Rotax 912iS & Fuel Injection

[roger lee]

The rub is usually the fuel tanks. Depending on the type of tank material some tanks can be sloshed like FD does for the CT.

[drseti]

With a wet wing, my concern would be: what do you do if the ethanol does attack the sealant? Now, you have to drill out all the rivets, remove the wing skins, clean all the metal surfaces, put new sealant on the edges of all the skins, re-assemble the wing, let the sealant dry, and then test the tank for leaks. If the factory doesn't want to do all that, probably neither do you!

[CTLSi]

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[IFlyRC]

My apologies. To be honest, I don't really have a good sense of the overreaction in regards to ethanol. I'm familiar with the various issues from the plentiful resources and forum such as this one, but I wasn't sure if it was similar to late 90s cars that couldn't run ethanol and the ones from 2000 and beyond that had less of an issue. Sounds like it's a non-issue in regards to corrosion at <10% in either case. Thank you for write up on ethanol in real world usage. I get where you're all coming from.

I was also going to ask about any concerns in regards to fuel injectors and 100LL or mogas, but that might be another non-issue with the redundancy that's built-in to the iS.

[CTLSi]

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[drseti]

I own one and have been using Mogas exclusively for 170 hours.

The fact that you haven't had any issues in 170 hours is encouraging, but it doesn't mean you can say with certainty that you won't have issues over the 2000 hour TBO of your engine. We can hope for the best, but should always be checking for hidden damage at every condition inspection. I recommend periodic borescope inspections of the piston crowns, cylinder heads, and valves, for example. You're probably OK, but shouldn't take that for granted.

[MrMorden]

I own one and have been using Mogas exclusively for 170 hours.

The fact that you haven't had any issues in 170 hours is encouraging, but it doesn't mean you can say with certainty that you won't have issues over the 2000 hour TBO of your engine. We can hope for the best, but should always be checking for hidden damage at every condition inspection. I recommend periodic borescope inspections of the piston crowns, cylinder heads, and valves, for example. You're probably OK, but shouldn't take that for granted.

If both the engine and airframe manufacturer are fine with ethanol mogas, why would you expect any damage from the fuel?

[drseti]

I wouldn't necessarily expect any problems, Andy, in an ethanol-approved engine and airframe. I'm merely pointing out (for those whose aircraft has not been tested and approved by the manufacturer) that "I've been using it for 170 hours with no problems" is scant assurance.

[Flocker]

Just curious, what would the estimated annual maintenance expenses be on a new 912iS flying mostly on Mogas and about 100 hours per year? i.e. oil changes, 100 hour, annual, etc.

[MrMorden]

Just curious, what would the estimated annual maintenance expenses be on a new 912iS flying mostly on Mogas and about 100 hours per year? i.e. oil changes, 100 hour, annual, etc.

Assuming nothing breaks...

Gas about 4gph, 100 hours = 400 gallons = $800 @ $2/gal

Oil changes every 50 hours, so figure two of them. Filter is ~$20, oil about $30. So $100 total.

You *might* need a plug change in there, my plugs go about 200 hours before changing, and even then they don't really need it. A set of plugs is about $25. Basically less than ONE plug for a Lycoming or Continental! So you might as well change them more often, maybe even at every annual.

You could add in the cost of the 100hr Rotax maintenance, which many shops do as part of the annual. An annual at Lockwood, as a data point, is about $800.

You could also amortize the cost of the 5 year Rotax rubber replacement, which costs about $2500. That is another $500.

All together, it looks like around $925 a year for "basic" operation. A more comprehensive number including all operational costs would be closer to $2225 or even a little higher. IF nothing breaks.

[Flocker]

Thanks!

[drseti]

Those figures are a good start, but I wouldn't take them to the bank. For example, the 912iS burns 91 octane minimum mogas, so even if regular stays at $2/gal, you'd better figure more like 2.40 for premium. The Rotax oil filter is more like $25 at present, and though Aircraft Spruce sells AeroShell Sport+4 for around $10 a liter, the bottles are heavy, so add another $1 to $2 per bottle for shipping (depending on where you live). 5 year Rotax rubber kits cost about $2k, but depending on the airframe, labor varies widely - 30 hours labor (not unusual for many an LSA) at $85/hr (an average shop rate at most Rotax authorized Independent Repair Centres) is another 2.5k. I tell my customers to budget $1k/year for rubber.

Still, having owned a Lycoming powered Beechcraft for 30 years, I can tell you LSA maintenance and operating costs will be 1/2 to 1/3 of what it costs to fly a higher performance aircraft. Your fixed costs (hangar, insurance) will be about the same, but you can expect to be way ahead of the game with a 912iS powered LSA. If it will satisfy your mission, you can't go wrong.

[Nomore767]

Those figures are a good start, but I wouldn't take them to the bank. For example, the 912iS burns 91 octane minimum mogas, so even if regular stays at $2/gal, you'd better figure more like 2.40 for premium. The Rotax oil filter is more like $25 at present, and though Aircraft Spruce sells AeroShell Sport+4 for around $10 a liter, the bottles are heavy, so add another $1 to $2 per bottle for shipping (depending on where you live). 5 year Rotax rubber kits cost about $2k, but depending on the airframe, labor varies widely - 30 hours labor (not unusual for many an LSA) at $85/hr (an average shop rate at most Rotax authorized Independent Repair Centres) is another 2.5k. I tell my customers to budget $1k/year for rubber.

Still, having owned a Lycoming powered Beechcraft for 30 years, I can tell you LSA maintenance and operating costs will be 1/2 to 1/3 of what it costs to fly a higher performance aircraft. Your fixed costs (hangar, insurance) will be about the same, but you can expect to be way ahead of the game with a 912iS powered LSA. If it will satisfy your mission, you can't go wrong.

In my part of SC I can buy 93 non-ethanol mogas for $2.99 gallon. I schlepp the gas to the hangar myself. I just bought 93 non-ethanol at Barnwell airport at their pump for $3.66 gallon.
Personally, I have avoided using mogas with ethanol (even though it is approved by Vans), again just personal preference. I'm not a fan of the ethanol, others may disagree. I believe Dr Dehave posted on this forum a catastrophic experience in his LSA after using E-10 auto gas.

When I looked at a couple of 912iS powered airplanes I know from talking with mechanics, Rotax and the airplane manufacturer, that maintenance was more complex and thus more expensive than the carb 912ULS which I have. Its heavier and more expensive to buy too. In return the gph is around 4gph in cruise compared to the 4.4 to 4.6 gph I've been getting at cruise in the 5000-5300 rpm range usually at 3500/4500 feet.

My Rotax trained mechanic charges $350 for the basic annual condition inspection plus extra work, parts etc. Mine ran $550.

If I recall correctly, he charges about $3500 for the 5 year rubber replacement including labor and the hose kit.

I just had an oil change and rather than do it myself I have my mechanic do it. Oil is the new Aeroshell Sport Plus 4 at about $10 litre and the filter was about $25.
Using 93 non-ethanol for the past 8 months, and 50 hours since the last oil change, I believe I could go to 100hours, but we've agreed to do the changes at 50 hours.

He inspected the plugs, magnetic plug and filter and all were really clean and no signs of lead sludge in the oil tank. I have used 100LL very sparsely and not for at least the last 8 months.

Personally, the 912iS engine is 'okay' but I'd opt for either the 912ULS for being less complex, lighter and less expensive. The 914 engine runs very smoothly but the main benefit seems to be the extra power in climb and this is probably more important to pilots flying in terrain and conditions where the extra performance is more beneficial. I see that Tecnams demo LSAs are almost exclusively 914 engines, it would be interesting to ask them why that is.

Flocker, in addition to asking questions here, I would recommend that you seek out Rotax qualified mechanics in your area and ask them about doing service and maintenance on all models of Roatx engines. Also compare their shop rates and estimates for the maintenance schedule.
Rather than buy the plane/engine you think you want…buy the ones which best suit your personal mission as well as finding a Rotax shop/mechanic who will do the service and maintenance on them.

[Jack Tyler]

"Still, having owned a Lycoming powered Beechcraft for 30 years, I can tell you LSA maintenance and operating costs will be 1/2 to 1/3 of what it costs to fly a higher performance aircraft."

Paul creates quite a gap with that statement, since his Beech had retractable gear, CS prop, and a supply chain that included Tiffany's-like Beechcraft. I'm not sure what each of us would think when reading the term 'higher performance aircraft': MTOW? Number of seats? Speed? Weather capability? I fly a 4-seat Part 23 a/c (or a 3-seat a/c with 5.5 hrs of fuel), it is IFR equipped & certified, I flight plan for 130 kts (not mph), the plugs haven't needed changing since overhaul 500 hrs ago and I have no 'rubber reserve'. My maintenance/repair costs were $300/month in 2015, which was a bit higher than in 2014. I averaged ~110 hrs/year in flight time in those 2 years, paying ~$25/hr for fuel. A Part 23 a/c that's closer to an LSA in performance and capability would no doubt cost less, other things being equal (which of course they aren't). I mention this just to offer more context than Paul's more general formula of '1/2 to 1/3 less cost' since it depends so much on what performance parameter we're looking at. E.g. I was walking around the ramp at KHEG the other day and looked at four 150's & 152's which were in decent shape and looked like they were used regularly. I don't think they are seeing the much additional cost. I'm a big fan of the SPL and light sport aviation, and I agree with Paul about the basic premise that one ends up paying for performance. I also agree that the operational cost side of sport aviation is generally more affordable IF all things were equal and IF sport aviation meets one's aviation desires. But there are lots of variables involved, as we all know. And the two biggest variables WRT the cost of flying aren't mentioned above: the age of the aircraft and its sunk cost. Newer SHOULD cost less to operate with so many life limited items and the general condition of the airframe in their early years...and newer surely costs more. I have no way of knowing of course, but I'm betting most of the LSA a/c being flown today cost their current owners more than the $50K I paid for my Grumman. 'Cost' is a devilish thing about which to generalize, whether discussing LSA or Part 23.

[drseti]

Jack, you've done extremely well with your Grumman, in terms of operating and maintenance costs (and I'm indeed happy for you). We should, of course, warn forum members that YMMV.
A word about that rubber reserve: in certified aircraft, rubber is replaced "on condition". I've had hoses replaced that looked ratty on the outside, but you can't see inside them, and I've had hoses fail that looked great on the outside. The Rotax requirement is a highly conservative approach, designed to prevent a common cause of inflight engine failure. I for one appreciate the peace of mind it gives me. A hose failing on a trip can end up costing you a whole lot more than budgeting a rubber reserve.