What are my options for a light muffler to use on a LA 25? Looking to use muffler pressure. Are the Big Art mufflers very light, an can I use muffler pressure on them?

           My personal choice would be a Randy Smith tongue muffler with the holes opened up slightly. The stock holes might be too restrictive , but rather than add additional holes, you can open the hole using the next drill bit size. A pressure fitting is provided and a fiber washer which is screwed into the back. I add a bit of loc-tite on that fitting. The stock size of a LA can differ sometimes. I found the ID to be about .265" . Randy can be found in the vendors section Aero Products

What are my options for a light muffler to use on a LA 25? Looking to use muffler pressure. Are the Big Art mufflers very light, an can I use muffler pressure on them?

  Ay yi yi! The "new" version 25LA with the *stock* parts exactly as it comes out of the box makes for a remarkable effective stunt engine system, far better than most people have ever had since CL was invented in about 1937. Every single "improvement" people have tried on this engine (and it's logical predecessor the 20FP) has made it work much worse.

     Big Art mufflers are top notch but as far as I know they are not tuned the same way that the stock E2030 muffler is. Chip mufflers are not tuned at all and will certainly degrade the run quality compared to the stock unit - far more degradation than the weight saved will make up.

   The stock system should use muffler pressure from the existing pressure tap into tank set up with a suction vent.

    The stock venturi is the same as a 20/25FP, ~.257, which I expect is really 6.6mm. With the *stock* spraybar/"nozzle" and the *stock* muffler set up per the instructions, with a 9-4 or 10-4 APC, this works perfectly. If you replace the spraybar with an ST-type, it will remove about 30% of the power which will make it very difficult to use with a 4" pitch prop. And since you have to drill out the case to get it to fit, you can't easily go back to the superior stock arrangement.

   I very strongly urge you to *use everything stock straight out of the box* and I have never seen any modification or alternate parts make it run better for stunt. At least, if you absolutely must experiment with alternative parts, don't do anything that will prevent you from putting it back the way it came out of the box, screws, muffler, venturi, spraybar, etc.  because that's where you will end up at the end of the experiment.

     Brett

  Ay yi yi! The "new" version 25LA with the *stock* parts exactly as it comes out of the box makes for a remarkable effective stunt engine system, far better than most people have ever had since CL was invented in about 1937. Every single "improvement" people have tried on this engine (and it's logical predecessor the 20FP) has made it work much worse.

     Big Art mufflers are top notch but as far as I know they are not tuned the same way that the stock E2030 muffler is. Chip mufflers are not tuned at all and will certainly degrade the run quality compared to the stock unit - far more degradation than the weight saved will make up.

   The stock system should use muffler pressure from the existing pressure tap into tank set up with a suction vent.

    The stock venturi is the same as a 20/25FP, ~.257, which I expect is really 6.5mm. With the *stock* spraybar/"nozzle" and the *stock* muffler set up per the instructions, with a 9-4 or 10-4 APC, this works perfectly. If you replace the spraybar with an ST-type, it will remove about 30% of the power which will make it very difficult to use with a 4" pitch prop. And since you have to drill out the case to get it to fit, you can't easily go back to the superior stock arrangement.

   I very strongly urge you to *use everything stock straight out of the box* and I have never seen any modification or alternate parts make it run better for stunt. At least, if you absolutely must experiment with alternative parts, don't do anything that will prevent you from putting it back the way it came out of the box, screws, muffler, venturi, spraybar, etc.  because that's where you will end up at the end of the experiment.

     Brett

The stock spraybar is the same one you use for the LA 46 right?

If it fits, yes.  If you find yourself getting close to the engine with a drill bit or a file, set the tools down, go someplace quiet, and relax until the urge passes.

 

Do you use the same launch rpm as a LA 46 when using a 10-4 on the 25?

Faster.  When I was using them all the time I'd just needle them so that there was an audible rise in RPM when I pinched the exhaust pressure tube, and a drop again when I let it go.  That leaves you with a pretty constant RPM run (because of the muffler).

If you're flying something Skyray sized then a 10-4 is a good prop.  If you're flying something a bit bigger, like a Nobler, or if you're flying at high altitudes, a 9-4 will let the engine spin a bit faster and develop more power.

You don't use them anymore?

I'm on to bigger planes.  There's some Classic planes that originally flew with Fox 35's that I might put a 25LA into, or I may go crazy and do a twin.

The World already has a trike-gear, twin engine design with dihedral in the horizontal tail, all the design elements to make it perfect for a Tim's Enginearing (sic) LLC project.  It was a 1:1 scale prototype, did not reach production, technically, it's never been tackled as a CL Stunter, yet would considered Classic Legal. How could this be? Can you name it?    Steve

                     The LA .25 works fine with the tongue, try it you will enjoy it.

So you say. Personally, I'll go with Brett and stay STOCK!

I detest those NASTY tongue mufflers. They DON"T muffle worth a da*% AFAIC. 

Jerry

I tried my hand at making a venturi for the LA 25. For you guys that have 46's an 25's are the venturi heights the same? I just copied a 46 venturi with a smaller hole size.

The Venturi heights are the same. Far as I can tell. The small hole venturis can be used in LA25s thru LA46s. Depends on the application. Jim Lee makes venturis for these engines that are higher-longer. They work a bit better, I think, smoothing out the airflow some. One critical dimension is the relationship of the needle valve hole to the base of venturi that bottoms on the crankcase. You need some squish on the o-ring.

.257 stock opening


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I do not believe that you'll change the run significantly by using one or the other, so I would use whichever is more convenient.  Probably the bottom.  Block off the unused one in flight -- I use a BB shoved into a short section of fuel line.  Get the smallest tube of BBs you can find; it'll be a lifetime supply.

Hey! Slick BB idea! Teach me more!

This ought to be worth at least 100 words.

Ehhhhhh...

Teach me about Colman fuel in airplane fuel! What's that all about?

DO NOT use  Coleman fuel in your model fuel, unless your trying to get a couple  more laps out of a tank...in a " Temporary situation "
and then Acetone works better
If you need it for cold weather use lighter fluid direct into the engine

Randy

Why?  Or maybe -- what have I been doing to my engine for the last few years?

The only reason to use Coleman fuel is because you do not have enough run time, the fix for that is a larger tank or engine adjustment,
Or the  nitro can be adjusted down.
at any rate it should be temporary, and acetone is better to use than lantern fuel, if you need it for cold weather starts, then a small bottle of lighter fluid is much better to use, squirt into the engine.

Randy

Imagine all the molecules of your engine expanding outward at the speed of light.....

Cooool 

Hey! Slick BB idea! Teach me more!

I can help you there, do what Brett says,, he has more hours invested in experiementing with these motors than most people do flying. and He has wond the NATS, made top 5 numerous times, so I am thinking his advice is pretty good

You can definitely expect 10 minutes on 3.5 oz with that rpm on an LA25. I have the new-style (or at least latest production, they all look the same) LA25 set up as Brett suggests and use 2.5 oz or less for full pattern on 25-size Sakitumi with plenty of time after completing pattern. This is totally stock, plastic backplate, remote NVA, stock muffler with baffle in place. 9x4 APC, but run at higher rpm than you are using, 10-10-10 Sig fuel.

I take it 10,600 is too fast?

Mike says he's running it at a higher RPM than you're using.  I ran mine higher, too.  So no, a 10,600 RPM isn't too fast.

Study the Brett Buck Tune Up for the 20FP.  You can't get that engine any more, but the directions for the 25LA should be similar.  I think you want to stick with the 10-4 prop on a Skyray -- a 9-4 would probably be too much power on a Skyray.

I think 11,000 was all she would do before dying. It's on a profile Tomahawk. Ran nice but once the tank got low it was choking, but ran a bunch more laps after.  Maybe I need a different tank.

I think 11,000 was all she would do before dying. It's on a profile Tomahawk. Ran nice but once the tank got low it was choking, but ran a bunch more laps after.  Maybe I need a different tank.

It sounds like you may have been running right on the edge of lean and if its a standard plumb tank, NON uniflow, it will lean out at the end of the flight and might be causeing what you are thinking is choking

  11000?  Mine will barely run that slowly, and would be dead rich. Are you sure your tach is functioning properly?

    With the stock parts, it will 4-stroke at about 13100 or so. Really, just put it back to stock, put on an APC 9-4, and see what happens. I think the Tomahawk is *far too small* for this much power. That might ending up being a more daunting problem.

    Brett

I don't know I thought it ran pretty good besides when it was lower on fuel. Yes Tach reads 3600 on a light bulb.

Your flying is looking pretty good. You could bring a trophy home from a beginner contest.
When you find the setup and RPM you want to stick with, it's time to meter your fuel. Since you don't know for sure how much is left in it after any given shutoff, fill the tank and then record how much you draw back out to hit that proper amount that gives you about 10 laps after the last stunt. That way you'll always launch with the same amount, and won't shutoff early or run overtime.
Rusty

Thanks! I'm running out of time to figure all this stuff out

I know the feeling Chris. But once you get there and actually do it, you'll feel really great no matter the score. All the others from beginners to experts do everything they can to make sure you have a good time. It's like no other sport in that sense, especially in the lower ranks. Beginner is all about getting comfortable in the pits and the circle. I'm not too far removed from the same place.
Rusty

My Android audio tach doesn't give me a steady reading from your video sound track, but it does read peaks a tad over 22,000. Could that be correct?

Still learning how to use this tach, but at the field it reads the same as my optical tach up to the 22,000 a Norvel was turning.

Bill

My Android audio tach doesn't give me a steady reading from your video sound track, but it does read peaks a tad over 22,000. Could that be correct?\

   No, that's not correct. It might be double-counting, which would mean 11,000. The engine sounds wrong, and very tired, although I wouldn't make any rash judgements on recorded sound.

   Brett