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General control line discussion => Open Forum => Topic started by: Kafin Noe’man on December 24, 2022, 05:20:40 AM
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Hi, I have few questions regarding engine setup tips:
1. Do you always need to readjust the needle-valve setting on every flight? If you do, what could be the main cause? I have the case where I always need to open (rich) the needle-valve in order to start the engine, and close (lean) it a bit afterward to get the best running engine. If I don’t do the things above, the engine won’t start easily most of the time.
2. How do you know if the engine is not running too lean on the ground? By pinching the fuel line that goes into venturi and see if the engine speeds up?
Looking forward to hearing your experience and suggestions.
Thanks a lot!
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1[/b]. Do you always need to readjust the needle-valve setting on every flight? If you do, what could be the main cause? I have the case where I always need to open (rich) the needle-valve in order to start the engine, and close (lean) it a bit afterward to get the best running engine. If I don’t do the things above, the engine won’t start easily most of the time.
2. How do you know if the engine is not running too lean on the ground? By pinching the fuel line that goes into venturi and see if the engine speeds up?
1. No, apart from the slight need to close the needle during the day as fuel warms up and air density goes down.
If your engine does not want to run when cold, you may have a too cold plug, or too little compression. Starting the adjusting from lean setting is not a good practise.
2. You don't, as the ground setting is also a function of tank lateral position. Pinching gives you an idea, for sure. L
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People who know more than me will
have better information, but my needle
settings evolve over a few flights as I dial
it closer to the ideal.
After that I might go one or maybe two
clicks either way to allow for air density.
If I have to do large changes. something else
is wrong.
I run PA, RoJetts, LA 46's, ST V.60 and others.
Cheers! - K.
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Here's a thought or two.
First: either make yourself remember or make it a point to check the ground RPM with which you are familiar will provide the setting you prefer for the plane/engine combination.
If the engine setting was fine the last time you flew it do the following: In preparation; Before doing anything, have a helper hold the model so that the engine is upright. Put a few drops of fuel in the intake: flip it a few times until it sounds and feels loose and ready to run; put the battery on and "burp" the engine which, because there's not yet any fuel in the tank, will simply warm the engine up. You may want to "burp the baby" a couple more times if it's particularly cold or if its been a long time since the engine was run..This warmup will insure that the next "for real I'm gonna fly that puppy" start will be from a mixture, engine tension (temperature internal freedom, etc) condition similar to when it last shut down.
After it burrns out that "prime" fuel the engine will be warmed up and loosened up and close to the last "good" setting flight you've flown with it. (The boys out here in California call that process "burping the baby). Now simply fill up the tank, crank it up, and check the RPM to insure its the same or close to that you know from vast past experience will provide essentially identical performance to the last time you flew the plane/engine combination.
Worth noting that the above is pretty much the "standard" for the CLPA top guns around the planet (at least those that still fly greasy power trains)
p.s. If you don't have a tachometer...get one...and you're halfway to "PROdom"!
Ted
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Thank you all for the suggestions.
I’ll try to do those on my next flying sessions.
Cant’t wait to see the improvement.
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Thank you all for the suggestions.
I’ll try to do those on my next flying sessions.
Cant’t wait to see the improvement.
As noted, you shouldn't have to (nor do you want to) move the needle to get it started, tach or no. Burping it helps first thing in the morning, but between flights, you don't want to move it unless you need to adjust to the conditions. You generally do need to get more fuel to start it than you want to run it. The way you do that is choking or priming the engine. Choking by pulling the engine through forward with your finger over the venturi some number of times, or priming by squirting fuel in the exhaust or venturi. This will get fuel in the engine enough to get it going until it can suck fuel on its own.
Like everything, its a matter of learning the technique and it is not always the same from engine to engine or setup to setup.
What engine to you have and how is it mounted (sideways, cylinder down, cylinder up)?
Brett
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One thing to remember about needle valves is that even if you are using a fuel filter, you will get some debris that will collect right where the needle meets the seat in the spray bar. Everything from dust , dirt, castor sludge, fibers, etc. will lodge there and affect your needle setting . Every now and then you will have to, once the engine starts, see the need to open up the needle to a very rich setting to let this stuff get through and rese to the RPM that you need. This may take 2 flights or 20, or 200 flights depending on "things." Then as Ted mentions, reset to the RPM ground setting that you like best. If you fly A LOT!!! and I mean several times a week, weekends and such, needles can wear. I have a lot of time with Super Tiger engines, and with ST needles, because of the way they work and function, can wear the needle from fuel flow and from vibration, and it sort of make a fish mouth or wear spot right where the seat is in the spray bar. This can make getting your favorite needle setting and RPM really hard to get. When I was flying a lot of contests and practicing a lot, I would have to change a Super Tiger needle out once a year it seemed like. When the needle setting starts to get hard to achieve, that is the first thing I look at. Stock ST needles are anodized black, and the point where it meets the seat in the spray bar will start to get shiny silver and isn't too difficult to see. But again, this is after hundreds and hundreds of flights. OS needles can do the same thing but not as bad.
MERRY CHRISTMAS,
Dan McEntee
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One thing to remember about needle valves is that even if you are using a fuel filter, you will get some debris that will collect right where the needle meets the seat in the spray bar. Everything from dust , dirt, castor sludge, fibers, etc. will lodge there and affect your needle setting . Every now and then you will have to, once the engine starts, see the need to open up the needle to a very rich setting to let this stuff get through and rese to the RPM that you need.
The same effect can be used to tell you when something is wrong (air leak, fuel clog, some other issue), because you should almost never have to make a big change to the needle unless you make an intentional change somewhere else. I think my #2 engine hasn't had to move more than about 1/4 turn since the 2007 Team Trials. So, if all of a sudden, it comes up way faster than you expect and you haven't changed anything, stop and figure out what is wrong, because good engines don't just change and suddenly require a large needle change for no reason.
Brett
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I love this forum. Experts helping others climb the stunt ladder.
"The only time I look down on others is when I am helping them up".
Quote unknown.
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I too do not check engine every flight. Even first flight of day I go. I think if engine is happy and I'm happy after a flight why change it. Maybe that is why I fly for fun now. D>K
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At the risk of "overkill"...
I repeat the foregoing: Unless there is some "significant difference" in site altitude and/or temperature from the last time you flew it::: Burp it and fly it. The vast/vast/vast majority of times you'll find the first flight of the day the same as the last flight of last week!
If, however, you start it and it runs "grossly" different...find out why...check for tank leaks, glogged fuel lines etc. etc. The engine's a mechanical device and will do the same thing every time you fire it up unless something is "wrong" with it or somebody fiddled with it who shouldn't have.
As Brett so accurately says, a properly installed and maintained model airplane engine will nearly always run the same way when you start it today as it did a week...a month...or even a year ago. Constantly needing to "needle the needle" is almost always the result of constantly needling the needle when it never needed needling in the first place!
Get used to "burping the baby" when you get all the "stuff" outta the car and to the site and then, when it's your turn to fly, fire it up, disconnect the battery and strut out to the handle and emulate Brett Buck at the handle!
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Hi:
I have always questioned why people are constantly adjusting their needle valves. I use a 1973 Lawn Boy mower all Summer, also a 2 stroke, and I never changed the nv adjustment. The grass was cut in the temperature range of 50-95 degrees. Prime two times and pull the rope, starts first time most of time!
Perhaps this is not an valid test but it gives me food for thought.
Stay well,
Frank
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Hi:
I have always questioned why people are constantly adjusting their needle valves. I use a 1973 Lawn Boy mower all Summer, also a 2 stroke, and I never changed the nv adjustment. The grass was cut in the temperature range of 50-95 degrees. Prime two times and pull the rope, starts first time most of time!
Perhaps this is not an valid test but it gives me food for thought.
Stay well,
Frank
It has a governor, and it changes the throttle instead of the needle valve. It's like you are changing the venturi and the needle (because it sucks fuel proportionally to the air very accurately over the small range it needs to). If you checked it under no load, you would find the throttle less open at 50 degrees compared to 95 degrees.
Note that this is an entirely different situation, and, in fact, you can use venturi changes (over *small* ranges, like .005" +-) to get sort of similar power levels as the air density changes. Unfortunately, since we do not have a governor and only some of us have regulators of varying effectiveness, and are counting on load changes over the period of a few revs, it's not that comparable.
If you stick with a single fuel type, and compare 50 to 95, you absolutely will have to move the needle to adjust it to get similar results. We do that all the time, same altitude, same fuel, from 50ish in the morning to maybe 100-105 in the afternoon. On my regular engine (that has a regulator...) this is about 30 degrees of needle movement from morning to afternoon.
Try to do the same going from here at sea level, to the NATs in Muncie (1000 feet), it's more like 3/4 turn, which is a rather extreme change that made the engine run extremely hot. That's why we no longer to that, I switch from 10% nitro to 15% nitro, that is about 15 degrees of needle movement depending on temperature, and it runs the same as at home. In a month, David and I are headed to Tuscon for the Southwest Regionals. It's 2200 feet, and I will be running 20% nitro.
Point being, you definitely DO need to change the needle some every time, particularly if you don't have a regulator/tuned pipe. But over tiny increments, not half a turn just to start it, then back in. If it suddenly needs 1/2 a turn in similar conditions and no intentional changes, then, something is wrong, find out what and fix it.
Brett
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Here's a thought or two.
First: either make yourself remember or make it a point to check the ground RPM with which you are familiar will provide the setting you prefer for the plane/engine combination.
If the engine setting was fine the last time you flew it do the following: In preparation; Before doing anything, have a helper hold the model so that the engine is upright. Put a few drops of fuel in the intake: flip it a few times until it sounds and feels loose and ready to run; put the battery on and "burp" the engine which, because there's not yet any fuel in the tank, will simply warm the engine up. You may want to "burp the baby" a couple more times if it's particularly cold or if its been a long time since the engine was run..This warmup will insure that the next "for real I'm gonna fly that puppy" start will be from a mixture, engine tension (temperature internal freedom, etc) condition similar to when it last shut down.
After it burrns out that "prime" fuel the engine will be warmed up and loosened up and close to the last "good" setting flight you've flown with it. (The boys out here in California call that process "burping the baby). Now simply fill up the tank, crank it up, and check the RPM to insure its the same or close to that you know from vast past experience will provide essentially identical performance to the last time you flew the plane/engine combination.
Worth noting that the above is pretty much the "standard" for the CLPA top guns around the planet (at least those that still fly greasy power trains)
p.s. If you don't have a tachometer...get one...and you're halfway to "PROdom"!
Ted
Hi Ted,
After a while, I’m getting more familiar with my engine and how to start it properly.
However, the more I’m getting familiar the more questions that come to mind.
I’m currently in the middle of finding out the “Stunt Range” for my engine, and I think I have found it.
Let’s say, the perfect engine run is at 11,500 RPM at 1 full needle turn.
And then when you go out again for the next flight on other weekends, without changing anything on the engine, somehow the tach is telling you that same needle setting is revving at 11,850 (this can happen, right?)
What should I do if I’m facing this? Fine tune the needle a bit to get back to 11,500?
Looking forward to hearing more from you guys!
Best,
Kafin
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What should I do if I’m facing this? Fine tune the needle a bit to get back to 11,500?
I'm not Ted, but -- yes. Except: I've found that I can't really get a reliable tach reading on my engines when I first start them up -- if I don't do anything special, it can take a few laps for them to settle in to a constant speed.
However, if I pinch off the muffle pressure line or put my finger over the tank vent, depending on the fuel setup, I can make the engine run lean for a few seconds. When I let off from that, it always seems to settle into the same spot. I assume that what's happening is that I'm either forcing the engine to warm up to operating temperature, or I'm scavenging any stray fuel out of the crank case.
At any rate, when I was just starting it up and immediately taching it I'd be chasing my tail forever.
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I'm not Ted, but -- yes. Except: I've found that I can't really get a reliable tach reading on my engines when I first start them up -- if I don't do anything special, it can take a few laps for them to settle in to a constant speed.
However, if I pinch off the muffle pressure line or put my finger over the tank vent, depending on the fuel setup, I can make the engine run lean for a few seconds. When I let off from that, it always seems to settle into the same spot. I assume that what's happening is that I'm either forcing the engine to warm up to operating temperature, or I'm scavenging any stray fuel out of the crank case.
At any rate, when I was just starting it up and immediately taching it I'd be chasing my tail forever.
I go back to the days of the "5 point start and get in the air before 1 minute/no starter era. Get it started, needle set and out to the handle and in the air for a 5 point bonus, and at a time when I wanted every point I could get!! I don't remember exactly when that went away, around the time pipes and carbon props made the scene and starters were wanted by those using the carbon props for safety. Getting out of that habit was difficult and it took a while for me to understand that to get a good solid setting the engine sometimes needed 30 seconds or more to really get to operating temp. I can't run at all so no way to make the mad dash for the last 60 feet, but at least we didn't need to put on the safety thong!!
Type at you later,
Dan McEntee
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I'm not Ted, but -- yes. Except: I've found that I can't really get a reliable tach reading on my engines when I first start them up -- if I don't do anything special, it can take a few laps for them to settle in to a constant speed.
However, if I pinch off the muffle pressure line or put my finger over the tank vent, depending on the fuel setup, I can make the engine run lean for a few seconds. When I let off from that, it always seems to settle into the same spot. I assume that what's happening is that I'm either forcing the engine to warm up to operating temperature, or I'm scavenging any stray fuel out of the crank case.
Exactly, peak it out by cutting off the air, then release, and you will get a much more reliable needle setting. In any case, I would rely more on the needle position to be stable, than trying to match RPMs. Unless something is wrong (air leak, fuel clog, or something else), the in-flight speed will be the same at the same needle position, aside from the air itself changing (which only happens very slowly).
Brett
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There have been many times where some one makes a post where they claim that their set up is so reliable that they haven't touched the needle in years , or some other lengthy period of time, and I always question that statement because there are just too many factors that can make a needle adjustment necessary. One of them is just microscopic debris in the fuel and tank. When making successive flights, where a good quantity of fuel flows through everything, there WILL be accumulations of debris either in the filter in the feed line, and even past that where the needle passes through the seat in the spray bar. I have always been in the habit of at least once a flying session to open the needle to a really rich setting, let it flow a bit to allow stuff to pass through, and then reset the needle. That gap between the needle and seat is quite small, and doesn't take much to alter the run on some engines. I always thought that was something everyone did, but was surprised to read a Dirty Dan column once when I was well into my climb up the ladder of stunt , that he had just discovered this phenomenon! Now to be fair, I know that Dan was a combat guy and combat guys crash a lot and have to service and clean their stuff way more that what most normal stunt guys do, and he hardly ever had more than 4 flights in a row on the same plane, engine and needle valve setting with out having to service something just from all the action those planes see. But it was a surprise to me at the time.
Type at you later,
Dan McEntee
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There have been many times where some one makes a post where they claim that their set up is so reliable that they haven't touched the needle in years , or some other lengthy period of time, and I always question that statement because there are just too many factors that can make a needle adjustment necessary. One of them is just microscopic debris in the fuel and tank. When making successive flights, where a good quantity of fuel flows through everything, there WILL be accumulations of debris either in the filter in the feed line, and even past that where the needle passes through the seat in the spray bar.
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
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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
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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 may be wrong, and often am. If you have "debris" build up in your spraybar, I think you have a problem and you should probably fix it, but up to you, it's just advice.
But I don't just make stuff up, and I don't appreciate the implication.
Brett
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Muffler pressure or a forward facing uniflow vent can be a surprising source of debris, but those are still upstream of your fliter which "should" catch it. I suppose carbon from the muffler pressure might sneak past a filter and build up in a needle, it is a thought but I'd still think anything that gets past a good filter should make it past the needle and be ingested... or maybe just dried castor if you use a lot of oil, could gel in the needle after a long layoff. But week to week in season flying, I'm with Brett for the most part. The needle is the needle. As for the tack, its pretty useless after the first few seconds. If you sit there tacking it as the motor heats up on the ground, the rpm for hot will be different than for a cold motor and will vary everywhere inbetween hot and cold. Flight to flight referencing is best. Typically once you have it set properly you can almost wing it and just know by looking at the needle like the face of a clock, and know you have to move the needle in 5, 10 or 15 minutes on the clock face from breakfast to lunch on a typical Muncie hot July warming trend. 😀
The only other thing I'll add as an aside, the one setup I do remember being more sensitive to dirt in the needle and actual fuel viscosity was the ultra low consumption 4 stroke run where guys were doing a pattern on like 2ounces of fuel. In that rare case the needle is closed so tight I think it was more sensitive to any change in fuel viscosity and debris. But, running any modern engine or pipe rig using a reasonable amount of fuel, just refer back to the previous advice of better filtration etc.
EricV
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Hi, I have few questions regarding engine setup tips:
1. Do you always need to readjust the needle-valve setting on every flight? If you do, what could be the main cause? I have the case where I always need to open (rich) the needle-valve in order to start the engine, and close (lean) it a bit afterward to get the best running engine. If I don’t do the things above, the engine won’t start easily most of the time.
Thanks a lot!
One reason the needle needs to be adjusted is fuel temperature. I believe that the viscosity of the oil decreases as temperature rises. Thus, the setting of another time is no longer correct. Even on the same day, as the temperature rises the setting must change. To be on the safe side, I enrich the mixture a little at the start of a session and work back to the optimum mixture.
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I may be wrong, and often am. If you have "debris" build up in your spraybar, I think you have a problem and you should probably fix it, but up to you, it's just advice.
But I don't just make stuff up, and I don't appreciate the implication.
Brett
I'm not implying that at all Brett, and don't understand how you come to that conclusion. I'm just relating what I have found and dealt with in my lifetime. I'm not making any of this up either, just relating what I find, consistently. I learned most of what I know before the internet and didn't have any of that to influence me in any way, just the guys I have gotten to know through the years of contest flying. I have spent my working career building and fixing things, diagnosing and determining problems with machinery and electrical components. Flying model airplanes is just an extension of that. When you fly these type of engines , certain things are just gonna happen. You might go a really long time and not have any issues, then suddenly Murphy's Law kicks in when you least expect it and you have trouble staying ahead of them. I'm just saying that you can't control or prevent everything. @#$% still happens despite all the effort to prevent it. If I have to open the needle every now and then and get a reset to my desired take off RPM, I don't mind. It takes about 10 seconds and almost always works. A similar and common discussion in my racing days was about how an engine develops power and whether or not 'breathing" an engine now and then helps it develop it's peak horsepower better coming up the RPM range when getting to the peak of the powerband, over just staying on the gas all the time. it's interesting to discuss and argue about but one thing you could always count one was something in all the parameters will change. I'm not college educated but still attending the school of "Hard Knocks" and I have found the best way to learn something is by doing it and then learn from your experiences and mistakes, and those of others.
Type at you later,
Dan McEntee
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I often see sport fliers, perhaps even Beginner and Intermediate fliers, start their engine, set the NV immediately, then have the engine go rich just as they are picking up the handle. CANNOT get a good setting on a cold engine. Our barometric pressure and temperatures can change significantly from day to day and hour to hour. A bad NV setting isn't a good use of your flight time, so IMO, it's much better to get it right! Setting the NV wrong is a good way to find yourself needing a new airplane.
If you go out flying and put up 3-6 flights in a couple of hours, you can probably skip the warm-up drill I use, but if you are flying in a contest where you put up a flight before the official flying (maybe 7am, when it's cold outside), then your first round flight two hours later, and your second round flight mid-afternoon, you'd better be warming up the engine and setting the NV after it's warmed, using a tachometer...the same tachometer, OBTW.
The alternative would be to infuse your fuel with extra nitro for higher afternoon temp. I've never tried that. I could perhaps get behind spicing up the basic fuel mix with some nitro/oil 'special sauce' to boost nitro percentage while keeping the oil % the same, and creating a chart that would tell me how much of this to add to the base fuel to keep the NV setting the same. The chart would probably be related to ambient temperature, maybe barometric pressure also, but then you'd have to carry around a lot more stuff than I'm willing to carry. It's just not that hard to warm up the engine and set the NV with the tach before each flight. D>K Steve