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Engine basics => Engine set up tips => Topic started by: Matt Colan on March 28, 2009, 07:36:33 PM
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On my Ares, I am running an OS .35 in it. I have a 4 ounce tank in it. When I start it, it tachs at about 8600 to be about right for half of the flight. The next half it picks up RPM by maybe 500 and leans out. I can still finish the pattern, it doesn't lean out that much. To me that isn't normal, I have run OS .35s in 2 other planes and never leaned out in the middle of the flight. Does this mean it needs more break in time or is that something I am going to have to get used to.
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I'm guessing there is an issue in the tank.
Maybe a crack in the uniflow tube inside the tank which uncovers roughly half way through the flight. Once the crack is in air, the it can easily bleed air into the rest of the tank. At that point the tank begins to act like a normally plumbed tank (with the vent located midway in the tank) for the rest of the flight.
If you can, try to change tanks and see if the problem clears up.
Or something like that!
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I agree, you have a tank issue. You could try changing to a different tank and my bet is it will solve it. My Shoestring which also has an OS Max-s 35 is doing the same thing. I have a repaired tank on it and it starts out rich and as the fuel gets lower it leans out some. I also find that it starves on outside loops after about 2/3's of the fuel is gone. I'll be changing it tomorrow. More experienced guys have told me that anytime you have an inconsistant running engine the first thing you need to do is check your fuel system.
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I agree to a point, check the fuel system, but Matt knowing how thourough your approach has been on other issues, I am betting its not a tank issue. I refer you to the first rule taught me by Pat,, if it leans towards half flight, add oil. this is classic symptoms for low castor in the fuel, the engine builds heat as it goes through the flight and there is not enough castor to cool it. My guess would be that it leans in a manuever and doesnt come back down again..
add 3 or 4 oz of castor to your fuel ( per gallon that is_) and blend it,, I am willing to bet you will have a sweeter run. Some needle tweaking will need to be done and if you are marginall on fuel load to complete the pattern you COULD run into some issues there. but, it sounds like a classic case of needing a dose of castor.
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I agree to a point, check the fuel system, but Matt knowing how thourough your approach has been on other issues, I am betting its not a tank issue. I refer you to the first rule taught me by Pat,, if it leans towards half flight, add oil. this is classic symptoms for low castor in the fuel, the engine builds heat as it goes through the flight and there is not enough castor to cool it. My guess would be that it leans in a manuever and doesnt come back down again..
add 3 or 4 oz of castor to your fuel ( per gallon that is_) and blend it,, I am willing to bet you will have a sweeter run. Some needle tweaking will need to be done and if you are marginall on fuel load to complete the pattern you COULD run into some issues there. but, it sounds like a classic case of needing a dose of castor.
I am running Sig Champion 5/22 with a little extra castor mixed in. I can't remember how much though. I do need to shim the tank because it leans out and doesn't stop until the maneuver is done on inside rounds. Outsides it richens up, I move the tank closer to the motor mounts right?
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Hi Matt - How big is the exit area of the muffler? Too much backpressure can cause heat retention/ runaway and its indistinguishable from too little oil. Tom H
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Good information Mark, thank you.
Terry
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Well I popped the back of the tank off, and none of the tubes were leaking. My only other guess is to take muffler pressure off and see how it runs like that.
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Tom Hampshire's muffler tip is also solid information! So, what sort of muffler ya got on that OS .35S, Matt? If it's a tongue muffler, try flying without it, or swap to a tube muffler. I like Randy Aero's tube mufflers. The one I put on my .46LA got the outlet drilled out and a 'rubber ducky' installed. That same muffler will fit your .35 and therefore, the outlet should be big enough, but the straight outlet will oil down your whole plane. Thus, the rubber ducky, and therefore the outlet drilling. :! Steve
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Tom Hampshire's muffler tip is also solid information! So, what sort of muffler ya got on that OS .35S, Matt? If it's a tongue muffler, try flying without it, or swap to a tube muffler. I like Randy Aero's tube mufflers. The one I put on my .46LA got the outlet drilled out and a 'rubber ducky' installed. That same muffler will fit your .35 and therefore, the outlet should be big enough, but the straight outlet will oil down your whole plane. Thus, the rubber ducky, and therefore the outlet drilling. :! Steve
Steve, I'm running a Big Art tongue muffler that we put a pressure fitting on. I don't want to put on a tube muffler since I don't want it become more nose-heavy than what it is, which is why i have a tongue muffler on.
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I guess I'm getting confused on which actual OS engine you are using---is it an old OS-35S, or the newer OS-35 FP? I ask because the 35S isn't that heavy and I wasn't aware that you could get a Big Art muffler for the 35S since it doesn't have "normal" muffler lugs unless you tap the upper and lower "plugs" on the exhaust port (don't know what else to call them)! The 35FP has a standard bolt-on muffler while the 35S came with a strap-on muffler.
The reason I ask is that in your first post you say "I have run OS .35s in 2 other planes ....." which I can interpret in at least 2 ways!
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I guess I'm getting confused on which actual OS engine you are using---is it an old OS-35S, or the newer OS-35 FP? I ask because the 35S isn't that heavy and I wasn't aware that you could get a Big Art muffler for the 35S since it doesn't have "normal" muffler lugs unless you tap the upper and lower "plugs" on the exhaust port (don't know what else to call them)! The 35FP has a standard bolt-on muffler while the 35S came with a strap-on muffler.
The reason I ask is that in your first post you say "I have run OS .35s in 2 other planes ....." which I can interpret in at least 2 ways!
Hi Alan, I can understand the confusion, I am running an OS .35S, not the FP. This engine my grandfather bought from Mike Tufano, who has passed on, but he drilled through the exhaust ports to put a bolt on muffler on. We also have a 35-40 year old OS .35S that I guess had a bolt on muffler. I originally had with that engine a wrap around muffler on my first plane, but it kept on coming loose so he had an aftermarket muffler for it. That engine could have had bolt on mufflers and that is what there was on that one particular OS .35S.
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Could this be it, my grandfather was talking to Hank Womble and he mentioned my problem. He said it could be the venturi is too big and is sucking in air instead of fuel causing it to lean out. Could that be it?
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During a flying session today, I took muffler pressure off and the motor ran beautifully. Now I got to get the tank shim right.