Rotax 912 iS: Better than predicted

On a recent visit to Rotax near Wels, Austria, I was privileged to examine the immense Rotax engine factory and test facilities with executive Christian Mundigler.

Taking a whole day from his many duties, Christian gave us a thorough tour of the many departments both non-aviation and for Rotax Aircraft Engines.

RotaxFactoryIn our discussions, I revealed that with about 5,500 hours logged, the majority of my flight time has been behind — or in front of — Rotax powerplants. I hadn’t realized it myself, but after many years of flying nearly every ultralight aircraft and the majority of Light-Sport Aircraft for sale in the USA, my Rotax time now exceeds my Lycoming or Continental time … with some hours for Jabiru, HKS, Hirth and a few others adding to the total.

Most recently, I have been able to log more than 30 hours on the newest Rotax of all, the 912 iS. I have found it to offer significantly better fuel economy; I have been able to consistently burn less than four gallons per hour by slightly backing off max performance.

The engine produces speeds of 120 knots, topping out the LSA category in the sleekest models (and it can give more speed in countries that allow in-flight adjustable props). When setting the 912 iS at just under 5,000 rpm I see about 125 mph (about 110 knots) at lower altitudes, at which speed digital instruments calculate 30 miles per gallon.

912iSSince 1989, Rotax has sold more than 46,000 four stroke engines in the 912/914 family (80 to 115 horsepower); that’s nearly 2,000 a year. The company says this fleet of four stroke engines has now logged more than 40 million flight hours — not even counting many more from the older two-stroke line* — and is presently adding 5 million flight hours every year. More than 220 aircraft manufacturers use two and four stroke Rotax aircraft engines supported by a worldwide network of Rotax authorized distributors and their service or repair centers with more than 150 sales outlets.

While the 912 iS is essentially the same engine as the carbureted 912 ULS, it has seen numerous changes, including fuel injection and computer controls.

Running up an iS requires some procedural changes for those used to Lycoming or Continental engines. Instead of checking magnetos with small power drops (when operating on only one mag), you switch between “lanes” and generally see hardly any power drop, although you do observe a momentary hesitation as the computer senses which lane was selected.

In flight, rather than tach readings of 2,200-2,700, you use power settings of 4,200-5,500.

Gone is any concern about carb icing. The mixture is idealized at any altitude, and generally maintenance is eased, for example, the old balancing of two carburetors is no longer needed.

Every time I’ve asked the engine to start it has done so instantly though I should note I only operate in warmer climates. I don’t start taxiing for takeoff until the engine reaches 120° Celsius and you maintain power at 2,000 rpm or higher.

The computer checks the engine frequently and shows a light if something needs attention. It couldn’t be much easier and using 91 octane auto gas, fuel costs about $15 per hour. For comparison, a Cessna 172 will cost roughly $35-50 per hour using 100LL avgas.

Rotax engineers have set the engines to run in what they call Eco mode (until 97% power is demanded). In common use, you’ll only need “Power” mode in takeoff phase.

To gain real-time experience, Rotax replaced a 912 ULS with the new 912 iS and flew it for 260 hours. They tried to keep all other factors constant: The same airframe, similar speed, the same atmospheric conditions and temperature, the same fuel volume, and even the same pilot. Most comparison was done in a Tecnam P92 Echo Classic.

One series of tests used 60-minute flights with five minutes taxi out and five back plus 50 minutes of pattern training work (doing seven landings), which they called the “flight training scenario.” The average burn was 2.65 gph.

Over 260 hours of testing at a variety of altitudes consumption averaged 32.6% less (in a range of 26-36% lower consumption) burning an average 3.25 gph. In either mode, fuel use was substantially less at high altitudes.

Rotax’s test plane is lighter than the LSA I used so fuel use was a bit lower than what I typically see. I’ll probably get better at maximizing fuel economy. However, even at my use experience in an airplane that weighs 280 pounds more, the 912 iS is simply excellent on fuel burn. That’s more flying for less money … and that’s a great thing.

*Rotax is no longer making some very successful two stroke engines described as 277, 377, 447, or 503. However, it continues to produce the 65-horsepower Rotax 582 and have sold more than 30,000 of this single model.


    • says

      E-Feel Aeronautics SARL in Europe has a STC to put the Certified Rotax engine on the cessna 150. But that is for EASA countries. I haven’t seen one in the states. Try googleing cessna-rotax should get a few pages that talk about it. Not sure if you got one done under EASA type certificates if you could then import it?

    • says

      I am not so sure that installing one of these engines would be economical. By the time one pays for the engine and accessories, makes the modifications required, the installation cost would greatly offset the potential savings in fuel cost. You could get some extra speed, if a constand speed prop is installed, but this would further add to the cost.

      The 150 has a Continental O-200 in it, which I am not that familiar with, but the 152s have Lycoming O-235, same as my Colt. I am burning on average 5.5 gallons of auto fuel per hour. I have an auto fuel STC for my plane, and a fuel flow gage by EI, that is remarkably accurate. I verify my fuel visually with a preciselly calibrated stick before each flight, and record all fill ups.

      With the new Rotax, due to the weight of my aircraft which is almost identical to the 150, I would likely save about a gallon per hour, so whith the potential savings it would be hard to recover the retrofit cost. Perhaps it makes sense in Europe, where the fuel cost is much higher than in here.

    • fritz katz says

      Why on or above earth would you swap out a bulletproof O-200 or O-235 for this piece of nazi-designed crap?
      Are you a masochist?
      Or maybe an A&P?
      Do you have ANY idea how complex this chatterbox engine is, how many hideously expensive components will need replacement ON SCHEDULE, how many hoses, valves, shunts, connectors are waiting to FAIL, and what both the MANDATORY inspection and pre-flight rituals involve if you do them properly?
      “Do you like “burping” your engine pre-start?
      Do you like checking the oil and turning the key with O-200/235 and no maintenance (other than oil changes) till annual or would you prefer a half hour of inspecting dozens of hoses and clamops for leaks and three step fluid level checks and a calendar full of expensive appointments with your A&P for scheduled interval work? NONE mentioned by old DJ above.
      The 912 is in wide use because of euro noise and pollution regs that made it the only mass-produced powerplant as LSA was created.
      Even lying shill Dan Johnson might admit Erwin’s CZAW Sport Cruiser, Mermaid, etc were designed for the superior Jabiru 3300 but supply (and Aussie disgust at Erwin’s business “practices”) forced him to resort to 912.
      As usual, Dan fails to mention critical issues beyond even complexity and cost of ownership.

      He fails to mention the historic failures rate of rotax vs continental/lycoming or thst he was nearly killed in one that, as typical, failed during takeoff.

      Fails to mention the constsnt synchs and tinkering that most of these require for routine ooeration.

      Fails to mention whether he was paid for this report BY Rotax… or if at least they covered his euro vcation that took him there.

      But never mind. What do I know? I only tried to run a flight school full of these fussy, money-and-labor-pit 912s (and like UND gave up) that cannot be THAT different from this model. I could be wrong but YOU take the chance, OK? I’m sticking with direct drive non-nazi powerplants (did I mention gearbox issues?).

      • Edward Dolejsi says

        As I was reading your rants, insults and accusations, I concluded that you must have had a really bad day.

        Here is a thing. Some of the points you mentioned may actually have some value, but you lost all credibility by spewing anger throughout your message. You also accused, and insulted Mr. Jonson, which certainly didn’t add any value to the discussion either.

        If I have a bad day, and say something inappropriate, I apologize.

      • Guest says

        To “fritz katz”:
        Wow! That is some preposterous assembly of words. Laughable. Did you string all of this together by yourself? Really? By the way, Fritz and Katz are both German names. I guess that makes you a nazi, right? You must be – based on your logic. But then again, calling this ludicrous rant logic is dignifying in ways it doesn’t deserve. Sieg heil!

        • Fritz Katz says

          Good factual responses from you two.
          I guess I was mistaken.
          1. Dan Johnson NEVER had a crash in a CZAW factory aircraft (while departing to represent them at SunNFun) in front of Erwin himself and the US importer whose combined factory personnel couldn’t keep all the cables and hoses and linkages and parts of a 912 sorted out and operating properly MIA06LA078
          2. I never had a flight school fleet of 912 powered Katanas which — as UND found out, returned, and sued for their money back — would not start in the winter without installation of preheaters (notice how Johnson WHO KNOWS THAT WELL word parses around it above) and overheated in the summer and required FIVE TIMES the scheduled maintenance of Lyc/Cont for carb synchs (wow – big improvement there… except additional checks for FI now) and gearbox shimming/replacement and hose lifetimes and radiator flushes. Must have been a bad dream but sure seemed real.
          3. I guess I am the one who made up all those lovely graphics and performance charts with the CZAW logos on them showing climb rates and near-nil maintenance (after break-in) for the Jabiru 3300 vs 912. Funny how some of them are in a foreign language I didn’t know I knew.
          DOLEJSI and ‘GUEST”: You two pathetic dumb sacks of sheet would rather insult the messenger for bad manners than be informed…. and it is for you that glib, shallow marketing was invented and it is because of you and your reluctance to pierce the veil, look behind the curtain, and face unpleasant realities that aviation is currently subject to the same petty misrepresentations, outright lies and grandiose scams as any other industry when we once had a tradition of honesty as essential to safety.
          And a couple of control freaks too — telling me how I should write. Go fokker yourselves. See if you like this better: Johnson is an indefatigable whore shilling for whoever pays for the past ten years. You want ME to apologize when HE has never apologized for suckering hundreds of aviators into placing deposits on Parrots and Mermaids which he KNEW were not being produced and probably knew would never be produced yet pretended they were in production. Screw “probably” since he was repeatedly onsite at the Czech factory and the NakedLady ranch and Indiantown import/assembly sites.
          Johnson makes Jim Bede look like a god… sure Bede ripped off thousands of deposits but at least he was actually a decent engineer with some interesting concepts several of which flew and performed…eventually. Read that NTSB report and you’ll see Johnson is not even a pilot worthy of the name… just a leftover UL cowboy. He was punished enough for that by nearly dying and spending months in hospital with a broken back. But he has yet to apologize for misrepresenting CZAW back then and failing to do TODAY what ANY decent auto journalist would do and STATE CLEARLY if he was paid for an infomercial like the above (which of course he was — either by Rotax or since he is paid to represent LAMA…his position of President/Chairman never revealed above ) and/or for the travel and vacation behind it.
          I have personally confronted him on such points and he laughs it off all the way to the bank… sometimes hiding behind Ron Wagner of EAA… another self-serving “prize” whose rumored background ripping off student aviators we might all be interested to know. Oops… I forgot, You don’t WANT to know…. see no evil, hear no evil. STFU… there ARE those who do want to know… and deserve to… despite you two douchebags. Like self-flagellation, you two may enjoy being lied to and defrauded… not everyone does.

          • Edward Dolejsi says

            You are really having a bad day. Sorry if I insulted you. Please accept my apology.