Nice article! And something that most of us have all been through, almost word for word!! I had one experience with a burr in a needle on the OS.32F in my P-Force. It is Randy Smith set up engine, and when I put it on my P-force for more power to replace the FP.25, I had weird runs as I went through just about every 11-4 prop known to man in an effort to realize the extra power. I never had much luck with Zinger props, but tried the 11-4 Zinger Pro and things got better but erratic needle settings were the next problem. I pull the fuel line, took the needle out and held it up to the light to look through the bore of the spray bar and could see a little something hanging down. Blowing through it and flushing with fuel didn't clear it, so I rana piece of stiff wire through it, and then it was gone. I never did see what it was but must have been a burr from drilling the spray hole in the spray bar. Put everything back and have great runs on it ever since.
Something to keep in mind when changing fuels is that when going up or down in oil content, you make the mixture , what I call, fuel lean or fuel rich, depending on which way you go. I first experienced this in vintage dirt bikes. I got introduced to Optimol "Opti-2" premix oil by a world class off road rider in Canada, Helmut "Speedy" Clausen. Speedy had been working with the factory on the development of this synthetic, concentrated oil since the mid 1960s, and in all those years had never had an oil related engine failure , even when running up to 100:1 on the mixing ration. I don't use it at that rate but even when mixing to the chart on the bottle it is still in the 75:1 range, and when I ran that mix, I found that I needed to jet the carburetor several sizes leaner, because now there was much more gasoline in the fuel. Throttle response and transition from low end to top end speeds was where this was evident the most. Spark plugs still looked great, and I never had any issues with seizing and such. In our model fuel, it can have a similar effect but is more subtle and hard to tell because we don't throttle the engines and run at constant speed instead. It also seems to take several flight for the oil and/or nitro changes to take effect sometimes.
We don't get big elevation changes here in the Midwest but it's enough to make noticeable changes in fuel consumption. We are in the 400 foo above sea level range mostly here, but when I started going to the SIG contest years ago is when this first became evident to me. I think SIG Field is in the 800 to 900ft range, and in late June the weather could run from being unseasonable cool to damn hot and humid !! But in typical summer weather up there, I would have to sometimes short tank my ST.51s a whole ounce due to the extra altitude and hotter air temps. I never really tracked humidity levels but they had to be up there in the middle of corn country. Come back here and things went right back to normal. It took me a while to learn I couldn't change the las of physics, and when having run issues, to really pay attention to what I was hearing from the engine to know where to look for a problem. Fuel lines usually get changed at the beginning of the flying season, tanks get checked for leaks out of the airplane and plugs at least get examined, and if changed to potentially cure a problem, I'll put the old one back in after a few flights to see if the problem returns, and it it does, then it goes into the "old plug stash pill bottle." I am pretty consistent with what I use for fuel, mostly SIG Champion 10& nitro/20% oil half Klotz/half castor and add castor for Fox .35 and similar older engines. Since I can't buy SIG any more, I have started to mix my own to the Champion recipe and it seems to run just as well.. On my more modern OS engines, I may get a jug of Omega 10% to run in cooler temps but it's oil content is around 17% total so I never use it in old engines or ringed engines. It's acceptable for fun flying but is a bit down on power from what I get from Champion fuel., but it still works OK for fun flying.
I have often looked at the Gladiator, and always like the look and layout of the airplane, just been a lot of other designs ahead of it in the "want to build list" . After all the discussion about mufflers, I noticed in the pictures that you have the tongue muffler installed. What brand of muffler is that , and what is the hole size and configuration. Another lesson learned over the years is that tongue mufflers are restrictive and often need to be opened up a bit. There has to be a balance between the intake size and the exhaust opening. I have used tongue mufflers on just about everything I fly with OS engines with good results, but if I need nose weight to balance, I'll use stock mufflers also.. I have found over the years that a good stunt model is the sum of it's parts, everything has to work together for a good flight and it starts with the engine. I'll keep using what I have in engines, as to me, that is a big part of the attraction to the event. I get a lot of satisfaction from working with an engine and getting the best run out of it that I can. Electrics can bring in some more consistency, but as you found out with your profile model, they are not immune to problems either!!
Type at you later,
Dan McEntee
Topic: An Ongoing Saga of the... (Read 2822 times)