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OS 1.20AX Unexplained Flameouts.......>>>

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OS 1.20AX Unexplained Flameouts.......>>>

Old 07-23-2012, 06:07 AM
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Taz_Hobbies
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Default OS 1.20AX Unexplained Flameouts.......>>>

Finally maidened my Sea Gull Ultimate 90 BiPe with a OS 1.20AX this weekend. Two marvelous flights first thing in the AM. Ran like a swiss watch.
Switched to my 30cc MX2 for a bit then went back to fly the Ultimate. Fired up perfectly, sounded crisp, tuned a little on the fat side like I prefer them. Not blubbering rich, just a little thicker trail of smoke than most run. I run every glow motor a little fat.

3 minutes into the flight, straight and level flight crossing the fiel following a stall turn and... SILENCE. Just shuts off. I thought I had the idle trim too low. Bring her around into the wind land, re-fire her. 3 minutes, straight and level again, about half throttle after a Split-S and... SILENCE. Just shut off again.

Details -

Fuel tank is slightly below carb centerline, but this cannot be adjusted.
Motor is mounted horizontally.
Brand new "hot" plug after the first flameout.
Brand new "med-hot" plug after the second.
Bryon 10% fuel / 16% syntehtic (if memory serves)
Cowl is hogged out big time, Plenty of airflow in and out.
Pitts style Muffler.
No obvious signs of leaks, drips or airleaks,
Quick fueler receptacle in line.

Any ideas? I have heard about the "trick" of using a "F" plug in it, but hadn't tried that yet. Frankly I am alittle worried about that idea.
The Ultimate is an amazing flying airplane and I cannot wait to get her sorted out and back in the air.




Old 07-23-2012, 06:11 AM
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RCPAUL
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>

I use an "F" plug in all my engines 0.60 and above - especially STs. Sounds to me like a tank, fuel line problem. Pin hole? I also add a little castor to my fuels and never use less than 18% oil.

Paul
Old 07-23-2012, 06:44 AM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>

Agreed. OSengines with their nickel liners like more oil, and they like some castor.I would add 2-3 oz of castor to your 16% oil fuel. Then I would look for a fuel delivery problem.
It does sound like it got hot and shut off. Was it cool in the morning when you flew it with no problems? Did it warm up when you had it die in flight? Just a thought. Having the cowl "hogged out" does not always mean good airflow for cooling. The air needs to flow across the head and cylinder, and have a way out. Start by closing off the cheek entrance on the other side of the cowl so no air gets in that does not go over the cylinder. Give the air an exit of at least 3 times the area of the entrance, and again place the exit so the air flows across the engine to cool it on its way out. You can check this first by flying without the cowl on a hot day.
I am also not a big fan of pitts mufflers, but on a 120 it should not do too much harm. It will cost you some power, but you should have some to spare.

Good Luck
Scott
Old 07-23-2012, 07:10 AM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>

The fuel is actually 18% synthetic/castor blend, I was wrong on the 16%.

Yes it got hotter out. But I also fattened it up accordingly. The exit on the bottom of the cowl is almost the entire lower chin of the cowl. It is way more than 3x the entry.
I agree though, seems like it runs hot, even fattened up. I will make some runs next weekend without the cowl and see if that changes it's attitude any. I will also try the F plug.

Thanks guys.

Old 07-23-2012, 08:13 AM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>

The OS F is a little hotter than plugs like the #8. The OS A3 is even hotter. 

Maybe you could get someone at the field to tach your engine where it is 300-500 rpm richer from peak rpm. 

If the tank is too low in reference to the carb you may be plagued by poor fuel draw all the time.
Old 07-23-2012, 02:49 PM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>

Have you pumped the fuel out and then just put 1/2 a tank in it to see if your clunk line has a hole? What prop is on it? I have a APC 17x6 on mine.

david
Old 07-23-2012, 04:20 PM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>


ORIGINAL: daveopam

Have you pumped the fuel out and then just put 1/2 a tank in it to see if your clunk line has a hole? What prop is on it? I have a APC 17x6 on mine.

david
When I assembled the tank, I used a vacuum pump to check the lines, end to end including the pressure tap line. There are no leaks.
I have a 16x6 APC on her.

Old 07-23-2012, 05:33 PM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>

The OS 120 AX does not like to be run HOT. The OS 120 AX has two things goine against it for cooling. One is that it is the most powerfull 120 Size engine made to date.... it will out turn the Jett 120 also with the same muffler. The second thing going against it is that it is the lightest 120 engine to date. that means it doesnt have much aluminum to shed heat from the engine unless have proper cooling.

Like the other guy said you need to close off the other side of the cowl.
The other guy also said 3x times the inlet area that is usually bad advice. having hold to big on most cowls will cause a reverse or stagnant airflow as the air coming off the bottom of the cowl will try to enter the cowl and block off the air. I have ran many of the OS 120 AX engines in different planes and I know what works and doesnt. Sometimes also having to big of a hole will allow the air to bypass infront of the engine cylinder and go out the exit allowing very little air to cool the cylinder. you need to make a wood damn in in the cowl that goes up against the engine and diverts the air over the top of the cylinder. now once the 120 gets hot the head will lift off the cylinder and the bolts will loosen up this kills the compression and makes it run even more lean. if you are having problems check your rear two bolts on the head and most of the time they will be loose. I really wish they would have had more aluminum so could install the next bigger size head bolt.
Old 07-23-2012, 06:33 PM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>

ORIGINAL: Taz_Hobbies
ORIGINAL: daveopam
Have you pumped the fuel out and then just put 1/2 a tank in it to see if your clunk line has a hole? What prop is on it? I have a APC 17x6 on mine.
david
When I assembled the tank, I used a vacuum pump to check the lines, end to end including the pressure tap line. There are no leaks.
I have a 16x6 APC on her.
Actually there could be a tear or pin hole in the flex fuel line inside the fuel tank.When the fuel level drops below the hole, the engine sucks air and stalls out on you.

Old 07-23-2012, 10:48 PM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>


ORIGINAL: earlwb

ORIGINAL: Taz_Hobbies
ORIGINAL: daveopam
Have you pumped the fuel out and then just put 1/2 a tank in it to see if your clunk line has a hole? What prop is on it? I have a APC 17x6 on mine.
david
When I assembled the tank, I used a vacuum pump to check the lines, end to end including the pressure tap line. There are no leaks.
I have a 16x6 APC on her.
Actually there could be a tear or pin hole in the flex fuel line inside the fuel tank.When the fuel level drops below the hole, the engine sucks air and stalls out on you.

When I assembled the stopper for the tank, the final step I do before inserting the stopper assembly for the final time is to vacuum test the line from the clunk to the end of the line where it will go on the carb, that includes any inline tees, quick fuel receptacles, etc. I also heck the vent line from the brass tube to the muffler pressure tap. When it was installed, both lines held a vacuum.

Old 07-23-2012, 10:59 PM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>


ORIGINAL: airraptor

The OS 120 AX does not like to be run HOT. The OS 120 AX has two things goine against it for cooling. One is that it is the most powerfull 120 Size engine made to date.... it will out turn the Jett 120 also with the same muffler. The second thing going against it is that it is the lightest 120 engine to date. that means it doesnt have much aluminum to shed heat from the engine unless have proper cooling.

Like the other guy said you need to close off the other side of the cowl.
The other guy also said 3x times the inlet area that is usually bad advice. having hold to big on most cowls will cause a reverse or stagnant airflow as the air coming off the bottom of the cowl will try to enter the cowl and block off the air. I have ran many of the OS 120 AX engines in different planes and I know what works and doesnt. Sometimes also having to big of a hole will allow the air to bypass infront of the engine cylinder and go out the exit allowing very little air to cool the cylinder. you need to make a wood damn in in the cowl that goes up against the engine and diverts the air over the top of the cylinder. now once the 120 gets hot the head will lift off the cylinder and the bolts will loosen up this kills the compression and makes it run even more lean. if you are having problems check your rear two bolts on the head and most of the time they will be loose. I really wish they would have had more aluminum so could install the next bigger size head bolt.
Yeah, I agree, the huge opening in the lower chin of the cowl is a concern for me. I was actually bummed when I did it to be honest. Both because of the way it looks and the fact that you can visualize where the air is going to come in from and you can almost "see" where it will whirlpool and do nothing. Grabbing another cowl isn't a big deal.

As far as it lifting the head, sounds like a valid theory. Only down side to it is the engine never runs lean prior to shutting off. It never sags, labors or changes pitch. The smoke trail out the exhaust is heavier than most and the motor burbles a little thruout the range as I keep them a little fatter than most folks. I keep them fat for both cooling and lubrication. The head bolts are not loose when the engine is cold. But I will fire it up tomorrow on the bench and check the ehad bolts when she gets up to temp.

Thanks for the insight, I will look at the cowl issue for certain.

Old 07-24-2012, 05:55 AM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>

We need to correct a mis-info, the 1.20 AX has a steel liner. From the specs.

Construction: Steel piston ring and liner, aluminum piston
Old 07-24-2012, 06:34 AM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>

My experience with glow engines using a Pitts style muffler has been that there is insufficient muffler pressure to sustain WOT. The test for this is to see if you are able to run WOT and tune to overly rich. If you can, then you likely do not have this problem, as the tank is receiving enough muffler pressure. If it does not pass this test, the solution I have used is to plug one of the 2 exhaust stacks.

Good luck.
Old 07-24-2012, 07:11 AM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>


ORIGINAL: RCVFR

My experience with glow engines using a Pitts style muffler has been that there is insufficient muffler pressure to sustain WOT. The test for this is to see if you are able to run WOT and tune to overly rich. If you can, then you likely do not have this problem, as the tank is receiving enough muffler pressure. If it does not pass this test, the solution I have used is to plug one of the 2 exhaust stacks.

Good luck.
So far none of the flameouts were at WOT. They were all straight & level flight with the engine in the low midrange area. I can get it fat running WOT on the ground and holding it in any orientation. Both initial flameouts were after an upline move. Once after a stall turn after getting levekl and back to mid-field and then again after a split-s and back to level and at mid-field.

I am puzzled. Between this and my hard as hell to start 30cc MX2, I think a couple of airplanes will be cowl-less this weekend and just working on tune-ups!
Old 07-24-2012, 07:50 AM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>

Hi!
If I were you I would change the tank set-up to a Uni-flow and if that won't work install a Tettra "Bubbleless" tank.
-And use the original silencer!
Here is how a Uni-flow tank set-up looks like.
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Old 07-24-2012, 08:37 AM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>

Jaka might have a point about a uniflow or bubbleless tank.

Years ago I had a Goldberg Ultimate bipe. The engine would quit every time I had the plane do a roll. Now it would look, fly inverted, do a really slow roll, four points, knife edges, stall turns and other manuevers AOK, but a roll a little too fast and the engine would quit. I tried three different brand engines, four different fuel tanks, even a Robart fuel pump too. It still did it. I eventually gave up and sold the plane to someone else who thought they knew what the problem was, but it did it for them too. Yeah dead stick landing a Ultimate bipe is like landing the Space shuttle as they both have about the same glide ratio. So maybe the better fuel tank setup would solve the problem.

Of course what the others state about the air flow through the cowl could be the problem and the engine is overheating. Did you try flying it without the cowl? If it works like that OK then it is the cowl causing the issue.


Old 07-24-2012, 10:05 AM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>


ORIGINAL: earlwb

Jaka might have a point about a uniflow or bubbleless tank.

Years ago I had a Goldberg Ultimate bipe. The engine would quit every time I had the plane do a roll. Now it would look, fly inverted, do a really slow roll, four points, knife edges, stall turns and other manuevers AOK, but a roll a little too fast and the engine would quit. I tried three different brand engines, four different fuel tanks, even a Robart fuel pump too. It still did it. I eventually gave up and sold the plane to someone else who thought they knew what the problem was, but it did it for them too. Yeah dead stick landing a Ultimate bipe is like landing the Space shuttle as they both have about the same glide ratio. So maybe the better fuel tank setup would solve the problem.

Of course what the others state about the air flow through the cowl could be the problem and the engine is overheating. Did you try flying it without the cowl? If it works like that OK then it is the cowl causing the issue.


I am not a big fan of the bubbleless tank. The hassle of inflating the bladder each time you fill up isn't worth it, in my opinion. The tank isn't much lower (or any for that matter) than some of my other planes so I doubt that is the issue.

Dead sticking my Ultimate is a breeze. I was hesitant of even building the Ultimate because of all that "flies like a brick" hype. I hear the horror stories of when she flames out you have to dive at the ground and flare in the last 2 feet and all that. I am here to tell you that is simply NOT the case. On her maiden flight, I was so comfortable with it just 20 feet off the deck, I ailerons rolled her into a left bank on climb out to start making my circuits around the pattern. That Ultimate is the best flying I have ever owned, to date. Anyone who has ever shyed away from flying an Ultimate because of the "drops like brick" stories needs to come and fly mine. She nearly flew hands off (2 clicks right aileron, 1 click down elevator) right from the building table and on all 3 dead sticks this weekend she had plenty of glide ratio to make it back to the field with air to spare. As i said, thee best flying plane I have owned/flown to date.

She will have the cowl off this weekend (along with my 30cc MX2) and I will diagnose and cure this ill. She is too sweet of a ride to not get corrected. I will have 2 or 3 other powerplants with me to test if the bigAX doesn't get in line.









Old 07-24-2012, 11:40 AM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>

Neither uniflow (brings me back to my U-Control days!) nor bubbleless tanks should be necessary. It is somewhere in the fuel system.

Paul
Old 07-24-2012, 02:16 PM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>


ORIGINAL: RCPAUL

Neither uniflow (brings me back to my U-Control days!) nor bubbleless tanks should be necessary. It is somewhere in the fuel system.

Paul
I think the guys who were talking about it getting hot and lifting the head may be on to something. I pulled the head for giggles. Being a guy who has been around some seriously high compression engines in the day and understanding the clamping method of the cylinder head, I was shocked at what I saw. Seems that there are some evidence of compression past the cylider head / liner / head gasket towards the rear. Oddly enough, it looks like it has an aluminum head gasket, I assumed it would be a copper shim. Not sure of the aluminum makes it more or less prone to leaking or pushing out, but I have ordered a new one.

Thanks for all the tips guys. I thinked I worked the kinks out of my 30cc MX2 today as well.

Old 07-24-2012, 06:45 PM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>

the stock head shim is fine its the stock bolts and design. It works just fine if it gets great cooling. its hard to get that great cooling though. yes many have that same problem. take the sleeve out of the cylinder. use some fine valve grinding compound on the head with out the shim. this will help clean out some of the carbon there. use a new shim. i dont remember the torque of the head bolts but dont make them super tight as this is worse than not tight enough. anyway tighten them up. then take your heat gun and warm the engine up to around 200 degrees F and then retorque the head bolts. i have done this and it helps some. the main thing though is keeping the engine cool... You have to have air go over both sides of the cylinder. most cowled engines will only have air hit the front of the engine and then go down the side where the exit is and not over the top of the engine.
Old 07-25-2012, 09:23 AM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>

I am not doubting your ability to assemble or test the tank. But the line can still get a small cut when going into the tank. It can also get cut from the inside by the brass, or hit the vent line on a hard landing. I may be way off and it could easily be the heat issue that was so well described above, but you still owe it to your self to see how it runs on a half tank. This would rule out the clunk line issue and let you move on.

david
Old 07-25-2012, 12:06 PM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>

David is right, big time. Tanks and all of the fuel lines/plumbing is a source of leaks. Don't forget the tubing from the muffler. Fuel lines can soften and collapse when warm. If you don't catch these things they will have you chasing you tail forever.
Old 07-25-2012, 12:44 PM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>

Have you adjusted the low speed screw? i had problems with my 75AX until i adjusted the low speed ,and it have never stopped in the air after that adjust according to manual.
Old 07-25-2012, 12:51 PM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>


ORIGINAL: blw

David is right, big time. Tanks and all of the fuel lines/plumbing is a source of leaks. Don't forget the tubing from the muffler. Fuel lines can soften and collapse when warm. If you don't catch these things they will have you chasing you tail forever.
The fuel line is all brnd new and firm and all of the vac testing is done from the pressure tap to the carb inlet. The entire fuel system will hold 5" of vacuum until dooms day. I am very confident that the fuel system, as far as leaks are concerned, is not the issue. It was the very first thing I checked. and it was checked before installation during the build and checked again the final time the engine was mounted. I am pretty thourough with those kinds of details.

Old 07-25-2012, 02:46 PM
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Default RE: OS 1.20AX Unexplained Flameouts.......>>>

If it's not already fixed, and if you determine that it actually quits at or near idle, you could have a throttle servo that is not centering or holding it's position well whether it is new or used. Vibration will get to these servos sometimes and / or new ones will be defective. It really shows up at idle.

Ernie Misner

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