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O.S. 46 AX question

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O.S. 46 AX question

Old 02-04-2007, 02:05 PM
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hemiram_05
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Default O.S. 46 AX question

Hey guys. I have a Hanger 9 P51 pts with a O.S. 46 Ax engine in it and when i do high speed low passes my engine does something weird. When i get to peak rpm and speed it sounds like my propeller has come off for a split second. The engine winds really high and then goes back to normal. It does this one or two times on just about every full speed fly-by. The rest of the time it sounds normal. I broke my 11x6 prop the other day and all i had was a 10x6 so i put it on. I didnt know if that prop was to small or what. I am running fairly rich on the high side due to the fact that im still breaking in the engine. Any comments would be appreciated.
Old 02-04-2007, 04:11 PM
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alan0899
 
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Default RE: O.S. 46 AX question

G'day Mate.
IMHO a 10x6 is a 40 size prop, & thus too small for a 46AX, go back to your 11x6 or 11x7, & let us know if the problems stop.
Old 02-04-2007, 08:38 PM
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sparkknocker
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Default RE: O.S. 46 AX question

Ha, you shouldn't have heard that even with a 10 6 prop. Sounds like the fuel line to your carb may be pinched off a bit or perhaps a little too lean. Keep in mind that your engine will lean out a little in the air so you must back off a couple 100 RPM's on the ground
Old 02-04-2007, 10:20 PM
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masonman
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Default RE: O.S. 46 AX question

Turn your highspeed out a 1/4 turn
Old 02-05-2007, 01:48 AM
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hemiram_05
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Default RE: O.S. 46 AX question

I know that my fuel lines aren't pinched and honestly i think im just about too rich on the high side. When im taking off i can definately tell that its really rich due to the lack of power. When the tank gets lower it acts a little better,but still rich. This is by far the best engine ive ever had and I want to keep it for a while so im trying to break it in well. I had a Magnum previously and i will NEVER go back to them. I had way too much trouble with it. Anyways, I can't really explain the sound but just for a split second it sounds like the propeller unloads completely and the sound fluctuates back and forth between that and normal a couple of times. Then on the way out it goes back to normal. Im going to go back to the 11X6 prop as soon as i get it in the mail. Maybe that will solve my problem.
Old 02-05-2007, 06:20 AM
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Default RE: O.S. 46 AX question

The way to determine if its rich is not by the power it provides on take off. The 10x6 prop is providing significantly less thrust than the 11x6 you broke. This translates to "weak" power on take off. The smaller prop, with much less load on the engine, may be causing the engine to run lean. Anytime you change prop loading, you need to adjust your high speed needle. Look for the peak RPM setting, and back it out a few clicks.

The noise you're hearing could be due to the engine leaning out at the very high revs. As the engine heats up, it loses compression. I'm not sure, but it could be the prop wind milling as it loses compression thats changing the sound.

Props are considered "consumables". Always have a couple spares in the right size.

Brad
Old 02-05-2007, 06:42 AM
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sparkknocker
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Default RE: O.S. 46 AX question

If your engine is rich it will cough and sputter from idle to full throttle. As said before, the power is not a way to determine if your engine is at the right mixture. I assume what the deal is the low end mixture screw is too rich and your compensating on the high end. That is if indeed it coughs a bit going from a 15-20 second idle to wide open rapidly. If that is the case screw in your low end idle mixture no more than 1/4 turn at a time. I would start with 1/8 of a turn...once complete back your high end off 1/4 and go wide open to for about 5-10 seconds to get the excess fuel out and repeat the process until you acheive a smooth transition from idle to full.
Old 02-05-2007, 11:09 AM
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hemiram_05
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Default RE: O.S. 46 AX question

No my engine doesn't cough and sputter all the way from idle. My idle mixture is fine. And I know that power isn't the way to tell about the mixture. I was just giving an example. I have set the mixture on the high side to where it barely breaks in from the "2stroke to 4 stroke sound". then i set the low to get the right mixture on it. When i tilt the plane up, it'll try to run a little faster but you can tell that its rich. I can set the high needle quit a bit leaner and then i really get into some rpms but since im trying to break it in well i back the high needle off quit a bit, then reset my low. The main answer i was after was about the propeller. I don't remember my engine ever doing this with the 11X6. Thank you guys for taking the time to answer my questions and sorry if i sound like i know it all.

P.S. i think this website is a great place. I can already see there are a lot of nice people here.
Old 02-05-2007, 11:24 AM
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hemiram_05
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Default RE: O.S. 46 AX question

Hey guys I have another question and it may have something to do with my problem. In your planes, is the pick-up line in your fuel tank flexible enough to allow the clunk to go forward towards the nose of the plane. I was just setting here examaning my plane and was looking at the fuel tank and when i tilted it forward all my fuel went to the front and the clunk stayed right were it was. I would say that this could be part of my problem and why it revs so high on the low speed passes. Im leaning out excessively when the nose points down. Im probably just used to the rich "bogging" sound and when it leans out the revs just shoot through the roof. Any tips or tricks to stop this? Thanks guys
Old 02-05-2007, 01:02 PM
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Default RE: O.S. 46 AX question

That's typical of an air leak (in the engine or lines) or bubbles in the line; both of which cause the engine to go to lean when the air hits the carb jet. Hopefully, it's not the new O.S. Check to make sure the tank is isolated from the frame and firewall (vibration causes bubbles) and check the line from the tank to the carb to make sure it doesn't have a tiny tear or pin-hole. These can be almost invisibly small, so it's usually easier to just replace that line before checking anything else.
Old 02-05-2007, 02:26 PM
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hemiram_05
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Default RE: O.S. 46 AX question

Thats one of the flaws of the p51 pts. My tank doesn't have any foam at all around it.. It is held in place by being sandwiched beween the firewall and a piece of wood behind it. Vibration may be some of my problem. The only thing is whenever its on the ground i can run it at any speed i want and look at the line going into the carb and there are NO air bubbles so i don't think its that. If it was air wouldn't it happen all the time, not just on high speed passes.
Old 02-05-2007, 03:06 PM
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Default RE: O.S. 46 AX question

hemiram_05, if you can run at different rpm's on the ground with no bubbles, I don't think that is your problem. The wheels touching the ground wouldn't dampen the vibration that much.
Old 02-06-2007, 01:46 AM
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Default RE: O.S. 46 AX question

G'day Mate,
The clunk does not have to reach the front of the tank, ever, in fact I solder a piece of brass tube onto my clunks, so they can't swing & kink the fuel pickup tube.
When the plane is flying, & you go into a dive the forward movement of the plane stops the fuel from rushing forward, that will only happen if you stop suddenly in flight, which is unlikely, or tilt it nose down on the ground.
Old 02-06-2007, 08:40 PM
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Default RE: O.S. 46 AX question

It just occurred to me that it might be hitting the harmonic frequency of the muffler on the high speed pass. At that point, the back pressure from the muffler can be causing higher compression and a boost in power (the tuned pipe effect). Because its not truly a "tuned" pipe, it probably comes off it quick. If this is the case, a larger prop should fix it.

Brad
Old 02-06-2007, 09:07 PM
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Default RE: O.S. 46 AX question

ORIGINAL: hemiram_05

Hey guys. I have a Hanger 9 P51 pts with a O.S. 46 Ax engine in it and when i do high speed low passes my engine does something weird. When i get to peak rpm and speed it sounds like my propeller has come off for a split second. The engine winds really high and then goes back to normal. It does this one or two times on just about every full speed fly-by. The rest of the time it sounds normal. I broke my 11x6 prop the other day and all i had was a 10x6 so i put it on. I didnt know if that prop was to small or what. I am running fairly rich on the high side due to the fact that im still breaking in the engine. Any comments would be appreciated.
What you are describing is a phenomenon know as unloading. What this means as you make your high speed pass you reach the maximum speed that your prop can produce. When this happens the prop is not able to push enough air to load the engine.
Put the larger prop back on and the problem will go away
Old 02-08-2007, 12:03 PM
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gbrandt1
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Default RE: O.S. 46 AX question

Iron Eagle is correct...go to a larger prop and Im sure youll see results
Old 02-09-2007, 08:49 PM
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rotccapt
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Default RE: O.S. 46 AX question

What this means as you make your high speed pass you reach the maximum speed that your prop can produce. When this happens the prop is not able to push enough air to load the engine.
just a little fyi this is the reason that a prop plane can not break the sound buerier because a prop can only pull a plane so fast and after that it cant go faster. where a jet works better the faster you go.

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