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Engine basics => Engine set up tips => Topic started by: Steven Kientz on August 06, 2014, 06:50:24 PM
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A local flyer has a profile with a ST 51 for power. We can't seem to get the air out of the fuel line. The tank has been pressure tested twice. It doesn't seem to matter whether it has muffler pressure or not. We have considered a different tank, thinking the internal lines might be the problem. He does have a small piece of foam between the tank and fuse.
Steve
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I'd first change the fuel line and be sure the filter isn't leaking air. A pinhole can cause this. Otherwise it's likely vibration foaming the fuel. You can check the prop for balance or change props. You might try rotating the prop 90 degrees and see that it's not compounding the internal mis-balance of the crank. Most likely he'll just need to stiffen the nose. I have on one occasion sanded dope mostly off, glassed the whole fuselage and refinish. That solved the issue completely on that soft profile.
Dave
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Does it effect the way the engine runs when the plane is flown? It may not. If not, don't worry about it. If you don't have one, put a filter in the line, sometimes that will break up the bubbles between it and the engine. As stated below, make sure the filter doesn't have an air leak. Try another tank, make sure no holes in the flexible fuel lines. 8)
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The plane is a Brodak Hellcat, I don't know how stiff the fuse is on this kit. He doesn't run a filter, we did check the lines and tank for pinholes, didn't see any. He just started balancing props, will try changing its orientation. The engine currently runs rich, very little change without a major needle adjustment. The end it goes very lean. I didn't mention we noticed airbubbles in the pressure line headed to the tank.
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The Brodak profile series have pretty stiff fuselages in my experience. ST-51 is a pretty strong engine for a plane that size. Curious as to what props you are using. I would definitely put a filter in the system. Stock ST-51s don't like to be run too rich. Try leaning it out from the start and use a lower pitch prop. 8)
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I would say we have our best luck with the .51 running it just like the old .46- pretty rich launching in a solid four stroke. We liked the APC 11/6 well on it pulling a 69 ounce airplane with little trouble. I burnt up a couple until I learned ( to my amazement) it doesn't run like a typical Schnerle motor, ie OS FP/LA etc. I don't remember tach settings now but I would guess 8500-8800 rpm to launch. I cooked em' on 4 pitch. Curiously it sounds overloaded on more the 11" diameter unlike the .46 which I preferred to use the Rev Up 11 1/2 - 6 EW.
Dave
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That's one of the beauties of IC engines...often there is often more than one correct way to get them to work. One often has to experiment and find out which setting/prop/rpm etc. works for you. 8)
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I believe the prop is a 12x5, Sig 5% all castor, tongue muffler on pressure. I don't know the brand of tank, 4.5oz all forward tubes. We won't fly again until midweek, hopefully he tries another tank before then. The needle was turn a good 1/4 turn on the ground -no response. Engine goes WAY lean near the end of the tank.
Does no response from the needle say" venture too big or small?" This was a used engine, somewhat square head, Chinese manufactured? It has a black delrin venture and I would assume a ST nva.
Thanks for all the help.
Steve
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Steve I'd pull that Venturi and clean out the sprinkler hole (s) with a straight pin or similar. Those tiny holes can accumulate crap and block fuel flow. I just dug a pretty good cocklebur out of one of my RO Jett's that didn't respond much to the needle. Yes I run a filter always but stuff still builds up in those jets over time. My .51s had aluminum venturis-not familiar with a black one.
Dave
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thanks
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What Dave said. I question the use of all castor fuel. With all the finning on these G-51s they tend to be cold blooded.. Try some 10/22 10% and see what happens. Try direct uniflow, as in no muffler pressure, sometimes this helps. 8)
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In my opinion, a major cause of bubbles in fuel tube is the micro vibration generated by the engine. Check out nicely, the balancing of the propeller and spinner. The engine mount must be hard too. Try to fly with mixture less rich and a warmer glow plug.
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dont forget to add a couple of drops of ARMERAL
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I'm going to print this thread on Tuesday so he has a list of possible solutions.
Thanks!!
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That would be a couple of drops of ArmorAll...PER GALLON, effective anti-foaming agent if that is the issue. 8)
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I had a Brodak uniflow oval tank that had steady a stream of big bubbles going through the fuel line. It turned out the uniflow tube interior opening was too close to the pickup and feeding it air. If you haven't tried it, capping the uni vent(and opening the overflow) would troubleshoot that possibility. But i think it's normal to see a few bubbles from that very thing. That's where the filter helps too.
Rusty
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I want to thank everyone for their suggestions. Problem was solved by changing tanks. He is currently running a Hayes plastic clunk tank.
Steve
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Is this the G.51 (as I think many assumed)? ST did make some earlier .51's, including a sleeve bearing one as well as the ball bearing little brother (sister?) to the famous ST .60bb.
Good choice on the Hayes tank! Might not be the ultimate tank, but they're simple and reliable. My G.51 needed under 6 oz of 10% with a .285" venturi. I used mostly Powermaster 10-22 GMA.
An APC 12-5 is a good baseline prop. The Thunder Tiger 12.5 x 5 and RSM 12 x 5.5 would be worth trying. I also used the 12.25 x 3.75 APC, and it worked fine. I don't recall what the launch rpms were for each prop. H^^ Steve
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I believe it is the g.51. When to a LHS today and passed on a Como 51. It had good compression, but I have 3 Os la46s, didn't figure I needed it.