OS .55AX problem???
09-07-2008, 07:34 PM
#26
RE: OS .55AX problem???
ORIGINAL: show871
I stand corrected!.. But for some reason, the bottom few inches of my jugs produce dead sticks. I wonder why then? I just assumed it was moisture
I stand corrected!.. But for some reason, the bottom few inches of my jugs produce dead sticks. I wonder why then? I just assumed it was moisture
09-08-2008, 12:32 AM
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RE: OS .55AX problem???
i wouldn,t be using a jett stream muffler on a 3D model as these mufflers do produce a slight power band like normal tuned pipes and you really dont want this when doing 3D stuff. use the stock muffler supplied with the engine and find the right prop combo.
09-14-2008, 02:23 AM
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RE: OS .55AX problem???
Andres try a Macs muffler the one for OS 46 fits ok and engine have better exhaust , I have my 55 Ax with it and runs very well.
Saludos de MĂ©xico.
Rafa
Saludos de MĂ©xico.
Rafa
10-04-2008, 10:31 PM
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RE: OS .55AX problem???
After reading both pages I've found lots of sound Ideas. I have 3 AX 55 on 3 3D profiles I have run every combo prop. APC 12.25X3.75 12x4 13x4 13x4W zinger pro 12x4 13x4 Axor 12x4 13x4 MAS 12x4 13x4 balanced everything. I've found the high needle has a very large adjustment. The low needle also has a lot of adjustment. Castor has helped lots but I still get dead sticks. I pinch the line at an idle and at full throttle runs great and dies 3 minutes later. I'm not new to RC 2 stroke motors. Air bubbles don't show up on the ground. Glow plugs are OS #8s everything is tight I don't think I'm getting air leaks. I'm not alone one of my flying buddies has the same setup and dead sticks every flight!
10-05-2008, 05:24 PM
#31
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RE: OS .55AX problem???
Andres and especially Bob Brassell,
Fuel foaming??? Come on and get off this nonsense!
1. Even if the fuel contains no anti-foam agents and vibrations are such that foam forms in the tank, fuel foam will never attain the consistency of thick lather... It will never be thick enough to support the weight of the cluck and to hold it out of the liquid fuel on the bottom of the tank (or where acceleration forces carry it).
2. A fuel tank full of foam is actually the equivalent of 2-5 cc of liquid fuel... not a really large amount that would noticeably reduce the level of the liquid fuel in the tank.
3. Vibrations (from insufficient fuel tank isolation, or very high RPM vibration levels) cause the walls of the fuel-tank to vibrate and even to reverberate, deflecting the clunk all over the place and also up in the air/fuel foam, above the liquid fuel in the tank. The result; whenever the clunk is not in the liquid fuel, it ingests air, causing bubbles to appear in the fuel-line. But this is still not caused by fuel-foaming in the tank...
4. The reasons a bladder-tank (within an external rigid tank) works so well are:
...A. The bladder contains only liquid fuel and virtually no air, so the only substance the fuel pickup can ingest is liquid fuel.
...B. There is no clunk to jump around and even if there is one, it cannot 'leap' anyplace where it can find air to ingest...
...C. With no air in the same space as the fuel, fuel foam obviously cannot be 'churned out', but the lack thereof is not the reason for the bladder-tank to work so wonderfully.
So, even if fuel-foam does form, blaming it for all your engine's maladies, is somewhere between a myth and a wife's tale...
Fuel foaming??? Come on and get off this nonsense!
1. Even if the fuel contains no anti-foam agents and vibrations are such that foam forms in the tank, fuel foam will never attain the consistency of thick lather... It will never be thick enough to support the weight of the cluck and to hold it out of the liquid fuel on the bottom of the tank (or where acceleration forces carry it).
2. A fuel tank full of foam is actually the equivalent of 2-5 cc of liquid fuel... not a really large amount that would noticeably reduce the level of the liquid fuel in the tank.
3. Vibrations (from insufficient fuel tank isolation, or very high RPM vibration levels) cause the walls of the fuel-tank to vibrate and even to reverberate, deflecting the clunk all over the place and also up in the air/fuel foam, above the liquid fuel in the tank. The result; whenever the clunk is not in the liquid fuel, it ingests air, causing bubbles to appear in the fuel-line. But this is still not caused by fuel-foaming in the tank...
4. The reasons a bladder-tank (within an external rigid tank) works so well are:
...A. The bladder contains only liquid fuel and virtually no air, so the only substance the fuel pickup can ingest is liquid fuel.
...B. There is no clunk to jump around and even if there is one, it cannot 'leap' anyplace where it can find air to ingest...
...C. With no air in the same space as the fuel, fuel foam obviously cannot be 'churned out', but the lack thereof is not the reason for the bladder-tank to work so wonderfully.
So, even if fuel-foam does form, blaming it for all your engine's maladies, is somewhere between a myth and a wife's tale...
10-07-2008, 12:37 PM
#32
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RE: OS .55AX problem???
"Fuel Foaming": an American term to colloquially define what happens when a model engine's vibrations are allowed to vibrate the fuel tank and the fuel in it such that the air in the tank is agitated into the fuel. This adds air to the fuel that is being picked-up by the internal fuel pickup line and effectively leans the mixture.
Symptoms are an engine that is running very lean and will not richen easily unless the high-speed needle valve is turned out a large amount. The engine will then suddenly stop running very lean and start running very rich. That's because the vibration level in the tank will become low enough that the air will no longer be agitated into the fuel. The engine can then be gradually leaned towards peak RPM. At some point, the RPM of the engine can reach the point where the fuel in the tank starts being agitated enough to mix air back into it, and the process repeats.
Many times, "fuel foaming" will happen in the air and not on the ground. That's because the model's modes of vibration are restrained on the ground by the modeler holding it and by the model's wheels. In the air, it is free to vibrate in all directions.
Fuel foaming can be reduced or eliminated by well-balanced propellers and spinners, isolating the engine from the airframe, and by using vibration-absorbing foam rubber (or similar product) around the fuel tank.
Symptoms are an engine that is running very lean and will not richen easily unless the high-speed needle valve is turned out a large amount. The engine will then suddenly stop running very lean and start running very rich. That's because the vibration level in the tank will become low enough that the air will no longer be agitated into the fuel. The engine can then be gradually leaned towards peak RPM. At some point, the RPM of the engine can reach the point where the fuel in the tank starts being agitated enough to mix air back into it, and the process repeats.
Many times, "fuel foaming" will happen in the air and not on the ground. That's because the model's modes of vibration are restrained on the ground by the modeler holding it and by the model's wheels. In the air, it is free to vibrate in all directions.
Fuel foaming can be reduced or eliminated by well-balanced propellers and spinners, isolating the engine from the airframe, and by using vibration-absorbing foam rubber (or similar product) around the fuel tank.
10-07-2008, 01:04 PM
#33
Senior Member
RE: OS .55AX problem???
Bill,
No matter how vigorously the fuel tank is agitated by engine vibration, the air bubbles that form within the fuel will never remain suspended throughout the volume of fuel, or for that matter, anywhere near the clunk.
Any fuel foam (bubble concentration) will be on top of the fuel, or opposite where the G forces put the liquid fuel...
Since gravity and the G forces will also draw the clunk to where the liquid fuel is, the only effect that can temporarily place the clunk where the bubbles are, is its deflection off the tank walls, due to non-isolated vibration.
This will happen, whether the emptied volume of the tank is full of fuel foam, or full of air, with nary single bubble of foam.
It will also happen to the same extent in both instances.
So, 'fuel-foaming' is very much a misleading term to describe this phenomenon.
No matter how vigorously the fuel tank is agitated by engine vibration, the air bubbles that form within the fuel will never remain suspended throughout the volume of fuel, or for that matter, anywhere near the clunk.
Any fuel foam (bubble concentration) will be on top of the fuel, or opposite where the G forces put the liquid fuel...
Since gravity and the G forces will also draw the clunk to where the liquid fuel is, the only effect that can temporarily place the clunk where the bubbles are, is its deflection off the tank walls, due to non-isolated vibration.
This will happen, whether the emptied volume of the tank is full of fuel foam, or full of air, with nary single bubble of foam.
It will also happen to the same extent in both instances.
So, 'fuel-foaming' is very much a misleading term to describe this phenomenon.
10-07-2008, 01:55 PM
#34
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RE: OS .55AX problem???
Dar,
Air and gasses of all types can becomes suspended/disolved in a fluid solution. Some gas is disolved there in its natural state.
There is oxygen gas disolved in sea water or common fresh tap water (as an example). Fish breath this disolved oxygen. The oxygen exists throughout the volume of water, not just floating on top. If you have stagnet water where the water is not moving/splashing/airating in some fashion to allow oxygen to enter and disolve in the water, fish die. This is basic example.
Fuel is not any different. Add energy to it in the form of vibration, and it will readily disolved and retain the surrounding atmosphere. Sure, remove the energy, and the larger bubbles come out of solution quickly, some remains disolved in the liquid a longer period of time.
Simply pull a vacuum on fuel and watch how foams up from the natural disolved gasses coming out of solution (just like depressurizing a pop bottle). In fact, this is observable on some remote-needle systems since the pressure drop occurs at the needle - microbubbles and disolved gases can and do come out of solution and turn into visible bubbles (under the right/wrong conditions with vibration energy and/or heat energy to help out).
"Fuel foaming", or what ever you like to term it, can be and has been scientifically observed, characterized, replicated and can be prevented. Even full size JP-8 military aircraft jet fuel contains "anti-foaming agents" in its chemestry.
No need to elaborate further.
Bob
Air and gasses of all types can becomes suspended/disolved in a fluid solution. Some gas is disolved there in its natural state.
There is oxygen gas disolved in sea water or common fresh tap water (as an example). Fish breath this disolved oxygen. The oxygen exists throughout the volume of water, not just floating on top. If you have stagnet water where the water is not moving/splashing/airating in some fashion to allow oxygen to enter and disolve in the water, fish die. This is basic example.
Fuel is not any different. Add energy to it in the form of vibration, and it will readily disolved and retain the surrounding atmosphere. Sure, remove the energy, and the larger bubbles come out of solution quickly, some remains disolved in the liquid a longer period of time.
Simply pull a vacuum on fuel and watch how foams up from the natural disolved gasses coming out of solution (just like depressurizing a pop bottle). In fact, this is observable on some remote-needle systems since the pressure drop occurs at the needle - microbubbles and disolved gases can and do come out of solution and turn into visible bubbles (under the right/wrong conditions with vibration energy and/or heat energy to help out).
"Fuel foaming", or what ever you like to term it, can be and has been scientifically observed, characterized, replicated and can be prevented. Even full size JP-8 military aircraft jet fuel contains "anti-foaming agents" in its chemestry.
No need to elaborate further.
Bob
10-07-2008, 04:01 PM
#36
Senior Member
RE: OS .55AX problem???
Bob,
It is not gases which are in solution in the fuel (like oxygen in water), that occupy a significant enough volume of the fuel and cause the engine to run leaner than intended.
It is gases that are in suspension in the fuel, in their original gaseous state (you mention this in the fourth paragraph, but in a different context)... causing the fuel to appear somewhat opaque, that actually do take some of the fuel's volume and effectively lean the mixture. But even these bubbles are not prominent enough to be called 'fuel foam'.
Foam is in general mostly gaseous material, within small bubbles of liquid (with very thin walls).
And yes, there is some break-up of the fuel, usually due to rather high ambient temperatures (notoriously in older, metal remote needle OS.91FX engines), where some of the methanol component in the fuel actually evaporates and travels to the carburettor as bubbles... But this is not 'foaming' as such and it does not happen in the fuel-tank...
I still say that any and all cases blamed on "fuel foaming", are actually cases where the clunk simply leaped all over the place, instead of remaining submerged in liquid fuel; and ingested air from the 'vacant' areas of the tank.
It is not gases which are in solution in the fuel (like oxygen in water), that occupy a significant enough volume of the fuel and cause the engine to run leaner than intended.
It is gases that are in suspension in the fuel, in their original gaseous state (you mention this in the fourth paragraph, but in a different context)... causing the fuel to appear somewhat opaque, that actually do take some of the fuel's volume and effectively lean the mixture. But even these bubbles are not prominent enough to be called 'fuel foam'.
Foam is in general mostly gaseous material, within small bubbles of liquid (with very thin walls).
And yes, there is some break-up of the fuel, usually due to rather high ambient temperatures (notoriously in older, metal remote needle OS.91FX engines), where some of the methanol component in the fuel actually evaporates and travels to the carburettor as bubbles... But this is not 'foaming' as such and it does not happen in the fuel-tank...
I still say that any and all cases blamed on "fuel foaming", are actually cases where the clunk simply leaped all over the place, instead of remaining submerged in liquid fuel; and ingested air from the 'vacant' areas of the tank.
10-07-2008, 04:56 PM
#39
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RE: OS .55AX problem???
After reading both pages I've found lots of sound Ideas. I have 3 AX 55 on 3 3D profiles I have run every combo prop. APC 12.25X3.75 12x4 13x4 13x4W zinger pro 12x4 13x4 Axor 12x4 13x4 MAS 12x4 13x4 balanced everything. I've found the high needle has a very large adjustment. The low needle also has a lot of adjustment. Castor has helped lots but I still get dead sticks. I pinch the line at an idle and at full throttle runs great and dies 3 minutes later. I'm not new to RC 2 stroke motors. Air bubbles don't show up on the ground. Glow plugs are OS #8s everything is tight I don't think I'm getting air leaks. I'm not alone one of my flying buddies has the same setup and dead sticks every flight!
Sorry to hear you are having the same problem I had, This engine was driving me crazy too.
As I said in post 21, the big difference was after I added Castor oil to my fuel and changed the plug from an F to an 8. Now, the engine is running perfect, starts with one flip and has insane power with Jett muffler. I have adjusted the carb a little bit better and with some expo in the throttle, I have better midrange for 3D now.
Maybe you don't have enough castor in your fuel ??, try adding al little bit more...
Andres
10-08-2008, 08:16 AM
#40
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RE: OS .55AX problem???
ORIGINAL: DarZeelon
I still say that any and all cases blamed on "fuel foaming", are actually cases where the clunk simply leaped all over the place, instead of remaining submerged in liquid fuel; and ingested air from the 'vacant' areas of the tank.
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I still say that any and all cases blamed on "fuel foaming", are actually cases where the clunk simply leaped all over the place, instead of remaining submerged in liquid fuel; and ingested air from the 'vacant' areas of the tank.
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You can have fuel foam/bubble/air issues on a fixed pick up too. My QM15 tanks were fixed pickup. Just ask a CL vet too. Additionally fuel issues can occur with a full tank of fuel... not sure if the clunk can jump that high just from vibration maybe but it would be a stretch. Amazing what a set of out-of-balance main rotor blades can do in a helicopter to turn the tank into a violent bubbly mess.
To move beyond this, and to allow the thread to get back to the original posting subject - it is clear you have an opinion on the matter, and that is fine.
But please do not profess that opinion, that fuel foaming is not "real" fuel system issue that must be properly addressed, to anyone owning and operating a Jett engine.
10-08-2008, 08:58 AM
#41
Senior Member
RE: OS .55AX problem???
Bob,
I am sure you understand that I am not in this thread to argue for the sake of it...
After all, Andres is using a 'run of the mill' OS.55AX, with a large 3D prop, at quite a sane 14K.
These are not conditions that can potentially 'gassify' the methanol out of the fuel mixture, or cause suction of bubbles with a fixed clunk, as you describe in you last post.
With a reasonably well isolated fuel tank, this installation should allow the engine to suck-up, all but the last 10-15 cc of fuel from the tank.
It should cause no problems with the tank over ÂĽ full.
If the clunk is actually sucking from where the liquid fuel is located, hardly any bubbles should appear in the fuel-line.
If the clunk is NOT where the liquid fuel is, because it is bouncing all about the tank, air bubbles will appear in the fuel-line.
These bubbles will appear whether or not fuel foaming has occurred in the tank.
So, what I am saying is not that fuel-foaming does not happen... After all, Andres did see foam in the tank (but he did not mention if there were also gas bubbles in the fuel-line to the engine...). I am saying fuel foaming is not the issue; especially not in such 'civil type' models that don't vibrate at 30+K all day...
I am sure you understand that I am not in this thread to argue for the sake of it...
After all, Andres is using a 'run of the mill' OS.55AX, with a large 3D prop, at quite a sane 14K.
These are not conditions that can potentially 'gassify' the methanol out of the fuel mixture, or cause suction of bubbles with a fixed clunk, as you describe in you last post.
With a reasonably well isolated fuel tank, this installation should allow the engine to suck-up, all but the last 10-15 cc of fuel from the tank.
It should cause no problems with the tank over ÂĽ full.
If the clunk is actually sucking from where the liquid fuel is located, hardly any bubbles should appear in the fuel-line.
If the clunk is NOT where the liquid fuel is, because it is bouncing all about the tank, air bubbles will appear in the fuel-line.
These bubbles will appear whether or not fuel foaming has occurred in the tank.
So, what I am saying is not that fuel-foaming does not happen... After all, Andres did see foam in the tank (but he did not mention if there were also gas bubbles in the fuel-line to the engine...). I am saying fuel foaming is not the issue; especially not in such 'civil type' models that don't vibrate at 30+K all day...
10-08-2008, 09:20 AM
#42
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RE: OS .55AX problem???
Dude.....
This is perhaps the worst fuel-foaming plane I encounter in the past few years.
AeroWorks 40 size edge.
Jett 76L engine, turbo-jett
14x4W APC at 11,000 rpm peak
Similar enough to the run-of-the-mill OS55AX with a large 3D prop - to allow me to continue
Clearly not a 30K rpm racing plane.
I was able to duplicate the foam resonance on the ground while observing the fuel tank. The entire airframe had a harmonic in it that went nuts around 9500 rpm and shook the fuel like crazy. Everything added up to the "wrong" situation.
Engine ran fine, tank didnt foam, even at the same rpm, with a Zinger 14x4, or regular APC 14x6. Completely different harmonic.
Stock ARF 10oz tank installation was just not easily padded.
I installed a 8oz bubble-jett tank anyway because I needed more usable fuel anyway.
Problem went away entirely. Took 5 minutes. Done.
Although the 14x4W prop was balanced, I later found that the hole was not perfectly centered in the hub. That may have contributed.
Again, teach people what you will.
This is perhaps the worst fuel-foaming plane I encounter in the past few years.
AeroWorks 40 size edge.
Jett 76L engine, turbo-jett
14x4W APC at 11,000 rpm peak
Similar enough to the run-of-the-mill OS55AX with a large 3D prop - to allow me to continue
Clearly not a 30K rpm racing plane.
I was able to duplicate the foam resonance on the ground while observing the fuel tank. The entire airframe had a harmonic in it that went nuts around 9500 rpm and shook the fuel like crazy. Everything added up to the "wrong" situation.
Engine ran fine, tank didnt foam, even at the same rpm, with a Zinger 14x4, or regular APC 14x6. Completely different harmonic.
Stock ARF 10oz tank installation was just not easily padded.
I installed a 8oz bubble-jett tank anyway because I needed more usable fuel anyway.
Problem went away entirely. Took 5 minutes. Done.
Although the 14x4W prop was balanced, I later found that the hole was not perfectly centered in the hub. That may have contributed.
Again, teach people what you will.
10-08-2008, 09:41 AM
#43
My Feedback: (11)
RE: OS .55AX problem???
One more statement about this....
"Fuel foaming" is the term used. I've NEVER observed a clunk being thrashed about a fuel tank when it was in a high-vibration environment, and that means the fuel tanks on lightweight profile models, where the airframe doesn't provide a lot of vibration dampening. I HAVE observed fuel being thrashed about the fuel tank. While the clunk on the fuel pickup remained submerged in fuel, there was enough movement of the surface of the fuel to produce bubbles on the surface. That also means that some air was also being agitated deeper into the fuel. The engine would start running very lean when this happened.
Be it what you want to call it, the phenomenon exists. Change the vibration mode and it will go away, and the needle will operate normally. During "fuel foaming", the engine will not richen until you have turned the needle a significant amount, and then the engine will drop to very, very rich operation. You can then lean the engine. At some point, the RPM will then go back into the RPM range that excites the fuel in the tank and you get "fuel foaming" again. The engine will suddenly jump to a very lean state.
This has been observed by modelers at all levels of competence for decades, and has been written about over those same decades. I first read about it myself in the early 1960's in engine columns by Peter Chinn, Clarence Lee, and others. It's real, and it happens. The name may not be quite exact, but it does adequately-describe what happens.
'nuff said.
"Fuel foaming" is the term used. I've NEVER observed a clunk being thrashed about a fuel tank when it was in a high-vibration environment, and that means the fuel tanks on lightweight profile models, where the airframe doesn't provide a lot of vibration dampening. I HAVE observed fuel being thrashed about the fuel tank. While the clunk on the fuel pickup remained submerged in fuel, there was enough movement of the surface of the fuel to produce bubbles on the surface. That also means that some air was also being agitated deeper into the fuel. The engine would start running very lean when this happened.
Be it what you want to call it, the phenomenon exists. Change the vibration mode and it will go away, and the needle will operate normally. During "fuel foaming", the engine will not richen until you have turned the needle a significant amount, and then the engine will drop to very, very rich operation. You can then lean the engine. At some point, the RPM will then go back into the RPM range that excites the fuel in the tank and you get "fuel foaming" again. The engine will suddenly jump to a very lean state.
This has been observed by modelers at all levels of competence for decades, and has been written about over those same decades. I first read about it myself in the early 1960's in engine columns by Peter Chinn, Clarence Lee, and others. It's real, and it happens. The name may not be quite exact, but it does adequately-describe what happens.
'nuff said.
10-08-2008, 11:23 AM
#44
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RE: OS .55AX problem???
Well, I've been reading this intently as I have the same problem. I have 2 OS 55AX's on profiles. They are the most powerful engine I have and also the most frustrating. I have worked together with Victor on our engines (5 total) and all our other motors work fine...except the 55's.
We have adjusted the needles endlessly. I have had every type foam I can think of under the tanks. Replace the lines numerous times. Positioned the tanks in various locations. I do have a sintered bronze pickup in the tank at the moment. One of mine is currently doing pretty good but the other one is driving me nuts. (a short drive I realize)
I am going to check the engine bolts for tightness. I will mention one thing I did once last summer was at home with the plane tethered to a bench it would not run or transition well no matter what. It wouldn't even maintain even RPM's unless it was wide open. I C-clamped a 2x4 on the bench sticking up vertically right in front of the wing beside the tank. I took the tank rubber bands off & strapped the tank to the 2x4 instead of the plane & the engine ran perfect...put back on the plane & probem was back. Did this a few time to prove to myself....It IS the vibration of the plane causing it. Ive had mine run somewhat reliable until the foam under the tank loses it "memory". replace the foam, use light rubber banding to hold tank in place & it helps.....I have also lost the tank during a radical manuver because it was so loose
I have always kept the props balanced. I have always kept the stock mufflers. I have not removed the baffles.
I don't know exactly why one of mine is doing ok now but I'm glad cause its my favorite plane. I think the only difference is it has the sintered bronze pickup & the other doesn't. At the same time I never know when I fire it up what to expect.
I will stay tuned...
Ken
We have adjusted the needles endlessly. I have had every type foam I can think of under the tanks. Replace the lines numerous times. Positioned the tanks in various locations. I do have a sintered bronze pickup in the tank at the moment. One of mine is currently doing pretty good but the other one is driving me nuts. (a short drive I realize)
I am going to check the engine bolts for tightness. I will mention one thing I did once last summer was at home with the plane tethered to a bench it would not run or transition well no matter what. It wouldn't even maintain even RPM's unless it was wide open. I C-clamped a 2x4 on the bench sticking up vertically right in front of the wing beside the tank. I took the tank rubber bands off & strapped the tank to the 2x4 instead of the plane & the engine ran perfect...put back on the plane & probem was back. Did this a few time to prove to myself....It IS the vibration of the plane causing it. Ive had mine run somewhat reliable until the foam under the tank loses it "memory". replace the foam, use light rubber banding to hold tank in place & it helps.....I have also lost the tank during a radical manuver because it was so loose
I have always kept the props balanced. I have always kept the stock mufflers. I have not removed the baffles.
I don't know exactly why one of mine is doing ok now but I'm glad cause its my favorite plane. I think the only difference is it has the sintered bronze pickup & the other doesn't. At the same time I never know when I fire it up what to expect.
I will stay tuned...
Ken
10-08-2008, 11:59 AM
#45
Senior Member
RE: OS .55AX problem???
OK, Bill, Bob,
Maybe you are both right... I can accept that.
It is just that from what I have seen in the models that I observed, I never saw any model that had its resonance issues so extreme, as to cause bubbles to actually get low enough in the tank, to be picked up by the clunk... Maybe you have seen more models than I and did encounter a few such cases.
I did, however, see quite a few models that had the clunk jumping about; deflected from the tank walls... This was apparently caused by improper tank installation (insufficient vibration isolation). Some did show fuel-foam and others didn't, but all suffered from repeated dead-sticks...
I have never personally experienced this in any model I had built/assembled.
Also, there were a few models I observed, with some 'non anti-foam' fuels, that at high RPM, repeatedly churned the fuel so hard that the empty volume of their tank almost resembled the inside of a Twinkie™... But still, they still never suffered from air in the fuel-line, dead-sticks, or from lean-runs, since the clunk was always submerged in the liquid fuel.
Maybe you are both right... I can accept that.
It is just that from what I have seen in the models that I observed, I never saw any model that had its resonance issues so extreme, as to cause bubbles to actually get low enough in the tank, to be picked up by the clunk... Maybe you have seen more models than I and did encounter a few such cases.
I did, however, see quite a few models that had the clunk jumping about; deflected from the tank walls... This was apparently caused by improper tank installation (insufficient vibration isolation). Some did show fuel-foam and others didn't, but all suffered from repeated dead-sticks...
I have never personally experienced this in any model I had built/assembled.
Also, there were a few models I observed, with some 'non anti-foam' fuels, that at high RPM, repeatedly churned the fuel so hard that the empty volume of their tank almost resembled the inside of a Twinkie™... But still, they still never suffered from air in the fuel-line, dead-sticks, or from lean-runs, since the clunk was always submerged in the liquid fuel.
10-08-2008, 11:44 PM
#46
RE: OS .55AX problem???
What the heck, I'll dive into this too. Fuel foaming is a well known issue especially with CL profile models and an engine only turning maybe 10,000 revs. In a profile model the nose area is very rigid in the vertical direction but rather flexible sideways because of the lack of structure. This can easily set up a harmonic vibration (tuning fork) caused by the inability to balance a single cylinder engine no matter if it's mounted upright or on its side. Mounting an engine at 45 degrees would be the best compromise if possible. However, with CL models when fuel foams the easy fix is just to use a prop that turns at a different rev (higher or lower) so the harmonic doesn't set in. The better way of course is simply to make the nose area a little more rigid which puts its harmonic vibration level much higher than the engine is capable of revving. With a pylon engine turning 30K you could likely get away with making the nose area less rigid. Of course it's not just the nose area that can cause the problem, the wings, tailplane etc can have their own particular modes of vibration.
Oh yes, and the other suggested cure for foaming is a shot of Armorall in the fuel. From what I've seen, castor is more likely to give foaming presumably because it gives a much higher surface tension to any bubbles. Armorall breaks the surface tension down to a point where the largest bubbles are only about the size of what you get in carbonated drinks.
Oh yes, and the other suggested cure for foaming is a shot of Armorall in the fuel. From what I've seen, castor is more likely to give foaming presumably because it gives a much higher surface tension to any bubbles. Armorall breaks the surface tension down to a point where the largest bubbles are only about the size of what you get in carbonated drinks.
10-09-2008, 02:19 AM
#47
Senior Member
My Feedback: (14)
RE: OS .55AX problem???
ORIGINAL: KenVW
Well, I've been reading this intently as I have the same problem. I have 2 OS 55AX's on profiles. They are the most powerful engine I have and also the most frustrating. I have worked together with Victor on our engines (5 total) and all our other motors work fine...except the 55's.
We have adjusted the needles endlessly. I have had every type foam I can think of under the tanks. Replace the lines numerous times. Positioned the tanks in various locations. I do have a sintered bronze pickup in the tank at the moment. One of mine is currently doing pretty good but the other one is driving me nuts. (a short drive I realize)
I am going to check the engine bolts for tightness. I will mention one thing I did once last summer was at home with the plane tethered to a bench it would not run or transition well no matter what. It wouldn't even maintain even RPM's unless it was wide open. I C-clamped a 2x4 on the bench sticking up vertically right in front of the wing beside the tank. I took the tank rubber bands off & strapped the tank to the 2x4 instead of the plane & the engine ran perfect...put back on the plane & probem was back. Did this a few time to prove to myself....It IS the vibration of the plane causing it. Ive had mine run somewhat reliable until the foam under the tank loses it "memory". replace the foam, use light rubber banding to hold tank in place & it helps.....I have also lost the tank during a radical manuver because it was so loose
I have always kept the props balanced. I have always kept the stock mufflers. I have not removed the baffles.
I don't know exactly why one of mine is doing ok now but I'm glad cause its my favorite plane. I think the only difference is it has the sintered bronze pickup & the other doesn't. At the same time I never know when I fire it up what to expect.
I will stay tuned...
Ken
Well, I've been reading this intently as I have the same problem. I have 2 OS 55AX's on profiles. They are the most powerful engine I have and also the most frustrating. I have worked together with Victor on our engines (5 total) and all our other motors work fine...except the 55's.
We have adjusted the needles endlessly. I have had every type foam I can think of under the tanks. Replace the lines numerous times. Positioned the tanks in various locations. I do have a sintered bronze pickup in the tank at the moment. One of mine is currently doing pretty good but the other one is driving me nuts. (a short drive I realize)
I am going to check the engine bolts for tightness. I will mention one thing I did once last summer was at home with the plane tethered to a bench it would not run or transition well no matter what. It wouldn't even maintain even RPM's unless it was wide open. I C-clamped a 2x4 on the bench sticking up vertically right in front of the wing beside the tank. I took the tank rubber bands off & strapped the tank to the 2x4 instead of the plane & the engine ran perfect...put back on the plane & probem was back. Did this a few time to prove to myself....It IS the vibration of the plane causing it. Ive had mine run somewhat reliable until the foam under the tank loses it "memory". replace the foam, use light rubber banding to hold tank in place & it helps.....I have also lost the tank during a radical manuver because it was so loose
I have always kept the props balanced. I have always kept the stock mufflers. I have not removed the baffles.
I don't know exactly why one of mine is doing ok now but I'm glad cause its my favorite plane. I think the only difference is it has the sintered bronze pickup & the other doesn't. At the same time I never know when I fire it up what to expect.
I will stay tuned...
Ken
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I have yet to see an engine that causes this type of problem. It is always related to the mechanical resonance of the model and the particular fuel tank installation.
However, I will say that I have seen situations where a more powerful engine can cause problems to arise in models that flew (performed) perfectly well with less powerful engines.
Ed Cregger
10-10-2008, 03:54 PM
#48
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Join Date: Jan 2006
Location: Floro, NORWAY
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RE: OS .55AX problem???
Has anyone checked their liners for any abnormal wear? I've seen similar issues and found defective liners! Just unscrew the cyl.head and check. It takes less than 5 minutes.
