Uniflow Tank

[Richard Becker]

I am fitting a metal uniflo wedge tank to a Smoothie with a Brodak .40 with standard type muffler. Question: Do I use muffler pressure or just point the uniflo tube forward into the slipsteam? If I use muffler pressure, where is the best point on the muffler to fit the nipple? 

[Bill Little]

I am fitting a metal uniflo wedge tank to a Smoothie with a Brodak .40 with standard type muffler. Question: Do I use muffler pressure or just point the uniflo tube forward into the slipsteam? If I use muffler pressure, where is the best point on the muffler to fit the nipple? 

Muffler pressure seems to be an engine to engine, plane to plane preference for most people.  I seldom use it with a uniflow tank, but many do.

The nipple usually goes on the "manifold" section of the muffler, between the engine and the tube.

[Bob Reeves]

Here is the one on my Skylark, sporting it's new Brodak spinner. I usually try to find the thickest area to drill and tap for the pressure fitting. Sometimes tongue mufflers are so thin I put a nut on the inside and use lock tight to keep everything together.

[Andrew Hathaway]

Oooh... The spinner is nice, but its the Rev Up prop crafted from pure unobtainium that really caught my eye.

[Bob Reeves]

Ya my Classic ship just had to have a ST 46 with a Rev-Up 11-6 EW, took me a while to locate enough EW's to have a couple spares but tell you what.. I stuck a new 11-6 Pro Zinger on it once just to see if it would work and was highly impressed.  If I didn't have the Rev-Ups wouldn't hesitate to run a lightly reworked Pro Zinger.

[Andrew Hathaway]

I've got a small stockpile of Rev Up props, probably more then I'll ever truly need, but I'm still afraid to use em.  Around here I am flying off of grass and usually very rough grass at that, so the risk to the props is pretty substantial.  I can get Zingers at the local hobby shop so I've run some of them with very good results.  I got so distracted with the prop that I forgot to comment on the initial question...

With a uniflow tank and the vent facing forward into the slipstream, the air pressure can fluctuate when the plane comes into the wind since the air will be blowing into the pipe.  You'll notice cause the engine will run rich into the wind and lean downwind.  By running muffler pressure instead you get a more consistent flow of air.  Of course all of this is hypothetical and theoretical, it's still a good idea to try different configurations and see what works best for the plane in question.

[john e. holliday]

If I had a camera I would show you how John Bender cured the fluctuation.  His vent on the ARF Nobler is inside just behind the engine.  It does work as I have seen many flights with that setup.  I will be converting my setups when quit being so lazy.  DOC Holliday

[Jim Thomerson]

When not running pressure, I run a one way valve on the uniflow. I have one tank which does not work with the one way valve for reasons I do not understand.

[Andrew Hathaway]

We tried a one way check valve a long time ago on the uniflow vent.  This particular application had a problem where the tank would fill the muffler with fuel.  At any rate, with a check valve on the uniflow line the break from 4-2 in maneuvers would cause a surge of pressure in the tank that didn't have any way to escape.  The result was that the engine would die shortly after a maneuver.  It did fix the fuel dumping in the muffler though. 

[Jim Thomerson]

I tried a check valve with muffler pressure and did not like it.  I use a check valve with crankcase pressure. The problem I had with one application-- I filled through the uniflow. then plugged the vent line, then attached the muffler line to the uniflow.  No problem.  Got some short runs, noticed siphoning;  realized I was attaching the muffler line before I plugged the vent.  Plugging the vent started fuel running down the muffler line  (profile side mount).