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Author Topic: Ringmaster LA25  (Read 2302 times)

Offline Motorman

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Ringmaster LA25
« on: August 12, 2022, 03:50:30 PM »
I have a Ringmaster with box stock LA25 9-4 apc 10% nitro on 60' radius. I played with props, needle settings ect to get the best speed for calm air. Problem is the air is always turbulent and gusty. I'd like to get just a little more speed to cut through bumpy air. I tried a 9-5 apc but it drags the engine down too much. I tried to lean out the needle some more but it breaks into a full two stroke and it's too fast like that so, I'm maxed out on the needle. I want to get the same fuel/air mix I have now with the same prop, fuel, lines only with a little more rpm. I was thinking of making the venturi a little bigger, do you think that would work?

Thanks,
Motorman

Online Brett Buck

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Re: Ringmaster LA25
« Reply #1 on: August 12, 2022, 06:02:09 PM »
I have a Ringmaster with box stock LA25 9-4 apc 10% nitro on 60' radius. I played with props, needle settings ect to get the best speed for calm air. Problem is the air is always turbulent and gusty. I'd like to get just a little more speed to cut through bumpy air. I tried a 9-5 apc but it drags the engine down too much. I tried to lean out the needle some more but it breaks into a full two stroke and it's too fast like that so, I'm maxed out on the needle. I want to get the same fuel/air mix I have now with the same prop, fuel, lines only with a little more rpm. I was thinking of making the venturi a little bigger, do you think that would work?


  No- its already too fast, you don't want to make the venturi bigger. If you make it bigger and run it slowly, you will have trouble drawing fuel.

   If you absolutely must try to run it in a 4-stroke, the more obvious change is to use 15% nitro, it will go faster at the same "setting" without hurting the fuel draw. But, I predict that you will not be happy with this because I expect it will not be very stable trying to run way below the peak.

  I think the better solution is to run it as previously described, and when it is too fast (which you found), you will need to keep running it that way, but with a smaller venturi.

     The alternative is to depitch the prop, but it will take A LOT of twisting to get it down to the ~ 3 1/4" you probably need.

    Brett

Offline Motorman

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Re: Ringmaster LA25
« Reply #2 on: August 13, 2022, 12:08:25 PM »
I did some measuring and found my venturi is stock size at .260" but my spray bar is .156" giving me an effective area of .0151186. The area with stock .138" spray bar is larger at .0189771. To get that same area with the .156" spraybar I'll need a venturi diameter of .275". So, I can go bigger and still have the same fuel draw as the stock set up. 
« Last Edit: August 13, 2022, 01:20:58 PM by Motorman »

Online Brett Buck

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Re: Ringmaster LA25
« Reply #3 on: August 13, 2022, 01:50:46 PM »
I did some measuring and found my venturi is stock size at .260" but my spray bar is .156" giving me an effective area of .0151186. The area with stock .138" spray bar is larger at .0189771. To get that same area with the .156" spraybar I'll need a venturi diameter of .275". So, I can go bigger and still have the same fuel draw as the stock set up.

   So, you or someone else has modified the engine to use an ST or similar spraybar, so it is not "box stock".

    I thought it was already too fast?  It is not at all unusual - in fact, perfectly normal - to have to detune the engine to get a Ringmaster to fly at subsonic speeds, since a stock 25LA is much too powerful for the airplane.

    Again, I would not suggest trying to fly it in a 4-stroke due to potential instability, run it in a 2-stroke and adjust the speed with the venturi, because the needle is not a throttle.

    Brett
« Last Edit: August 13, 2022, 02:36:27 PM by Brett Buck »

Offline Motorman

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Re: Ringmaster LA25
« Reply #4 on: August 13, 2022, 05:30:12 PM »
No, it's too slow but it's right at the rich/lean break point so I can't go any leaner and still run it in a 4 stroke. 

Online Brett Buck

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Re: Ringmaster LA25
« Reply #5 on: August 13, 2022, 05:51:22 PM »
No, it's too slow but it's right at the rich/lean break point so I can't go any leaner and still run it in a 4 stroke.

   Then don't run it in a 4-stroke.

     Brett


p.s. this is how to set a needle:

Start engine, lean out to a 2-stroke, then slowly lean it out until it is absolutely as fast as it will go, and one click more makes it sag. Then, back off needle until you just get a distinct RPM drop, just a bit off peaked out in a 2-stroke. If you get it rich enough to start misfiring in a 4-stroke, even occasionally, you have gone *much too far*. This is about 5 clicks open from peaked-out lean using the stock OS front needle, about 5 clicks open using the 20FP rear-needle (all-metal on a metal bracket). It is about 3 clicks open from peaked out lean using the stock 25LA rear needle (gray metal needle in a plastic backplate mount). You do not need a tachometer, but it will be 2-300 RPM from peak.

   Launch the airplane and it should get slightly richer-sounding in level flight, and then peak out in the maneuvers. If it peaks out and then sags in the maneuvers, you are too lean, open needle *1* click for the next flight, try again, until it does not sag lean in the maneuvers at any point. If it ever hits a 4-stroke, you are too rich, close the needle one click and try again.


Offline Christopher Root

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Re: Ringmaster LA25
« Reply #6 on: August 23, 2022, 04:40:42 PM »
Is this advice for all engines, including old iron piston Foxes, etc, or “newer” ABC engines like OS?

Online Brett Buck

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Re: Ringmaster LA25
« Reply #7 on: August 23, 2022, 05:41:17 PM »
Is this advice for all engines, including old iron piston Foxes, etc, or “newer” ABC engines like OS?


  These are the specific instructions cut/pasted from the (innumerable and tedious) threads about how to run a 20FP and "new" 25LA, at least a few dozen of them, they are all the same.

  As a general rule, virtually ALL, repeat, ALL consumer glow engines are intended to be set and run as described by default. Being able to do this and not sag from overheating or getting too tight is the indication that it is broken in. Peak them out lean, back off until it is as rich as possible without losing RPM, good luck and happy flying.

    Nobody (or at least, nobody at a major commercial engine manufacturer) ever designed 2-stroke glow engines to be run blubbering rich in a 4-stroke. For stunt, people have found that this is the best way to run *some* of them, trading off power for in-flight response to load. The 25LA is certainly in the former category.

    In this case, a specific case for the 25LA,  it needs to run in a 2-stroke.  The problem Motorman ran into is the prototypical example of why you can't run engines this large on such a small airplane - although it's closer to working than a lot of other cases. However, having done this experiment multiple times and witnessed this particular set of circumstances dozens of times, I know exactly how it is going to go, and was hoping to head off any more of the "drill this and grind that" that nearly always follows.

  The problem is to get it to run properly (that is, in a 2-stroke) while still being slow enough to be visible in flight. The proposed plan (slightly increasing the venturi size to move the 4-2 break point to a higher RPM)  and running it in a 4-stroke could possibly "work", but makes it extremely likely to be unstable due to decreased fuel draw. This is the old "use the needle as a throttle" approach.

    My alternate solution (since we have already disregarded the best solution , which is to use a 15FP) is to reduce the venturi, which both makes the engine more stable and will slow down the 2-stroke to a workable degree. The goal is to get the engine running in a "medium" 2-stroke in level flight at a reasonable speed. He tried that as is, it was (as predicted) far too fast. The most straightforward solution if it is too fast at an otherwise good "setting" is to reduce the throttle, e.i. use a smaller venturi. Do that, and it is *extremely stable* and you can adjust the power variation in flight by slight mixture changes up or down.

    I will note also that he already modified the engine in such a way that it reduced the power by drilling out the crankcase to install an aftermarket spraybar (probably ST or clone) , and it's still too much. This tells you that it would be even further over the top if it was stock - again, because the *engine is far too powerful for the airplane*. Stock, and set properly, the engine will pull the airplane at about 3.6-3.8 seconds a lap on 60' lines - I know exactly, lots of people have done exactly that, we know he result within a gnat's ass.

   BTW, before anyone asks, other engines:

20FP = 3.8 seconds+-
Veco 19bb = 4.2 seconds
"Old" 25LA = 4.2-4.3 seconds
"New" 25LA = 3.6-3.8 seconds
25FP - 3.4-3.6(!)
15FP (8.5-4.5 Circus Hobbies)- 4.5-4.8 seconds


    If nothing else, given it is patently obvious that the engine is too powerful for the airplane, *enlarging the venturi and making it even more powerful* and hoping you can needle it down isn't a very good idea.

  As always, this ws just (in this case, highly informed) advice, and I am quite well aware that it's probably going to be disregarded. I get nothing from it either way. I just feel I need to do what I can to steer people in the right direction.

   
    Brett
« Last Edit: August 23, 2022, 05:59:15 PM by Brett Buck »

Offline Colin McRae

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Re: Ringmaster LA25
« Reply #8 on: August 23, 2022, 06:25:40 PM »
I don't know if this helps or hurts what you are trying to achieve, but I have Brodak Shark 402 (similar size model) with an OS 25LA (stock). I was running a 9-6 prop and the model was flying fast but struggled a little on stunts. I switched to a 10-5 prop and it really helped. Slowed the model down a bit, but increased power during stunts. On the needle, I run it like 20 degrees rich from peak speed. The 25LA turns the 10-5 prop fine. Even the OS manual for the 25 mentions a 10-5 prop as an option.

Just my 2 cents.

Offline Motorman

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Re: Ringmaster LA25
« Reply #9 on: August 23, 2022, 07:31:58 PM »
I made a larger venturi to get a little more speed but for some reason it didn't go faster with the same mixture. I went from .260" to .272" I guess that wasn't enough to make a difference. Just as a side note, there is no problem with fuel draw until you get up around .320" with the Tigre spray bar.

Anyway, switching gears to take Brett's advice. I made a tiny 13/64 venturi, I peaked the needle for max rpm then backed it off all I could without 4 stroking. The needle was one full turn in from where it was on the big venturi. RPM with a 9-4 apc sport prop was only 10,000. I found his old post were he said you need 11,300 on that prop so I've got to open it up a little. Shooting for a lap time of 4.2 - 4.3 so I can penetrate turbulent winds. Looks like from your chart that's possible.

Motorman 8) 

Update, I drilled the venturi out to 7/32" and now getting 11,300 rpm. Waiting for breakfast and the grass to dry out then going to the field.
« Last Edit: August 24, 2022, 07:04:17 AM by Motorman »

Offline Dave Moritz

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Re: Ringmaster LA25
« Reply #10 on: August 24, 2022, 09:09:05 AM »
Brett

Thanks for the Ringmaster lap speed on the Veco 19bb. The motor I’ve on hand is carbureted, so will be able to adjust lap time upward just a tad.

Dave Mo…
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Offline Christopher Root

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Re: Ringmaster LA25
« Reply #11 on: August 24, 2022, 11:00:05 AM »
Wow Brett, those are some fast lap times!! I thought my Top Flite Peacemaker was going fast with 5.5s lap times, 60' lines and OS-FP .25!

C R

Offline Motorman

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Re: Ringmaster LA25
« Reply #12 on: August 24, 2022, 01:56:15 PM »
Ok, drilled the venturi to a "B" drill and got it up to 4.3 on level flight in turbulent winds. It was a little smoky a little burbley but it wasn't 4 stroking. When I went into maneuvers it would sag a bit but still got through. Not really enough power/drive in the 8's.

I'm going to drill it out again then open the needle to keep the 4.3 second/lap speed. This should give me a little more head room for maneuvers. I just hope it doesn't have to be so rich it cools the engine into a full 4 stroke going level.

Motorman 8)

Online Brett Buck

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Re: Ringmaster LA25
« Reply #13 on: August 25, 2022, 01:44:45 AM »
I made a larger venturi to get a little more speed but for some reason it didn't go faster with the same mixture. I went from .260" to .272" I guess that wasn't enough to make a difference. Just as a side note, there is no problem with fuel draw until you get up around .320" with the Tigre spray bar.

Anyway, switching gears to take Brett's advice. I made a tiny 13/64 venturi, I peaked the needle for max rpm then backed it off all I could without 4 stroking. The needle was one full turn in from where it was on the big venturi. RPM with a 9-4 apc sport prop was only 10,000. I found his old post were he said you need 11,300 on that prop so I've got to open it up a little. Shooting for a lap time of 4.2 - 4.3 so I can penetrate turbulent winds. Looks like from your chart that's possible.

Motorman 8) 

Update, I drilled the venturi out to 7/32" and now getting 11,300 rpm. Waiting for breakfast and the grass to dry out then going to the field.

    OK, you know that these are *huge* jumps in choke area. 13/64 (.203"*) is .004 square inches, 7/32 (.219") is 0.0065 square inches, and you started with the stock venturi, which gives you .0142 square inches. So, you first changed the choke area smaller by a factor of 3.6X (!), then changed it >50% larger. So, massive leaps.

    In any case, the way to determine whether to make it larger or smaller is to set it as described - peak out lean, back off until you get a distinct drop in the RPM. Launch the airplane, and it should go into a medium 2-stroke, ideally half way between pealed and 4-stroking. Adjust needle until you get that, then check the speed. I think shooting for 4.3 is a bit faster than necessary, but, certainly flyable. I would suggest that 4.5-4.6 is a better compromise.

   At any rate, when you get the mixture in the air as described, it will either be too fast, or too slow, or right on. Too fast, make it smaller (maybe .005 smaller), too slow, make it larger (like .005 larger). That will get you in the ballpark where you actually can control the speed slightly up or down, or the boost up or down, with small needle adjustments.

  The richer you run in level flight, the more boost you will get in the maneuvers, the leaner, the less boost. Again, you are way off the end of any scale we have because you will

   I wouldn't go by my posted RPM, because, to be honest, I forget what a Ringmaster needs, and in any case, the degree of unload for a 25LA VS a 15FP will be radically different, so any number I would have for a 15FP would not be applicable anyway. The 15 will unload FAR MORE, of course, launch your choked down 25LA at the same RPM and it will be much slower in the air than it would be at the same launch RPM on the 15FP. You have to fly it and see.

     Go by the speed and the boost/brake characteristics, since that is what matters for performance. It is possible/likely that when you get the speed about right, the engine will be too "flat", IOW, not enough boost and brake, compared to something like a 15FP.

      Brett

p.s. If you just used a 13/64 drill, it's probably larger than .203, maybe .205-.206 depending on the material or the grind on the bit. Normally that doesn't matter too much but in this case, with the diameter so close to the spraybar, it could make a big difference.

Online Brett Buck

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Re: Ringmaster LA25
« Reply #14 on: August 25, 2022, 12:07:26 PM »
Brett

Thanks for the Ringmaster lap speed on the Veco 19bb. The motor I’ve on hand is carbureted, so will be able to adjust lap time upward just a tad.

Dave Mo…

   Please don't misunderstand - these are not the desirable lap times, they are just what you get with the unmodified engines when they are otherwise set to the proper in-flight needle setting (i.e medium 2-stroke). Most are FAR TOO FAST for good flying - that's why I say they are too large for the airplane. Check the cube of the ratio of the speeds, from 4.8 to 3.8 seconds is about twice as much power.

    I will also note that we have flown Ringmasters even faster. David and I were flying Ted's Ringmaster at the NWR one year. Veco 19 but it didn't have a prop on it. We didn't know what to use, so we bought a 10-5 Master Airscrew. I take off, and it's going somewhere between 2.8 and 3 second laps, and almost any touch of the controls bent in about 2" of dihedral. We later got a 10-4 (I note, after my official flight and before Davids - the situation that seems to work out in his favor time after time...), and got about 3.5, which was a lot more tolerable. During my flight with the airplane about to fly apart, up walks Ted, in full United Captain uniform, from having flown up as a passenger to the Eugene airport across the street.

    It was a lot more tolerable with the APC 9-4, less diameter = less efficient, slowing it down while maintaining the fuel draw. 4.2 is still faster than necessary and still puts you in serious risk of pulling the wings off.

    Brett

Offline Steve Helmick

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Re: Ringmaster LA25
« Reply #15 on: August 25, 2022, 02:22:28 PM »
Ok, drilled the venturi to a "B" drill and got it up to 4.3 on level flight in turbulent winds. It was a little smoky a little burbley but it wasn't 4 stroking. When I went into maneuvers it would sag a bit but still got through. Not really enough power/drive in the 8's.

I'm going to drill it out again then open the needle to keep the 4.3 second/lap speed. This should give me a little more head room for maneuvers. I just hope it doesn't have to be so rich it cools the engine into a full 4 stroke going level.

Motorman 8)

Dang it! Made me reach up top of my computer desk for a Starrett drill chart to find a "B" drill is .238". I put a .156" (K&B Veco .19 NV spraybar) in my .25LA and drilled the venturi out to .272". Worked fine. IMO, the rear NV is awful, with loose threads, plus when I'd choke the engine, the fuel would run back to the tank, leave the hose empty when it started. Using an electric finger would make that Rear NV more practical, of course. Maybe they improved the NV thread fits over the years? One would hope so!  y1 Steve 
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Offline Motorman

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Re: Ringmaster LA25
« Reply #16 on: August 25, 2022, 07:39:21 PM »
.275" with the .156 nva is the same as the OEM set up. You'll have to run it rich to slow it down. Runs ok that way.

One thing I noticed about Bretts set up is it seems to fly twice as long on half the fuel. I might have to make a new, smaller tank. Anyway, I drilled it out to 1/4" but didn't get a chance to fly today.

Motorman 8)

Online Brett Buck

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Re: Ringmaster LA25
« Reply #17 on: August 25, 2022, 09:25:24 PM »
.275" with the .156 nva is the same as the OEM set up. You'll have to run it rich to slow it down. Runs ok that way.

One thing I noticed about Bretts set up is it seems to fly twice as long on half the fuel. I might have to make a new, smaller tank. Anyway, I drilled it out to 1/4" but didn't get a chance to fly today.

Motorman 8)

   1/4" (.250) = .0126 square inches, so if I am following correctly, that is another factor of 2.

   If you posted some lap times under the conditions I discussed, I could make an estimate.

    It will definitely use a lot less fuel - you are not wasting half of it (as you would in a 4-stroke) and you are burning it at higher temperature, releasing more energy per unit volume. I would not be surprised if you wind up well below 2 ounces of 10%.

   And to be clear, this will be *your* setup - I don't have a setup for a 25LA on a Ringmaster, because I would use a 15. That's the other reason you are using very little fuel, it takes very little power to get a Ringmaster up to the necessary speed. I am happy to help you find a reliable setup that also provides the expected tremendous performance improvement over a 4-stroke system.

    Brett

Online Dan McEntee

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Re: Ringmaster LA25
« Reply #18 on: August 25, 2022, 10:05:42 PM »
No, it's too slow but it's right at the rich/lean break point so I can't go any leaner and still run it in a 4 stroke.

  Then why not just shorten the lines a bit to get the lap time you want?
  Type at you later,
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Offline Mike Greb

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Re: Ringmaster LA25
« Reply #19 on: August 26, 2022, 11:19:51 PM »
I like a OS25FX  or similar motor on ringmaster size airplanes. ;D

Offline Dave Hull

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Re: Ringmaster LA25
« Reply #20 on: August 27, 2022, 12:03:56 AM »
Ok, Mr. Greb--you got my attention with that statement. Is your OS.25FX setup for the Ringmaster a Mach 2 deal for club racing, or how are you controlling the considerable power of the FX for sport flying...?

The Divot

Offline Mike Greb

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Re: Ringmaster LA25
« Reply #21 on: August 27, 2022, 01:08:56 PM »
Dave, Have them set up to do 3.0-3.2 sec laps on 60 ft lines.   I also use them on AMA slow combat airplanes with a 75mph with streamer speed limit.  Have problems keeping them below the speed limit.

Offline Motorman

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Re: Ringmaster LA25
« Reply #22 on: August 27, 2022, 04:58:54 PM »
I'd like to put my OS 25xz on a ringmaster but I'm sure it would shear the wings right off. Maybe a 300 sq Ringmaster with better wing construction. Would make a cool looking slow rat.

Motorman 8)

Offline Al Ferraro

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Re: Ringmaster LA25
« Reply #23 on: August 31, 2022, 07:50:36 PM »
The best engine I recommend foe a ringmaster is a McCoy 35 Lightning bolt with my piston ring modification. It’s the Sweetest sounding 4 stroking engine you ever heard using GMA 10-22 fuel.
 I just had my LA 25 Nobler out just a few weeks ago after not flying it just over a year. I put up two patterns, a real joy to fly.
Al

Offline Steve Helmick

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Re: Ringmaster LA25
« Reply #24 on: August 31, 2022, 08:08:43 PM »
I did some measuring and found my venturi is stock size at .260" but my spray bar is .156" giving me an effective area of .0151186. The area with stock .138" spray bar is larger at .0189771. To get that same area with the .156" spraybar I'll need a venturi diameter of .275". So, I can go bigger and still have the same fuel draw as the stock set up.

Am I the only one scratching my head trying to figure out how the stock size is .260" but you then drilled it out to a "B" drill (.238") bore? And then drilled out further to .250". Weird science!  LL~ Steve
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Offline Motorman

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Re: Ringmaster LA25
« Reply #25 on: September 01, 2022, 08:43:58 AM »
Yes, I think you are. The stock venturi is .260" I wanted to go faster but still keep it rich so I drilled it out to .275". That didn't work so I made a much "smaller venturi" so I could lean it out but still keep it slow. Then it was too slow so, I started drilling it out bigger each time. I'm up to .250" with the Tigre spraybar and hoping to fly it today to see if I can get a lap time of 4.3 and still keep it in a 2 stroke flying level.

Motorman 8)

Online Dan McEntee

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Re: Ringmaster LA25
« Reply #26 on: September 01, 2022, 09:03:00 AM »
No, it's too slow but it's right at the rich/lean break point so I can't go any leaner and still run it in a 4 stroke.

    9/1/2022 08:43 AM:
   Yes, I think you are. The stock venturi is .260" I wanted to go faster but still keep it rich so I drilled it out to .275". That didn't work so I made a much "smaller venturi" so I could lean it out but still keep it slow. Then it was too slow so, I started drilling it out bigger each time. I'm up to .250" with the Tigre spraybar and hoping to fly it today to see if I can get a lap time of 4.3 and still keep it in a 2 stroke flying level.
 

        Are you sure you know what you want?  Lots of contradictions here. Why not just get the engine happy and then adjust line length? All that bouncing around with venturi sizes just puts you all over the power band. You want to be able to penetrate turbulence, so get the engine near max power and adjust line length for lap time. If you want more thrust, start with a APC 10-4 and start clipping the tips until you get what you want it to do.

     Type at you later,
      Dan McEntee
« Last Edit: September 01, 2022, 09:38:51 PM by Dan McEntee »
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Offline Al Ferraro

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Re: Ringmaster LA25
« Reply #27 on: September 01, 2022, 09:44:21 AM »
The stock venturi is .260" I wanted to go faster but still keep it rich so I drilled it out to .275". That didn't work so I made a much "smaller venturi" 

Motorman 8)
  Instead of making a small venturi add layers of pantyhose, works great.
Al

Offline Al Ferraro

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Re: Ringmaster LA25
« Reply #28 on: September 01, 2022, 07:20:19 PM »
  I'd like to get just a little more speed to cut through bumpy air. I tried a 9-5 apc but it drags the engine down too much.
Motorman
  Did you try the APC 9.625 x 3.75N? Great prop for a LA 25.
Al

Offline Motorman

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Re: Ringmaster LA25
« Reply #29 on: September 01, 2022, 07:28:31 PM »
Looks interesting, thanks for the tip. Maybe I'll get a couple.

Online Dan Berry

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Re: Ringmaster LA25
« Reply #30 on: September 02, 2022, 08:44:11 AM »
  Did you try the APC 9.625 x 3.75N? Great prop for a LA 25.
Al

That prop works well on a Nelson 36.
At a FF meet.

Offline Steve Helmick

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Re: Ringmaster LA25
« Reply #31 on: September 02, 2022, 03:25:10 PM »
Yes, I think you are. The stock venturi is .260" I wanted to go faster but still keep it rich so I drilled it out to .275". That didn't work so I made a much "smaller venturi" so I could lean it out but still keep it slow. Then it was too slow so, I started drilling it out bigger each time. I'm up to .250" with the Tigre spraybar and hoping to fly it today to see if I can get a lap time of 4.3 and still keep it in a 2 stroke flying level.

Motorman 8)

Clearly, you need to read through all your own posts! LL~ Steve
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In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

Offline Reptoid

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Re: Ringmaster LA25
« Reply #32 on: September 02, 2022, 10:59:26 PM »
Only on Stunt hanger could 13 people debate for three weeks on how to get a Ringmaster to fly correct lap times
 LL~ LL~ LL~ LL~ LL~ HB~> HB~> HB~> HB~> HB~>
Regards,
       Don
       AMA # 3882

Online Dan Berry

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Re: Ringmaster LA25
« Reply #33 on: September 03, 2022, 08:40:25 AM »
Only on Stunt hanger could 13 people debate for three weeks on how to get a Ringmaster to fly correct lap times
 LL~ LL~ LL~ LL~ LL~ HB~> HB~> HB~> HB~> HB~>

Especially when asking the best Ringmaster pilot ever would be very easy.

Offline Motorman

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Re: Ringmaster LA25
« Reply #34 on: September 03, 2022, 09:43:27 AM »
actually don't need to ask anybody or post anything, just trying to part of a community. Why I'm trying to be part of this community I'll never know. ::)

Offline C.T. Schaefer

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Re: Ringmaster LA25
« Reply #35 on: September 04, 2022, 05:52:18 AM »
Walt, My Ring flys best at about 4.6 on 58x.012 lines.  about 25oz with B-25. Just a guideline.  Me and Doug worked with another one at about 30 or so with an LA .25. Never got it to be really nice.  The motor worked great but the thing did not want to maintain speed in the tight maneuvers of AMA pattern.

Offline Allen Eshleman

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Re: Ringmaster LA25
« Reply #36 on: January 10, 2023, 04:52:51 PM »
I don't know if this helps or hurts what you are trying to achieve, but I have Brodak Shark 402 (similar size model) with an OS 25LA (stock). I was running a 9-6 prop and the model was flying fast but struggled a little on stunts. I switched to a 10-5 prop and it really helped. Slowed the model down a bit, but increased power during stunts. On the needle, I run it like 20 degrees rich from peak speed. The 25LA turns the 10-5 prop fine. Even the OS manual for the 25 mentions a 10-5 prop as an option.

Just my 2 cents.

I have a similar problem with my Shark 402 with an LA 25.  I was thinking, 10/3, but seeing this, I am going to try a 10/5 and possibly a 10/4.

Offline Allen Eshleman

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Re: Ringmaster LA25
« Reply #37 on: January 16, 2023, 06:45:40 PM »
I used a 9.625x3.75 today.  It seemed to work better than the 9x4 but was not really a good test because I only did inside loops.  I didn't have anyone to time the laps and there was very little wind.  I can't wait until I can do extensive testing, trying the 10x3, 10x4 and 10x5.  Today was just some fun cold weather flying.

Online Dan McEntee

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Re: Ringmaster LA25
« Reply #38 on: January 16, 2023, 09:57:05 PM »
I used a 9.625x3.75 today.  It seemed to work better than the 9x4 but was not really a good test because I only did inside loops.  I didn't have anyone to time the laps and there was very little wind.  I can't wait until I can do extensive testing, trying the 10x3, 10x4 and 10x5.  Today was just some fun cold weather flying.

   Is that an APC prop in that size? I need to spend some time on the APC site looking at what they have. For most of my models with LA or FP-25s the APC 10-4 is what usually works for me, and just clip tips a bit if I need to adjust down a bit. It depends on the size and weight of the airplane and how draggy it might be.
  Type at you later,
   Dan McEntee
AMA 28784
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AMA 480405 (American Motorcyclist Association)

Online Dan Berry

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Re: Ringmaster LA25
« Reply #39 on: January 17, 2023, 07:42:18 AM »
   Is that an APC prop in that size? I need to spend some time on the APC site looking at what they have. For most of my models with LA or FP-25s the APC 10-4 is what usually works for me, and just clip tips a bit if I need to adjust down a bit. It depends on the size and weight of the airplane and how draggy it might be.
  Type at you later,
   Dan McEntee

It's what several of us run on the Nelson36. For Free Flight. Weird prop.

Offline Allen Eshleman

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Re: Ringmaster LA25
« Reply #40 on: January 17, 2023, 08:02:58 PM »
It is worth it to order your APC props from the company web site.  I first saw here some time back that Al Ferarro was using the 9.625x3.75 on his ARF Nobler, with an LA-25.  I bought a few and have really liked it for a Magnum 25XLR on my Doodle Streak - a Flite Streak with a lengthened fuselage and enlarged tail feathers (a very smooth traditional .35 type plane.  I also ordered the two different 9x3's and used the one for combat for awhile.  I highly recommend going on the APC web site.  There are some very surprising propellers which I never knew existed. BTW, the 9.625x3.75 is shaped very much like the 10.5x4.5 which I use on LA 40's and B-40's.
https://www.apcprop.com/

Offline Allen Eshleman

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Re: Ringmaster LA25
« Reply #41 on: January 21, 2023, 11:47:42 AM »
Question:

Let's say I buy a used LA-25 or LA-46.  It's already drilled out for a ST type needle. What size venturi should I use and is there a drop-off in power from one that's set up with smaller diameter OS needle and smaller (say 6mm) venturi?  What is the effect on fuel consumption, if both are set up correctly - right corresponding size venturi for the needle?

I wrote that question.  I think I figured it out by doing more research on what has already been written - as you say Brett and others - in volumes. The answer to the above - and ST NVA would be a .275 venturi.  If it has the factory OS Needle, the venturi would be a .235. Differences for the venturi size can probably be in .5 increments smaller or larger.   

Now, what I need to have very clear is this.  What is the effect of smaller set and larger set on 1. power? 2. fuel consumption?  Thank-you ahead of time.

« Last Edit: January 21, 2023, 05:43:14 PM by Allen Eshleman »

Offline Dennis Toth

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Re: Ringmaster LA25
« Reply #42 on: January 22, 2023, 08:22:58 AM »
Allen,
Small set will have better fuel draw, stable engine run, lower fuel consumption but less power. The larger set goes just the opposite. What you want is to search for setups for the FP/LA 25 and FP/LA 46 to see were others have run them successfully. Both these engines like to run in a rich 2 cycle not a 4-2. This puts the prop pitch around 4 and the rpm around 11,500. No need to do any mods to the engine. Once you get the engine in its happy rpm range adjust the pitch to get the lap time (might have to trim the diameter 1/8" at a time to hold happy rpm). The FP/LA 25 prop 9x4, FP/LA 46 prop 11x4.

Best,   DennisT

Online Brett Buck

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Re: Ringmaster LA25
« Reply #43 on: January 22, 2023, 01:13:07 PM »

Now, what I need to have very clear is this.  What is the effect of smaller set and larger set on 1. power? 2. fuel consumption?  Thank-you ahead of time.

   Smaller venturi = better fuel draw, less power, more tolerant needle, leaner run
   Larger venturi = less fuel draw, more power, less tolerant needle, richer run

   The problem I usually see is (as in many threads here), people using larger venturis to Get More Power, and then not being able to get reliable runs. Then, to "solve" the problem, start trying to adjust other things like stacking in handfuls of head gaskets, blocking the boost ports, or carving up the heads. The effect of this is is to *reduce* the power, sometimes drastically, which just exacerbates the original issue. Venturi adjustments in small amounts can have remarkable effects on the performance. We have changed venturis by .005" diameter, and had the pilot pick up *50 points* in about 2 practice flights.

    Look at it this way - the engine is self-powered air pump. The more air that goes through, the more power you get - and, more importantly, the less power you have, the less air goes through it. Since the fuel has to be sucked out using a venturi, if it is passing less air, and you leave the venturi size alone, you are also able to pull less fuel. So anything that you do to reduce the power (reducing the compression, blocking the boost port, using less nitro) will drive you to *require* a smaller venturi.

   Note also that over the range of power we use, the power is more-or-less a function of RPM - the more RPM, the more power. Since we run only a small range of speed, this also means that the inflight power is a function of propellor pitch, higher pitch leads to less RPM and less power. Less power also means less venturi.

  The same effect is also at play in performance. For IC engines, anyway, less power = less performance. This is why baffle-piston 4-2 break engines running 6" of pitch are effectively obsolete.

   Venturi, compression, nitro are all perfectly valid adjustments that I and many others have used for useful effect for years. But you have to understand the relationships above to make proper use of them. Wild, massive changes (like above, replacing the stock OS spraybar with an ST, ST Clone, 4 mm Enya, etc) jump you clear across from one side of the usual range to the other.

     Brett

Offline Allen Eshleman

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Re: Ringmaster LA25
« Reply #44 on: January 24, 2023, 12:39:41 PM »
Thank-you so much Brett and Dennis,

Explained this way, I am able to pull together all the things I probably need to know about LA and FP engines in regards to needles and venturis. 

I would guess that this applies to clones also - Magnum, APS, Tower, and even CS (I have a 46 but never tried to run it) and probably the ball bearing variants of these engines.   

I appreciate the advice about experimenting with venturis in .005 increments, if I choose to do so.

Online Brett Buck

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Re: Ringmaster LA25
« Reply #45 on: January 24, 2023, 07:35:32 PM »
Thank-you so much Brett and Dennis,

Explained this way, I am able to pull together all the things I probably need to know about LA and FP engines in regards to needles and venturis. 

   My post was generally applicable, it was not geared to specific engines. There may be exceptions, but you can probably rely on the general case until proven otherwise.

   The example case for the 50 points was a piped 40VF. As it started, with a .270 venturi it was running pretty good, but in level flight, was dropping into a 4-stroke.   On the ground, it was also getting the required 11,000 rpm just off the break, rather than about halfway between the break and peaked. There result is that entering a maneuver, it would break, get a boost and then the pilot had to react to it about halfway through the corner.

     There are a number of things you could try, but everything else was set as per standard. All it really needed was to raise the operating range fully into the 2-stroke. Replaced the .270 with the .265, the ground setting was much closer to peaked, in-flight it was in a low-medium 2-stroke and never touched a 4. Breaks are gone, pilot no longer had to react to anything, it just went around like nothing happened, and all the square maneuvers immediately cleaned up. Ted and I both estimated that he picked up 40-50 points in two flights. 

    This is typical of the sort of adjustments you want to make. This was aided by having long experience with the combination, we know that a 40VF works the best with particular props, pipe lengths, nitro, etc, and that you can adjust for the power of a particular 40VF with just venturi changes. New, they generally want a .260 or .265, if you have a lot of wear, maybe a .270, over-the-hill, .275.

     Brett


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