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Thread: Curious about engines

  1. #1

    Join Date
    Nov 2018

    Curious about engines

    So my best friendís son is a structural engineer, and he and I are talking about designing an ultralight. We were talking about which engine to use RE: power/weight ratios, engine weight, etc. and I mentioned that I see a lot of folks using the Rotax 503, but that I didnít have enough information to offer an informed decision. Does anyone out there want to offer a few pro and con bullet points about this particular engine? Especially if you have experience using this. Thanks.

  2. #2

    Join Date
    Sep 2011
    I don't believe Rotax makes the 503 anymore. You would have to find a used one and assure it's airworthy.
    They required major servicing every 300 hrs or so.

  3. #3
    cluttonfred's Avatar
    Join Date
    Oct 2011
    World traveler
    It would make a lot more sense to design a new ultralight around a current engine in production. Hirth still makes some small two-strokes as do a few others, but I would come down to the 25-36 hp range to use any of several very light, two-stroke paramotor engines in the $2,500-$5,000 price range (Vittorazi, Simonini, Cors-Air, Polini, etc.) It will require a cleaner design than something like a Quicksilver, though.
    Matthew Long, Editor
    A site for builders, owners and fans of Eric Clutton's FRED
    and other safe, simple, affordable homebuilt aircraft

  4. #4
    Dana's Avatar
    Join Date
    Jul 2011
    The 503 is a good engine. Not made any more, but readily available used or freshly overhauled. But an aircraft with a 503 will likely be overweight and/or too fast to be a legal ultralight, a 447 (or Cuyuna) might be a better choice. But you need to work out the basic design before selecting an engine; successful ultralights are flying on as little as 25HP, half of what a 503 makes and much less than half the weight. What type of configuration did you have in mind?

  5. #5

    Join Date
    Jul 2011
    Clarklake, MI
    If by "ultralight" you mean one that complies with Part 103, I agree a 503 will be too heavy and it will have too much power.

  6. #6

    Join Date
    Aug 2011
    If I were building an ultralight, I'd go with the "Big Twin" from Valley Engineering. Four stroke, auto carb heat, PSRU, etc..
    The opinions and statements of this poster are largely based on facts and portray a possible version of the actual events.

  7. #7

    Join Date
    Oct 2018
    Franklinton, Louisiana
    Rotax 582 is still made and sold. TBO is 300 hours. You can overhaul a 582 for less than what it costs to overhaul one Continental cylinder. I would explore the 582 or the half VW aero engines.

  8. #8

    Join Date
    Dec 2018
    I do not know much about the topic, but i have seen a few videos of people doing it. I would explore electric power. I know the batteries are big and heavy, but you can get some pretty powerful motors (I think). I may be very wrong because i have not done that much research into it, but it may be worth checking out.

    Christian L.

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