I take mild exception to that, since it is more-or-less what I said above, and I can assure you I am not just making it up. Your premise that you need to adjust it for "debris" building up is really not a good one, you cannot allow "debris" to build up because it really would require repeated and inconsistent needle setting, and the usual sitting on the ground screwing the needle in and out trying to hit a number on the tach. Yo adjust the needle in or out tiny amounts for temperature or density changes, or to adjust the speed up or down based on the previous flights, you don't sit there screwing needles in and out half a turn to try to hit some magic number. The tach is there to get it in the ballpark or compare the effects of needle changes, not to tell you to change the needle,
In any case, "debris" should absolutely *not* accumulate. Your filter should be stopping anything larger than the needle opening, if it doesn't, you need to get a better filter. Additionally, there should be nearly no "debris" in the first place - it doesn't come in any fuel from the factory, and you shouldn't be introducing it. While I don't fly nearly as much as some people, I have thrown out an awful lot of gallon fuel cans over the years, and I cannot recall a single case where I could trace more than a speck or two to debris that came in the fuel from the factory.
The only time I get anything in the airplane filter is after I make a new tank. Despite my best efforts, I always get a flake or two of rosin that comes out in the first run or so. That usually gets stopped by the coarse end of the Crap Trap filter. On extremely rare occasions I will see a "thread" or something like it in the downstream filter, I don't know where they come from, but they always gets stopped at the downstream filter element.
If you do find the needle suddenly "lean", in flight or on startup, opening the needle a turn to try to run it out is an OK idea that sometimes works. But if you are having to do this routinely, you have a fuel contamination issue that I would highly recommend you solve. For reference, my fuel can setup is the DuBro plastic fuel can fitting kit, it has a pickup with a screen on it, and I run a "Russkie" removable-element filter and then the larger of the two Sullivan "crap-trap" filters. The "up" line is the large-diameter silicone tubing, all the way to a "small" filter right at the end near the "fill".
The only time I have seen anyone with repetitive contamination are those using the plastic condiment/ketchup pumps like Paul Walker. He puts and recommends people put a huge automotive fuel filter on the outlet which seems to solve the problem, but woe be unto you without it, at least in my experience. I think at least some brands of them "shed" plastic or rubber into the fuel.
Point being, unless you are making a real change, different fuel, or a large change in the altitude or air density, you shouldn't have the screw the needle around too much just for adjustments.
Brett
Well, I post information and statements that get repeated all the time. I even repeated myself on this one, just not awake enough yet I guess! But I stand by what I stated. I mainly fly engines that use some castor, at least 50/50, plain bearing engines, ringed engines and vintage iron engines. Through the years i have my own experiences to learn from, learned a lot from other guys experiences, and learned a lot from some really good engine guys, that I have applied with satisfactory success and consistency. Most C/L modelers in my time run the same type of engines, and experience the same problems. Everything that I pointed out has worked consistently for me. I filter my fuel twice, once coming from the container, and again with an inline filter I run both metal and Sullivan and plastic tanks. Both have their pluses and minuses. I use both for a lot of reasons. Plastic tanks are cheap, easy to work with and adjust, and can be cleaned if need be. The rubber stoppers that they use are one detriment. The deteriorate, and material flakes off, and creates loose debris in the tank. Big flakes, little bits and such. The tubing corrodes from the nitro and alcohol and that flakes off from vibration, copper or brass but I mainly use copper. When the tank portion sees a lot of fuel in heavy use, and then sits for a while, they can split at the seams. You throw it all away and then start over with a new one.
I use commercially made metal tanks some times and occasionally modify those, and fabricate my own when needed. I always open up commercially made tanks to check them out and you would be amazed at what kind of crud is inside some times. After cleaning, I re-solder with minimal Ruby Fluid flux and .030" rosin core solder. They usually will be fine for a while, but the fuel and nitro gets to the tubing in those also. I've seen tubes split length wise with not much time on them. That debris ends up in the fuel line, sometimes gets through depending on the size of the mesh in the filter. I have pulled the back off of tanks that I know were squeaky clean, but causing problems that went away when switched out to another tank. Pull the back off again and find "stuff" inside. i don't always run muffler pressure, and nearest I can figure is that "stuff" makes it way into the vent line and gets pushed into the tank on the next fuel fill. I tend to run some kind of air filter on the venturi, either panty hose or the green foam filters, to try and keep debris out of the engine, but sometimes even material from those gets ingested when they start breaking down. I firmly believe that 'stuff" gets ingested into the engines and can actually make it through and exit with the exhaust, and if muffler pressure is used, it can get force fed into the tank also. Where we fly at Buder Park, there are LOTS of all manor of flying insects, and I think I have found traces of those inside engines and tanks. Not on an everyday basis, but over 40 years of doing this, I have been inside my engines and others and I can't figure out what else some of this stuff can be. The environment is a dirty place.
And that leaves the castor oil in the fuel. The lint pellets I pull from both filters is pretty amazing some times. Loose fibers from that process of the castor passing through can still let single fibers get through to the needle seat. . In the last 20 years or so, I have been able to fly quite a bit, anywhere from 2 to 10 flights a session, so that tends to let things accumulate. If i have a problem with a needle setting, I start at the needle with richening up at the next start, and return to the same tach setting. If it's a profile, I pull the filter and check that because it's number two in line anyway. Those are the usual main culprits.
This is all stuff I've seen and experienced with my equipment, and when helping anyone that asks. One thing I haven't mentioned yet is needle wear. I think it's mostly from vibration but who knows. is fuel abrasive at all in large quantities when under muffler pressure? I have a LOT of experience and time running ST-G.51s. When I get to a point where it's hard to get a needle setting, I check the needle itself. If it's been in service for a year or more and has had a lot of fuel run through it, the needles tend to get fish mouthed right where it meets the seat. If I catch it in time, I have polished them out by chucking them up in something and spinning against a fine stone. Some times it works and some times it doesn't, and these are genuine Tiger needles. I've learned what all this is, and how to deal with it. It's the nature of the beast with these engines. I've tried all the tricks to try and keep things clean. The upgrade syringe plungers like Jim Lee and some others sell have eliminated one source of little black bits that used to flake off from the rubber pistons. The O-rings last much longer and the better grades don't 'shed" and there are even some Teflon coated O-rings out there that look like a clear coating that are hard to find and pricey but are worth it if you fly al lot. All the other parameters are the same. i pretty much run the same fuel (SIG Champion 50/50 10% nitro) or any equivalent I can find now that SIG is gone. I have used Glow Devil R/C longs for a great deal of that time, as soon as I was introduced to them, Props are generally off the shelf, balanced and sometime reworked. I have learned through my other racing endeavors to try and use the same components and supplies from the same place as much as possible to try and keep things consistent.
This is what I have learned and experienced over 40 years of having fun flying stunt with the type of equipment that I fly and like. It's probably what drives a lot of guys to electric and that's fine. I happen to like it, and with what I have accumulated in parts and supplies, I see no real need to change. I do spend more time flying than working on things after all this time and experiences. I think anyone that has judged me here in the Midwest at any of the contests I have flown in can tell you I get quick starts, no fooling around trying to get started while they are boiling in the hot sun. I got enough trophies from lots of different contests to satisfy me that I am doing something right. I have a lot more runway behind me now than I have in front of me, so I will continue with what I know, enjoy and have fun with.
Type at you later,
Dan McEntee
Topic: Needle-Valve Setting on Every Flight? (Read 2872 times)