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  1. #1

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    OS 50sx prop size

    I was advised that an APC 12.25x3.75 prop would be appropriate on my Katana GS 40 powered by an OS 50sx. The engine tacks at 11500 rpm, but the engine itself has less than half a gallon through it. Is 11500 rpm enough for this prop? thx. Jim

  2. #2
    Moderator w8ye's Avatar
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    RE: OS 50sx prop size

    This is a very common combination.

    I havn't tached one lately but I was thinking they went faster than that? Do you have your engine mixture set correctly?

    12,600 is the usual rpm with this prop.

    Enjoy,

    Jim
    Attended the CutFinger Institute of DirtNap University for years but never did graduate....
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  3. #3
    seanychen's Avatar
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    RE: OS 50sx prop size

    That's way too low. With stock muffler, you should get at least 13000 rpm with this prop. With tuned muffler, like Tower 46 muffler or Rossi 46 black tuned muffler, people are getting 14k.
    E_Total = M*G*H + 1/2 M*V^2
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  4. #4

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    RE: OS 50sx prop size

    His ringed 50sx may not be broken in yet as well as an apc 12x4 for will turn a few more rpm's.

  5. #5

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    RE: OS 50sx prop size

    I am looking for a good .50. What is the difference in the sx over fx. and what is the sx?

  6. #6
    Moderator w8ye's Avatar
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    RE: OS 50sx prop size

    The SX engines are their higher performance engines
    Attended the CutFinger Institute of DirtNap University for years but never did graduate....
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  7. #7

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    RE: OS 50sx prop size

    I have a 40 size MOJO which is VERY close to your katana. They should weigh about the same and are intended for no holds-bared 3D. On my mojo I run 3 props depending on what I can get.

    I prefer APC prop because I hit the ground a lot and even when the get shorter I just keep flying for the day.

    My favorite APC's are
    1. 12 x 4
    2. 12.25 x 3.75
    3. 11 x 4

    If they spool up a little slower than you would like try a master airsrew or preferably a wood prop like a 12 x 4. The wood props spin up MUCH faster although they give a little less thrust in the end I think, from flexing.

    Hope it helps,
    Dave

    Hey try the tower hobbies .46 muffler, its a gem for 15.00 bucks
    Damn, did YOU see where it landed (#$@$)

  8. #8

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    RE: OS 50sx prop size

    I get 13,100 with a 12.25x3.74 APC on my 50SX
    Mojo 40 - OS 46FX | Morris BalsaNova 120 - 160FX | Morris BalsaNova 40 - 50SX

  9. #9

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    RE: OS 50sx prop size

    Get yourself a Tower muffler and APC 12X4 prop and adjust the needles.
    Buzz

  10. #10

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    RE: OS 50sx prop size

    ORIGINAL: kf6gub

    I was advised that an APC 12.25x3.75 prop would be appropriate on my Katana GS 40 powered by an OS 50sx. The engine tacks at 11500 rpm, but the engine itself has less than half a gallon through it. Is 11500 rpm enough for this prop? thx. Jim

    Jim, that's a little lower than it should be. Like the guys are saying, 13k+ is more the norm for that engine/prop combo. Does the muffler still have the baffle installed? Install a Tower muffler - this should be worth at least 500 rpm on its own. The .50 SX also responds well to a little nitro, with good gains in power up to about 15%.

    Good luck and report back on progress.

  11. #11

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    RE: OS 50sx prop size

    deleted duplicate post

  12. #12
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    RE: OS 50sx prop size

    I build a moosecan for a friend of mine for his OS.50SX he was getting 15,000 with a 12x4. It would pull a 5lb profile out of sight. It has so much power the whole fuselage would flutter on full power uplines. and yes the prop was balanced.
    Everybody wants to go to heaven, but nobody wants to die...

  13. #13
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    RE: OS 50sx prop size

    If the engine has less then a half gallon through it I would give it some time most engines need a couple gallons before the really wake up
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  14. #14
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    RE: OS 50sx prop size

    As some have pointed out, this is a ringed engine. It's just not broken in yet. Less than 1/2gal is not even half way through the break-in process for ringed engines. Run it slightly rich for no less than a full gallon of fuel. Don't try and get max rpm until you do that. Then, very gradually lean it during your second gallon of fuel. It will get there.

  15. #15

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    RE: OS 50sx prop size

    Oh, my 13,100 tach reading is still within the first gallon of fuel. I am still running it rich, about 1.8 - 1.9 revolutions on the needle.
    Mojo 40 - OS 46FX | Morris BalsaNova 120 - 160FX | Morris BalsaNova 40 - 50SX


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