Uniflow fuel tank set-up  
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All Forums >> RC Airplanes >> Questions and Answers >> Uniflow fuel tank set-up
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Uniflow fuel tank set-up - 7/3/2005 2:48:52 AM   
Firewalkerd1


 

Posts: 128
Joined: 10/19/2003
From: Southeastern, KY, USA
Status: offline 		Read an article in Fly RC on a fuel tank setup called, uniflow system. Has anyone used this system? Please let me hear pros and cons. The article mention a check valve to keep the fuel from interring the muffler. Where can this type of valve be found that the fuel won't affect it? Maybe at the local auto parts store. Hope I have this in the right form.
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RE: Uniflow fuel tank set-up - 7/3/2005 5:29:17 AM   
redfox435cat



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Joined: 3/7/2005
From: Lompoc , CA, USA
Status: offline 		yea I'd like to hear about this. how is it phsycally possible?

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RE: Uniflow fuel tank set-up - 7/3/2005 6:13:19 AM   
50%plane



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Joined: 3/8/2005
From: x, , USA
Status: offline 		Muffler pressure.

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RE: Uniflow fuel tank set-up - 7/4/2005 12:11:14 AM   
redfox435cat



Posts: 1030
Joined: 3/7/2005
From: Lompoc , CA, USA
Status: offline 		Oh I get it. air from muuffler but no fuel to muffler. then how do you fuel up the tank. their is no were for the air to go when ya fill it up?

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RE: Uniflow fuel tank set-up - 7/4/2005 12:24:12 AM   
RCKen



Posts: 14744
Joined: 7/10/2002
From: Lawton, OK, USA
Status: offline 		Firewalkerd1,
Well, I've never heard of a "uniflow" fuel system but I'm pretty sure that it's similar to what get's used with a YS motor. On YS motors pressure for the fuel tank it provided by the motor instead of from exhaust, and a check valve in the pressure line is used to maintain postive pressure in the tank. Whenever you remove the fill line to fill with fuel you will here the "hiss" as the pressure is released.

The same thing can be accomplished with exhaust pressure too, just use a check valve in the pressure line. You can get these check valves at your LHS or you can order them from Tower Hobbies.
http://www2.towerhobbies.com/cgi-bin/WTI0095P?FVSEARCH=check+valve&FVPROFIL=++

Hope this helps

Ken

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RE: Uniflow fuel tank set-up - 7/4/2005 12:56:13 AM   
Ed Smith


 

Posts: 2835
Joined: 12/29/2001
From: Brantford, ON, CANADA
Status: offline 		With the Uniflow system there are three lines. The feed line and the pressure line both have a clunk and got to within 1/4 to 3/8 of the back of the tank. The third line is the vent and goes to the top of the tank. As the pressure line is usually the most accessible it is used for filling the tank however either line can be used for filling. Some fuel will run up the feed or the pressure line but very little as the escaping air is easier to push out of the vent. when the tank is full fuel will come out of the vent. the vent will have to be plugged for flying. A check valve is not necessary.

In very basic terms, because both lines are submerged the only time that air can enter is when fuel exits, so there is a better balance of pressure/fuel in the tank. That is the very short answer. One of the disadvanteges is that the engine will quit at the end of the tank with no warning splutters.

Ed S

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RE: Uniflow fuel tank set-up - 7/4/2005 1:49:18 AM   
RCKen



Posts: 14744
Joined: 7/10/2002
From: Lawton, OK, USA
Status: offline 		Ed,
Thanks for clearing that up. Sorry if I confused anybody. No matter how hard I fight it, I wind up learning something new every day!!!

Ken

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RE: Uniflow fuel tank set-up - 7/4/2005 5:45:03 AM   
JoeAirPort



Posts: 7149
Joined: 8/11/2003
From: Milwaukee, WI, USA
Status: offline 		What I read in a magazine recently was that because both the vent clunk and fuel supply cluck are right next to one another at the bottom of the tank, the mixture of the engine stays the same througout the entire tank. With a vent at the top of the tank, the mixture is rich at the start of the flight and lean at the end. The thing is that while the Uniflow this is better, it does not replace a pump or fuel regulator (the tank cannot be on CG).

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RE: Uniflow fuel tank set-up - 7/4/2005 5:46:31 AM   
Mad Mad Max


 

Posts: 63
Joined: 1/14/2004
From: Silverdale, WA, USA
Status: offline 		In control line flying, espically racing, mufflers are not allowed. A uniflow tank is used as it allows a very steady engine run and uses almost every drop of fuel. One tube, the uniflow, points into the air steam for pressure and ends very close to the pick up tube. The pick up tube does not have a clunk but ends about 1/3 into the tank. The tank has a shape to it that allows this method to work. There is a third tube is used during filling. Fuel is added thru the uniflow tube and the third tube is the vent. This vent line generally uses a piece of surgical tubing and an alligator clip to open the line for venting and closes the line to run the engine. Go over to the control line forum and you'll get the whole story plus pictures on how it works

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RE: Uniflow fuel tank set-up - 5/10/2007 10:31:40 PM   
jrpav1


 

Posts: 190
Joined: 9/11/2003
From: New Milford, CT, USA
Status: offline 		Guys,
I wrote the article in Fly RC so maybe I can clear things up a bit (I hope): the check valve's main purpose is to keep fuel from entering the muffler when you go from full throttle to idle. In a Uniflow system this can happen rather easily because the muffler pressure line is always submerged in the fuel. With a conventional 2-line system this can't happen when the plane is upright. Now, think about this: a conventional 2-line system actually becomes Uniflow when you're flying inverted! Most of the time you don't fly inverted at idle so you'll never notice the condition I described. I've installed the Uniflow system in quite a few airplanes and I have used the check valve, but only with motors that have 2-needle carbs. It does create a lot of pressure - similar to a YS system. You end up closing the idle needle a bit but other than that it tunes just like a 2-line system except that you can run a little leaner on the top end since you don't have to worry about the mixture changing as the fuel level drops. You CAN run a Uniflow without the check valve but you run the risk of filling the muffler with fuel if you close the throttle really fast.
As far as filling the tank with a cowled motor, I've started using an external feed line between the carb. and the pickup in the tank. This works really well and it allows you to pinch the fuel line to set the top-end mixture. If the motor is exposed, just drain and fill through the carb. feed line. Give it a try.

John Pavlick

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RE: Uniflow fuel tank set-up - 5/11/2007 1:33:20 AM   
N1EDM



Posts: 1903
Joined: 7/19/2002
From: Brockton, MA, USA
Status: offline 		Hi John,
I read your article. There was a lot of info in it.

I hate to sound like a skeptic, but perhaps you can clear something up for me... From what I can tell from reading you (and other) articles on Uniflow, it seems like just the 'head' pressure of the fuel in the tank is enough to create the difference between this and a conventional two-line system?

I am considering using this for my Cermark Javelin II with OS 55AX, but I just can't seem to wrap my brain around the concept that this small difference in pressure is enough to make a difference. I'm not trying to argue with you, just wondering if my concepts are correct..

Thanks,

Bob

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RE: Uniflow fuel tank set-up - 5/11/2007 2:10:19 AM   
iron eagel



Posts: 1268
Joined: 7/15/2004
From: Middleboro, MA, USA
Status: offline 		Bob,
Don't feel bad I have a new OS 70 Fl and can not figure this 3 line setup out myself with the manual in front of me. They have a coupe of T's check valves, stoppers, two clunks, a vent and two nipples to the muffler. I kid you not there are 9 sections of line running between the motor tank and muffler. This is what they suggest for the "aerobatic" set up.
Although after reading this post it makes a bit more sense.

< Message edited by iron eagel -- 5/11/2007 2:36:11 AM >

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RE: Uniflow fuel tank set-up - 5/11/2007 2:39:12 AM   
N1EDM



Posts: 1903
Joined: 7/19/2002
From: Brockton, MA, USA
Status: offline 		Paul,
Do you get Fly R/C? I was wondering if you had had a chance to read John's article? Not sure which edition it was in, but I might have it here.

Bob

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RE: Uniflow fuel tank set-up - 5/11/2007 3:03:42 AM   
iron eagel



Posts: 1268
Joined: 7/15/2004
From: Middleboro, MA, USA
Status: offline 		Bob,
No I have not seen that ....
Although what was said here does make some sense out of what I was looking at. From what I can see this should make it a constant flow of fuel to the engine at all times makes some sense.

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