OS LA .15 Set up and Reliability

Tell us what you do to get the best performance from your engines.

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mark s
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Post by mark s »

Alex,

I disagree with a lot of your engine setup article. I do agree that you can get a stock engine to turn 17,500 RPM if you use enough nitro. But, more nitro means more heat, and the more heat you have the faster you will wear out an engine. You should also, break in your engines using some castor oil in your fuel. If you don’t it will take a lot longer to break the engine in. I do agree in using an all-synthetic high oil content fuel (at least 20% oil) after break in. Break in your engine in a controlled environment with a smaller prop (less load), and for short periods of time. This allows the heating and cooling cycle (required for break in) to take place without wearing the engine in to far.
With a few simple modifications you can get your engine to turn 17,500 RPM on 5% nitro (with a lot less heat).
Why take a chance on breaking the back plate by leaving the needle valve attached. One good hit and that engine is done for the day. If you leave the plastic back plate on, no matter what you do it will eventually leak, causing you to have a lean run. Besides the aluminum FP back plate is only $3.39 compared to $6.00 for the plastic back plate and never leaks.
Drilling out the baffle and stinger reduces engine back pressure and by reducing engine back pressure you also reduce engine heat. Now with a clunk you will need a certain amount of back pressure for the fuel system. But with a clunk tank setup this pressure changes as the amount of fuel decreases in the tank.
“Secondly the aluminum motor mounts act as a huge heat sink which keeps the engine coolerâ€
Lou Melancon
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Post by Lou Melancon »

Mark,
Increasing oil content to a point will reduce heat, but only to a point. Once you get past that point the increased oil, which should not burn, adds density to the mixture, increasing hydraulic pressures which in turn raises cylinder temperatures. After a certain point, more oil equals more heat.

From my bench testing, using an infrared heat gun, I found that anything beyond 18% oil caused a drop in rpms and an increase in cylinder heat temperatures measured at the glow plot. The disclaimer I would make is that my fuel is PowerMaster 5% nitro, 18% oil with the oil being a 1/3rd - 2/3rds blend of castor and synthetic. I believe that PowerMaster uses a very high grade of oil in its fuels and that in part accounts for the results I got in testing.
Alex Treneff
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Post by Alex Treneff »

Roid,

During most of the heats at Tuscaloosa I was the first up and at least usually within the first two. I didn't have to fool around with the bladders. Not saying bladders are bad, It's just a personal preferance to have the reliability of a clunk tank.

I always had consistent engine runs (except two heats that string caught in the prop, but nobody can help that).


<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Break in your engine in a controlled environment with a smaller prop (less load), and for short periods of time. This allows the heating and cooling cycle (required for break in) to take place without wearing the engine in to far.<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
We've done that actually.

but Mark, where does the heat of a 20,000+ rpm engine go while it's sitting on the bench?

Our engines run great breaking them in as we described. You could use a small prop, but like the article says, our opinion is that an 8x3 in the air is the best way.


<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by mark s</i>
<br />Alex,
“Secondly the aluminum motor mounts act as a huge heat sink which keeps the engine coolerâ€
Lou Melancon
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Post by Lou Melancon »

The argument of tank vs bladder will rage on for years, and no one will change anyone else's minds. So what? If what you are doing works for you then do it.

I have seen both Mark and Alex's planes fly and tach'd their engines. They both achieve excellent performance. The end result in this case is what matters more than how you get there.

The set up I run is the one that worked for me. I would change if it didn't but since it does see no reason to change.

The argument about oils in fuels has also raged for years, again with no one changing anyone else's minds, especially on the internet. What is correct for us in Combat is not necessarily correct in Pylon Racing or CL Combat, each discipline has its own unique challenges. If what you've got is working tell us all about it without, we all want to know what it is why and why it works for you.

On a personal note there are very few engine experts in model aviation. There are many folks who will preach to you as long as you will listen, but few who can point to a set of results that have been actually generated by testing.

I trust Dave Gierke's information about engines. I trust Dubb Jett on racing engines. I trust Don Nix on fuel blending. Why? Because each one is an absolute expert in their fields.

Personally I haven't tested enough set ups with either OS LA .15s or Norvel .25s, which are the two engines I have the most of, to tell you what single way is the absolute best. I can tell you what has worked for me and what hasn't but I sure haven't tested all the fuels, plugs, and specification changes to know what is the dead solid "best". If someone near you is having success and it is reliable and repeatable, do the manly thing, copy it and do what they do.
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boiler
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Post by boiler »

I have used clunk tanks and still do. I have used bladder tanks and still do. I have used bubbleless tanks and still do. All are good systems. Use what works reliably for you. I did change a clunk tank to a bladder at the last Terror at Hilltop. I tested the tank and it seem fine but I couldn't get a consistant run. Put on a bladder and it ran fine. It may not have been the fault of the tank but something else. I was in a hurry at the time and didn't worry about it after it ran fine. This week I plan to find out what was wrong back then. As far as LA15 break--in and fuel. Do what works for you. Myself, I break the engine in on the plane on the ground. I do it with three 30 second runs using 30% heli fuel, no muffler, and a 6x2 APC prop. Let it cool completly between runs. It tacks about 32000 rpm. Put an 8x3 on it and 5% Wildcat or Powermaster and it will tach about 17000 untill you have about a quart of fuel run through it. After that it should be very close to 17500. I like the 5% fuel because it not only costs less but will run longer on each ounce. The alcohol is what burns for the power. The nitro helps ignition and heat which I have enough of on 5%. The nitro also attacks the rubber bladders and paint jobs.[:(]
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