help os 46 ax quits in flight
09-22-2019, 11:46 AM
#1
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help os 46 ax quits in flight
Hello there,
I have an os 46 ax that is stopping in the air. I can get 3 - 5 minutes of an engine run before it just stops running like I pulled the throttle. It runs great on the ground. I have replaced the glow plug and checked the fuel system. I am looking for ideas for things I have not checked. This is a strong running engine but all of a sudden it wont keep going. It was a 95 degree day but I fly in these conditions all the time. The engine didnt seem too warm once I got it down. Im running the same fuel I always run, 15% nitro synthetic oil blend. The engine starts right up and runs fine right after the deadstick. Im stumped.
Dave
I have an os 46 ax that is stopping in the air. I can get 3 - 5 minutes of an engine run before it just stops running like I pulled the throttle. It runs great on the ground. I have replaced the glow plug and checked the fuel system. I am looking for ideas for things I have not checked. This is a strong running engine but all of a sudden it wont keep going. It was a 95 degree day but I fly in these conditions all the time. The engine didnt seem too warm once I got it down. Im running the same fuel I always run, 15% nitro synthetic oil blend. The engine starts right up and runs fine right after the deadstick. Im stumped.
Dave
09-22-2019, 12:27 PM
#2
What size prop are you useing. Does it respond to needle changes on the ground . If it has a lot of run time it might just be getting tired. Normally if a engine is getting worn out they are hard to tune and tend to burn out glow plugs. But you say glow plug are not going bad. My guess is either fuel is being restricted or fuel starts to foam bad from vibration after fuel is lower in tank.
09-22-2019, 03:28 PM
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Thanks A.J. I am running a 11x6 prop. I have been running this engine/airplane combo for a while. Its a great planes stick with about 50 flights on it. I rebuilt the engine before I put it in the stick.The engine had hundreds of flights on a great planes sportster before I pulled it. Wore that plane out. I put in new piston/sleeve and wrist pin. It was getting hard to start before the rebuild. The engine runs great on the ground. Responds to needle valve nicely. Great compression too. I suspect the fuel system. Maybe there's a hole somewhere. I had the tank out and everything looked ok. I think I will replace all the tubing. Maybe replace the whole tank. I will post back when I find out what is going on.
09-23-2019, 07:52 AM
#5
It could be that the engine is overheating in the air. After it deadsticks for a landing, wet your finger and touch it to the head. If it sizzles, it's overheating. Try richening up several clicks or more on the high speed needle and see if the problem goes away. You want a nice smoke trail in the air. We had this problem at our field recently.
If that doesn't do it then make sure the tank is well padded with foam to prevent foaming. Also check the tank for a cut fuel line right at the brass tube. (both already mentioned above).
carl
If that doesn't do it then make sure the tank is well padded with foam to prevent foaming. Also check the tank for a cut fuel line right at the brass tube. (both already mentioned above).
carl
09-23-2019, 10:35 AM
#6
11/6 is a lot of prop. That said, your change is too dramatic to be the prop. I'd look again at the fuel system. A leaking muffler could lower the muffler pressure. A hung up (stuck) clunk line is a possibility. Sometimes the clunk line gets stuck in the front of the tank? A pin hole, or tare in any of the fuel lines could be the problem. I'd replace all the fuel lines. A loose rear cover will lower the crank case vacuum, and pressure. Check the the O ring under the carburetor for a good seal. Run it on the ground starting with 1/2 tang of fuel, and watch for air bubbles in the fuel line. Good luck.
09-24-2019, 06:51 AM
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Hi!
Most likely you have set the high speed needle too lean! What happens if you turn it out 1/4 of a turn ?
Or...It could be a worn out piston to cylinder fit! Or...a tank that is leaking. I have seen many tanks where the expanding rubber stopper up front has gone hard and thus leaking ...or there is a slight crack in the seem of the tank.
The correct tank size matters! You should use a 8-10 oz tank ! Anything larger will make your engine harder to set as it will lean out when the fuel lever sinks.
11x6 prop is just fine, at least at sea level, best props are RAM, Graupner G-Sonic and APC. 15% is way ,way too much nitro! 5% is all it takes to have all glow engines run just fine.
Most likely you have set the high speed needle too lean! What happens if you turn it out 1/4 of a turn ?
Or...It could be a worn out piston to cylinder fit! Or...a tank that is leaking. I have seen many tanks where the expanding rubber stopper up front has gone hard and thus leaking ...or there is a slight crack in the seem of the tank.
The correct tank size matters! You should use a 8-10 oz tank ! Anything larger will make your engine harder to set as it will lean out when the fuel lever sinks.
11x6 prop is just fine, at least at sea level, best props are RAM, Graupner G-Sonic and APC. 15% is way ,way too much nitro! 5% is all it takes to have all glow engines run just fine.
09-24-2019, 08:19 AM
#8
My take - too much prop for a .46 and too lean of a needle setting. IMO an 11x5 or 10x7 would be more inline with keeping the engine in its powerband and give a little more latitude with the needle setting. IMO an 11x6-7 is more of a .55-.61 prop size.
10-01-2019, 08:35 PM
#10
if tuned right, an 11x6 shouldn't cause a deadstik, or it to overheat, provided there sufficient airflow....post some pics if you can please...ive used slightly larger props in a pinch, to keep flying ...just a quick retune of hsn, pinch test, etc, to avoid a hot lean run once airborne
10-05-2019, 06:14 PM
#12
Even at 850ft ASL, an 11x6 is too much prop for a .46 unless you pipe it for the prop and adjust your fuel and glow plug to suit. Possibly a need to shim the head a bit too. Quite a bother for a novice to accomplish. If a guy can’t get an O.S. to fly right, they’re doing something wrong. If you run it lean and/or overheat it a couple times, you’re sure to be spending money on spares too.
11-23-2019, 08:39 PM
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Solved.
I finally got around to addressing my engine problem. Turns out those of you who suspected the fuel system were right. The rubber tank stopper was deformed with age. I replaced it and all the tubing and the problem is gone. Two good flights today. No engine problem. And I am running an 11x6 because that's the prop recommend in the instructions for the engine by the manufacturer. I usually run on the rich side. The tax says I'm turning around 12,000 rpm with that prop. I can lean it for more but I'm flying the stick at half throttle now so I don't need the extra power. Thanks to you all for the help and advice.
11-24-2019, 08:01 AM
#14
Good to hear you found the problem, and I have had that happen too. I usually do a suction test on new planes to make sure the tank can hold suction for at least a minute at least to ensure no leaks. Just give a pull with on the fuel tube with the vent line plugged and cap it with your finger. A bit messier to do with an old installation though!
11-29-2019, 09:19 AM
#18
Tettra or BubbleJet tanks use a bladder inside the tank where the fuel goes. This kind of tank makes it virtually impossible to have aeration of the fuel during operation that can cause all sorts of problems. I’ve got one 14oz Tettra tank and I’ve made several 5oz tanks at home with simple stuff I had on hand. It can make a big difference in certain situations.
12-01-2019, 09:00 AM
#19
My Feedback: (2)
So where do get those kind of tanks? I have always used Sullivan tanks and really had no issues but my ax is doing the same thing and I had it fixed but then it died the last time i flew it. I took the bottom of the fuel tank compartment our because the nose wheel had back into it on a landing. I replaced the bottom and covered it yesterday I just need to put everything back in the airplane. I am running a 10-7 prop but have used 11-7's for years as this was the recommended prop by both my club members and the manufacture. I run 10% Omega and its been a great fuel for years!
Thank You
Michael Johnston
Thank You
Michael Johnston
12-01-2019, 01:07 PM
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Tettra bubbleless tank
Hi!
Problem with "ordinary fuel tanks" is the expandable rubber stopper up front that often leak (or split the fuel tank at the seam). Tettra use another version of stopper that does not expand ,but instead is clamped down with a steel ring. There is two versions of Tettra tanks, with bladder and without.
Central Hobbies and Darryl Caddy are some that sell Tettra tanks. A 240cc tank (8oz) cost around $28.00
Last edited by jaka; 12-01-2019 at 01:15 PM.
