RE: Uniflow fuel tank set-up  
View related threads: (in this forum | in all forums)

Tower Hobbies
Enter up to 4 keywords or Tower stock numbers
Logged in as Guest



Users viewing this topic: none
  Printable Version
       


Wheely King 14mm Hex Wheel Extensions - RTR
Seller:  wheelextensions
Details:   $20.00   |  8/30/2008   |  Classified Ad
We will rotate YOUR AD in this spot if you select "Forum Featured" when placing or editing your ad!

All Forums >> RC Airplanes >> Questions and Answers >> RE: Uniflow fuel tank set-up
Page: <<   < prev  1 [2]

Login
Message << Older Topic   Newer Topic >>
RE: Uniflow fuel tank set-up - 5/23/2007 3:38:52 AM   
FlyI Bus Driver


 

Posts: 75
Joined: 9/24/2004
From: Easton, PA, USA
Status: offline 		I have a question...

When filling up the tank with a uniflow set up through the muffler line (with a check valve to prevent fuel from entering the muffler), will the fuel flow out the tank through the carb line before reaching the fill line port in the tank, or will it flow out the fill line first? Will closing the carb prevent fuel from flowing out or do you need to clamp the fuel line to the carb closed during fueling?

(in reply to Sport_Pilot)
       Post #: 26

RE: Uniflow fuel tank set-up - 5/23/2007 1:48:37 PM   
Sport_Pilot



Posts: 7728
Joined: 1/21/2002
From: Acworth, GA, USA
Status: offline 		Yes fuel can go back through the carb, be sure the carb throttle is closed and the vent is open. Ususally this is enough, any fuel that gets to the carb is small and makes a good prime. However, on some it can flood the carb. For those use some hemastat's or something to clamp the line while fueling.

_____________________________

“I Saw Elvis at 1000 Feet” John Force

(in reply to FlyI Bus Driver)
       Post #: 27

RE: Uniflow fuel tank set-up - 6/6/2007 10:27:36 PM   
AA5BY


 

Posts: 263
Joined: 9/7/2006
From: White Oak, TX, USA
Status: offline 		I'm having some mental blocks in accepting the theory here. I certainly accept that a normal system gets leaner as the tank drains due to the the change of fuel line pressure. At startup, fuel exist above the needle center line and seeks to drain to the needle valve under some very slight amount of pressure, whereas as the tank gets below half full and the fuel level is below the needle center line, some degree of suction is needed. That the fuel line pressure goes from positive to negative I understand.

Why is that not also true for the uniflow system.

I just ran a test on a three line tank... whether the vent line is plugged or the bottom line makes no difference... there is positive pressure whenever the outflow (carb line) gets below the fuel level of the tank and the flows appear to be equal.

What am I missing about understand this or is it that it is not understandable because it is not reality?

< Message edited by AA5BY -- 6/6/2007 10:28:36 PM >

(in reply to Sport_Pilot)
       Post #: 28

RE: Uniflow fuel tank set-up - 6/6/2007 11:55:40 PM   
vertical grimmace


 

Posts: 1145
Joined: 3/13/2004
From: ft collins , CO, USA
Status: offline 		Actually for a uniflow system to work properly the tank must be sealed. The vent line must be plugged. I feel there is no doubt that this type of plumbing is superior to the conventional methods and all you have to do to find out is fly a Control line aircraft with a standard vent tank and a uniflow vent. A 3 line fuel tank is almost mandatory anyway with the rear needle carbs as they are not very accesible for filling.
A second clunk does not have to be used for the uniflow line. A solid piece of brass tubing ran straight back to around 1\4" from the rear of the tank will suffice. It is best to use muffler pressure on the uniflow line as ram air is inconsistant.
Also with my many years of use with this type of tank I would not recommend the check valve. It is unnesesary and will probably cause problems of it's own.

< Message edited by vertical grimmace -- 6/6/2007 11:57:44 PM >

(in reply to AA5BY)
       Post #: 29

RE: Uniflow fuel tank set-up - 6/7/2007 2:18:38 PM   
Sport_Pilot



Posts: 7728
Joined: 1/21/2002
From: Acworth, GA, USA
Status: offline
quote:

A solid piece of brass tubing ran straight back to around 1\4" from the rear of the tank will suffice.


But then it wouldn't be uniflow when inverted. See if this helps you to understand it. Take a small can of soda or whatever. Punch a small hole in the bottom. Turn it upside down, only a small amount or no soda will come out. Now put another small hole in the bottom and attach a small tube, maybe a coffie stirring stick to it. Now turn it upside down and again little or no soda will come out. Now if you blow thru the tube the soda will come out, but only the same amount as the air you blow in.

_____________________________

“I Saw Elvis at 1000 Feet” John Force

(in reply to vertical grimmace)
       Post #: 30

RE: Uniflow fuel tank set-up - 6/9/2007 1:34:12 AM   
AA5BY


 

Posts: 263
Joined: 9/7/2006
From: White Oak, TX, USA
Status: offline 		Sport Pilot... your illustration finally turns the light on. Even so, having read the problems associated with a uniflow system... I'm not sure I'll ever rig it.

(in reply to Sport_Pilot)
       Post #: 31

RE: Uniflow fuel tank set-up - 6/9/2007 2:21:27 PM   
Sport_Pilot



Posts: 7728
Joined: 1/21/2002
From: Acworth, GA, USA
Status: offline
quote:

Even so, having read the problems associated with a uniflow system


Problems? There are no problems! Only people who don't understand them and plumbing them up incorrectly.

_____________________________

“I Saw Elvis at 1000 Feet” John Force

(in reply to AA5BY)
       Post #: 32

RE: Uniflow fuel tank set-up - 8/6/2007 3:39:49 AM   
D.O.A.F.S.


 

Posts: 29
Joined: 4/3/2006
From: Red Lion, PA, USA
Status: online 		Any Help appreciated. I tried the uniflow set up on a profile plane I have. I have not flown with it yet but have started and ran just to tune the motor. I thought I had a grasp on this yet it raises other questions in my mind. With the motor running it creates tons of air bubbles in the tank, why will this not creat a problem in it self? It seems that the feed line with being next to the pressure line will take some of this to the carb. The motor was already tuned and flown with the traditional tank with no problems. With the uniflow it seemed to have all kinds of problems. This uniflow tank set-up really intrests me and maybe I've done something wrong. I have both hoses and clunks the same length inside the tank and I ty-rapped them together so they would not get tangled. Did I do the rite thing or should they be a different length?

(in reply to Firewalkerd1)
       Post #: 33

RE: Uniflow fuel tank set-up - 8/6/2007 4:55:26 AM   
da Rock



Posts: 6704
Joined: 10/11/2005
From: western, NC, USA
Status: online 		Different lengths.

In metal CL stunt tanks, the two tubes are brass and soldered in place. And the pressure line has to be shorter. Some guys built their tanks with 1/2" difference.

The idea is that both lines are submerged all the time. Or at least, the pressure line is under most of the time. Or more than it would be if it was at the top of the tank where it usually is as an overflow on a two-line setup.

But the pressure line shouldn't be so close it blows the fuel away from the pickup line.

(in reply to D.O.A.F.S.)
       Post #: 34

RE: Uniflow fuel tank set-up - 8/9/2007 9:57:29 PM   
srxripper


 

Posts: 75
Joined: 11/5/2003
From: ocala, FL, USA
Status: offline 		i'm setting up a inflow on a profile, cause the engine ran super rich inverted, when it was inverted the fuel supply is a uniflow!

i'll update you on a flight sometime soon!

(in reply to da Rock)
       Post #: 35

RE: Uniflow fuel tank set-up - 8/9/2007 10:05:29 PM   
da Rock



Posts: 6704
Joined: 10/11/2005
From: western, NC, USA
Status: online
quote:

ORIGINAL: srxripper

cause the engine ran super rich inverted, when it was inverted the fuel supply is a uniflow!




And it wasn't uniflow when it was right side up. Which is why it ran two different ways.

If both the uniflow outlet and the fuel intake are clunks, they will both stay under the fuel together all the time. And you set your needle to suit and you're good to go. With VERY steady fuel draw from then on.

(in reply to srxripper)
       Post #: 36

RE: Uniflow fuel tank set-up - 8/9/2007 10:16:13 PM   
WILDCRASHWILLY



Posts: 462
Joined: 10/20/2003
From: Symsonia, KY, USA
Status: offline 		I have uniflow whith a YS check valve on a Saito 100. The engine is mounted inverted in a Great Planes Lancair Arf. I love the performance this system offers, however I'm still having to lean the low jet at idle as it will flood out if I bring the idle two low. Ive flown the plane about four times and still have to put more time on it. I have made several adjustments to the low speed and every time I fly it, it gets better. I need to add that this is a new engine and not fully broken in., " only about 3/4 of a gallon of fuel to date. I will mention that if you land and still have fuel in the tank, you should unplug the vent and relieve the pressure to keep from forceing excessive fuel in the carb.

Thanks for your article John Pavlick , I used your diagrams to set my plane up. Once I get the tuning completed I think I'm going to like this system.

< Message edited by WILDCRASHWILLY -- 8/9/2007 10:21:11 PM >

_____________________________

Bill

(in reply to da Rock)
       Post #: 37

RE: Uniflow fuel tank set-up - 8/10/2007 12:28:39 AM   
srxripper


 

Posts: 75
Joined: 11/5/2003
From: ocala, FL, USA
Status: offline 		wild, a good cure for saitos is a cline regulator, there somewhat pricey but work great, i had one on a saito100 which allowed me to put the tank near the cg, constistant runs every time, but the low end became very touchy, but once sorted i didnt have to touch untill huge temp changes in climate

in most all cases if you put a check valve which (seals) the fuel system, you need a regulator, what happens without the reg you dont meter the fuel going in which in all my cases cuease irratic mixture settings at different throttle settiings, all ys that i've seen have a check valve and reg, the cline system is very similar, the new os 90 heli engine combines a pump and reg, pump alone usually dont need a check vavle

(in reply to WILDCRASHWILLY)
       Post #: 38

RE: Uniflow fuel tank set-up - 8/10/2007 12:29:49 AM   
srxripper


 

Posts: 75
Joined: 11/5/2003
From: ocala, FL, USA
Status: offline 		ROCK your exactly right on

(in reply to srxripper)
       Post #: 39

RE: Uniflow fuel tank set-up - 8/10/2007 6:09:38 PM