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single point failures

in 912iS Technical Questions 7 years ago
In my first flight behind a 912ULS, the designer of the airplane didn't recommend the iS, claiming there were "too many single point failure modes." Looking over some older literature on the iS, it's not obvious what those are. It appears there are two independent control systems, each with a generator, ECU, ignition module, fuel pump, and injectors. It seemed odd the two ECUs are on a single circuit board in a single housing, but they are surely not connected electrically.

  • Re: single point failures

    by » 7 years ago

    All engines have single point failure options...ie a single crankshaft.

    The IS engine has less than the ULS eg there are two injectors per cylinder the ULS has only one carb for two cylinders loose a carb you loose two cylinders, loose an injector all four cylinders still run. Your friend is incorrect, or has not done sufficient investigation. The ECU's are in a single housing but separate electrically, I also believe they are not on a single circuit board, or at least they weren't a few years ago when I was at the RC factory looking at them.
      
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  • Re: single point failures

    by » 7 years ago

    The designer of the airplane was not always correct: He also said the 912 series has a lower piston speed than the traditional engines.

    [url="https://fahrzeugtechnik.fh-joanneum.at/veranstaltungen/2012-2013/2013-02-27-Rotax-912iS.pdf"]Here is that older document[/url] I referred to. Given the number of stand-offs visible (page 10), it sure appears there was a single circuit board inside the ECU box. Of course the two lanes will not be connected on that board. Surely the copper between them is removed during manufacture. One board in one box is far cheaper to make, and you can still get decent isolation. The current parts catalog only lists the module, not its components.
      
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  • Re: single point failures

    by » 7 years ago

    Yes...
    Well I only saw prototypes of the ECU in the factory before they went into production and the document you linked shows you are correct.

    There is really little difference in mean piston speed and it depends on what you call a "traditional" engine

    the 912ULS has a MPS of 13.3 m/s, a Lycoming 0360-JRA of 10 m/s and a R-3350-45 of 14.9 m/s.

    the engineers rule of thumb is that anything below 16m/s will give very long life and anything over 22m/s is short life eg F1 engines are up around 28-29 m/s
      
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  • Re: single point failures

    by » 7 years ago

    Keep in mind the document is from 2012, so that board may well not be what's in the ECU case today.

    By "traditional" I meant the O-200, O-235, etc. I agree the MPS of the 912 is not a concern, as 20+ years of service has demonstrated. I was only pointing out the guy making the claim, while a good designer of LSA planes, is not always correct in his estimations of engines.
      
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  • Re: single point failures

    by » 7 years ago

    Thanks Understood.
      
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