Author Topic: Motor sputters at the bottom of an inside loop (Read 2235 times)

Allen Eshleman · « **on:** August 15, 2023, 10:52:14 AM »

I have an LA-46 on a Brodak Pathfinder ARF. I am using a clunk tank. The plane is sputtering at the bottom of inside loops. I haven't tried outside loops yet. The clunk in the tank doesn't quite reach the far end of the tank, but very close so it can be free swinging.

Any thoughts?

Should the clunk scrape the back end of the tank?

Motorman · « **Reply #1 on:** August 15, 2023, 11:12:09 AM »

You don't want the clunk to drag on the bank of the tank. Is it getting hung up on anything? Sputtering rich or starving for fuel? Is the tank pretty much centered on the cylinder? Is the tube on the clunk too stiff, does the tube kink? You can see how it will act without going inverted if you just do some agressive climb and dives. Could be a bad glow plug.

MM

Allen Eshleman · « **Reply #2 on:** August 15, 2023, 12:13:03 PM »

The tank is set up with the fill line going almost full length to the clunk. It was tied together but the wire that tied the two came loose and I fished out the wire, so the other tube is in there but not connected to the clunk line.

Is it necessary to even have that second line in there? If so, what is the purpose of it? Would it be alright to take that line off the (brass???) tube that goes through the cap? My Hayes type tanks only have a soft plastic line with the clunk. I just fill them through the middle nipple.

I will check the centering of the tank again.

john e. holliday · « **Reply #3 on:** August 15, 2023, 01:37:35 PM »

Maybe your pick up tube and vent tube our too close together. I usually have at least a 1/2 inch between the ends.

Dave_Trible · « **Reply #4 on:** August 16, 2023, 10:51:29 AM »

I'd suspect it's glow plug related. I'd try a new and maybe hotter plug.

Dave

Brett Buck · « **Reply #5 on:** August 16, 2023, 08:03:05 PM »

Try less oil, particularly, less castor.

Brett

Reptoid · « **Reply #6 on:** August 17, 2023, 02:19:19 AM »

Define "Sputtering" rich or lean? Suction, Uniflo, or Muffler Pressure?
Everyone seems to be assuming you mean rich from their answers but: I've never seen a profile side mounted engine go rich on insides unless your tank is very high.
Generally on side mounted profiles running uniflo the tank has to be 1/8" to 1/4" above centerline for equal speed upright and inverted. If it's on the center you will get leaner insides and richer outsides.

Dennis Toth · « **Reply #7 on:** August 17, 2023, 12:26:44 PM »

Allen,
From what you described it sounds like you have the vent line set up like a uniflow except it is not following the fuel just sticking near the back flopping around. This is not good, you need to put another clunk weight on the end so it follows the fuel. Make sure your vent line is close to the fuse but above the fuse side by ~1/4". This keeps the vent in clean airflow with less pressure fluctuations. On profiles I do mine off the rear engine bolt with a short piece of copper tube soldered to a tab and connect the uniflow vent to it. To check inverted at least do a ground run and flip the ship over and see if it goes rich or lean and adjust that for stability consistent rpm. The FP's run better in a 2-2-2 setup high rpm/low pitch. Something like a 11-4 seems to be a good starting point for the prop. Don't try to fly to slow if you lines are 60' you want a lap time around 4.8 for 63' lines around 5.1.

Best, DennisT

Allen Eshleman · « **Reply #8 on:** August 17, 2023, 02:14:50 PM »

Thank-you all for the advice. Actually, it almost quits running for a split second. I want to follow the last advice first here to get the vent line where it should be. I will either wrap it together with the feed line inside the tank or put a clunk in it also. If that doesn't cure it, then I will do some of the other steps. I will also run a vent tube up into the propeller air.

Ken Culbertson · « **Reply #9 on:** August 17, 2023, 02:32:18 PM »

Quote from: Allen Eshleman on August 17, 2023, 02:14:50 PM

Thank-you all for the advice. Actually, it almost quits running for a split second. I want to follow the last advice first here to get the vent line where it should be. I will either wrap it together with the feed line inside the tank or put a clunk in it also. If that doesn't cure it, then I will do some of the other steps. I will also run a vent tube up into the propeller air.

Very un-OS. Are you sure the logo stamp was not covering up "FOX"? Glowplug, are you running a shielded? My 46LA ran steady as a rock in a fast 4 throughout the pattern with a shielded plug. Does it just come back on or does it go lean or rich. Does it also do it on outside loops?

IC is such fun - Ken

FYI, this is what an OS46 is supposed to sound like, clunk uniflow tank on muffler pressure (ignore the pattern, it sucks). Stock motor w/7mm venturi and ST needle valve was setup by Phillip Nichols for this run.

Brett Buck · « **Reply #10 on:** August 17, 2023, 06:24:42 PM »

Quote from: Allen Eshleman on August 17, 2023, 02:14:50 PM

Thank-you all for the advice. Actually, it almost quits running for a split second. I want to follow the last advice first here to get the vent line where it should be. I will either wrap it together with the feed line inside the tank or put a clunk in it also. If that doesn't cure it, then I will do some of the other steps. I will also run a vent tube up into the propeller air.

I would be very surprised if this turns out to be a tank problem. This is not a terribly uncommon problem, although it usually happens with inverted engines, not sidewinders. I would guess fuel (as noted above) or plug. If you are running it too slowly, it will be more prone to this, and if it is modified, then all bets are off.

Brett

Allen Eshleman · « **Reply #11 on:** August 17, 2023, 08:58:24 PM »

It didn't do this before. Just the last time out. I don't know what changed. I haven't looked at it again yet. Probably won't until Monday or so. I got the engine off e-bay. It was already set up for Stunt. Looks to be a Shtterman NVA with the 6mm venturi.

Colin McRae · « **Reply #12 on:** August 18, 2023, 08:25:41 AM »

The stock OS venturi size is 7 mm for the 40 and 46LA-s engines. The OS stock size is 6 mm on the 25 LA-s.

Steve Dwyer · « **Reply #13 on:** August 18, 2023, 09:59:25 AM »

How about trying a run with the muffler pressurizing the tank or switching out to a metal wedge tank (standard vented or uniflow) to see if the sputter goes away?

Ken Culbertson · « **Reply #14 on:** August 18, 2023, 10:21:21 AM »

Maybe we need a larger sample size that one session. Was that one flight or multiple? You said the motor run was OK before the fateful session? If that is the case, please don't mess with the fuel delivery system until you have put in a new glowplug. Everything that wears out and goes bad was working the flight before. A dead plug would quit, a dying one will act like that.

Ken

Allen Eshleman · « **Reply #15 on:** August 18, 2023, 04:24:22 PM »

It was three flights. I will make a few adjustments for next time out. It's not hard to make any of the adjustments mentioned.

BYU · « **Reply #16 on:** August 18, 2023, 08:35:05 PM »

Add a clunk to the second line , make sure it is at least 1/4 inch shorter than the fuel line , preferably 1/2 inch.
Do not tie the lines together.

The 46 with a stock 3.5 mm needle assy (shttrman) works best with the 25 size venturi.
If you drill the case for a 4mm tigre needle or similar , go with the larger 7mm venturi.
(This is a Randy Smith piece of guidance.)

Allen Eshleman · « **Reply #17 on:** August 19, 2023, 06:11:12 AM »

Add a clunk to the second line , make sure it is at least 1/4 inch shorter than the fuel line , preferably 1/2 inch.
Do not tie the lines together.

The 46 with a stock 3.5 mm needle assy (shttrman) works best with the 25 size venturi.
If you drill the case for a 4mm tigre needle or similar , go with the larger 7mm venturi.
(This is a Randy Smith piece of guidance.) (Quote from BYY above. I haven't figured out the quote mechanism yet}

I will add the clunk to the fill line and make it shorter. This one is the stock NVA and it will stay that way. I have several and I have some Smith NVA's so I will convert at least one to the larger NVA/venturi set-up. Thanks. That answers my other post.

Steve Helmick · « **Reply #18 on:** August 20, 2023, 06:42:49 PM »

Quote from: Allen Eshleman on August 19, 2023, 06:11:12 AM

Add a clunk to the second line , make sure it is at least 1/4 inch shorter than the fuel line , preferably 1/2 inch.
Do not tie the lines together.

The 46 with a stock 3.5 mm needle assy (shttrman) works best with the 25 size venturi.
If you drill the case for a 4mm tigre needle or similar , go with the larger 7mm venturi.
(This is a Randy Smith piece of guidance.) (Quote from BYY above. I haven't figured out the quote mechanism yet}

I will add the clunk to the fill line and make it shorter. This one is the stock NVA and it will stay that way. I have several and I have some Smith NVA's so I will convert at least one to the larger NVA/venturi set-up. Thanks. That answers my other post.

Click on the "quote" button on the upper right side of the post. I've seen some guys quote from two different posts, but other than to copy & paste one of them onto the other, I dunno how that would work.

Steve

Allen Eshleman · « **Reply #19 on:** August 20, 2023, 07:31:44 PM »

Quote from: Steve Helmick on August 20, 2023, 06:42:49 PM

Click on the "quote" button on the upper right side of the post. I've seen some guys quote from two different posts, but other than to copy & paste one of them onto the other, I dunno how that would work. Steve

I just did do the quote thing. How easy!

Allen Eshleman · « **Reply #20 on:** August 21, 2023, 07:52:57 PM »

Question: Inside the clunk tank, assuming the fill line is 1/2 in shorter than the feed line to the engine, both having clunks, does it matter how they are positioned inside the tank, as to higher and lower? I have worked on the tank a little reworked the tubing. However, there wasn't much there. I will fly it this way and see how it does. The next step will be to change the glow plug. (A funeral took my flying time today). I will also make sure the tank is positioned correctly in relation to the center of the spray bar, 1/8 to 1/4 inch above it. Then I will report.

Steve Dwyer · « **Reply #21 on:** August 22, 2023, 07:01:06 AM »

This summer I have to say has been my first year using clunk tanks, first on the Imitation Profile and second on the RD-1. Without chasing around here for the sketch I followed to configure both tanks (Sullivan rigid clear slanted outlet style) I installed the uniflow line at the midpoint of the outer tank wall. Midpoint meaning midpoint from the front to rear and top to bottom just touching the the tank wall using tubing cut at an angle to assure no blockage. On the RD-1 I have the tank mounted so I can easily adjust the height using a slider. What has worked best on both models is to simply position the center of the tank in-lign with the center of the engine and then slightly rotate the cap on the tank to assure the supply outlet line on the cap is positioned in-lign with the venturi inlet. You do, however, have to slightly adjust the position of the pickup, uniflow and clunk lines going through the tank cap when you rotate it. The pick up clunk is free to float up and down very close to the outer corners of the tank without touching. Yes there is a brief run away when the uniflow line is no longer submerged l but It's brief before the tank goes empty and a good signal, time is up. I have read if the uniflow is too close to the clunk, entering air can result in a disturbance of the fuel flow getting to the pick up. This set up has been working fine. I will add I had to tweak the cap outlet position on the RD-1 to get a similar performance from upright and inverted flight especially when climbing into an inside and outside loop respectively. Seems to work well for me.

Steve

Dave_Trible · « **Reply #22 on:** August 22, 2023, 08:36:54 AM »

When you are at the bottom of a loop you are at maximum fuel delivery- especially with clunk tank. The fuel and clunks are forced to the bottom of the tank so are totally submerged. Therefore fuel starvation cannot be the problem. The plug is being drowned by either being weak or the coil having a tater or being pushed up into the cavity (yes it still glows- means nothing- it’s trash) or as Brett suggests could be drowning in a little too much oil. It’s the simplest thing to check or fix. Why not try this first?

Dave

Dan McEntee · « **Reply #23 on:** August 22, 2023, 08:42:26 AM »

Quote from: Dave_Trible on August 22, 2023, 08:36:54 AM

When you are at the bottom of a loop you are at maximum fuel delivery- especially with clunk tank. The fuel and clunks are forced to the bottom of the tank so are totally submerged. Therefore fuel starvation cannot be the problem. The plug is being drowned by either being weak or the coil having a tater or being pushed up into the cavity (yes it still glows- means nothing- it’s trash) or as Brett suggests could be drowning in a little too much oil. It’s the simplest thing to check or fix. Why not try this first?

Dave

This could also be a symptom of the tank being mounted too high. Allen mentions having the tank centered on the centerline of the engine, but the physical location of the tank isn't critical, it's the location and position of the pick up and uniflow vent. There is lots more to add but I can't see the tank and model in question..
Type at you later,
Dan McEntee

Steve Dwyer · « **Reply #24 on:** August 22, 2023, 11:31:57 AM »

Quote from: Dave_Trible on August 22, 2023, 08:36:54 AM

When you are at the bottom of a loop you are at maximum fuel delivery- especially with clunk tank. The fuel and clunks are forced to the bottom of the tank so are totally submerged. Therefore fuel starvation cannot be the problem.
Dave

Dave, When entering the bottom of a loop the fuel should be migrating to the bottom rear of the tank with the clunk pick up following and remaining fully submerged. But if the tubing from the cap to the clunk is a little stiff or too short because the brass line is too long or dragging on the back of the tank and it takes longer for the centrifugal forces to bring it down into the fuel there could be a moment of "starvation". I did experience this and suspect this would be more of a concern with our use of short 3 to 4 oz tanks while the larger tanks used on RC would be less susceptible? Something to consider also, I ended up curling a piece of solder around the clunk tube connection to help it along but eventually the clunk and the weight came off. End of flight!!

Replacing an older plug goes without question before assuming anything else.

Steve

Reptoid · « **Reply #25 on:** August 22, 2023, 03:26:52 PM »

Since the OP based his post on "sputtering" and can't seem to tell us whether it was rich or lean, all of this advice is likely not going to fix the problem. He also said "it didn't do that on previous flights" I will say it again: Side mounted side exhaust engines do NOT go rich on inside loops, EVER unless the tank is Ludicrously high. As for too much oil; there are hundreds of LA46's out there running on GMA 22% oil fuel that run perfect. We fly them every week-end and experience no issues what so ever. In addition, we don't run idle bar plugs and they run perfect, 4-4, 4-2, wet 2-2 depending on aircraft and propeller. Any plug with a heat range in the #3 zone works fine, or Thunderbolt Std. Typically a properly designed Schnuerle port engine doesn't require an idle bar. Of course, none of us run a clunk tank with questionable plumbing and we know how to adjust a needle valve.
When people post questions about things like "Quits inverted", "Sputters", "Won't Start", "has no line tension" the most helpful thing to do is ask for more information and explain that you can't diagnose the problem without it. The OP's problem could be as simple as the needle setting is too lean (or too rich but doubtful)

Dan McEntee · « **Reply #26 on:** August 22, 2023, 08:12:11 PM »

Quote from: Steve Dwyer on August 22, 2023, 11:31:57 AM

Dave, When entering the bottom of a loop the fuel should be migrating to the bottom rear of the tank with the clunk pick up following and remaining fully submerged. But if the tubing from the cap to the clunk is a little stiff or too short because the brass line is too long or dragging on the back of the tank and it takes longer for the centrifugal forces to bring it down into the fuel there could be a moment of "starvation". I did experience this and suspect this would be more of a concern with our use of short 3 to 4 oz tanks while the larger tanks used on RC would be less susceptible? Something to consider also, I ended up curling a piece of solder around the clunk tube connection to help it along but eventually the clunk and the weight came off. End of flight!!

Replacing an older plug goes without question before assuming anything else.

Steve

How do you know all of that?? Some where on this forum is a video some one posted of a flight with a small camera on top of the outboard wing root of a profile model and pointing forward at the back of a Sullivan tank mounted with the widest part of the RST tank against the fuselage. He flew a regular pattern and I was amazed at how little the fuel sloshed around. If the airplane is flying a typical 5+ second lap, the fuel load stay pinned against the outboard surface. On loops I don't think it varied at all and on squares it moved very little. As the fue load burned down to a certain point, then it used up the remaining load with the load running from the front to the back. This is one of the reasons you usually can't do a cutoff loop with a clunk tank. There is a lot more fuel present until the end than with a wedge tank. There is a lot we don't know about this specific situation and really need to know more, but my money is on the guess that it is "sputtering" rich from the tank being too high, and just not set up correctly.
Type at you later,
Dan McEntee

Steve Dwyer · « **Reply #27 on:** August 23, 2023, 05:20:00 AM »

I'd like to see the video Dan, just thinking out loud here like most. If only we could be like in the movie where someone was shrink into a capsule and placed into the blood stream to travel about we'd easily se what's going on here for sure.

Steve

Dave Hull · « **Reply #28 on:** August 23, 2023, 05:23:49 PM »

Here's the first of them.

https://stunthanger.com/smf/open-forum/in-flight-videos-on-youtube/msg527018/#msg527018

Dave

Steve Dwyer · « **Reply #29 on:** August 24, 2023, 10:23:25 AM »

After watching the video I must say the movement of the fuel in relation to the clunk pick up is still a mystery. Yes the fuel appears to stay relatively static in the rear outer corners of the tank following the configuration of the airplane in flight. But we cannot determine here whether the clunk pick up comes out of the fuel momentarily as the airplane changes configuration? We cannot see inside the tank to verify this point. BUT how do we know if this potential sudden void in fuel is causing a sputter problem? I’m reconsidering my thinking here.

So now my curiosity leads me to wonder what fuel starvation really means and if this is not another problem after all. Don't we often see bubbles in the fuel line reaching the venturi on a good running engine that performs well in flight? What is really taking place at the spray bay venturi (eductor)? Doesn’t the engine take what fuel it receives from the (bubble/fuel) mixture and we adjust the volume of fuel flashing into the engine by turning the needle valve to achieve the rpm? Does the clunk momentarily falling away from the fuel result in a fuel interruption enough to cause a sputter? I'm beginning to doubt this. We all know tank height position relative to the ventri inlet can affect the “pressure head” of fuel at the venturi in flight. Wouldn’t a sudden fuel pressure change at the venturi have a direct effect on the volume (richness) entering the engine causing a sputter? Why does this occur on some engines and not others? What about plug heat range? Could this all be related to the choke area/velocity and flow configuration within different engines? I'd sure like to learn more, from some of the experts out there.

Steve

Ken Culbertson · « **Reply #30 on:** August 24, 2023, 11:29:23 AM »

Until Allen gives us some more test info we are all guessing as to what "sputter" means and what the problem, hence solution is. So, what are factors, and my guess:

1. Tank position
2. Plumbing
3. Spray bar
4. Needle valve
5. Glow Plug.
6. Engine Make

Now ask yourself which of these can change on their own.
1. No - IT IS NOT THE TANK
2. Maybe a leak - Only sputters in one place, questionable
3. Possibly coming loose - See #2
4. Not by itself but a possible cause - again see #2.
5. YES - Spoiler Alert - It is the plug.
6. It is not a Fox

If we have checked and therefore eliminated 2 and 3 what is left? Why is changing the glow plug not the first thing you try?

Sputter to me means that the high fuel pressure is flooding the glow plug but not putting it out before the pressure normalizes. Either a hotter plug or an idle bar should cure this problem. Sometimes it really is the simplest solution.

Now you can start to appreciate why so many are going electric - Ken

PS - If it turns out to not be the glow plug this post was made by a hacker impersonating me.

Steve Dwyer · « **Reply #31 on:** August 24, 2023, 12:29:55 PM »

Now you can start to appreciate why so many are going electric - Ken

But Ken, electric motors have no personality, they only know load and voltage. Be kinda like being married to a Stepford Wife.

Steve

Ken Culbertson · « **Reply #32 on:** August 24, 2023, 12:43:28 PM »

Quote from: Steve Dwyer on August 24, 2023, 12:29:55 PM

Now you can start to appreciate why so many are going electric - Ken

But Ken, electric motors have no personality, they only know load and voltage. Be kinda like being married to a Stepford Wife.

Steve

Stepford Wives don't sputter.

Ken

Allen Eshleman · « **Reply #33 on:** September 09, 2023, 12:00:11 PM »

I reworked the tank plumbing by shortening the "fill" line a bit. It still acted about the same.

Then...............................

I changed the glow plug. Bingo! Running much better. I use S&W 11 1/2 11 1/2 with 10 % nitro. No more sputtering at the bottoms of maneuvers. Thank you all very much.

Brett Buck · « **Reply #34 on:** September 09, 2023, 01:42:36 PM »

Quote from: Allen Eshleman on September 09, 2023, 12:00:11 PM

I reworked the tank plumbing by shortening the "fill" line a bit. It still acted about the same.

Then...............................

I changed the glow plug. Bingo! Running much better. I use S&W 11 1/2 11 1/2 with 10 % nitro. No more sputtering at the bottoms of maneuvers. Thank you all very much.

Check the plug, see if it has a glob of something on the element - a "tater". If so, then switch to Powermaster.

Brett

Joe Ed Pederson · « **Reply #35 on:** September 09, 2023, 03:42:26 PM »

Quote from: Ken Culbertson on August 24, 2023, 11:29:23 AM

Now you can start to appreciate why so many are going electric - Ken

It took me a while to catch that Paul Walker's trimming charts assume you fly electric. He says the first thing is to get the wings level -- and of course you can do that with a tank that's a little too high or low, not the best needle setting, or lap times that are out of whack, BUT it seems to me, that with an IC motor model, getting the engine run right is right up there in priority with getting the wings level. And getting the perfect IC motor run can be a bear. And attaining the perfect run doesn't mean a dying glow plug can't mess it up, or air leak, tank leak, filter leak, bad fuel, etc. etc.

I read somewhere that a dirty glow plug can sometimes be saved by soaking it in acetone overnight. Anyone have experience with that?

But I still like IC motors.

And I am building an electric model so I can practice early in the morning without angering the people close to my flying field here in town.

Joe Ed Pederson

Brett Buck · « **Reply #36 on:** September 09, 2023, 04:10:00 PM »

Quote from: Joe Ed Pederson on September 09, 2023, 03:42:26 PM

It took me a while to catch that Paul Walker's trimming charts assume you fly electric. He says the first thing is to get the wings level -- and of course you can do that with a tank that's a little too high or low, not the best needle setting, or lap times that are out of whack, BUT it seems to me, that with an IC motor model, getting the engine run right is right up there in priority with getting the wings level. And getting the perfect IC motor run can be a bear. And attaining the perfect run doesn't mean a dying glow plug can't mess it up, or air leak, tank leak, filter leak, bad fuel, etc. etc.

I don't think that flowchart assumes electric. But, certainly, even small detail changes in the way the engine runs can have a huge effect on the way the airplane flies. I thought Billy was nuts when he said that the engine run was 90% of the game. Since then, I think he underestimated it.

Brett

realSteveSmith · « **Reply #37 on:** September 09, 2023, 04:33:13 PM »

Quote from: Joe Ed Pederson on September 09, 2023, 03:42:26 PM

I read somewhere that a dirty glow plug can sometimes be saved by soaking it in acetone overnight. Anyone have experience with that?

This sounds like the kind of thing that could leave a guy chasing his tail for hours...and wasting precious time at the field. Once a plug self-identifies as a problem, throw it away and move on. Remember, you can always get more money....you can never get more time.

Ken Culbertson · « **Reply #38 on:** September 09, 2023, 05:04:28 PM »

Quote from: realSteveSmith on September 09, 2023, 04:33:13 PM

This sounds like the kind of thing that could leave a guy chasing his tail for hours...and wasting precious time at the field. Once a plug self-identifies as a problem, throw it away and move on. Remember, you can always get more money....you can never get more time.

but then "time is money"? Confusing
Glad he finally figured out that the thing most likely to go wrong is more often than not the thing that went wrong. Try that one first!

Ken