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Thread: Constant speed prop on a 912 ULS

  1. #1
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    Default Constant speed prop on a 912 ULS

    Thinking about the cost versus benefit of a constant speed prop on a Rotax 912 ULS.

    Background; my home airport is 5,000 feet and with density altitude I am taking off at 7,000 plus feet DA more times than not. To go west, I need to climb to 12,000 plus feet. At my current prop pitch setting I get 5,100 RPM at WOT and about 400 to 600 fpm on climb-out depending on weight, which is not bad. The negative side is that I only see about 120 true mph at 5,500 rpm.

    A constant speed prop will take my S-19 out of Light Sport and add 10 pounds to the nose. (Which is okay). I would take the opportunity to increase gross weight up to 1,440 area.

    My goal would be able to achieve 5,800 rpm on take-off climb out, 5,500 rpm climb, I don't know if that would significantly increase climb performance, and 138 mph true at cruise.

    Does it make sense to put a constant speed prop on a 912 ULS S-19 all things considered?

    Appreciate your thoughts.
    Mike Duggan

  2. #2
    Basic Member Denali's Avatar
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    I am curious what a normally aspirated stock 912ULS puts out torque and HP wise at 12,000 feet.

    There are also turbo upgrade kits which I know zero about.
    Link: http://zlinaero.com/allegati/note/28...on%20Sheet.pdf

    Also those fine Zipper folks offer the following:
    Link: http://zipperbigbore.com/zipper-1417-turbo/
    You can also build your own turbo using a Rotax 912 UL, 912 ULS at your own expense.

    This kit produces 130-135HP depending on the amount of boost
    .
    Just mentioning these things for consideration before you pull the trigger on the final decision.
    " It's Always Something" - Gilda Radner (1946-1989)

    " I love Horsepower, but love love love Torque "

    " Nothings says poor workmanship like uneven duct tape "

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    Premium Member (Donated) GravityKnight's Avatar
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    I have a zipper kit, plus some other mods to give a bit more power... so keep that in mind. But I also live at 6650ft elevation and fly up to 16k pretty often to clear mountains in CO. I really, really would love a constant speed prop! I think there are definitely some benefits! Maybe the zipper opens that door up some, but my guess is that it would help regardless!

    Here is some info from my plane to illustrate my thinking. I have the 75" WW STOL prop. I pitched it up high and I could indicate 127mph wide open at ~8000ft. True was whatever that ends up being. My plane is fairly draggy with 3 large tires hanging in the breeze. But with the prop pitched for take off and climb like I have it. I can maybe do 112 or so flat out. Maybe 115mph iat.
    Cruise suffers quite a bit too. I can squeeze about 100mph indicated at 4 gph fuel flow (my happy spot) with it finely pitched like I have it, at the elevations I fly at. It was 105 or I think even higher with a lot of pitch. 105-108
    Rotax states it's best not to lug the motor below 5200rpm when wide open. The way mine is pitched, I can take off in Leadville at 10,000ft and still stay above 5200rpm in a slow climb. On a warm day at 6650ft where I live I can see somewhere around 5350 or higher in that steep climb (highest I see, cold days drag the prop rpm down with the thicker air). So I'm not really getting the best of either world, but a compromise like we all do with a fixed pitch.
    I don't know how it would climb if I pitched it for 5800 in a climb, it will already exceed 6000 flat and level so it's pitched as finely as I can get away with in some aspects. Giving up performance everywhere, and efficiency at cruise. And my plane is more draggy vs. an s19, so quite possibly you would see more benefit. I know I would love to be able to crank it up to almost 130mph level without exceeding rpm when I don't care about fuel flow... and I bet this thing would be a monster on take off getting the rpm up to 5800! I'd love one.. maybe on the next plane since I already have plants to go to an s7/20 (tailwheel) in the next year or two.



    There are several variable pitch options out there for the rotax, but in my research I want to say the Airmaster hub is the best option, paired with Whirlwind blades...... $$$$$$ though!!!!!
    S6S 116 w/VGs|MGL/FDS
    114hp zipper912|homebuilt headers/ram-air
    75"WW STOL|22x8.50main/21x8.00nose

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    Premium Member (Donated) WWhunter's Avatar
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    Only negative that I know of, is for those flying under Sport Pilot can't use the constant speed prop. As Gravity mentioned, I looked at the Airmaster and want to use my WW blades. I have both the 70" & 75" props. I would like to see the difference in performance. The cost is definitely at the high end

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    Basic Member maverick's Avatar
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    Mike, as well, it comes down to the wt. on the gearbox. Also on 912ULS, I ran a IVO Magnum 2 bl. for a wile. Ronnie Smith, LS of Miss., told me it'd run all day + then the dog ears on the gearbox would one day = ..engine wouldn't start. @ 22# 4 oz., Phil Lockwood on the phone had a fit w/ the wt. Thus, Sold it to Harmon Rocket pilot. Morris, Ronnie's son would never give me a max. gearbox prop wt., nor, would Jack in the engine shop @ LEAF.... both concerned re. gearbox chatter, harmonic balance, carbs. synch'd, etc. In a S19, I'd consider the IVO Med. @ 15.7# + ck. w/ some one else to confirm gearbox wt. long term OK, before putting $2,500 on the Cr. card. The 3 bl. @ 19.2 # = too hvy. Perhaps the listed wts. a comp. for other prop's to consider.

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    Trent over on team kitfox has one for sale. I believe his was on a 912 with a zipper high performance package. You might contact him for his opinions. Here is the link to his ad: http://www.teamkitfox.com/Forums/showthread.php?t=8263

    BTW, while you are over there - search for some of his video's - he does a great job! Some done with drones that he flies for a living. Pretty cool.

    Scotty

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    Guys, on the S-6 forum " Float plane build in New Zealand", that would be on page 15, there is some interesting thoughts from chucklesfly on this subject. Look at post #68 and go from there.

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    Basic Member maverick's Avatar
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    Mike- if inclined, consider also contacting George Happ, S.L.C., Matco CEO. He had an Airmaster on his Blue & White S-19, although 914T. He'd know wt., blade, info. (As well, diff. app., he also had an Airmaster on his 914T S7, app. 11 yrs. ago when seen.)

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    Premium Member (Donated) Randy Clark's Avatar
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    Mike, I think I would pitch the prop to get the cruise speed I wanted, then see if I could live with the rate of climb that pitch could produce. If not re pitch to get your 5800 on climb. I would think that would give you a pretty good idea of what the constant speed prop could do for you. George Happ built an S19 with a turbo and a constant speed prop. I think he would a good source of information. It doesn't sound like it matters to you, but keep in mind that if you take your plane out of LSA it can never return LSA. Might affect resale. Keep us posted, I would like to know the results if you go that route.
    Randy
    S19 Jabiru 3300
    N726RC
    ATP A&P EAA Technical Counselor
    http://www.mykitlog.com/randyclark

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    Thanks for the responses, a lot of things to consider and to research.

    The zipper or turbo kit are interesting but I hate to mess with a newer (100 hr) engine at this point plus could I be complicating things too much.

    I did talk with George and based on what he said there are clear benefits for a constant speed prop on the 914. He couldn’t speak for the 912 but assumed there would be a benefit, the question is by how much.

    I do have contact with someone with a “inflight adjustable” prop on a 912. I will post what I find out.

    Thanks
    Mike Duggan

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