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Thread: PROs and CONs of Engine Choices

  1. #1

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    Default PROs and CONs of Engine Choices

    Looking at all of the historical, current, and upcoming engine choices, its really hard to find something that is the best "all around" choice.

    I would really like to buy a flying Kitfox in about 2 years and get to know the plane and capabilities and all that before building a new Kitfox - but the used market is pretty thin and I may just end up building first.

    What I am trying to figure out is the best engine choice, or better yet, the best all around build setup.

    My flying mission would include a lot of normal airport to airport flying, local area stuff, lots of 200-300 XC trips and many of those being for seasonal camping trips to places with good condition turf (Cavanaugh Bay, Sullivan etc). I would also like to ability to install some larger tires and get into the backcountry like so many kitfox pilots do. 29" tires would be a seasonal thing also - as would floats in the future. Having the ability to convert multiple times in a single flying season is what really sells me on the Kitfox.

    Ok - so I am currently thinking a standard Super Sport kit, but with STi gear and shocks/TW like what AirFox has done. His build is very close to what I think would be perfect for my mission.

    The STi wing is awesome and performance is great - but I think I would stick with a standard wing to facilitate better cruise speeds and I would plan landing ground roll and locations accordingly.

    Now to the engines. Ive never flown behind a Rotax, but I trust the engine and its long history of success in the experimental community. That being said - I do like the Titan X340 option used on the STi. My questions there is, would it be a good choice on the standard SS kit? My initial thoughts are W&B, useful load (EAB, not LSA), and prop clearance if on standard gear.

    I really like the factory SS with the Lycoming 233, but I can't find much data on that since the testing. It seems like a Rotax and 233 are pretty darned close overall - but the Rotax has better fuel economy and is much more 'standard' in the Kitfox community.

    I am really thinking here and I think a 912iS or Titan 340 will be the competing engines here. The Titan on a standard SS with STi gear and 26" tires seems like a good fit in the (easier) backcountry strips and still have lots of power for good cruise numbers - but could also pull power and cruise closer to 100TAS and see really great fuel numbers.

    Anyways - theres my brain spaghetti for the afternoon. Long story short - there are way too many options and they all have their merits - and I think that is a compliment to the Kitfox community and the versatility of an awesome kit plane.

    Jake

  2. #2
    Senior Member efwd's Avatar
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    Default Re: PROs and CONs of Engine Choices

    Hi Jake
    I wanted my aircraft to be LSA compliant. I really wanted the radial engine. I chose the 912iS. John M of Kitfox told me power to wt ratio is best with the 912. I toured the factory with John and he assured me I would decide on the Rotax when all was said and done. When I flew behind the 912iS the next day I was surprised to say the least. As dumb as this sounds, I really didn't like how a Rotax sounds, but with Noise cancelling headsets I couldn't tell what kind of engine was up front. Certainly there are those with experience who could tell even if deaf. Anyhow, that's how I came to the 912iS. Yours and my flying needs read identical.
    Eddie Forward
    Flying
    SS7, 912iS, Garmin G3X

  3. #3

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    Default Re: PROs and CONs of Engine Choices

    Thanks for the input - I do feel that I will eventually find myself behind the Rotax, I am just way comfortable and familiar with the Ly/Con engines and it will take some getting used to.

    I do really like what Vans has done with the 912iS in the RV-12. Very impressive cruise performance - just not a very STOL-y airplane.
    I like the economy of the 912iS and the injected configuration.
    Are there any negatives of an injected/FADEC engine in the backcountry? It seems like a 'breakdown' or electrical issues would be a bit more difficult than a carb issue in the bush. Also - there are kits out there to bump the HP of the 912 - would the 912iS be able to have the same power upgrade? I imagine a tune or flash would be required also.

  4. #4
    Senior Member Esser's Avatar
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    Default Re: PROs and CONs of Engine Choices

    Quote Originally Posted by jfrantz View Post
    Looking at all of the historical, current, and upcoming engine choices, its really hard to find something that is the best "all around" choice.
    I hate to be this guy but power to weight to fuel burn to longevity history it’s REALLY easy to find an all around choice and that choice is a Rotax every time.
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  5. #5

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    Default Re: PROs and CONs of Engine Choices

    The more I read and research Kitfox and talk to builders/flyers, read trip reports and build logs etc etc etc.. the more I find that a Rotax really is right.
    Now... which one.. the new 912iS seems to be a logical choice - but a turbo model sounds appealing too. The 915iS is pretty $$$ and the benefits would most likely be worth it- I also understand it requires a c/s prop? How does owning and operating a turbo Rotax (maintenance/inspections/parts) differ from a naturally aspirated Rotax?

  6. #6

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    Default Re: PROs and CONs of Engine Choices

    I'll add my overly lengthy and fairly limited knowledge based opinion for whatever it's worth.. I am building an STi and having the same inner conflict with myself. I currently fly a M20K 252 Mooney. So for me, everything about the choices screams turbo. The confidence in knowing your making all available power no matter the condition is a very reassuring feeling. Your ground roll and climb out typically are not as proportional to altitude as they are with an NA motor. Plus modern technology is pretty dang reliable these days. However, let us all be honest for a second. These planes are not fast, they are not built to fly cross country at 200kts. They cannot get you from coast to coast within daylight hours. Therefor, why toss in the extra turbo'd HP right? Dollar for dollar the 912ULS wins everytime. The 912is is almost the perfect little engine for these planes. Modern fuel injection (which isn't that modern in the grand scheme of all things petroleum powered... it's 2018 people.) If the Titan wasn't such a heavy install, it would be my first choice (and was). The 912ULS is the lightest of the installs and by far simplest. So I see a very strong argument for going that direction, the KISS principle is a real thing... Personally, I don't know how I am going to afford it, but I know how much time, hard work, heart and soul will be put into this build, so I would kick myself if I did not put the latest and greatest into this plane.. I am sold on the 912is. But, the wife says we are putting the 915 in it soo... happy wife, right?!

    Ask yourself this, if you were to buy a brand new car tomorrow, would you want it to be carbureted with a 8 track and AM/FM radio?

    As far as STi or SS7.. Only you can deside that one. I argued with myself there as well. Dollar for dollar option for option it was cheaper for me to go the STi route, I'll make up the speed difference with the 915.. If I built a second plane, it would be a ULS powered speedster.
    Last edited by Swanny; 09-04-2018 at 07:56 AM.

  7. #7
    Senior Member Esser's Avatar
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    Default Re: PROs and CONs of Engine Choices

    Quote Originally Posted by jfrantz View Post
    The more I read and research Kitfox and talk to builders/flyers, read trip reports and build logs etc etc etc.. the more I find that a Rotax really is right.
    Now... which one.. the new 912iS seems to be a logical choice - but a turbo model sounds appealing too. The 915iS is pretty $$$ and the benefits would most likely be worth it- I also understand it requires a c/s prop? How does owning and operating a turbo Rotax (maintenance/inspections/parts) differ from a naturally aspirated Rotax?
    There really isn’t too much difference. I have a 914 in my plane that I after market fuel injected. I haven’t flown behind it yet but I’ve flown 20 hours behind the 914. Just have to watch some operating parameters a little more closely temps etc.

    For maintenance, once a year you have to check your waste gate cable and adjust it if required. That’s it for extra maintenance.

    My wife and I flew two kitfoxes for 20 hours each. She was in a 912iS powered plane with a constant speed prop and I was in a 914 powered Kitfox with a fixed pitch and a heavier instructor. After watching the side by side performance of the two planes, I would always go with a turbo if that was an option
    ------------------
    Josh Esser
    Flying SS7
    Rotax 914iS
    AirMaster Prop

    Edmonton, AB, CWL3

  8. #8
    Senior Member aviator79's Avatar
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    Default Re: PROs and CONs of Engine Choices

    I only have about 8 hours behind 912iS with Stick and Rudder. I am in the process of installing a 914 on my plane. I had dinner with Paul L. and one of his instructors, and I asked them directly what engine they would choose. Paul said that the 912iS mated to an Airmaster prop was the best value in terms of performance per dollar. He said that if your budget forced a decision between a turbo or the Airmaster, go with the Airmaster. He then said "But (dramatic pause)... If you really want the best performance, the turbo and the CS prop is amazing." His instructor, Gary, grinned and bobbed his head enthusiastically. I figure he knows better than just about anyone.

    In my case, if I lived at sea level, I would have saved some money and gone with the 912iS+Airmaster. However, our density altitudes often run between 9-10k feet in Los Alamos, and I wanted all the power I was paying for. I was tempted by the 915, but you have to draw the budget line somewhere.
    --Brian
    Flying - S7SS

  9. #9
    Senior Member jmodguy's Avatar
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    Default Re: PROs and CONs of Engine Choices

    And now for something a little different...
    I went with the 340. It's not a Titan though, I built it from parts I bought from Airpower. Saved half the cost of buying one outright and I know how my engine went together!
    Is it heavier? yup It also puts out gobs more power and torque. I made it light everywhere I could and went with the FlyEFII system, cold air sump, taper fin cylinders, 9:1 pistons and an 80" GA200 STOL prop from whirlwind. My main gear is by John Roberts of AV Weld with 22" Dessers and I have 14" of clearance prop tip to ground in a level attitude. I will be a bit over 900 lb when its all said and done. I am keeping the rest of the airframe light as well, such as no side panels and other niceties.
    Dare to be different!
    Jeff
    KF 5
    340KF

  10. #10

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    Default Re: PROs and CONs of Engine Choices

    Are you far enough along to know what your CG is in this configuration?

    I am moving back to a higher altitude area and am still trying to make the 914 vs 340 decision.

    As the cost is similar and my pessimistic 66% of rated horsepower number makes them about a wash at my target altitude it is a hard choice. I don't think it is an issue on the 7 but a couple of people with o-200 IV's have told me they were a bit nose heavy with the smaller original tail feathers but those individuals also didn't have in flight adjustable trim either.

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