AndresAM

Hello,

I have an OS .55AX in a bad boy 3D profile with the following set up:
APC 12.25 x 3.75
10% nitro fuel
OS 8 and F plugs (Both work well)
14,000 RPM`s on the ground
Jett stream tuned muffler
The problem is that I take off, one circle to the field and the engine quits in the air exactly at the same time every flight. I have tried everything and cannot find the cause. I know how to tune an engine so it has to be something else.

Transitions, idle, top end power are superb as with any OS carbs. I suspect it is related to fuel foaming. This is my first profile and with the tank so close to the engine I can see a lot of bubbles in the tank.

The problems also began with the Jett muffler. So far I have like 30 flights and most of them have ended in deadsticks. I have not been able to replicate the problem in the ground, but the amount of vibration should be different in flight and that could increase the fuel foaming problem.

I think I read about a similar problem in an old thread but have not been able to find it.

Any suggestions??

Andres

liquid_TR

check your in-tank fuel pick-up line, most probably it's come off or there is a crack on it.

AndresAM

I have already checked all the fuel lines and found everything OK. I might add that the problem happens not matter what the level of the fuel in the tank is.

Andres

NM2K

My Feedback: (14)

When I talked to Dubb Jett about using his muffler with an OS.55AX, he strongly recommended that I not use a prop larger than an 11x6, preferably smaller.

I'm talking about Jett's muffler that resembles an Ultrathrust muffler, not the round muffler.

He said that the muffler is inflexible in its rpm range/tuning and that the engine will not run correctly with that muffler if loaded down with too much prop. I can't see running a 12x4 something or another making the engine quit, but I would try a smaller prop just to see if it is the problem, as long as nothing else becomes apparent.

Dubb said that the 11x6 was right on the edge of being too large with this engine and his muffler.


Ed Cregger





After a night or two of sleep (finally), I agree with those that are saying that fuel foaming should be the number one suspect.

Ed Cregger

AndresAM

Ed,

The jett muffler I have is the one similar to the ultrathrust. This problem is very strange as the engine runs perfect on the ground for a full tank of fuel if I wanted it to. I might try an smaller prop but I doubt this is the problem, the engine screams on the current prop.

Andres

freakingfast

My Feedback: (3)

I'd guess it's foaming due to the higher rpms or change in mass weight due to the Jett muffler. Somtimes, but not always, you can see foaming bubbles in the fuel line by holding the plane by the wing tips with a helper and run it up to full power. Try using Du-Bro's foam rubber between the tank and fuse. The OS bubbless clunk works amazingly well too but pricy. For 3D work transition is not as good with the Jett compared to the stock muffler + baffle.
I have seen this engine sag or quit when using fuel without caster.

PlaneHeli

If its bubbling bad. Have you tried to balance the prop to reduce vibration.

If the problem only occurs with the Jett muffler it may be foaming more due to the higher RPM.

Not familiar with your plane. Is the tank mounted in foam. Or could you mount the tank with some sort of rubber or foam mount to reduce vibration.

Also apparently these engines need good muffler pressure into the fuel tank.

BlackB12

My Feedback: (9)

I've got my 55ax on a profile and it hasn't had one deadstick in 10 gallons of fuel so I think you're right in that it's bubbles in the fuel. try more foam insulation or loosen the straps around the tank. A lot of guys will use rubber bands simply because they give. I use zip ties but I don't cince them down overly tight. Also check all the engine bolts, like the head and backplate bolts. I'm wondering if they're not tight then as the engine heats up you're getting an air leak somewhere causing the flameout.

Mike

Oly

I have an OS 55AX also, in a Telemaster 40 (not exactly a 3D plane, eh?). I run a 12x5 APC, Coolpower 15%, stock muffler and only tach it to about 11,500. I've never had a deadstick, and the engine is at normal running temperature when I land.

That said, you're either developing 'fuel foaming' because of undue vibration/lack of tank foam dampening, or you're trying to lean it too much and causing overheating.

I don't know anything about the muffler/prop combination you're running

I hope this helps.

Oly

asmund

One little squirt of ArmorAll cocpit shine into a full jug of fuel will cure any foam issues

AndresAM

Thanks guys for the help, I think I am going to replace the zip ties holding the tank with velcro bands and try to put more foam under the tank. The prop was balanced but I will do it again too.

I really don't see this engine being reliable for 3D, even with the OS muffler it has had some odd behavior. There is something with the fuel supply that doesn't work right. I agree with others saying that it needs a lot of back pressure. I might try a perry pump if I cannot get it to work well as it is.

Has anybody tried a perry pump with this engine?.

microsprint9

This might sound stupid but have you tried to tach it down to 13700-13800 on the ground and then try it. I've had engines that run great on the ground, put'er in the air and start climbing and bang, deadstick, richened it up a few clicks and the problem was solved. On the ground if you run it full throttle and hold it straight up and to either side does the engine quit ?

Harold356

I'm having the same problem with my 55AX,runs perfect on the ground,but quits every flight. I'm using one of the new Slimline mufflers.It runs without any problems with the stock muffler. I also tried a Bison pitts muffler,same thing.
Don't waste your money on the new Slimline Pitts muffler it doesn't work on the 55AX.

Rambler45

Didnt somebody says something about blocking one of the slim line muffler holes or something ?

AndresAM

Yes, top RPM's are around 14100 I fly at 13800.

As others have said, this engine needs a lot of backpressure to run right.[] I think I am going to need a perry pump if I want to keep the Jett muffler. The fuel foaming is not helping either, so I will try to fix that first before trying the pump.

Andres

Harold356

Talked to Slimline this morning. Very nice guy. Said they had over 500 of these mufflers out there with no problems.They are going to have their head GURU call me when he returns to work.Will keep everyone informed.Maybe I jumped the gun.

bob27s

My Feedback: (19)

As most have mentioned, what you described is fuel foaming.

With the Jett muffler installed, there is a good deal more power being produced, and more energy transfered to the airframe.

symtom - It runs great on the ground, you do not even see foam or bubbles in the fuel lines but when the engine unloads in flight it runs like junk .... that is foam. If the tank is hard mounted, if the fuselage has a large amount of natural flex, or if there is other source of relative motion... foam will occur at higher power levels.

Fuel foam was a plague for pylon racing for a number of years. We switched to bubble-free tanks exclusively and eliminated the issue.

My suggestion to start with.... put the 12.25 prop aside....

Ensure the tank is well padded.

Ensure a solid engine mount location.

Go with a stock blade 11x6, 11x7 or a 12x4 or 12x5 (regular blade, you might be impressed). It will change the rpm and dynamics of the setup. If the foam is no longer an issue, then you can play with the props to avoid the airframe harmonic and the foam.

Also, for flight, find peak rpm on the engine, and back off on the needle from there appx 500-600 rpm for flight.

The jett muffler provides the proper balance of backpressure, and also generates more tank pressure than the stock muffler. Fuel delivery should not be an issue.

Avoid using a pump to put a bandaid on another problem. They sometimes create problems of their own.

If you want to make a change at all, consider either a Tetra bubble tank or one of the Bubble-Jett fuel tanks. Eliminates air in the system, and thus eliminates the primary the cause of fuel foam.

Bob Brassell

proptop

My Feedback: (8)

FWIW I have noticed that of the three 12.25 x 3.75 props that I have, the holes of all three are drilled / moulded at a slight angle? If I put them on the (Highpoint ) balancer and spin them, I can see that the hub is eccentric and the blade tips don't track evenly.

That could be a contributing factor to your foaming...

I would agree with changing the prop just for the heck of it and see if you have less foaming. I went back to a 12 x 4 for that reason.
(engine: Magnum .52 2 stroke in a H9 Tribute profile )

BlackB12

My Feedback: (9)

I've used the 12.25 x 3.75 prop for literally hundreds of flights with no problem so I don't think it's the prop. It's probably as simple as bob says and it's fuel foaming. Or there's a hunk of dirt in the high speed needle seat. Happened twice on mine. Never quit but the top end would hunt going from normal power to sagging and back. Took the needle out and saw some dirt. Flushed it with fuel, problem solved. The thing still never quit though.

Mike

AndresAM

Keep in mind that the engine flew fine with the OS muffler. The jett muffler produces a lot more power which could make the fuel foaming worst as bob27s said. However, I would think that the jett muffler produces less backpressure being a less restrictive muffler but I might be wrong though.

I will try different props for sure.

AndresAM

Just an update for people facing the same problem.

First the things that didn't work:

-Putting more foam under the tank.
-Changing the zip ties for velcro bands.
-Replacing all the fuel lines.
-Removing the fuel filter.
-Trying any possible carb settings.

The things that worked:

-Adding Castor oil to the fuel (my fuel was supposed to have Castor oil on it, but I think it was not enough). After doing this, the engine quited too but it lasted longer into the flight.
-Changing the OS F plug with an OS 8 coupled with more CAstor in the fuel finally made the difference and the engine rus fine now.

Some final thoughts:

-I was using an F plug, because I was having better transition with it, but It was also making the engine run too hot.
-This engine really needs Castor oil in the fuel.
-The Jett muffler really adds power (at least 1500 RPM`s with a 12.25 x 3.75 prop). However, transition is not as good as the OS muffler. You can actually feel the engine getting in to the tuned band and making some RPM`s jumps in the air but it still can be used for 3D.-
-This engine starts as easy as a gas engine and also has a very good carb. In my opinion OS carbs are the best in the industry.
-This engine is incredible powerful with the Jett muffler. My profile wights 5 pounds - 6 Oz and the engine pulled it out of a hover with authority. I can't imagine this engine in a 4 pound profile.
- I am going to try different props to see if I came up with a better combination for 3D.

Hope this hepls people with the same issue.

Andres

rcdude7

My Feedback: (264)

Just a FYI, the OS clunk is a repackaged walbro. I bought one of these for $$$ and found that it is the same thing as the walbro felt clunks I purchased on *bay for $2 ea. They are standard felt clunks you would find in the tank of any weedwacker, nothing special.

show871

Are you using gas towards the bottom of the jug?? I had the same problem twice, and found when I run the fuel on the last few inches of the jug I have the same prob. Condensation in the jug adds water, which stays on top of the fuel.....

Try a fresh jug, and a brand new glow plug

871

rcdude7

My Feedback: (264)

Water bonds with metanol, so it would be throughout the jug, if it were in there. Methanol weight is 791.3 so if it didn't mix with water, it would sit on top of the water in the jug.

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