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  1. #1

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    Anyone got readings OS Fx 91?

    I could really use some readings and performance results with 2 and 3 blade 12" to 14" props an FX91.
    Anybody got?

  2. #2

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    Anyone got readings OS Fx 91?

    Not quite the prop range you are interested in, but
    91FX on it's first gallon of 5% fuel

    APC 15x6 = 9,600
    Master 15x8 = 7,900
    Master 15x8 clipped to 14.5 = 8,400

  3. #3

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    Anyone got readings OS Fx 91?

    Not fully run in with 5% home brew and an APC 14x4W (and a pitts style silencer with one outlet blocked): 10800 rpm.

    Cheers,

    Fredde

  4. #4

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    Anyone got readings OS Fx 91?

    Thanks guys.

  5. #5

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    Anyone got readings OS Fx 91?

    I've run two tanks through mine (NEW) with a APC 14x6 prop.

    Peaked at about 10,500, but only momentarily as I richened it back down to about 10,000 for break in.

    Seems to run very well, and the transition is good after I leaned the low end about a 1/4 turn. I do notice that you can turn the needle A LOT with little effect. I had almost completely unscrewed (Richened the engine and it only was about 1,000 rpms off peak).
    Dave Norman
    29w

  6. #6

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    Anyone got readings OS Fx 91?

    13-10 MAS Scimitar.....9500
    13- 8 MAS....................10000

    Both not real smooth. Leaned out in flight. Still new with about 4 tanks full through the engine.
    Morgan Cool Power 15%

    Gonna try 12-8...stay tuned

  7. #7

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    Anyone got readings OS Fx 91?

    I have 91SX-H with 91FX muffler, Perry Pump By-Pass setup on a test stand with APC 13x8. 20% Coolpower (15 % mixed with 25%).

    Tached today 11100rpm.

    Is this good enough or need to lean more?

  8. #8

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    RE: Anyone got readings OS Fx 91?

    Fairly new 91FX on 10% fuel.
    Modified Slimline muffler, Perry pump carb and a Perry VP-30 pump.
    Menz 15x8 prop
    8900 RPM
    30 degrees F, 2700 ft ASL and it was snowing!
    Hope to get a little more RPM when the engine loosens up and the OAT gets a little higher.
    Good Luck
    John

  9. #9
    Zafer's Avatar
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    RE: Anyone got readings OS Fx 91?

    Hi,

    If I dont remember wrong, my OS 91FX was turning APC 14x4w about 10500 rpm ( only one hour breaking in time ) very rich with 18% oil and 5% nitro.

    But it was summer time. I was getting very bad flutters with 14x6 in the beginning (didnt tacho with that prop), so I changed it to 14x4w and with less throttle travel.

    Regards.

    Zafer

  10. #10

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    RE: Anyone got readings OS Fx 91?

    O.S. 91 FX beautiful engine. tons of power BUT...........take a tip from a fool, look at your backplate needle valve assembly and determine if it is all one casting (backplate and valve body is one casting) if it is send it back to tower and tell them that the engine lacks full power and there must be a leak in the casting because there is allways air bubbles between the valve and carb. They will probably replace the back plate with the needle valve standing alone on a heat sinked stainless steel plate. If the engine is damaged they will replace piston, ring, sleeve, and both bearings at no charge. Your engine will have more power, broader needle, and those "air bubbles" you are seeing at full throttle will dissapear. now you can run 15% nitro and you will fall in love with that engine.
    They don't like to run much above 10000 R.P.M. so prop accordingly. An A.P.C. 15x8 will turn about 8900 and a master airscrew 14x9 three blade , about 9600. The MA 14x9 can be difficult to find Though and a 14x7 three blader will churn about 10000 R.P.M.
    I put mine on a Ultrastik 60 PHEW. talk about vertical......... straight up and out of sight in about the time it takes to draw a breath.
    I put a supertigre 91 in the stik though caus I needed the O.S. for a spitfire that my Dad built. the spit weighed over 11 pounds and with a 14x7 three blader the O.S. pulled it vertical too. I kidd you not. unfortunatly the spit crashed on its first landing as the wing loading was too high, but my Dad spent two years building it and deserved to see it fly. The plane was a handfull and only got of the ground thanks to the brute power of the O.S. and the skill of the pilot I asked to fly it. I hated my O.S. 91 untill a friend told me to send it back to tower and the needle valve on its own plate made all the differance in the world. BTW the "air bubbles" you are seeing at full throttle are not air bubbles at all, but fuel vaporising in the needle valve due to heat transfer to the needle valve casing because it is all one casting with the back plate.
    Insanity is endlessly repeating the same process and expecting a differant result

  11. #11

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    RE: Anyone got readings OS Fx 91?

    MAS 13x10 Scimitar @ 10400rpm using 5%nitro 15%Klotz & 5%BeNol. This engine is a excellent, it pulls like a train, runs consistently throughout the whole tank and starts on the first or second backflip - so long as it is quite wet with fuel. Yes it's the older model with needle valve housing integral to backplate.
    RTD

  12. #12
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    RE: Anyone got readings OS Fx 91?

    .91FX
    15% cool power --long, rich break in

    15 x6 apc stock muffler, baffle removed 10,200
    15 x6 apc ultra thrust muffler 11,300 -- Pulls 10 pound plane out of hover!
    Good Flying to you!
    See Blog for RCU Video\'s

  13. #13
    Zafer's Avatar
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    RE: Anyone got readings OS Fx 91?


    Hi again,

    Today, I tachoed my .91Fx with 15x4W APC prop. at 10,000 Rpm exactly. I was using 18% oil and 5% nitro. It had enough power to pull the 7,75 Lbs. plane ( Acromaster 3D - Same as Bravo 3d of Black Horse but this one has Kyosho\Hype brand nameon) out of a hover with authority. I was using diffent props 14x6, 14x4W etc. I think 15x4W is the right one. It is not very fast so plane doesnt get bad flutters at full throttle.

    I can still go a little bit leaner if I need more RPMs. .

    Regards/

    Zafer

  14. #14
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    RE: Anyone got readings OS Fx 91?

    What RPMs should this engine be ran at? I saw (I believe on Tower) that effective RPM is 2k-16k yet it seems like everyone is running them around 10k. Also what percentage of nitro should be put through it?
    2007 Resolutions: Do more flying then fixing, Have a plane last at least one season.

  15. #15
    Zafer's Avatar
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    RE: Anyone got readings OS Fx 91?

    I tachoed my new Magnum .91 ( O.S. Clone ) 2 stroke at 10.760 Rpm with 14x6 prop and 5%nitro. Less than an hour in life so it is still rich. I think I will see 11K or more in near future. I am suprised to see this engine is so good maybe better than the original (O.S. .91FX)
    and happy off course.

    Regards.

    Zafer

  16. #16
    strulag's Avatar
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    RE: Anyone got readings OS Fx 91?

    Is that a pattern prop? I tried finding a 14x6 for mine but the APC one says Pattern where the 15x6 one says sport/fun fly (or some like that). Is there a 14x6 sport? I noticed the shape is different between the 2.
    2007 Resolutions: Do more flying then fixing, Have a plane last at least one season.

  17. #17
    Zafer's Avatar
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    RE: Anyone got readings OS Fx 91?

    Strulag,

    I think APC 14x6 is a sport prop. I have also a 14x8 which is a pattern prop. But I use 14x6 with my 3D trainer plane. It is a little bit slow for pattern IMHO. I have used this prop and also a 14x4W[>:] and a 15x4W in the same plane. 15x4W was broken so I returned to 14x6 It has more speed so I have to be easy on the throttle. It is not bad for hovering either. Cheaper than the wide blades I dont think that I need to buy any other prop for this plane.

    If you prop .91FX properly ( 11 or 12 inch props) you can get 13 - 14K rpms which will give you more speed only . I would like to have more thrust rather than speed, so I am happy with 10,5K rpms and 14x6 prop. (I hope this will reply your previous post)

    Regards.

    Zafer

  18. #18

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    RE: Anyone got readings OS Fx 91?

    The best prop for any 91 engine is and as always been a 13 X 7 or a 14 X 6 the brand matter. what ever lets your engine run at least 11,000 Rpm is correct prop under that and you overload your engine. You can alway tell when you have overloaded your when it always changes speed when going up or down slightly and I don't mean diving. Thing of it like driving a VW Beetle up and down the hills of West Virgina. 15 X 8 are for 1.08 not .91. Oh by the way 4 pitch props made of wood are good for one thing, stirring paint.
    Bob Davis, Owner - Davis Diesel Development

  19. #19

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    RE: Anyone got readings OS Fx 91?

    Have any of you guys tried a Saito 91 Special, And is it better than the OS 91 ?
    Theres only 1 way to see if your plane is built strong, How You Ask?
    BLENDER!

  20. #20

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    RE: Anyone got readings OS Fx 91?

    Gee I ran them as high as 16x6 last weekend. Lovely thrust and pull albeit the rev is slower, and yet I don't feel it is not responsive. Hovering power is easier too. It run sweet compare to 15x6. 14x6 is too fast for my liking. 15x6 is nice, but 16x6 is sweet. Knife edge loop too!

    I think my rpm is in range of 8500.

  21. #21
    Moderator w8ye's Avatar
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    RE: Anyone got readings OS Fx 91?

    There's not much difference in over all power between the Saito 91S and the OS 91FX. But they produce their power at different rpms. The Saito has a lot of low end torque and instant throttle resonse. It would be good for 3D. The OS FX 91 would be better for a speedy plane or a groovy pattern type.

    Enjoy,

    Jim
    Attended the CutFinger Institute of DirtNap University for years but never did graduate....
    Recipient, Mangledhand award August 2008
    Club Saito Member #7
    Original AMA #31261

  22. #22

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    RE: Anyone got readings OS Fx 91?

    There's not much difference in over all power between the Saito 91S and the OS 91FX???????

    My 91FX turns a 15x8 Menz at 8900 rpm and that sure sounds like 120 4-stroke power!!
    APC 15x8 at a little over 9k rpm.
    The Saito 91 doesn't even come close.

    Good Luck
    John


  23. #23
    Moderator w8ye's Avatar
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    RE: Anyone got readings OS Fx 91?

    That 91FX with the 15-8 will certainly turn close to 9000 but it's the sickest sag sound anyone ever heard.

    There is a very slow throttle response with the over propped OS 91 FX.

    The 91 FX with a 15-4 is OK though.

    There's a tremendous difference in the way a 120 four stroke swings a 15-8 and the way a 91FX swings one.

    If you try them together, you will certainly think that the 120 four stroke has more usable power even though there's no major difference in maximum rpm of the 120 over the 91FX.

    I've been there and done that.

    As mentioned in the previous post, the four strokes perform better with certain kinds of flying and planes. And if I had a high speed plane, I would certainly choose the 2 stroke over the four stroke.

    Maximum static rpm with a certain prop is not a complete measure of the available power of a engine.

    Enjoy,

    Jim
    Attended the CutFinger Institute of DirtNap University for years but never did graduate....
    Recipient, Mangledhand award August 2008
    Club Saito Member #7
    Original AMA #31261

  24. #24

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    RE: Anyone got readings OS Fx 91?

    My 91FX sounds great and not like it is "overworked" at 8900 rpm.
    Throttle response is easily as good as any other glow engine I have run in my 40 years of flying glow engines.
    I have a modified(for better breathing) slimline pitts muffler on it.
    I don't believe that these 90 and up glow engines are supposed to "scream" like a .40 glow engine.
    Their max power occurs at under 10k and more likely under 9k rpm and I want to make use of that power.
    Great combo for me and the guys at the field like it too!
    Works for me!

    Good luck!
    John


  25. #25

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    RE: Anyone got readings OS Fx 91?

    Dang, I recently used APC 16x6 on my 91FX with cool power 5%. Did not tacho them, but prolly estimate at 9k. WIth 14x6, it hit 12000.

    I used Bisson pitts muffler and rev respond is good. 15x6 is better on rev up but the thrust of 16x6 is ridiculous on my WM Velox RevII. It will ROG in less than 60 feet.


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