Tango Juliet

I have an OS 46AX on my 4*40 ARF and although it runs well, I do have an issue with it. Admittedly, I'm not the best at tuning an engine, I just never developed an ear for the proper sound. When I start it in the pits, it starts easily and transitions from low to high throttle and back are fine. When I get it to the runway and start advancing the throttle for takeoff it dies just as I'm getting it to flying speed. After about the third time, it will run to get airborn, then about half way through a tank it wants to die again. I can throttle back and fly around at 3/4 throttle, but if I try to idle down for say a touch and go, in most cases it will die. Give me some input fella's.

Hobbsy

My Feedback: (102)

The HS needle is set too lean. You need to set it rich enough to allow for it leaning itself as the tank empties. Next time set it with the tank half empty and about 300 rpm below peak rich.

rainedave

My Feedback: (1)

Hobbsy's method works great. But, just for variety's sake, here what I do sometimes: Have someone hold the plane with the nose up at around a 60° angle, or so, with the engine running. Go to WOT and pinch the fuel tubing very quickly behind the needle valve. Either open or close the needle valve until you hear an increase in rpms after pinching the line. If there is no change in rpms, or the engine sags when pinched, then it's too lean. I usually find the setting where there is no increase and open the needle valve a few clicks from there. This will seem a bit rich when the plane is held level, but during vertical maneuvers you will not go lean and die. There's really no need to totally peak out sport flying engines. If your plane doesn't have enough power at a slightly rich setting, then the engine is too small for the plane, IMO. But, I'm certain that the AX .46 is more than enough power for your plane.

David

mike109

G'day

AT a first guess as I cannot see the engine and play with it - the low speed needle is set too rich and the high speed needle may be too lean.

Can you tell us a bit about the engine?

1. How old - how many hours running?
2. Did you get it new/second hand
3. What adjustments have you made?
4. Prop size/brand?
5. Fuel type?
6. Plug type?

All these things will affect any answers we can give you.

And now a bit of background. When I tune an engine I have not seen before or that is playing up, the first thing I do (with the the throttle fully open) is to turn the high speed needle (HSN - the big one) out until the engine is running quite rich (four stroke sound, lots of oil and smoke out the exhaust). I then turn it in gradually and eventually the engine will smooth out and start running in two stroke mode. At this point I note where the needle is (how many turns open) and then keep closing the needle until the engine just starts to die a bit. At this point it is running lean and should not be left here long so I quickly open the needle about half a turn or perhaps even more. Once the engine is again running smoothly I lean it out again but I try to find the point where it is revving at its maximum. If you cannot do this by ear, you need a tacho. Once I have established the peak rev point, I wind the needle out again until the revs drop between 300 and 500 rpm. This is usually between 1/4 turn and 1/2 turn. This is a "slightly rich" setting. Set like this, the engine will not tend to stop in the air as the level of the fuel in the tank drops during the flight.

But ...

We are only half way. Now we need to set the low speed needle (LSN). If the engine is very new, it will probably not idle well even if the setting is correct so it is generally best left in the factory setting until it has some running under its belt. New engines idle better once they have started to run in after about half an hour of running or even more for some engines. With a new engine, it may help to keep the glow driver connected to the engine while you try to find the low speed setting. To adjust the LSN, the engine needs to be running with the throttle at its low setting. The factory setting on OS engines is usually on the rich side and OK for running in the engine but you usually need to slowly turn it in to gradually find the right setting. I only make the change about 1/8 turn at a time and then rev the engine to full revs and then back to idle to see how the transition is and then how well it idles. This will also get rid of any excess fuel that will build up in the crank case if the LSN is set too rich and you try to make the engine idle for too long. If you make a large change to the LSN you will then have to adjust the HSN again and then repeat the process as the two needles affect each other. If you go too lean on the LSN, the engine may not start at low throttle settings. The LSN is more critical than the HSN.

If the engine is idling and when you try to rev it up, it splutters and spits out lots of fuel and then speeds up, it is almost certainly too rich on the LSN. If you try to rev up and it dies, it is probably lean on the LSN. A simple test for checking the LSN setting is to get the engine idling then pinch the fuel tube to cut of the fuel. If the engine revs up slightly then stops, you are pretty right. If it just dies, it is probably lean and if it revs up a lot, it is probably rich.

If you get the needles completely mucked up, try reading the manual or if you don't have it there are some tricks you can try. More of them next time.

If after all these things have been done and you still can't get a stable idle, suspect your fuel and or your glow plug. Old fuel which has picked up some water almost always results in a poor idle. When in doubt, see if you can borrow some known good fuel. An OS No 8 plug is a pretty good starting point for your engine. OS F (four stroke) plugs also work well in some difficult engines but are more expensive.

Hope this helps abit.

Mike from Oz.

Tango Juliet

G'day Mike

I'll have to print your reply and commit it to memory. I know I've read this or heard it before, but it just doesn't sink in I guess. I don't have the engine in front of me right now (I'm at work), but I have the recommended prop size on it (whatever that was) and an OS 8 plug I believe. I bought it new and it has six or more tanks of Omega 10% run through it. It has been flown rich and a few of the more knowledgeable members of our club have adjusted the screws on it, but not enough evidentally. One of the other fellows has the 55AX on his Kadet Senior and it purrs so beautifully at low idle it sounds like a four stroker, it makes me jealous[:@].

ChrisAttebery

My Feedback: (15)

Go with Mike's advice. I've got a couple 46 AXs so I'll throw in my $.02. Go to the OS A3 plug it is hotter and will give you a better idle and make more power.

Good luck,



Chris

Bax

My Feedback: (11)

Check the location of the fuel pickup in the tank. If it's too close to the rear of the tank, then the engine can go rich and quit on takeoff when the model accelerates. That's because the model's acceleration drives fuel to the back of the tank. If the pickup's too close, it 'sees' quite an increase in fuel pressure, and the engine goes rich. Move the pickup a bit farther away from the rear of the tank and the problem will go away.

Sport_Pilot

If the engine is sensitive to mixture from the tank level I would suggest using a uniflow setup. That way it will stay set throughout the run.

Tango Juliet

Yeah, I was reading about those over the weekend. It's definitely something I intend to try on future models. If the other suggestions don't work, I'll do that to this one.