $18,600. That's a lot cheaper than the Continental.

I actually came very close to buying an O200 powered LSA four years ago. It was a great plane, but had nearly 100 pounds less useful load than the SportStar.

The 912iS sounds like an improvement with no carbs to maintain and adjust, no choke, better fuel burn despite the extra weight, but then some say there's minimal advantage.

I can't justify the cost of the iS just on the basis of fuel savings. Unless fuel costs go WAAAAY up, the cost of the engine just doesn't get recovered. What you do save is labor hours. An injected engine isn't as maintenance intensive as a carbureted one.

Then I've heard from a few sources about contamination in the carb bowls.

I've known some folks who experienced this. Usually, if you use clean fuel (and drain all contamination from the tanks at preflight), change the fuel filter regularly, and replace your fuel lines at the required 5 years, before they start to crumble, this shouldn't be a problem. Even if it is, it's trivially easy to get those float bowls off and on.

All this, and then I have to locate a Rotax shop who still may be in training? Hmm....

I can't help you with that one, unless you want to come to Central PA for your maintenance. Maybe the best solution is to move to Europe, where they've been flying the 912 for 20 years, and have trained thousands of mechanics to work on the 40,000 of them that they've produced. In fact, most European mechanics even have metric spanners!

[drseti]

Ethanol is fine so long as you don't let it sit and routinely inspect rubber parts.

Yes for the engine; maybe NOT for the airframe. It all depends on the manufacturer.

The biggest disadvantage of an O200 though is weight

Absolutely true, Helen. Even the new Lycoming 233 is heavy compared to a 912.