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General control line discussion => Open Forum => Topic started by: John Lindberg on October 06, 2020, 07:42:18 PM
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Does it make a difference if the exterior uniflow tube (the one that connects to the tank uniflow tube) is on the inner part of the fuse nose, (the leadout side), or the outer ( the tip-weight side of the wing)? D>K D>K
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John,
In general it is better to have the uniflow vent in the free air stream on the in board side of the fuse. I have had a few ships that gave inconsistent runs when I tried to put it in the back of the engine. I was thinking it would eliminate the upwind/downwind fluctuations. It didn't and when I remembered the old advise of having the vent inboard it solved all the problems.
Best, DennisT
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John,
In general it is better to have the uniflow vent in the free air stream on the in board side of the fuse. I have had a few ships that gave inconsistent runs when I tried to put it in the back of the engine. I was thinking it would eliminate the upwind/downwind fluctuations. It didn't and when I remembered the old advise of having the vent inboard it solved all the problems.
Best, DennisT
You can solve the up wind and down wind variations by making a plug that has a step down piece of tubing to 1/16" tubing fitted into a short length of fuel line and put that on the vent after filling the tank. Just periodically check it to make sure it stays free and open.
Type at you later,
Dan McEntee
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Mark Scarbourough showed me about running the uniflow vent to the inboard side and then turning it into the airstream with a forward 90 deg bend. My FP’s sure seemed to respond well to it. Uniflow pressure is virtually a constant.
Gary
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INBOARD works for me
Fred Q
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Yes, the way Fred has it on a profile is the way to go. Seems the airflow over the fuse gets turbulent and causes pressure fluctuations that make the uniflow tank unpredictable on some ships. I had a Ringmaster with an OS 25 on it, hard tank with the uniflow vent just off the tank (on the outboard site of the fuse), this gave inconsistent runs, some great most to lean. Again, after I moved the vent to be clear of the fuse up in the free air stream BOOM solid runs no matter what the weather conditions. As for up wind/ down wind I use 1/16 hole in the end of the vent line (it naturally gets shaped down from the tubing cutter) and I haven't had any real issues.
Best, DennisT
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The Uniflow vent will always be in the high pressure slipstream of the prop. Variations in air pressure upwind/downwind are minimized compared to the prop blast. Air movement through the uniflow tubing is the same as fuel movement through the pickup line. IOW, air molecules move slowly through the Uniflow line. Therefore, the opening to the outside air should be quite small. I restrict the Uniflow opening with a piece of fuel tubing and a smaller piece of metal tubing.
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Everything said above is generally correct. As long as the tube faces forward toward the prop blast you're good to go.
Where the unilfow tube exits the tank does not really matter as that is just plumbing. What is important is where the tube is soldered inside the tank. As long as is in the correct location your engine will run solid.
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Fred showed me how to do this on a Shark 402 and I have a better engine run - LA 25.
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It's been a while, but on my planes over the last few years, I brought the soldered tubes out a metal tank's front face. The fill, vent and overflow outside pieces are firmly located and mounted through the structure and connected with fuel tubing inside the cowl. (This doesn't work with slide-in tank mounting...)
The forward-facing uniflow inlet is sleeved down to 1/16" OD with short lengths of telescoping smaller OD tubes sweated in. Yes, 1/16" outside diameter! 1/16" OD tube has 1/32" ID. Keep in mind we take several minutes to empty the fuel tank, so plumbing resistance is much less significant. There is some restriction, but apparently less than inherent to uniflo venting. Pump a bit of fuel out the uniflow tube after filling to clean it out. The small front opening is less susceptible to upwind vs downwind effects.
YMMV
Added: the uniflow inlet goes inboard of the fuselage. ...and above the tank centerline to be certain nothing siphons or drains out while waiting on the ground.