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General control line discussion => Open Forum => Topic started by: Paul Taylor on June 01, 2009, 08:15:45 AM
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Yesterday while flying my new plane the engine went lean about half way through the flight.
Engine setup: LA .46, muffler pressurer, with the fill vent capped. Clunk tank with the brass filter in the tank. I also have a filter on the muffler pressure line. Air Filter on the intake.
Launch rpm 9800.
Nice running engine, then after doing a few outsides the engine started to lean out. Took it back over and did a few insides, no change. Then it was just hang on tight.
It did this on both flights.
I would rule out crap in the fuel because the fuel goes thru 3 filters before it gets to the NVA. Also a filter on the muffler so nothing from there. No bug or grass in the intake, air filter.
So what else would cause this type of engine run?
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Not enough Castor in the fuel.
That is typical of a situation where your engine needs more oil. It is building heat as it goes through the pattern. What fuel are you using, and what prop?what size venturi? Of course, it could also be your tank configuration, are you set up uniflow?
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Do you have enough cooling air thru and over the engine? I am hoping the engine was broken in. DOC Holliday
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Yea, there's really only one thing that causes this. The mixture gets changed. Now, what causes that can vary. Overheating, as Mark suggests, is one thing. The engine gets hot and causes more atomization of the fuel, bleeding off fuel and increasing air content. More oil in the fuel can help with this. Or you have an airleak in the system somewhere, though that will usually show in an erratic needle. Excess vibration can cause this problem. The fuel foams and increases the amount of air in the fuel system.
I'd try more oil in the fuel first.
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Would 28% castor be too much? That is what I run in my Foxes.
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Ya know RBD, I am curious about running a filter on the muffler pressure.
I ran a ST46 for 250 or so flights on pressure and never had a fuel draw problem but one time ; It turned out to be
a split in the pickup tube. I repaired it and went right on. never used a filter on the muffler line.
A fuel filter has a pretty fine screen and might be easily gummed up. Especially if your using a substandard fuel I E.
uncle charleys homeaide blend! ingredients no secret ! cruddy castor,shooddy synthetics/ Vintage nitro and agwa
methanol. Uncle Charlie may really have a good blend, but he doesn,t make the ingredients, just blends them.
from one batch to the next, things can change.
If the fuel is filtered going in, it shoud not be putting a lot of gum out the exhaust,or carbon.
I have seen chip mufflers with hundreds of flights and the holes still wide open.
I have seen some with a hundred flights closed to the point they had so much back pressure the engine could not make
any power ,so the user had to lean the enging out ,making the run even hotter and harder on the engine.
My best suggestion move this thread over to the one Mr. Smith moderates.
Write down on paper his reccommendations a check them off one at a time as you make the changes.
if you don,t write and check, you will leave something out. betcha he can cure your problem! y1
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Paul: 28% castor seems like a lot to me for an LA 46. We use Sig fuel with
20 or 22% oil (half syn./half castor) in our LAs. Also, 9800 rpm sounds like a lot, too. What prop
are you using. We have been using a Top Flite 12 x 5 wood prop on my son's
LA 46 on an Imitation with a 40 FP muffler that's had some add't holes drilled
into it. Great setup, runs the same everytime. I'd check all your fuel lines to
see if there are any splits or pinholes. I'd also check the stopper at the front
of the tank to make sure it is not leaking.
Later, Steve
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you have an air leak somewhere - probably in your pickup line - you dont need a lot od castr in an LA - I run 20% oil of which 5% is castor.........they run on full synthetic fine as well.....check for a pin hole/small split in your lines
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My fuel formula for the LA 40 has 15% castor and 5% synthetic. The engine loves it. I run a Tower 40 Muffler with the outlet tube drilled out as far as I can get away with.
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I would look at two things...
First, I would try fuel that is 50/50 castor and synthetic, at about 22-25%
Secondly, I would think thatt you might be over propping the engine...try using a 4 or 4 1/2 pitch X 11" prop....
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This may be out in left field, but the other day, I pulled apart a tank that had a sintered bronze filter. The filter had a film over it, and the airflow was obstructed. I soaked it in alcohol, and it was OK. I'm wondering if castor might build up in the bronze webbing, and gel; maybe some kind of reaction? The tank hadn't been used in a while, so that might have been why the film built up.
Glen Wearden
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Would 28% castor be too much? That is what I run in my Foxes.
That's a good % for a Fox but you don't need anything near that for the LA's. We use 22% half castor half syn. it works just fine. Double check all your fuel lines for splits and pin holes. Check the back plate. If it wasn't doing this before with the prop you're currently using I can't see that being the cause of your problem, although I agree with using a 4-4 1/2 pitch prop. If your setup was working at one time, but now it isn't, it's almost certainly a tank/fuel line or back plate problem. Especially if it does it after takeoff.
See you and Ryan in a couple weeks :)
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Paul,
If that is the engine I think it is...the head is leaking.
It flies a long time once it goes lean...doesn't it VD~
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I run all my LA 46's on 10% nitro 18% oil Powermaster fuel. I hate 4 inch pitch props so I use at least 5inch pitch props and at least 11 diameter. My runs have alwas been rock solid If I don't do somethin stupid like at the Regionals. These engines run best when they have a load on them. I do not think more caster is the answer. I would change all of your tubing and maybe even the tank and start over. If this is running on a profile vibration could be a problem so put about 3 drops of Armorall in the fuel to make sure. Without being there it is hard to diagnose a problem like this that's why I am suggestin you start all over. You could also have something in the neele valve body that is movein around so take the needle clear out and flush it with alcohal or glow fuel. HB~> HB~>
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Paul,
If that is the engine I think it is...the head is leaking.
It flies a long time once it goes lean...doesn't it VD~
You are right about the head leaking. We had that happen to an LA 46 this weekend and that is exactly what was wrong. The head screws were replaced by socket heads and they had loosened so it is really something to look at.
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Should add one thought. I had this happen with a pipe plane I was flying several years ago. Ran great for half a flight then went lean and it was hang on time. After doing all the usual stuff, I ended up changing out the tank and the problem went away. An autopsy of the tank showed that the pickup tube was spilt from the end to about half way up to the front. So, as soon as the spilt was uncovered (surprise, surprise, about half way through the flight) I developed an air leak.
Taught me never to use brass tubing for tanks. Only copper since then and no more problems with splits in the tubing.
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Paul
You didn't say what kind of plane the motor is in. The problem Leo made reference to was with my "hand me down" Cardinal from Art Zehner with a LA 46 for power. I could set the motor very rich at take off and within one lap it would be going lean. With the help of Leo all manner of cleaning and replacement of fuel lines and tank configurations were tried. Nothing worked, it still would lean out. The head bolts came loose from the four very long and hot engine runs. Tightening the head helped but little. I brought two new tanks to try the next day but the mounts were an 1/8 inch to wide. While figuring how much to widen the slots in the tank mounts I saw that the front bolt on the bottom of the motor clamp and the clamp were farther away from the motor lugs than the back part of the clamp. The front bolt had pulled from whatever kind of nut or threads it tightens into which are hidden in the cheek. Re-tightening the bolt resulted in a dull pop as the threads would pull again. Motor VIBRATION for sure. A long wire through the front bolt hole showed me where to cut out the cheek for a long bolt and nut. Problem over on the next three flights. Motor run is now perfect.
Richard
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OK this is on a scratch built Cardinal, engine is bolted with lock nuts. Foam pad under the tank, and a bubbleless clunk in the tank that also acts as a filter.
Update...
Here is what I did.
I took the engine off to get at the tank. I pulled the guts out of the tank. Filled the sink with water and did a pressure test on the fuel lines. No bubbles. I did replace the presure tubeing inside the tank. Then the screw for the tank cap would not get tight. Had to go with a little bigger screw.
It took forever to get the head screws out. I had to call Zuriel and he told me how to do the "quick" turn back and forth to get the screws to break lose. I also had to use my heat gun. Got them out- Whew!. I replaced with socket screws. I looked at the head to see if I could tell if it was leaking. Nothing really jumped out at me.
We will see.
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Engine runaway is a common issue, even with LA46s, a comparatively even tempered CL off the shelf engine. Getting these engines to run right is also complicated by the scatter shot advice you're likely to get at the field (or on the forum.) All of the above ideas no doubt have worked in a given situation. Problem is there can be many different causes or combination of causes that make an engine to go berserk, what worked in one situation may not work in another. An unsystematic approach can add to your frustration. In my experience a systematic approach, making incremental changes, works best. I would approach a new engine as follows. First would be initial setup. I would do a baseline engine configuration, one that has worked for me and other club members.
Baseline: if the engine uses a remote needles, swap it out for an OS FP needlevalve available from Tower or elsewhere. The FP25-40 part will fit through the venturi, match up perfectly. At times, in our experience, the needle out on a stalk can exaggerate vibrations issues, especially true for profiles. Use a second head gasket. This usually makes the engine milder and easier to tune. Our club has found two glow plugs that match up well with this engine. Thunderbolt RC long and an Enya no. 3. We've had good luck with the 111/2X4 apc. If you can get Powermaster fuel, try 22% (50/50) 5%. Fuel quality varies enormously. All oil, methanol, nitro is not equal. Also, fuel needs to be mixed accurately by volume. Even slight deviations in proportion of ingredients can be an issue. Two shots of original Armoral to the gallon. We have found the Tettra tank problematic. Symptoms include an issue like the one you describe. Not sure why. Could be the bladder doesn't collapse fully enough or easily enough (thickness of material?) causing a slight vacuum as the fuel runs out, aggravating a lean setting. Others have made the Tettras work. In any case, Tettras are a non-uniflo tank, like all non-uniflo tanks it's likely to experience a gradual leaning of the engine during a flight. A function of the reduction in fuel head pressure. Uniflo tanks (when they work) make for a steadier setting throughout the flight. I'd use a different tank, at least initially. Either a clunk tank or an RSM profile uniflo (the long one inch thick tanks). If you know someone who can configure a clunk for uniflo try that. Pressure test everything. Testing the new tank(s), underwater. Even a slight trail of bubbles is trouble. Tanks must be tight. Check your filter (use a filter that you can open up) a slight bit of dirt or gook can cause a big problem. I'd initially run muffler pressure to the uniflo. If any weirdness happens, I'd disconnect the uniflo, run muffler pressure to the overflow and cap the uniflo. I use muffler pressure in order to provide consistent pressure to the tank. In my experience vents open to airflow can vary pressure too much. Causing the engine to run differently upwind and downwind.
Profiles are subject to weird vibes more often than full bodied planes. This no doubt complicates your engine setup.
The above configuration is where I start.
I would then ear set the engine (not using a tac), I am looking for a setting that is on the rich side. Important. It's best to creep up on an accurate setting click by click, very gradually getting leaner. Fly. Listen to the engine. The flight setting is what counts (obviously). Often (most of the time?) ground setting and flying setting differs. This is a key issue and a common problem. Adjust one click or two clicks at a time. This adjustment is often very sensitive. One or two clicks too lean can cause a runaway. If the engine runs away, two clicks rich. See what happens. It's not uncommon for a plane, especially a profile, to run either too rich (or lean) but unload (or get out of a weird vibration harmonic) in the air and run great. When you find a setting that works well, leave the engine at the setting, at the end of the flying session. Use it, next time out. Weather condition, temperature, barometric pressure, can effect settings. Again. Make adjustments increment by increment, click by click. After a while you'll probably hear when the setting is right on the ground. Some plane/engine combos like to barely break lean on the ground, some like a more constant back and forth, etc. I even had a profile that took off in a dead lean 2 stroke but unloaded (got out of a bad vibe?) in the air and went into a very useful consistent break during the flight.