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Author Topic: OS 25 FP performance against OS 25 LA  (Read 2716 times)

Offline David Fretz

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OS 25 FP performance against OS 25 LA
« on: March 23, 2018, 09:22:06 AM »
Compairing these two engines both in new condition. Is the Performance better on the LA. Just curious.


Offline Chris Fretz / Formerly known as #Liner

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Re: OS 25 FP performance against OS 25 LA
« Reply #1 on: March 23, 2018, 10:17:11 AM »
The way everyone talks on here about the LA25  I'm beyond disappointed in almost every one I have! None of them will turn the 14,000 rpm I hear about. The only one OK is the one on my ringmaster and its a newer silver case. Blue case is said to not turn the 14,000rpm, however no one could tell me what is physically different between the blue case and the newer silver case. Box stock is suggested on the LA25 but I sware our altitude makes them suck.  I never got a box stock brand new one to knock my socks off. You got all the FPs so I hope they are better!  LA46 on the other hand I love them!
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Online Dane Martin

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Re: OS 25 FP performance against OS 25 LA
« Reply #2 on: March 23, 2018, 10:25:44 AM »
Chris, I had some minor issues with my LA25 at VSC. However, it was my "fault" I'd guess you could say. First, I was running an APC 9x6 because I couldn't get the RPM I thought was needed. Well I couldn't get the RPM because of my prop and fuel choice. I had Chris McMillin and Joe Gilbert explain what I was doing wrong  (so to speak). I went from barely being able to fly my 33oz plane to knocking out the entire pattern. No problem in power at all!

As for the differences in the LA from old to new, it's actually the crank. I posted pics somewhere. I can take more if necessary. It also has nothing to do with blue or silver. It's like a series difference. Unless you bought it new, and pulled it out the box yourself, there's really no way to know the difference externally. The external difference is the remote NVA version. However, the "new" crank did come out before that.

Offline Chris Fretz / Formerly known as #Liner

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Re: OS 25 FP performance against OS 25 LA
« Reply #3 on: March 23, 2018, 10:31:54 AM »
Chris, I had some minor issues with my LA25 at VSC. However, it was my "fault" I'd guess you could say. First, I was running an APC 9x6 because I couldn't get the RPM I thought was needed. Well I couldn't get the RPM because of my prop and fuel choice. I had Chris McMillin and Joe Gilbert explain what I was doing wrong  (so to speak). I went from barely being able to fly my 33oz plane to knocking out the entire pattern. No problem in power at all!

As for the differences in the LA from old to new, it's actually the crank. I posted pics somewhere. I can take more if necessary. It also has nothing to do with blue or silver. It's like a series difference. Unless you bought it new, and pulled it out the box yourself, there's really no way to know the difference externally. The external difference is the remote NVA version. However, the "new" crank did come out before that.
I had a thread 2yrs ago about a blue case barely pulling a Tomahawk and only getting 10,000 rpm out of it. I was told then that no blue case motors were the new series. I'd love to see those pictures!  I imagine you went to a 4 pitch prop not the 6?
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Offline RandySmith

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Re: OS 25 FP performance against OS 25 LA
« Reply #4 on: March 23, 2018, 10:40:53 AM »
The two  are  actually about the same, both are perfectly usable, however  you cannot  use  a  Small venturi (255) with a  large needle assembly, (157)  , you need the  281  venturi, and  you cannot use the  small OS 20 needle assembly (135) with the large ventuir, you need to use this
OS NVA = small venturi  255
PA , ST, Enya, Old Style OS NVA = large venturi 281

Of course you can very this some but you need to realize what you are using

The  stock OS needle  use to be  .157, when OS made the FP series back in 1980 they did not make the parts any longer so the pulled  the 20 NVA and made the tiny  20 venturi the stock one, this caused  massive problem with people using 275  281  290  295 venturis  with the   tiny  20 NVA, and  most people trying this got a lot of runaway    with the setup.  a larger  NVA  cured it.
OS kept  the  tiny 20 NVA  as the stock one, even as they came out with  the  LA series , so the  20  25  40 and 46   ALL use the  tiny 20 NVA, and the  rear needle motors  used a  bar that was the same diameter, this has continued to be a problem for people  because  they simply did not realize  what they where using.

There are  many hundreds of OS engines out there using the  larger  PA NVAs, and they needle and work better, BUT   you must use  the   L venturi not the  S venturi , this keeps  things  at the  correct size

Randy

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Re: OS 25 FP performance against OS 25 LA
« Reply #5 on: March 23, 2018, 10:43:24 AM »
I had a thread 2yrs ago about a blue case barely pulling a Tomahawk and only getting 10,000 rpm out of it. I was told then that no blue case motors were the new series. I'd love to see those pictures!  I imagine you went to a 4 pitch prop not the 6?

Chris    the motor must have had something wrong with it, the blue case and  silver case  will both run the same,  OS  did not make  a new casting for the silver case, they just stopped painting them

Randy

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Re: OS 25 FP performance against OS 25 LA
« Reply #6 on: March 23, 2018, 10:51:56 AM »
I had a thread 2yrs ago about a blue case barely pulling a Tomahawk and only getting 10,000 rpm out of it. I was told then that no blue case motors were the new series. I'd love to see those pictures!  I imagine you went to a 4 pitch prop not the 6?

Indeed, APC 9x4. However,  at that contest and just because I was in too much of a hurry, I did also try a Xoar 9x5. It's lighter. But all in all the 9x4 was definitely the way to go.

Offline Chris Fretz / Formerly known as #Liner

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Re: OS 25 FP performance against OS 25 LA
« Reply #7 on: March 23, 2018, 12:07:09 PM »
Indeed, APC 9x4. However,  at that contest and just because I was in too much of a hurry, I did also try a Xoar 9x5. It's lighter. But all in all the 9x4 was definitely the way to go.
Whay was your lsunch rpm with the 9x4 at the contest?
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Offline Chris Fretz / Formerly known as #Liner

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Re: OS 25 FP performance against OS 25 LA
« Reply #8 on: March 23, 2018, 12:17:46 PM »
Chris    the motor must have had something wrong with it, the blue case and  silver case  will both run the same,  OS  did not make  a new casting for the silver case, they just stopped painting them

Randy
Someone told me the internals were different from the blue case to the silver. 

Randy what are your thoughts on the FP25 vs LA25? Pretty much the same performance?

Chris
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Online Dane Martin

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Re: OS 25 FP performance against OS 25 LA
« Reply #9 on: March 23, 2018, 12:26:34 PM »
Whay was your lsunch rpm with the 9x4 at the contest?


I don't actually know. I've never tached my engines. Make it scream and a few clicks rich to protect it. When I move up to the bigger engines like on my Stuka, and then my Stylus I might start doing that.
But!  I say I haven't tached my engines because I have mostly flown speed and combat. So as much rpm as I can safely get is all I've ever had to set up for. That's why I love .25 sized stunt planes.

Online Tim Wescott

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Re: OS 25 FP performance against OS 25 LA
« Reply #10 on: March 23, 2018, 03:36:41 PM »
Whay was your lsunch rpm with the 9x4 at the contest?

I don't know where the 14000 RPM figure came from.  I usually tune mine by ear, but launch RPM is around 11000 to 12000 on an APC 9x4 prop.  That's plenty for a Sig Skyray 35 or similar, and way more than necessary for a Ringmaster.
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Offline Chris Fretz / Formerly known as #Liner

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Re: OS 25 FP performance against OS 25 LA
« Reply #11 on: March 23, 2018, 04:00:51 PM »
I don't know where the 14000 RPM figure came from.  I usually tune mine by ear, but launch RPM is around 11000 to 12000 on an APC 9x4 prop.  That's plenty for a Sig Skyray 35 or similar, and way more than necessary for a Ringmaster.
It came from this mess of comments... https://stunthanger.com/smf/engine-set-up-tips/options-light-muffler-la-25/
And the Completely Stock NIB LA25 I got from the a hobby shop last year that Was a factory control line motor certainly isn't over powering my ringmaster With a 9x4 APC prop.
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Online Brett Buck

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Re: OS 25 FP performance against OS 25 LA
« Reply #12 on: March 23, 2018, 05:05:52 PM »
I don't know where the 14000 RPM figure came from.  I usually tune mine by ear, but launch RPM is around 11000 to 12000 on an APC 9x4 prop.  That's plenty for a Sig Skyray 35 or similar, and way more than necessary for a Ringmaster.

   It came from me, because that's what both of mine turned on the second tank of fuel. All of the "new" type I have tested did about the same (about 10 so far). They are about 50/50 4-stroke at about 13300-13400 on an APC 9-4 and Powermaster RC "Air". This is VASTLY stronger than the old type, all of which also run about the same as each other, but about 2000-2500 rpm lower. I tested at Tucson one year (2200 feet real and density altitude) and got about 14200 peaked out on YS 20/20, which was a little off sea level and 10% for that particular engine.

   As previously mentioned, I have no way to tell before you buy which type it is, but there are clearly two performance ranges, and all the engines we have gotten in the last 5 years or so locally ( straight from Tower) are the upper performance range. All the blue ones I have tested were the lower performance range. The higher performance range is about a match for the 25FP, power-wise, but I have had a lot more luck with the LA as far as run quality goes. The 25FP runs were a long time ago and I don't have one to test with (and PLEASE do not send me one...) so I could be comparing apples to oranges.

   The lower performance range 25LA is in no way a match for either the 20 or 25FP (or the Veco 19BB, which is only vintage engine I have found that is It runs fine, but it will not fly as large an airplane.  The 20FP is crazy overkill on a Ringmaster, for example, but not the low-performance version of the LA.

     Brett

   

Offline Chris Fretz / Formerly known as #Liner

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Re: OS 25 FP performance against OS 25 LA
« Reply #13 on: March 23, 2018, 05:42:01 PM »
   It came from me, because that's what both of mine turned on the second tank of fuel. All of the "new" type I have tested did about the same (about 10 so far). They are about 50/50 4-stroke at about 13300-13400 on an APC 9-4 and Powermaster RC "Air". This is VASTLY stronger than the old type, all of which also run about the same as each other, but about 2000-2500 rpm lower. I tested at Tucson one year (2200 feet real and density altitude) and got about 14200 peaked out on YS 20/20, which was a little off sea level and 10% for that particular engine.

   As previously mentioned, I have no way to tell before you buy which type it is, but there are clearly two performance ranges, and all the engines we have gotten in the last 5 years or so locally ( straight from Tower) are the upper performance range. All the blue ones I have tested were the lower performance range. The higher performance range is about a match for the 25FP, power-wise, but I have had a lot more luck with the LA as far as run quality goes. The 25FP runs were a long time ago and I don't have one to test with (and PLEASE do not send me one...) so I could be comparing apples to oranges.

   The lower performance range 25LA is in no way a match for either the 20 or 25FP (or the Veco 19BB, which is only vintage engine I have found that is It runs fine, but it will not fly as large an airplane.  The 20FP is crazy overkill on a Ringmaster, for example, but not the low-performance version of the LA.

     Brett

   
What airplanes do you test these engines on?

All of my LA25s are apparently the bum low performance models.
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Online Tim Wescott

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Re: OS 25 FP performance against OS 25 LA
« Reply #14 on: March 23, 2018, 05:57:23 PM »
As for the differences in the LA from old to new, it's actually the crank. I posted pics somewhere. I can take more if necessary.

Would you?  Please & thank you?  I did a quick search and didn't find it.
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Online Brett Buck

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Re: OS 25 FP performance against OS 25 LA
« Reply #15 on: March 23, 2018, 06:34:20 PM »
What airplanes do you test these engines on?

All of my LA25s are apparently the bum low performance models.

      Most of them were on a SIG Skyray 35 with various degrees of deviation. Most of the original tests were in the early 90's, the LA tests were fist in the early 2000s when the FP was replaced by the LA, then a few years ago till now. Also included at varioius times were two different Dick Mathis Coyotes. Auxiliary tests were done on SIG Twisters, Fancherized Twisters, Top Flight "Green Box" Nobler, a SIG Banshee, and models like that. We (Jim Aron and I) have tested the Veco 19bb and 20FP on a Ringmaster (RSM Box Art Model, the 20-pointer from VSC), and he has tested a large number of variants on his Ted Goyet Stunt Feno.

    In almost all cases (the Skyray in particular), the main problem we had was keeping the airplane from flying too fast while maintaining the good run characteristics they have at high RPM. The only case we had a problem with "too slow"/not enough "power" was Bob Hazle's Fancherized Twister with a 25FP at the NATs. It had been too fast in terms of air speed or too slow in terms of RPM all week using 10-4's of various stripes. So we got a Brodak BY&O 10-3, Even set to supersonic RPM, the airplane was too slow (maybe 5.6-5.8 seconds). Knowing what I do now, we probably could have solved it with an APC 9-4, allowing enough revs for fuel suction which enough inefficiency to keep the airspeed under control. He also used the accursed ST spraybar - with a stock spraybar it probably would have been OK.

      The only problem I see on a routine basis is *not running the stock parts*, particularly the ST or other spraybar assembly, but sometimes the stock factory muffler (which is CRITICAL to making it run correctly) is discarded to "save weight".  Or, alternately, trying to run it on improper propellors like 9-6 or 10-6s at low revs. With the stock parts, it *will not* have enough fuel suction for reliably run at 10-6 revs (maybe 8500-9000 in the air). You might get it to be OK with the larger spraybar at those revs but that probably cuts the power in about half, at which point, you might as well get a McCoy 35 Redhead, and a time machine to take you back to 1956.

Changing them from rear to front intake is unnecessary but doesn't hurt anything in terms of performance.

    The other issue is a psychological phenomenon, where people hear a 2-stroke, and thing "that's going to BURN UP!". Just unwilling to peak the engine out for fear of damaging it. Thats a legitimate concern with a Fox (although people run them pretty hard in Foxberg events), but this engine was intended to be run by RC guys in "squeeze it till it screams" mode. You can't easily destroy it by setting it too fast.

      Assuming STOCK parts in all areas, don't give up. Trying to run a 9-4. you might not be able to get enough revs. So, go up a little in pitch and diameter. A Bolly 9.5-4.5, adjust pitch to get the desired speed at a decent setting. The intent is that the engine be running in a medium 2-stroke in level flight at normal flight speeds, and have it pick up "power"  in the maneuvers.  The only thing you don't want to do is attempt to run at low RPM, because it *will not* suck fuel sufficiently as it comes. That's why the APC 9-4 is better than other 9-4s and why it is usually better than any 10-4 - the smaller diameter allows it to rev up more while having low enough efficiency to keep the airplane from going like a bat out of hell.  But you can use the inverse if the airplane is too slow, or can't rev as high, add diameter or pitch *in small amounts* to increase the efficiency just enough to get it off of peaked out in level flight.

      Brett

Offline Chris Fretz / Formerly known as #Liner

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Re: OS 25 FP performance against OS 25 LA
« Reply #16 on: March 23, 2018, 07:11:08 PM »
      Most of them were on a SIG Skyray 35 with various degrees of deviation. Most of the original tests were in the early 90's, the LA tests were fist in the early 2000s when the FP was replaced by the LA, then a few years ago till now. Also included at varioius times were two different Dick Mathis Coyotes. Auxiliary tests were done on SIG Twisters, Fancherized Twisters, Top Flight "Green Box" Nobler, a SIG Banshee, and models like that. We (Jim Aron and I) have tested the Veco 19bb and 20FP on a Ringmaster (RSM Box Art Model, the 20-pointer from VSC), and he has tested a large number of variants on his Ted Goyet Stunt Feno.

   
      Brett
How did it preform in the Twister and Green Box Nobler? Were the tests on these 2 airplanes done with the higher performance LA25? And finally how did they test in any windy conditions?

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Online Brett Buck

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Re: OS 25 FP performance against OS 25 LA
« Reply #17 on: March 23, 2018, 09:07:38 PM »
How did it preform in the Twister and Green Box Nobler? Were the tests on these 2 airplanes done with the higher performance LA25? And finally how did they test in any windy conditions?

I haven't actually tried the LA in either of those, although a lot of people have tried the Twister/25LA. Our experiences were with the 25FP, which is about the same (at our revs) to the "good" 25LA. The 25FP is stronger at higher revs, but you can't use those revs for a stunt plane.

      I don't know why everyone always asks about the wind - when you have a Green Box Nobler or Twister going at 4.5 second laps, wind is not an issue, aside from maybe pulling the bellcrank out at the bottoms of round loops. The problem that we have had, when there were problems, was that the airplanes were too fast, or WAY too fast (Pat Johnston's 25FP, even with a reduced venturi, or even more insane, the Ringmaster/20FP at *3.8* second laps). They go faster and pull harder with the 25's than they do with Foxes, usually a LOT more, and we normally use longer lines than you would with a Fox (which might be 56 feet for a Nobler/Fox 35, or 63-63 feet for the 25FP).

   The first 25LA flights were mostly in a 15-18 mph wind. I asked the winner of Beginner in his first contest to fly a bunch of the break-in flights. He had no problem. 


     Brett

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Re: OS 25 FP performance against OS 25 LA
« Reply #18 on: March 23, 2018, 11:07:20 PM »
What airplanes do you test these engines on?

All of my LA25s are apparently the bum low performance models.

According to the thread you posted, you were getting nearly 11000 on a 10" prop. That might be normal. I'd say switch to the 9x4. What fuel are you running? I'm running 20% nitro in mine now.  Was 15%. The 20% made quite the difference.

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Re: OS 25 FP performance against OS 25 LA
« Reply #19 on: March 23, 2018, 11:11:34 PM »
Would you?  Please & thank you?  I did a quick search and didn't find it.

Well I can't find the pics either. But, this pic shows the cranks on the blue and silver case are the same. This is the "new" style. Color had no bearing on that difference.

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Re: OS 25 FP performance against OS 25 LA
« Reply #20 on: March 23, 2018, 11:15:20 PM »
Well I can't find the pics either. But, this pic shows the cranks on the blue and silver case are the same. This is the "new" style. Color had no bearing on that difference.

    I am sure that Randy is right, the case is almost certainly the same and the silver ones just weren't painted.

     I don't know what to tell anyone about this issue, I may not be too bright, but you don't have to be Alfred Einsteen to read a tachometer, particularly when it's a 2500 rpm difference, and its dead-nuts repeatable.

     Brett

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Re: OS 25 FP performance against OS 25 LA
« Reply #21 on: March 24, 2018, 10:20:38 AM »
Agreed. There was no announcement or "serial number break" as to when the change occurred. The blue case situation is either running out of paint, or another cost cutting measure. Again, no differences between the old vs new based on color. It was just a manufacturing year thing.

Here's my best take on it, based on my love for OS and research over the years ( only talking about the 25's here.  There's plenty more on the two different series in other sizes). The 25 FP was introduced in 1984 to be a lower cost alternative to the popular 25 F(SR). Plain bushing, lower cost in case production. All that. This was the engine of choice until about 1998. The LA series started in 1994 or 1995 with the LA 40. Then the 46 and I believe the 25 last. But in 1998 the production of the 25 FP actually stopped. Because of this over-lap, whatever interchangeable tooling was still being used. All internals from a 25fp fit in a 25la. The crank fits,  but will NOT work. It's actually too short. So, the early cranks in an LA were very FP like. There's not really a way to know exactly when the "old vs new" LA 25 changed, but I suspect as Brett says,  in the 99-00 date range.
The switch to the LA series was another leap in cost savings to produce a high quality engine. Less bolts, less machining, all the good high production stuff. As far as performance between the FP and the LA, I doubt you'd see enough difference between the two to worry. Buy whatever is cheap at the time. Lol.

Offline Dan McEntee

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Re: OS 25 FP performance against OS 25 LA
« Reply #22 on: March 24, 2018, 12:07:44 PM »
  The only difference I see in your photo is that the blue engine has a sharp corner to the counter weight area and the natural has more of a radius. I'm not sure how that will affect performance. My simple, barn yard testing of bolting them on a flying them shows me that the FP-25 has more power than the LA. This started withe when I built my first P-Force, and the LA-.25 was shown in the instruction booklet for the engine to use. I wanted to build it 100% to the instruction manual and use all kit materials if possible. The model flew right off the board and I placed second in our Ice-O-Lated contest with it in the P-40 class. The engine, though was right on the edge with nothing extra left to give. If it got windy at all it really suffered. I tried two other LA's but they ran the same. I tried 9-4, 9-5 and 10-4 APC props and the best was the 10-4 running in the 10,500 ROM range. I switched to the FP-25 and the same prop and got considerably more performance, but still not where I ultimately wanted it. I later switched to an OS .32F and have been really happy ever since. In recent times, I put together an Brodak ARF Ringmaster and set up the nose with hardware to take three engines for test purposes. I want to try the FP-25, LA25, Veco 19, and finally the Fox .35. I had a fairly new but broken in FP-25 that took quite a bit to tame it down, including sleeving the venturi down, layers of pantie hose, and settled on the 9-4 APC for prop to get what I wanted. Then just switched to the LA.25 and using the standard venturi, OS needle assembly, it is much more docile and uses considerably more fuel with the same APC 9-4. It has been an interesting process and still want to try the 10-4 on it to help settle down a jumpy corner before narrowing the line spacing. The rest of the testing on the other engines is yet to come with better weather. But the short story is, in my experience so far, I think the FP has the edge on power, but I don't think any of the LA-.25's that I have are from the later production runs.
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Re: OS 25 FP performance against OS 25 LA
« Reply #23 on: March 24, 2018, 02:01:54 PM »
Thanks Dan. I posted that pic only to show that a blue and a silver can be identical. Someone had said the blue ones have different guts, but that is not usually correct. I'd bet the old style 25 LA was a very small number of actual production. You probably wouldn't run into them very much at all

Also Dan, I have heard the FP is hotter. I could believe that. I haven't done a shoot out, but with my box car chief, it would be possible. It's got an aluminium motor mount, so it would be easy to do back to back flights.

Online Tim Wescott

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Re: OS 25 FP performance against OS 25 LA
« Reply #24 on: March 24, 2018, 02:05:44 PM »
Well I can't find the pics either. But, this pic shows the cranks on the blue and silver case are the same. This is the "new" style. Color had no bearing on that difference.

I would expect that such a dramatic power difference would result from either a different diameter bore in the crank, or different timing on the crank intake port.  I'm not sure that the difference in chamfer would be enough, but I haven't hot-rodded any two-stroke engines.
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Re: OS 25 FP performance against OS 25 LA
« Reply #25 on: March 24, 2018, 02:13:29 PM »
Someone told me the internals were different from the blue case to the silver. 

Randy what are your thoughts on the FP25 vs LA25? Pretty much the same performance?

Chris

Chris
I have only ran about a total of  12 to 14  25,  combo  of  LA and  FP, I have not found any with a  2500  RPM difference, and the ones I ran were  about the same, strong, and would fly a  Nobler as well as any FOX 35.
However  interesting enough , Bretts  post about the 2000 RPM difference  may  explain  why some of my customers  find  the  best prop for these  are  the  9.5 x 4.5  BOLLY, and  props like the  Cyclone  9.5 x 4.5,   BUT other find they need  lower pitch, like a  9 x 4  , 9.5 x 4 , and  10 x 4.  Then again, you have  people  running FAI fuel, many  run 5% nitro fuel, and  other  go straight  to  15, 20, 25%  nitro  fuel.  That will account for a  very large  RPM difference

Randy

Online Dane Martin

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Re: OS 25 FP performance against OS 25 LA
« Reply #26 on: March 24, 2018, 02:23:00 PM »
I would expect that such a dramatic power difference would result from either a different diameter bore in the crank, or different timing on the crank intake port.  I'm not sure that the difference in chamfer would be enough, but I haven't hot-rodded any two-stroke engines.

Those are the same cranks. Here's the different cranks. Completely interchangeable. One crank has a hollow rod pin and less crank weight.

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Re: OS 25 FP performance against OS 25 LA
« Reply #27 on: March 24, 2018, 02:30:09 PM »
I'm now measuring differences between an LA and an FP.
On an FP, the intake window in the crank is 6.15mm x 11mm. On the LA, it's 6.15mm x 10mm.
The FP liner length is 30.7mm. The LA liner length is also 30.7.
The biggest difference in the liner is pictured. Notice the absence of a boost port where the "hump" in the FP crankcase is.

The LA liner is on the right.

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Re: OS 25 FP performance against OS 25 LA
« Reply #28 on: March 24, 2018, 02:36:35 PM »
Alignment of the port behind the Hump.

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Re: OS 25 FP performance against OS 25 LA
« Reply #29 on: March 24, 2018, 02:41:25 PM »
Pics of the drastic porting differences between the LA and the FP. This certainly explains power differences. Also helps to show the lessened production cost of the LA series.

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Re: OS 25 FP performance against OS 25 LA
« Reply #30 on: March 24, 2018, 02:42:00 PM »
2 more

Offline Brian Gardner

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Re: OS 25 FP performance against OS 25 LA
« Reply #31 on: March 25, 2018, 04:25:21 PM »
I compared the liners between the FP and LA when I did a production run of these.

If I remember the exh timing was the same.

Yes the FP has a boost port, but the transfers on the FP are lower timed than the LA. I don't remember the actual numbers.

The production run I did duplicated the LA ports as this arrangement was more user friendly and could run a better 4/2 switch style run so it could be used either way. So my setup was just superior in fits and materials.

There's 45 of them over there in USA.

Offline Chad Hill

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Re: OS 25 FP performance against OS 25 LA
« Reply #32 on: March 26, 2018, 04:54:27 PM »
I have a couple of 25 FPs with damaged heads. Does anyone know if a 25 LA head will work in them? The OS part numbers are different for each type head. I have been unable to find any 25 FP heads although 25 LAs are still out there. Thanks, Chad

Offline RandySmith

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Re: OS 25 FP performance against OS 25 LA
« Reply #33 on: March 26, 2018, 05:18:40 PM »
I have a couple of 25 FPs with damaged heads. Does anyone know if a 25 LA head will work in them? The OS part numbers are different for each type head. I have been unable to find any 25 FP heads although 25 LAs are still out there. Thanks, Chad

NO they will  not  work

Randy

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Re: OS 25 FP performance against OS 25 LA
« Reply #34 on: March 26, 2018, 05:19:10 PM »
I have a couple of 25 FPs with damaged heads. Does anyone know if a 25 LA head will work in them? The OS part numbers are different for each type head. I have been unable to find any 25 FP heads although 25 LAs are still out there. Thanks, Chad

They are not interchangeable. The FP bolt pattern is very different. There's a few options though. I'll get back to you later today on brand interchange.

Offline Chad Hill

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Re: OS 25 FP performance against OS 25 LA
« Reply #35 on: March 27, 2018, 08:22:51 PM »
Thanks for saving me some trouble, guys. Chad

Offline Phil Spillman

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Re: OS 25 FP performance against OS 25 LA
« Reply #36 on: April 15, 2018, 08:03:21 PM »
There s a significant difference in the Blue VS Silver blocks of LA's: the blue versions have full length bearings in the block and the silver versions have two segments bearings. Which is to say the the front bearing segment goes part way back in the block and then there is a short segment at the rear of the main. Most likely this is too cheapen the overall price of production of these pieces! The blue engines .40,and .46 have full length bearing pieces as did the FP models of all varieties! I have run LA .46's since they were first introduced without one single failure! The fuel I use never contains less than 22 o/o total oil! I do not ever use fuel whose oil content is measured by weight only by volume so that the lubricant is sound!

Phil Spillman
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Online Brett Buck

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Re: OS 25 FP performance against OS 25 LA
« Reply #37 on: April 15, 2018, 09:53:17 PM »
There s a significant difference in the Blue VS Silver blocks of LA's: the blue versions have full length bearings in the block and the silver versions have two segments bearings. Which is to say the the front bearing segment goes part way back in the block and then there is a short segment at the rear of the main. Most likely this is too cheapen the overall price of production of these pieces!

      That's interesting, because the original blue types were generally weak and most of the silver ones perform very well. Certainly better than most of the "alternative" engines (many of which are designed around 50's ideas of a "stunt engines"), and on a par with the 25FP.

     Brett

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Re: OS 25 FP performance against OS 25 LA
« Reply #38 on: April 15, 2018, 10:51:37 PM »
I'll split my pics between two different posts. Please don't take this as argumentative, but I'm a huge os engine nerd. I've been researching them as long as I can remember.
 With that said, I'll stick to my original statement;  the color was never a differentiating factor. There were in fact series changes. There were tooling and production changes. However, the color was never a way to tell which engine was which. As you can see in the pics, these blue and silver engines have the same bearing. These 2 are 110% identical engines in every way except the color.

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Re: OS 25 FP performance against OS 25 LA
« Reply #39 on: April 15, 2018, 10:52:15 PM »
Front view.

Offline RandySmith

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Re: OS 25 FP performance against OS 25 LA
« Reply #40 on: April 16, 2018, 02:45:21 PM »
There s a significant difference in the Blue VS Silver blocks of LA's: the blue versions have full length bearings in the block and the silver versions have two segments bearings. Which is to say the the front bearing segment goes part way back in the block and then there is a short segment at the rear of the main. Most likely this is too cheapen the overall price of production of these pieces! The blue engines .40,and .46 have full length bearing pieces as did the FP models of all varieties! I have run LA .46's since they were first introduced without one single failure! The fuel I use never contains less than 22 o/o total oil! I do not ever use fuel whose oil content is measured by weight only by volume so that the lubricant is sound!

Phil Spillman

Hi Phil  that is really  not much, really of  little significance, the bearing setup ,either full or  two piece , will make for ZERO difference in performance, and  the steel crank  runs  well  on the  aluminum part of the  case.  FOX and  Others  had engines  that had  no bronze bearing in it, and  ran on the aluminum  case as a bearing, not as  good as  bronze, but  aluminum works  OK with a steel  crank, just look at he the  FOX 35 FOX 36

Randy
« Last Edit: April 16, 2018, 04:22:31 PM by RandySmith »

Offline David Ruff

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Re: OS 25 FP performance against OS 25 LA
« Reply #41 on: April 16, 2018, 04:56:16 PM »
Well I am happy that I have an older FP and newer FP.  And with all this discussion, I just pulled the trigger on a very nice FP 35 from Bob Brooks.

 8)
Retired Army

Offline Phil Spillman

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Re: OS 25 FP performance against OS 25 LA
« Reply #42 on: April 17, 2018, 08:52:04 AM »
Hi All, Be that as it may, I use both FP and LA engines with no mind to whether they have one kind of a bearing or another! I prop most it not all with the same APC 9 X 4 occasionally moving up to a 9 or 10 X 5 just for comparison on a given model. I am happy with all of them and have never needed to go to 14,000 rpm for any Stunt applications! Perhaps Combat would be different but I don't do that any more!
I do use mostly 10 11/11 fuel measured but volume and never weight!

Phil Spillman
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Offline RandySmith

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Re: OS 25 FP performance against OS 25 LA
« Reply #43 on: April 17, 2018, 10:26:33 AM »
With the  FP and  LA  25  you will not be running 14,000 RPMs, it will be  more like in the  11000  RPM range,  14,000  RPM  will be  very  noisy, and  most  STUNT  applications  will  never hit that, else you would be looking for  3  pitch  props

Randy

Offline Mark Mc

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Re: OS 25 FP performance against OS 25 LA
« Reply #44 on: April 22, 2018, 07:01:09 PM »
Well, I just did a bench run on the old, beat-up, blue .25 LA that I converted to control line use.  It's the one I posted about a couple of months ago asking how to remove the screws holding the carb in.  On the test stand, using 10% nitro fuel, no muffler, and an APC 10x4 prop, it was taching out static at 11,700 RPM.  Take that as you will.

Mark

Online Brett Buck

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Re: OS 25 FP performance against OS 25 LA
« Reply #45 on: April 22, 2018, 07:25:05 PM »
With the  FP and  LA  25  you will not be running 14,000 RPMs, it will be  more like in the  11000  RPM range,  14,000  RPM  will be  very  noisy, and  most  STUNT  applications  will  never hit that, else you would be looking for  3  pitch  props

  The 14,000 PRM was intended as a figure of merit for telling the difference between a "new" 35LA and the old one. The "new" version has no problem hitting 14,000 straight out of the box with an APC 9-4. The old one won't touch that. But not, you definitely will not be launching at that speed, that is what it will do peaked out lean. This is on the order of 800-1000 RPM more than a good 20FP, and 1000+ RPM faster than the "old" 25FP.

    They vary a little from example to example, but a typical launch RPM for a 9-4 on a Skyray is around 13,000, which with the "new" 25LA is about two clicks leaner than 4-stroking. The weaker the engine, the slower it will have to be set on the ground. The "old" 25LA goes off at about 11,100-11,500. Sea level, 90 degrees, 10%.

     Brett

p.s. since everyone seems to want to use 10-4, the RPM will have to be *much* lower, both because it is much more draggy on the ground and will be much more efficient in the air, meaning for a given flight speed and the same pitch, it will have to spin *much* more slowly. The entire trick to the 20FP is the 9-4 APC, exactly because the efficiency is so low that it can be revved up and still have a reasonable airspeed - and also, draw fuel better so it runs more smoothly.
« Last Edit: April 22, 2018, 08:15:30 PM by Brett Buck »

Offline Mark Mc

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Re: OS 25 FP performance against OS 25 LA
« Reply #46 on: April 23, 2018, 12:47:42 AM »
  The entire trick to the 20FP is the 9-4 APC, exactly because the efficiency is so low that it can be revved up and still have a reasonable airspeed - and also, draw fuel better so it runs more smoothly.

Well, that answers a question I've been mulling around in my head for a while.  I've been running the 10x4 APC on my .25 LA-S engines because that's what my mentor started me out on, and it's worked okay for me.  I've been considering going to the 9x4 to see how it performs on my 28-30 ounce Skyrays and a Flite Streak ARF rebuild.  As soon as I can fly again, I guess I'll bolt on the 9x4 and give it a go.

Mark

Online Brett Buck

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Re: OS 25 FP performance against OS 25 LA
« Reply #47 on: April 23, 2018, 01:18:39 PM »
Well, that answers a question I've been mulling around in my head for a while.  I've been running the 10x4 APC on my .25 LA-S engines because that's what my mentor started me out on, and it's worked okay for me.  I've been considering going to the 9x4 to see how it performs on my 28-30 ounce Skyrays and a Flite Streak ARF rebuild.  As soon as I can fly again, I guess I'll bolt on the 9x4 and give it a go.

   A 10-4 will work, and might be better for some conditions, but for sure try the 9-4 and see. Even the difference between a Tornado 9-4 and a APC 9-4 is remarkable. Actually, the best 20FP prop I ever found was a Circus Hobbies 9-4.5 cut down to 8.5 - but good luck finding one of those.

  It's a very important idea for modern-style systems. In the good old days the only way to improve your situation was to make the prop more efficient, because if you made it less efficient, you couldn't make up for it by spinning it faster. Try a 9-4 on an ST46 sometime if you don't believe me. But a 9-4 works dandy on a 20FP because you can spin it much faster, so the loss of efficiency doesn't hurt as much, or even makes it better.

  Same with bigger engines - pretty much no one who knows what they are doing runs the largest props the engines can safely turn. You could turn absolutely amazing props with something like  PA75 or Jett 88, maybe 16 or even 17-4. Good luck with that! You will be running less shaft HP than my 61 with a 12.5-3.75 3-blade - so why? A PA75 could probably put out 5 HP if you needed it - but not at 10,000 rpm, and what the heck would do with it.

   The second half of the problem also helps - by spinning it faster, you can either use a larger venturi (within reason) or the same venturi with a smoother run. This is why Leonard Neumann's "venturi chart" doesn't work, and why people want to categorically state that the 20FP venturi is "far too large". Well, it absolutely is "far too large" if you want to try to run the engine at 8500 RPM. It is not "far too large" if you run it at 12,000. So I am sure you can get the engine to run a 10-6 at 8500 if you put a small enough venturi on it. It will be feeble and no more powerful than a McCoy 29, but it will run.

   The other half of the fuel suction equation is rarely discussed but just as important - the ability to draw fuel is controlled by the suction available *and by how difficult it is to pull the fuel through the system*. Everybody has concerned themselves with the former, but not too many have bothered to consider the latter.

    Brett

Offline Bobs your Uncle

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Re: OS 25 FP performance against OS 25 LA
« Reply #48 on: April 23, 2018, 06:07:11 PM »
Why not just use the better FP 25?

There are a few New in Box for sale in in Classifieds right now. .


Online Brett Buck

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Re: OS 25 FP performance against OS 25 LA
« Reply #49 on: April 23, 2018, 11:07:39 PM »
Why not just use the better FP 25?

There are a few New in Box for sale in in Classifieds right now. .

   I can't speak for anyone else, but I am talking about it because that's what they were asking about, and people are more likely to have an LA than an FP.

    My experience is that the "new" 25LA is a much more tractable engine than the 25FP. The 25FP is better than the original 25LA, mostly because it has more power, but even then, it usually benefits from reduced venturi sizes. The 20FP runs much better than the 25FP with the (same) stock venturi, partly because it is less powerful.

   Having said that, I would note again that ALL the engines in the "small engine experiment" were perfectly usable with minor external tweaks *as long as you stick to the plan*, which is, again, 4" pitch props, running in a 2-stroke, backed off just enough to not go "over the top" in the maneuvers, and when in doubt, use less prop. Even the dismal Leo/Brat 22 and 28 were OK and had better handling and generally better performance characteristics than the engines I set out to replace - McCoy/Fox 35s and similar ancient 40 break engines from the 50's.

   Point being, if you have one of these engines, no matter whether we are talking about it or not, or it is the best possible or not, go ahead and use it!

     Brett


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