OS AX 0.75 cutout at WOT
05-27-2010, 11:56 AM
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OS AX 0.75 cutout at WOT
Gentlemen:
I havae a curious problem that the glow-engine experts at my club have not yet been able to help me solve. I have an OS 0.75AX on a FourStar 60. Engine ran perfectly on a previous FourStar 60.
I have it mounted transversely (about 100* off vertical).
The issue now is that at WOT, the engine will die suddenly after 5-30 seconds of flawless running. The HS and LS needles seem about right; it will idle at about 2100 rpm, and usually takes the throttle well up to WOT.
Have checked for leaks in the fuel lines (no bubbles) and tank. Cleaned the (already clean) fuel filter. Have changed out the (OS#8) glow plug which seemed for a run or so to solve the problem, but then it recurred. Last eve, had a dead stick on climb out; the engine had been running well at idle, rose to peak RPM at WOT, took off smartly, gained 50 ft altitude, and died. No stumbling or galloping. It just died. Fortunately, I had enough airspeed and altitude to bring her down without damage.
What else should I be looking at?
Thanks in advance.
I havae a curious problem that the glow-engine experts at my club have not yet been able to help me solve. I have an OS 0.75AX on a FourStar 60. Engine ran perfectly on a previous FourStar 60.
I have it mounted transversely (about 100* off vertical).
The issue now is that at WOT, the engine will die suddenly after 5-30 seconds of flawless running. The HS and LS needles seem about right; it will idle at about 2100 rpm, and usually takes the throttle well up to WOT.
Have checked for leaks in the fuel lines (no bubbles) and tank. Cleaned the (already clean) fuel filter. Have changed out the (OS#8) glow plug which seemed for a run or so to solve the problem, but then it recurred. Last eve, had a dead stick on climb out; the engine had been running well at idle, rose to peak RPM at WOT, took off smartly, gained 50 ft altitude, and died. No stumbling or galloping. It just died. Fortunately, I had enough airspeed and altitude to bring her down without damage.
What else should I be looking at?
Thanks in advance.
05-27-2010, 12:01 PM
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RE: OS AX 0.75 cutout at WOT
Sounds lean.
Could be the needle or the fuel tank foaming once in the air. What airframe and how is the tank mounted?
Another possibility is a pitts style muffler not giving enough back-pressure.
Could be the needle or the fuel tank foaming once in the air. What airframe and how is the tank mounted?
Another possibility is a pitts style muffler not giving enough back-pressure.
05-27-2010, 12:08 PM
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RE: OS AX 0.75 cutout at WOT
Thanks
On a FourStar 60; tank mounted in the nose, right behind the firewall; I'm using the stock muffler.
The HS needle seems OK on the ground; when I hold the plane vertical the rpms don't sag.
On a FourStar 60; tank mounted in the nose, right behind the firewall; I'm using the stock muffler.
The HS needle seems OK on the ground; when I hold the plane vertical the rpms don't sag.
05-27-2010, 12:19 PM
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RE: OS AX 0.75 cutout at WOT
Make sure the tank is not solidly mounted. Wrap it in foam rubber so it can move independent of the airframe vibrations.
Other things to try:
An OS F plug
A sintered bronze fuel clunk, [link=http://www.shopatron.com/products/productdetail/part_number=161/101.0.1.1]http://www.shopatron.com/products/productdetail/part_number=161/101.0.1.1[/link]
If you can hold it vertical at WOT without sagging or dying, that points to vibrations foaming the fuel.
When you are holding it, you are dampening the vibrations. When it's free in the air, it's free to vibrate.
Other things to try:
An OS F plug
A sintered bronze fuel clunk, [link=http://www.shopatron.com/products/productdetail/part_number=161/101.0.1.1]http://www.shopatron.com/products/productdetail/part_number=161/101.0.1.1[/link]
If you can hold it vertical at WOT without sagging or dying, that points to vibrations foaming the fuel.
When you are holding it, you are dampening the vibrations. When it's free in the air, it's free to vibrate.
05-27-2010, 01:35 PM
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RE: OS AX 0.75 cutout at WOT
The tank is supported by foam rubber, and the WOT cut out has happened on the ground also. I can pull the hatch and look at the fuel tank while it is running to see if i can detect any foaming.
Have tried resetting the needles to 'factory' and tuning from there - always having to lean out from that setting;
Have tried resetting the needles to 'factory' and tuning from there - always having to lean out from that setting;
05-27-2010, 02:34 PM
#7
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RE: OS AX 0.75 cutout at WOT
I believe fuel-foaming is rather a mis-representation of the fact...
Most commercial fuel contain an anti-foaming agent; and even if not, fuel cannot be 'churned' into 'lather' that can support the weight of the clunk; and keep it out of the liquid fuel...
Nor can any real percentage of the fuel become foam...
The problem is that with a non-isolated tank, the walls can reverberate and deflect the clunk into the air above the fuel, where it can temporarily ingest only gaseous fuel vapors, before it is again dunked into the juice...
This results in bubbles in the fuel-line... an obvious culprit to engine operation.
This is why isolation of the tank with latex foam, is necessary.
Also, make sure the fuel-tank center-line, is exactly at the same level as the carburettor's fuel-jet, with the model in level-flight attitude.
Did you complete the break-in properly? Model engines (even OS), are not ready-to-run 'out of the box' and some [link=http://www.rcuniverse.com/forum/m_1850473/tm.htm]proper TLC[/link] is necessary, before your engine an be expected to run reliably...
Most commercial fuel contain an anti-foaming agent; and even if not, fuel cannot be 'churned' into 'lather' that can support the weight of the clunk; and keep it out of the liquid fuel...
Nor can any real percentage of the fuel become foam...
The problem is that with a non-isolated tank, the walls can reverberate and deflect the clunk into the air above the fuel, where it can temporarily ingest only gaseous fuel vapors, before it is again dunked into the juice...
This results in bubbles in the fuel-line... an obvious culprit to engine operation.
This is why isolation of the tank with latex foam, is necessary.
Also, make sure the fuel-tank center-line, is exactly at the same level as the carburettor's fuel-jet, with the model in level-flight attitude.
Did you complete the break-in properly? Model engines (even OS), are not ready-to-run 'out of the box' and some [link=http://www.rcuniverse.com/forum/m_1850473/tm.htm]proper TLC[/link] is necessary, before your engine an be expected to run reliably...
05-27-2010, 02:48 PM
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RE: OS AX 0.75 cutout at WOT
I will respectfully dis-agree DZ.
The vibrating walls of the tank do in fact create small bubbles in the fuel that circulate around too fast to come to the top of the tank.
These small bubbles, which are kept from rising to the top, by the constant churning, will be sucked in through the clunk which is sitting firmly on the bottom of the tank.
Anti-foaming agent would have no affect on this. The anti-foaming agent will only keep the foam from forming above the fuel level.
Back to the topic, this has probably been ruled out by the OP.
The vibrating walls of the tank do in fact create small bubbles in the fuel that circulate around too fast to come to the top of the tank.
These small bubbles, which are kept from rising to the top, by the constant churning, will be sucked in through the clunk which is sitting firmly on the bottom of the tank.
Anti-foaming agent would have no affect on this. The anti-foaming agent will only keep the foam from forming above the fuel level.
Back to the topic, this has probably been ruled out by the OP.
05-27-2010, 03:44 PM
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RE: OS AX 0.75 cutout at WOT
TS - Agree
Also, this is an engine that HAS been properly broken in - some 200 flights on it, with previous flawless operation.
Agree on the imporance of the issue of tank height DZ; mine is properly positioned.
OTOH, having now looked at the fuel line during WOT running with the hatch off, i can see no air bubbles in the line at all, including immediately before the engine dies.
Also, this is an engine that HAS been properly broken in - some 200 flights on it, with previous flawless operation.
Agree on the imporance of the issue of tank height DZ; mine is properly positioned.
OTOH, having now looked at the fuel line during WOT running with the hatch off, i can see no air bubbles in the line at all, including immediately before the engine dies.
05-28-2010, 03:12 AM
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RE: OS AX 0.75 cutout at WOT
ORIGINAL: ThumbSkull
I will respectfully dis-agree DZ.
The vibrating walls of the tank do in fact create small bubbles in the fuel that circulate around too fast to come to the top of the tank.
These small bubbles, which are kept from rising to the top, by the constant churning, will be sucked in through the clunk which is sitting firmly on the bottom of the tank.
Anti-foaming agent would have no affect on this. The anti-foaming agent will only keep the foam from forming above the fuel level.
Back to the topic, this has probably been ruled out by the OP.
I will respectfully dis-agree DZ.
The vibrating walls of the tank do in fact create small bubbles in the fuel that circulate around too fast to come to the top of the tank.
These small bubbles, which are kept from rising to the top, by the constant churning, will be sucked in through the clunk which is sitting firmly on the bottom of the tank.
Anti-foaming agent would have no affect on this. The anti-foaming agent will only keep the foam from forming above the fuel level.
Back to the topic, this has probably been ruled out by the OP.
Please let me reiterate...
With a bubble-less tank, such as the Tettra; which in pylon-racing planes is mounted rigidly, with no padding at all; the problem of bubbling due to your description of what causes gas bubbles to form in the fuel, does not exist. Period!
... Despite the exponentially amplified level of vibration, with some of these engines spinning at over 30K RPM, in many planes that employ this type of fuel tank!
The difference; no air in the same space as the fuel and no clunk to bounce around in it...
Since Mr Calhoun already stated that he does not see any bubbles (although this was not observed in flight), the bubble issue should not be discussed anyway.
So, the only issues left to discuss are maladjustment of the engine; and a *real* malfunction of some sort in the engine (which can still be no more than a mere pin-hole in the fuel-line, located right at the carburettor's nipple...).
EDIT: Typo.
05-28-2010, 06:29 AM
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RE: OS AX 0.75 cutout at WOT
If you mounted the engine at a different angle than it was before you may need to adjust the low end. I have one on an Extra up side down and at first it ran great but recently on take of it would cut off. I leaned the low end and high end and it runs much better with no cut outs.
05-28-2010, 07:53 AM
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RE: OS AX 0.75 cutout at WOT
Richard
Thanks for that idea; the engine is mounted differently (about 100 degrees) from the old FourStar; I have tweaked the low end (as well as the high end), but can work on that more.
I think the sensible thing is to replace all the fuel tubing, including inside the tank, perhaps the stopper, and pressure test the fuel system for leaks. Consensus seems to be that the engine is going lean.
Thanks for that idea; the engine is mounted differently (about 100 degrees) from the old FourStar; I have tweaked the low end (as well as the high end), but can work on that more.
I think the sensible thing is to replace all the fuel tubing, including inside the tank, perhaps the stopper, and pressure test the fuel system for leaks. Consensus seems to be that the engine is going lean.
05-28-2010, 09:18 AM
#14
RE: OS AX 0.75 cutout at WOT
ORIGINAL: ThumbSkull
I will respectfully dis-agree DZ.
The vibrating walls of the tank do in fact create small bubbles in the fuel that circulate around too fast to come to the top of the tank.
I will respectfully dis-agree DZ.
The vibrating walls of the tank do in fact create small bubbles in the fuel that circulate around too fast to come to the top of the tank.
05-30-2010, 08:40 PM
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RE: OS AX 0.75 cutout at WOT
Just a 'problem solved' follow up. An unusual situation, so others may be interested.
I checked and rechecked the fuel lines - no bubbles at all. No foaming. Nothing with vertical attitude. Swapped the lines for new - no benefit.
The problem was NOT in fuel lines.
The LS needle was inset about 1/16", or one full turn, below flush. That seemed to produce best throttle response from idle, and still produced a small increase in RPM from idle with a pinch test. Everyone at the field thought my LS needle was OK. Factory setting for the LS needle is flush with the carb body.
I reset the carb needles back to factory again, just to see. Retuned the HS needle, and then leaned the LS needle about 1/6 turn. Problem solved.
The problem was apparently that the LS needle was too lean. I found that odd for a WOT issue, but I ran two tanks of fuel with nary a stall, so I think the engine is back to its reliable operations again. BTW, it stumbles very slightly after a prolonged (30 sec) idle, but WOT produces peak RPM in about 3-4 seconds.
I just wasn't looking at, or thinking about, my LS needle for a WOT issue.
I checked and rechecked the fuel lines - no bubbles at all. No foaming. Nothing with vertical attitude. Swapped the lines for new - no benefit.
The problem was NOT in fuel lines.
The LS needle was inset about 1/16", or one full turn, below flush. That seemed to produce best throttle response from idle, and still produced a small increase in RPM from idle with a pinch test. Everyone at the field thought my LS needle was OK. Factory setting for the LS needle is flush with the carb body.
I reset the carb needles back to factory again, just to see. Retuned the HS needle, and then leaned the LS needle about 1/6 turn. Problem solved.
The problem was apparently that the LS needle was too lean. I found that odd for a WOT issue, but I ran two tanks of fuel with nary a stall, so I think the engine is back to its reliable operations again. BTW, it stumbles very slightly after a prolonged (30 sec) idle, but WOT produces peak RPM in about 3-4 seconds.
I just wasn't looking at, or thinking about, my LS needle for a WOT issue.
06-01-2010, 11:20 PM
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RE: OS AX 0.75 cutout at WOT
It could have been foaming (sorry Dar)
. When you replaced the lines, you may have moved the tank or isolated it better. If it happens again remember, just because you don't see foaming on the ground doesn't mean it can't happen in the air.
. When you replaced the lines, you may have moved the tank or isolated it better. If it happens again remember, just because you don't see foaming on the ground doesn't mean it can't happen in the air.
06-02-2010, 12:20 AM
#18
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RE: OS AX 0.75 cutout at WOT
There are several modelers using an OS.75AX here...
They are seasoned, experienced people and I have seen no problem encountered with any of them.
It acts like a stronger .61; rather than like a weak .91.
So, I was pre-inclined to believe the problem encountered by Mr. Calhoun, had nothing to do with an actual engine-malfunction.
But mis-adjustment will have no engine running right and it appears to have been the case.
They are seasoned, experienced people and I have seen no problem encountered with any of them.
It acts like a stronger .61; rather than like a weak .91.
So, I was pre-inclined to believe the problem encountered by Mr. Calhoun, had nothing to do with an actual engine-malfunction.
But mis-adjustment will have no engine running right and it appears to have been the case.
06-02-2010, 08:13 AM
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RE: OS AX 0.75 cutout at WOT
Agree that the 75AX is reliable as the sun rising; that's been my experience up to now as well.
I'm not sure what you mean by 'stronger .61' or 'weak .91'. It has intermediate displacement, and needs to be propped properly. On the FourStar 60, it seems to like APC 13x6 the best.
Did a little more tweaking (richening) of the LS needle at the field last eve, and it ran well. Although vertical is not unlimted, it is very very good; large loops, strong uplines, etc, and will hold knife edge without losing altitude, although that does require WOT.
I'm not sure what you mean by 'stronger .61' or 'weak .91'. It has intermediate displacement, and needs to be propped properly. On the FourStar 60, it seems to like APC 13x6 the best.
Did a little more tweaking (richening) of the LS needle at the field last eve, and it ran well. Although vertical is not unlimted, it is very very good; large loops, strong uplines, etc, and will hold knife edge without losing altitude, although that does require WOT.
06-02-2010, 10:16 AM
#20
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RE: OS AX 0.75 cutout at WOT
ORIGINAL: wjcalhoun
I'm not sure what you mean by 'stronger .61' or 'weak .91'.
I'm not sure what you mean by 'stronger .61' or 'weak .91'.
Mr. Calhoun,
What I meant is 'capable of spinning .61 sized props faster'; rather than 'spinning .91 sized props more slowly'...
It is not particularly 'a lugger'...
06-02-2010, 02:46 PM
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RE: OS AX 0.75 cutout at WOT
ORIGINAL: gkpain
An OS No.5 glow plug fixed mine right up.
An OS No.5 glow plug fixed mine right up.
OS does not make a #5 glow-plug.
Their hottest plug is now called the #6 (previously the A3).
They do have an R5, which is a cold plug intended for road vehicles.
They also had the A5, which is now their #10; their recommended plug for this engine, which may explain why it runs right...
Which of them would your #5 be?
I can tell you the Rossi R5 is even better and is the right length for your engine.
06-02-2010, 04:20 PM
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RE: OS AX 0.75 cutout at WOT
Sorry,
My engine manual that came with my O.S.75AX states:
Recommended O.S. plugs are the No.8 andA5.
Straight from Tower Hobbies:
O.S. #10 A5 Glow Plug Cold Air
[link]http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCB29&P=0[/link]
We are talking about an airplane engine right>????
The R5 is designed for car/truck engines if I'm not mistaken
Maybe this is alittle more clear.
Thxs
(GK) PAIN!
My engine manual that came with my O.S.75AX states:
Recommended O.S. plugs are the No.8 andA5.
Straight from Tower Hobbies:
O.S. #10 A5 Glow Plug Cold Air
[link]http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCB29&P=0[/link]
We are talking about an airplane engine right>????
The R5 is designed for car/truck engines if I'm not mistaken
Maybe this is alittle more clear.
Thxs
(GK) PAIN!
06-02-2010, 10:30 PM
#24
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RE: OS AX 0.75 cutout at WOT
ORIGINAL: gkpain
We are talking about an airplane engine right????
The R5 is designed for car/truck engines if I'm not mistaken.
We are talking about an airplane engine right????
The R5 is designed for car/truck engines if I'm not mistaken.
This is clearer...
But then, once installed, any glow-plug does not know the purpose and the use of the engine it is installed in...
If it is cold grade, it will just be cold; regardless if the engine is an airplane engine, or a 'truck' engine...
The OS F is, after all, intended for four-stroke engines... But it is very good in many larger two-stroke; despite being nominally 'too hot' for them...
It behaves colder in two-strokes... and makes them more reliable.
So what, if it is a four-stroke plug?!
11-25-2012, 11:34 AM
#25
RE: OS AX 0.75 cutout at WOT
I have an o.s. AX 75 and when you tighting the prop, the motor starts to lock up. the motor is new BUT! i'm the 2nd owner, I know the owner and it has not been crashed and the day I got the motor, The owner got a prop strick and broke the prop, we replaced the prop and when we replaced the prop is when it started locking up. I performed a run out to see if the crank was bent and found that it was not bent. ??? go figuer??