Uniflow fuel tank set-up
02-19-2009 | 05:53 PM
#51
Senior Member
Joined: Aug 2008
Posts: 2,158
Likes: 0
Received 0 Likes
on
0 Posts
From: Burtchville,
MI
RE: Uniflow fuel tank set-up
ORIGINAL: marcelaw
Looking for help with a new uniflow setup on a boat. I'm running a Thunder Tiger Outlaw 7.5 boat, and have noticed leaning toward the end of my runs. In the constant pursuit of perfection, trying the uniflow setup.
Except for leaning toward the end of runs, boat was running pretty good on normal 2-line main tank, with 2oz hopper/header tank tied to muffler pressure. Setup the uniflow last night, and fired it up on stand. Once started, idle is more rough, and when giving it throttle has significant hesitation before RPMs jump up. I think I saw a post saying with uniflow you need to lean the low speed a bit...is that my issue? I'm not a tuning expert, but I would think the hesitation is caused by not enough fuel, so would need to richen low speed?? Thoughts?
Looking for help with a new uniflow setup on a boat. I'm running a Thunder Tiger Outlaw 7.5 boat, and have noticed leaning toward the end of my runs. In the constant pursuit of perfection, trying the uniflow setup.
Except for leaning toward the end of runs, boat was running pretty good on normal 2-line main tank, with 2oz hopper/header tank tied to muffler pressure. Setup the uniflow last night, and fired it up on stand. Once started, idle is more rough, and when giving it throttle has significant hesitation before RPMs jump up. I think I saw a post saying with uniflow you need to lean the low speed a bit...is that my issue? I'm not a tuning expert, but I would think the hesitation is caused by not enough fuel, so would need to richen low speed?? Thoughts?
If I were to assume that you were not running your fuel supply under muffler pressure before but are now after your modifications that you are rich on the low end and need to lean it out. If your low speed needle controls airflow turn the needle counterclockwise, if it controls fuel flow - clockwise.
Bill
02-19-2009 | 06:41 PM
#52
RE: Uniflow fuel tank set-up
ORIGINAL: marcelaw
Looking for help with a new uniflow setup on a boat. I'm running a Thunder Tiger Outlaw 7.5 boat, and have noticed leaning toward the end of my runs. In the constant pursuit of perfection, trying the uniflow setup.
Except for leaning toward the end of runs, boat was running pretty good on normal 2-line main tank, with 2oz hopper/header tank tied to muffler pressure. Setup the uniflow last night, and fired it up on stand. Once started, idle is more rough, and when giving it throttle has significant hesitation before RPMs jump up. I think I saw a post saying with uniflow you need to lean the low speed a bit...is that my issue? I'm not a tuning expert, but I would think the hesitation is caused by not enough fuel, so would need to richen low speed?? Thoughts?
Looking for help with a new uniflow setup on a boat. I'm running a Thunder Tiger Outlaw 7.5 boat, and have noticed leaning toward the end of my runs. In the constant pursuit of perfection, trying the uniflow setup.
Except for leaning toward the end of runs, boat was running pretty good on normal 2-line main tank, with 2oz hopper/header tank tied to muffler pressure. Setup the uniflow last night, and fired it up on stand. Once started, idle is more rough, and when giving it throttle has significant hesitation before RPMs jump up. I think I saw a post saying with uniflow you need to lean the low speed a bit...is that my issue? I'm not a tuning expert, but I would think the hesitation is caused by not enough fuel, so would need to richen low speed?? Thoughts?
The hesitation is cause by it taking time to clear the unburnt fuel before it will spool up, I have had this happen many times as an engine gets broken in.
Your engine has an adjustment to vary the low end mixture it is called the idle adjustment lean it a bit then reset your high end.
You may have to go back and forth a few times till you get a smooth engine response at all throttle settings you might want to look in the glow engine threads for hints.
Did you install a check valve on the pressure line from the muffler?
The reason I ask is that if you did when you throttle back from high to low the check valve will cause the motor to load up (flood). If so remove it the worst case is you will spit some fuel into the muffler when you chop the throttle.
02-19-2009 | 10:52 PM
#53
Junior Member
Joined: Jan 2009
Posts: 18
Likes: 0
Received 0 Likes
on
0 Posts
From: Katy, TX
RE: Uniflow fuel tank set-up
Thanks Ram Jet and iron eagel!
Ran it some more on the stand tonight and low speed was too rich...seems to be idling and revving great now. I am using muffler pressure, and don't have a check valve on the muffler (saw in a thread or two to stay away from the muffler check valves). I have seen a bit of fuel in the muffler but nothing major. Have also quickly learned to just let the engine prime itself on startup to minimize flooding.
So far so good on the uniflow...can't wait to hit the water...
Ran it some more on the stand tonight and low speed was too rich...seems to be idling and revving great now. I am using muffler pressure, and don't have a check valve on the muffler (saw in a thread or two to stay away from the muffler check valves). I have seen a bit of fuel in the muffler but nothing major. Have also quickly learned to just let the engine prime itself on startup to minimize flooding.
So far so good on the uniflow...can't wait to hit the water...
02-20-2009 | 11:12 AM
#55
Senior Member
Joined: Aug 2002
Posts: 1,301
Likes: 0
Received 0 Likes
on
0 Posts
From: Jonkoping, SWEDEN
RE: Uniflow fuel tank set-up
Using a check valve on the went line defeats the whole purpose of the uniflow tank system. As been previously stated, when the trottle is reduced to idle or low rpm after high speed running the pressure inside the tank will be maintained at a too high pressure for some time causing the engine to flood.
The uniflow tanks were developed for control line flying many decades ago. At that time the went was not connected to anyting, but ambient pressure. This resulted in a constant pressure head that the carburettor had to work against, resulting in a very constant engine rpm.
The principle itself is much older than this. It is known as known as Mariotte´s bottle (namned after the French physicist Edme Mariotte (1620-1684)).
The uniflow tanks were developed for control line flying many decades ago. At that time the went was not connected to anyting, but ambient pressure. This resulted in a constant pressure head that the carburettor had to work against, resulting in a very constant engine rpm.
The principle itself is much older than this. It is known as known as Mariotte´s bottle (namned after the French physicist Edme Mariotte (1620-1684)).
02-21-2009 | 03:41 AM
#56
RE: Uniflow fuel tank set-up
Agree with you red,constant fuel pressure that makes setting the lsn a breeze on my saito 82 which is inverted with a high tank in a decaff.Do i have too much exhaust pressure?? in that at under half throttle the fuel flows freely out of the exhaust and unplugging the vent line lets it syphon??..hoping to fix this without fitting a regulater
02-21-2009 | 11:50 AM
#57
RE: Uniflow fuel tank set-up
Hi!
You cannot have too much exhaust pressure and no check valve should be used!
But be sure the tank is mounted according to "the tank rule"!
The first picture shows the 110cc tin tank is what I have in my Marutaka DC-3 and the second the set used in ordinary R/C clunk tanks, both Uniflow!
You cannot have too much exhaust pressure and no check valve should be used!
But be sure the tank is mounted according to "the tank rule"!
The first picture shows the 110cc tin tank is what I have in my Marutaka DC-3 and the second the set used in ordinary R/C clunk tanks, both Uniflow!
02-21-2009 | 02:01 PM
#58
Senior Member
Joined: Jan 2007
Posts: 1,550
Likes: 0
Received 0 Likes
on
0 Posts
From: Lancaster,
NY
RE: Uniflow fuel tank set-up
If the object of your quest is to avoid pulling fuel lines off to refuel here is what I have done with good results. I start with the standard two line setup; feed line with clunk and bent up brass tube for vent (presure feed from muffler). I then use a short brass tube thru the third hole in the cap; this will be the fill line. I put the fill tube at the top position of the tank cap. I then put a fuel line attached to the fill tube thru the cowl and plug it with fuel plug. To refuel I just remove the plug and pump into the tank until I see fuel start to rise in the pressure line. I turn the prop so that the pistion is near TDC and close the carb barrel; this offers resistance to fuel running into the carb. If I overfill I just hold the plane upright to drain excess fuel from the muffler.
This seems to work well, no hydra locks.
This seems to work well, no hydra locks.
03-17-2009 | 12:46 AM
#59
Senior Member
Joined: Jan 2006
Posts: 1,057
Likes: 0
Received 0 Likes
on
0 Posts
From: Brandon,
MB, CANADA
RE: Uniflow fuel tank set-up
I have a couple questions about this... How far can this set up effectively draw fuel from? and can crankcase pressure be used instead of muffler pressure? The fuel tank in my plane will be located about 6 inches away from the engine, but pretty much level with the carb. I would like to avoid having to buy a pump if possible.
03-17-2009 | 10:30 AM
#60
My Feedback: (1)
RE: Uniflow fuel tank set-up
The Uniflow set up will not help you draw fuel from a distance. Case pressure is not a good idea either. What you need to get is a cline regulator and use case pressure with that. Case pressure or one way checks provide way too much pressure to the tank and you will not have good mixture through different throttle settings. Track down the cline and that will solve your problem.
03-17-2009 | 12:49 PM
#61
Senior Member
Joined: Jan 2006
Posts: 1,057
Likes: 0
Received 0 Likes
on
0 Posts
From: Brandon,
MB, CANADA
RE: Uniflow fuel tank set-up
I figured that i would have to. I have looked at the perry pumps, but they are expensive (at least for a student) I guess i will have to save up. thanks for the reply
12-19-2009 | 08:06 PM
#63
Junior Member
Joined: Dec 2009
Posts: 3
Likes: 0
Received 0 Likes
on
0 Posts
From: Decatur , GA
RE: Uniflow fuel tank set-up
Hey guys I just wanna say that all your info haas been very informative but I have a big problem maybe you can handle. I am having troubles with my first helicopter and I sprung for a nitro I have only a two line setup on it clunk to the carb, and a vent to the exhaust pressure needle. I have an os .37 engine and exhaust. I cannot get it to start for anything I have looked far and wide I even went 30 miles to a hobby shop that got it to start twice right away using the same setup I have using my drill and my starter but when i take it home it dosent work for me I get nothing but lots of fuel coming out the exhaust. ANy suggestions I have moved both needles all over trying to figure out its sweet spot but nothing happens. Anything would be nice thanks!!! Lj
12-20-2009 | 09:49 AM
#64
RE: Uniflow fuel tank set-up
Not enough information to nail down your problem. If there is fuel running out and no firing then suspect a problem with the glow system. It could be too wet (flooded), have inadequate voltage to heat up, or have a bad glow plug. Remove the plug, test it in your igniter and see if it glows bright. Disconnect the fuel line and purge the motor of excess fuel by turning it over with starter without the plug. If the plug is heating fine, reinstall and without hooking up fuel line, again try to get the engine to fire. If all the fuel was purged, it might not and it might need a slight bit of prime sprayed in the carb ventura. Get it to fire before hooking the fuel line back up.
Once it will fire and run for a second on a prime, then using factory needle valve settings, try to once again hook up fuel line and get it to fire and run.
Good Luck...
Once it will fire and run for a second on a prime, then using factory needle valve settings, try to once again hook up fuel line and get it to fire and run.
Good Luck...
12-20-2009 | 06:26 PM
#65
RE: Uniflow fuel tank set-up
I have run both a uniflow and standard setup in a .40 size plane with muffler pressure. I didn't see any benefit to the uniflow, and I didn't like getting my muffler full of fuel every time I let off the throttle. If you think about it, the muffler pressure is much greater than any variance caused by the fuel level in the tank. The uniflow does do what is claimed, but in our systems it is so small a difference that it just doesn't matter. I am happier with a single clunk setup and won't use a uniflow again unless I decide to run a plane that doesn't use muffler pressure.
12-21-2009 | 11:52 AM
#66
RE: Uniflow fuel tank set-up
Hi!
LJCraft 12!
It's probably you low speed needle that is screwed in too far.
I have noticed this many times since I started flying R/C 34 years ago. Just turn it out some and seehow the engine reacts.
And do use the two clunk system (Uni-flow)! It's the next best tank system there is. Only the Tettra "Bubbleless" tanks are better.
To be honest I cannot notice any difference between a one -clunk tank and a two-clunk (Uni-flow)set-up. But I know that the Uni-flow tank system is superior, and as it is so easy to just add one more clunk, I just use that system.
I have used the Uni-flow system in many models through the years and not notice any excess fuel in the silencer! And who cares!
As I always mount my engines on the side, all fuel that eventually runs into the silencer just flows out. But as I said earlier. I have never noticed any fuel coming out from the silencer because of the Uni-flow system.
LJCraft 12!
It's probably you low speed needle that is screwed in too far.
I have noticed this many times since I started flying R/C 34 years ago. Just turn it out some and seehow the engine reacts.
And do use the two clunk system (Uni-flow)! It's the next best tank system there is. Only the Tettra "Bubbleless" tanks are better.
To be honest I cannot notice any difference between a one -clunk tank and a two-clunk (Uni-flow)set-up. But I know that the Uni-flow tank system is superior, and as it is so easy to just add one more clunk, I just use that system.
I have used the Uni-flow system in many models through the years and not notice any excess fuel in the silencer! And who cares!
As I always mount my engines on the side, all fuel that eventually runs into the silencer just flows out. But as I said earlier. I have never noticed any fuel coming out from the silencer because of the Uni-flow system.
12-21-2009 | 01:19 PM
#67
RE: Uniflow fuel tank set-up
I'm curious, since you and I both can see no difference in how the planes run, how the uniflow is actually better? Sure, the principle is sound but it doesn't do anything to improve a standard muffler pressure setup. Fuel running into my muffler was an aggravation for me. It would up all over the side of my airplane and cost me some runtime. I found that I could get an extra 3-4 minutes of flying on a tank of fuel after going to a single clunk system, and fuel consumption became more consistent too.
12-21-2009 | 07:54 PM
#68
Member
Joined: Jun 2009
Posts: 58
Likes: 0
Received 0 Likes
on
0 Posts
From: Memphis, TX
RE: Uniflow fuel tank set-up
It's no surprise to me that you see no performance difference with the uniflow setup. The idea is valid only in a non-pressurized, open system (like the old control-liners once used). The previous reference to Mariotte's bottle is valid only in systems operating open to atmosphere (or at least at co-pressure). Once muffler or crankcase pressure is introduced, either via the vent, or via the "uniflow" line, the systems will function exactly as a pressurized 2-line system so far as fuel draw is concerned. The gas introduced via the uniflow line responds to Boyle's law exactly as does the gas introduced into the tank via the vent (using muffler or case pressure), and the forces placed on the fuel within the tank are accordingly the same. The addition of a check valve on the pressure line only serves to hold the gas (and fuel) pressure up for a bit when the throttle is cut. Sorry, but there aren't any free rides. To truly accomplish what you want, you will need either a regulator (such as Cline) or a regulated pump.
The above statement is only valid assuming the muffler or tank pressure exceeds the pressure of the height of the fuel column in the tank, but you can safely assume that it DOES in our RC applications.
The above statement is only valid assuming the muffler or tank pressure exceeds the pressure of the height of the fuel column in the tank, but you can safely assume that it DOES in our RC applications.
12-21-2009 | 09:10 PM
#69
RE: Uniflow fuel tank set-up
You guys should read some of this posted earlier...
[quote]ORIGINAL: Sport_Pilot
ORIGINAL: jrpav1
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
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
ORIGINAL: Sport_Pilot
With a two line system the vent is at the top and muffler pressure is supplied to that, the pressure in the tank is the same as the muffler pressure, and pressure to the carb is the differance in the height ot the fuel level to the carb plus the muffler pressure. For the following examples assume the tank is 4'' tall and the centerline is mounted level with the spraybar. So if you have 10'' of fuel head on the muffler pressure, and the tank is full and 2'' above the carb the pressure is 12 inches of fuel to the carb, if the tank is empty then you have 8'' of pressure to the carb. If you put a clunk on the vent or muffler pressure line so that it is at the same level as the pick up then the tank pressure is reduced by the head of fuel. So when the tank is full the muffler pressure is restricted by 4'' of fuel so the tank pressure is 10'' - 4'' or 6'', but the pressure to the carb is the muffler pressure plus the head on the carb or 8''. When almost empty the muffler pressure is not restricted so the tank pressure is the same so it is 10'' or the same as the muffler pressure, but the fuel level is 2'' below the carb so the carb pressure is 8'' which is the same as when it was full.
Perhaps the following link can explain it better.
http://www.fraserker.com/heli/uniflo...flow_works.htm
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?
With a two line system the vent is at the top and muffler pressure is supplied to that, the pressure in the tank is the same as the muffler pressure, and pressure to the carb is the differance in the height ot the fuel level to the carb plus the muffler pressure. For the following examples assume the tank is 4'' tall and the centerline is mounted level with the spraybar. So if you have 10'' of fuel head on the muffler pressure, and the tank is full and 2'' above the carb the pressure is 12 inches of fuel to the carb, if the tank is empty then you have 8'' of pressure to the carb. If you put a clunk on the vent or muffler pressure line so that it is at the same level as the pick up then the tank pressure is reduced by the head of fuel. So when the tank is full the muffler pressure is restricted by 4'' of fuel so the tank pressure is 10'' - 4'' or 6'', but the pressure to the carb is the muffler pressure plus the head on the carb or 8''. When almost empty the muffler pressure is not restricted so the tank pressure is the same so it is 10'' or the same as the muffler pressure, but the fuel level is 2'' below the carb so the carb pressure is 8'' which is the same as when it was full.
Perhaps the following link can explain it better.
http://www.fraserker.com/heli/uniflo...flow_works.htm
ORIGINAL: jrpav1
Yeah that's pretty much the idea. Basically, in a Uniflow the fuel mass does not affect the fuel pressure seen at the carb. the same way that it does in a conventional 2-line system. As someone pointed out, the net pressure in a Uniflow is sowewhat less than what you see in a 2-line system because the fuel mass does not ADD to the net pressure. Because of this, the higher pressure cused by running the check valve is a welcome side effect. I really need to get a good gauge and measure all of these parameters so that we have some numbers to compare. The only thing I can tell everyone at this point is that it DOES give you very consistant runs. Almost scary. You really need to keep trrack of your fuel usage (set a timer) because you have no indication that you're about to run out of fuel. If you're at all skeptical about this, don't take my word for it. Try it for yourself. Don't put it in your favorite plane and hover 3 feet off the ground until you're comfortable with it though.
John Pavlick
Yeah that's pretty much the idea. Basically, in a Uniflow the fuel mass does not affect the fuel pressure seen at the carb. the same way that it does in a conventional 2-line system. As someone pointed out, the net pressure in a Uniflow is sowewhat less than what you see in a 2-line system because the fuel mass does not ADD to the net pressure. Because of this, the higher pressure cused by running the check valve is a welcome side effect. I really need to get a good gauge and measure all of these parameters so that we have some numbers to compare. The only thing I can tell everyone at this point is that it DOES give you very consistant runs. Almost scary. You really need to keep trrack of your fuel usage (set a timer) because you have no indication that you're about to run out of fuel. If you're at all skeptical about this, don't take my word for it. Try it for yourself. Don't put it in your favorite plane and hover 3 feet off the ground until you're comfortable with it though.
John Pavlick
12-22-2009 | 11:04 AM
#70
RE: Uniflow fuel tank set-up
Hi!
Jester! I know from theory, and practice, that Uni-flow tank system is better than a two line system, that's why I use it. I said I can get a two line system to work good and that I cannot notice any difference when flying most of my planes, but in pylon racing I need the utmost reliability and performance and therefore I use it, both there and in all of my other planes as it is so easy to install. The difference is very small, seldom noticeable if you have done your homework, but it do exist!
I do not notice any fuel sipping out into the silencer, but that could be due to the pressure line exiting from the fuselage to the silencer, sits rather high (above the tank) in most of my planes.
Jester! I know from theory, and practice, that Uni-flow tank system is better than a two line system, that's why I use it. I said I can get a two line system to work good and that I cannot notice any difference when flying most of my planes, but in pylon racing I need the utmost reliability and performance and therefore I use it, both there and in all of my other planes as it is so easy to install. The difference is very small, seldom noticeable if you have done your homework, but it do exist!
I do not notice any fuel sipping out into the silencer, but that could be due to the pressure line exiting from the fuselage to the silencer, sits rather high (above the tank) in most of my planes.
