Uniflow Tank Venting

[EddyR]

 I have been building unfollow tanks for over 30 years. All types. I always brought the venting to the inside of the circle at the front of the tank. In the last year I have seen pictures of models with the tank vented on the outside of the circle. The uniflow vent exits the same side of the tank as the pickup tube. It must be that it works but I have never tried it. Does it make any difference?
  I first noticed it on this tank.Then on Dan Banjock new model.
EddyR
 
 

[Motorman]

Nobody really knows.

MM

[Mark Scarborough]

I have had issues with the uniflow vented on the outside of the circle . I cannot 100% proof that this was the issue, but the inconsistant runs went away when I moved the uniflow to the inboard side,,

there may be other factors at play, this is only an observation...
then when I went to muffler pressure it did not matter

[Motorman]

I made a nice 3oz tank for my ringmaster/veco19 with the vent tube coming out the top with 2/3rds of the tank on the inboard side. It worked so good I made another one for my Shoestring/LA25 and it too worked great. Then I used the same formula on a 4oz tank for my banshee/brodak40 and it ran from screaming lean to blubbery rich through the tank full. so I moved it to the 1/2 & 1/2 position and it still did the same thing, weird. Changed to a thinner Brodak tank with about the same venting and now it's ok, go figure.

MM

[Trostle]

In the late 60's through mid-70's, I flew several versions of my Focke Wulf semiscale designs, all with uni-flow tanks.  The earlier versions had the vent in the sort of scale supercharger on the inside of the circle.  The last version, flown and qualified at several Nats had the uniflow vent on the outside of the circle.  I had no problem with either way.  

I think that once the vent starts to act as a vent which is to allow air in the tank to replace the fuel being used, there is no way the fuel can force its way back out the vent, even if the vent is on the outside of the circle.

Later experience I have had with uniflow tanks with vent to the airstream is that under windy conditions, the engine tends to richen on the upwind side of the circle and tends to lean out on the downwind side.  With muffler pressure on the vent, it makes no difference where that vent is where the muffler pressure attaches to it.

Keith

(I apologize about the attachment.  Open it and zoom to 100% to see the photo.  Will try to get this right)

[Skip Chernoff]

I'm no expert at this stuff but I have fooled around with many types of tank set ups and always go back to muffler pressure. One other thing....I also prefer clunk tanks with really flexible clunk feed lines . Works for me....PhillySkip

[EddyR]

  It seems that most who have tried it got it to work.
Here is my reason for asking. On all my conventional stunters I have had great engine runs. BUT on my Bearcats nothing but trouble. The Rabe Bearcat with uniflow vent on the outside of the body the motor would go lean part way through the flight every time. I put the motor DS/60 in my JUNO and it ran normal. I tried every thing I knew but I could not use the outside venting. Even muffler pressure did not solve the problem. I vented the uniflow out the bottom and then the motor ran better but it would siphon out fuel.
  I then built the Brodak Bearcat and had the same problem with the ST/46. I put in my Rustler/40 with internal venting and the run was OK but power was not enough.
Internal venting with the 46 and the very small tank area is very difficult. The 46 goes lean with most things I have tried.
 My conclusion is you can not run the uniflow vent the long distance to the inside of the circle to vent it. On the Rabe Bearcat the vent is 1.5" inboard of the tank wall.
What do you think?
Ed

 

[dale gleason]

I place all my uniflow vents on the outside wall of the tank, relative to the flying circle. The uniflow vent stays submerged in fuel until the tank is almost empty and uncovers.

 I've  discussed with other flyers, notably Bob Gieseke, who had the uniflow vent on the inside wall of the tank. In his words, he wanted the uniflow to "uncover" quickly (in the first lap) because he liked the run to get progressively leaner throughout the flight so he would have more power in the later part of the pattern.

I believe when the uniflow "uncovers", it is no longer a uniflow tank, and that's ok....

FWIW,
dg


edit: Thanks for the clarification-I see I misunderstood which end of the uniflow tube we were discussing, my bad...

[EddyR]

I just watched Al Rabe video of him building a  square metal uniflow tank for one of his big Bearcats. On the one with the fixed copper tube uniflow it is against the outboard wall and it exits on the outboard side wall of the tank. That is what I was wondering about. All of mine have gone to the inside of the circle as they exit the tank. I will try it as I am doing a total rebuild of the Rabe Bearcat. His tank is1.5" thick so that is what I will do to get the volume I need. He has no vents on the out side of the plane.

NOTE    In case some do not understand I was not asking where the uniflow goes inside the tank but where you are exiting the venting outside the tank to the inside of the circle or the outside of the circle. 
EddyR

[Trostle]

Before I went to using muffler pressure on my uniflow tanks, there was one thing I did to minimize the difference in the engine run from the upwind/downwind portion of the circle.

First, I did not have a problem with the engine run on either side of the circle with the mid 70's Focke Wulf design I had with the vent on the outside of the circle (right side of the airplane).  This was with a ST .46 which did not seem to change its run anywhere on the circle regardless of the run.

Later, with several different airplanes/engines, I had the inconsistent engine run from the upwind to downwind of the circle.  I placed a restrictor in the vent.  This was a 1/8" OD tube filled with solder with a 0.020" hole through it.  That took care of most of the problem.  Muffler pressure took care of all of the problem.

(The only problem I have with using muffler pressure is once the tank is filled, then keeping the fuel from siphoning back into the muffler without resorting to one of several methods, all awkward, before starting the engine.)

Keith

[EddyR]

 Thanks to Keith and all the others who commented on there set up.
Keith on both of my Bearcats muffler siphoning was a problem when using pressure. I tried home built in the cowl mufflers but all of them failed. The DS re was nice but it self destructed. I now have two side manifolds and also a Slimline wraparound Pitts style muffler for 40 size engines. That was hard to find. I will be able to build a in cowl muffler system for the both Bearcats.
EddyR

[Dennis Toth]

Ed,
I have the uniflow vent exiting vertically upward directly behind the engine on my El Diablo with a Fox 35. I have flown this in some pretty strong winds (15+) with no problems with the engine run changing from up wind to down wind. For this ship it doesn't like running muffler pressure but you should try it on yours just to see what works best.

Best,  DennisT

[M Spencer]

 



  Except we assume gravity is lateral .  

This Dates from mid 50S !



BUT , the Original Pommy Drawings of the PALMER Tank are THUS : ( Except it had a Baffle 2/3 back , transverse .



( Meant to do this the last couple of tanks, assume Uni Pipe Fwd enhances Vertical lean / rich - up / down . STILL Havnt tried one ! )

Brain Effers forts ,





Anudder .

[M Spencer]

WELL THAT WAS QUICK ! .

this appears to be ' a ' real ' Palmer ' TANK .



flogged from here : http://www.modelarstwo.org.pl/forum/viewtopic.php?t=22811 . ( Watch out for Stress Raisers ! )

[Randy Cuberly]

Picture shows my Gieseke nobler with a Brodak medium wedge 5.0 oz tank with Figg style venting.  This venting places the uniflow vent
(top vent) and the overflow vent (capped bottom) well above the fuel level and prevents siphoning of the fuel into the muffler.  Muffler pressure vent is connected to the uniflow vent to prevent richening of mixture when upwind. This setup gives nice steady runs and is very consistent and easy to plumb!

Randy Cuberly

[Avaiojet]

I'm no expert at this stuff but I have fooled around with many types of tank set ups and always go back to muffler pressure. One other thing....I also prefer clunk tanks with really flexible clunk feed lines . Works for me....PhillySkip

I've been reading up on modelers who use R/C type tanks with clunks and set them up as uniflow.

One suggestion I was given was to have the feed and the uniflow line using flexible lines and clunks.

Charles

[EddyR]

[quote author=EddyR link=topic=45174.msg469489#msg469489 date=1481141

NOTE    In case some do not understand I was not asking where the uniflow goes inside the tank but where you are exiting the venting outside the tank to the inside of the circle or the outside of the circle. 
EddyR
[/quote]

It seems that most did not read the original question. I wanted to know what experience you had with bringing the uniflow to the out side of the body on the "OUTSIDE OF THE CIRCLE"  SEE PICTURE.
 
 On my orange Bearcat if I use a vent on the outside of the body INSIDE OF THE CIRCLE the motor goes lean in one lap.??
The engine and tank came out of a Vector that had worked perfect for several years. I tied several tanks but as soon as I used the external vent on the inside of the circle the engine goes lean. I had this same problem on the BLUE Rabe Bearcat also. Both of the Bearcats bodies are 5+" wide. When using in cowl mufflers behind the engine fuel siphoning is a problem as they are below the tank so muffler pressure is not a great idea.
 On the BLUE Rabe Bearcat I did go to muffler pressure and it did solve the lean run problem I do not want to use it.
Also see the picture of the nose of the Orange Bearcat and you can see the vent in the blue painted area. It is above the tank ,as in all my other models. If I use this vent the engine will go lean in one lap no mater what tank I have in the plane.

  Both of the Bearcats are going to in the cowl mufflers as I now have header manifolds that bring the exhaust to the back of the engine and no longer exit the side of the body. I am going to try a Rabe Beacat tank witch used the venting to the outside of the circle

[Randy Cuberly]

[quote author=EddyR link=topic=45174.msg469489#msg469489 date=1481141

NOTE    In case some do not understand I was not asking where the uniflow goes inside the tank but where you are exiting the venting outside the tank to the inside of the circle or the outside of the circle. 
EddyR


It seems that most did not read the original question. I wanted to know what experience you had with bringing the uniflow to the out side of the body on the "OUTSIDE OF THE CIRCLE"  SEE PICTURE.
 
 On my orange Bearcat if I use a vent on the outside of the body INSIDE OF THE CIRCLE the motor goes lean in one lap.??
The engine and tank came out of a Vector that had worked perfect for several years. I tied several tanks but as soon as I used the external vent on the inside of the circle the engine goes lean. I had this same problem on the BLUE Rabe Bearcat also. Both of the Bearcats bodies are 5+" wide. When using in cowl mufflers behind the engine fuel siphoning is a problem as they are below the tank so muffler pressure is not a great idea.
 On the BLUE Rabe Bearcat I did go to muffler pressure and it did solve the lean run problem I do not want to use it.
Also see the picture of the nose of the Orange Bearcat and you can see the vent in the blue painted area. It is above the tank ,as in all my other models. If I use this vent the engine will go lean in one lap no mater what tank I have in the plane.

  Both of the Bearcats are going to in the cowl mufflers as I now have header manifolds that bring the exhaust to the back of the engine and no longer exit the side of the body. I am going to try a Rabe Beacat tank witch used the venting to the outside of the circle

Theoretically it really shouldn't make any difference whether the uniflow vent exits on the outside or inside of the circle.  I have successfully used it in both places on profiles.  However, every time I've tried it exiting on the outside of the circle in full fuselage stunt ships it was gave inconsistent runs.  My theory is, and I can't prove it, that the airflow to the uniflow vent on the outside operates in affected air flow due to the "masking effect" or turbulent and inconsistent airflow around the outside of the fuselage.  This could be caused by the fact that our Control Line airplanes fly in slightly crabbed positions relative to the airflow generated around the outside of the fuselage. 

Conversely I have never had a problem with the uniflow vent on the inside of the fuselage. 

I have had problems like you described with small leaks in uniflow tanks, and even on two occasions split brass tubing inside the tank that caused inconsistent runs.

I really don't understand your reluctance to use muffler pressure.  It nearly always gives better, more consistent needle settings and more consistent runs, and eliminates the sometimes serious problem with richening going into the wind on high wind flights.

Randy Cuberly

[Motorman]

If your uniflow vent is too close to you pick up tube inside the tank then when the rpms come up after launch the bubbles will blanket the feed tube and you'll get lots of air to the engine making it go lean in one lap. Maybe your inboard vent gets more ram air than your outboard vent.


MM

[Steve Helmick]

My gut feeling is that if the uniflow vent is outboard, then centrifugal force would tend to push fuel out of that vent....so I wouldn't do it. Could be wrong, often am. I've been connecting a line fixed into the backplate cavity to my inboard uniflow inlet. Works good and stops the rich/lean crap in the wind. Brett has his plane rigged to do the same if he wants.

Using a fuel hose to connect the uniflow vent from the tank to the remote actual uniflow inlet tube is fair game. If you look at Randy Cuberly's "G-Nobler" uniflow and overflow vents...that can be avoided IF you wish. I would be concerned with vibration causing a failure in the very long tubes or (more likely) solder joints.

If you're going to use a clunk tank, I can't see how you'd get good results with two clunk lines and clunk weights. The uniflow line clunk would move around all the time, and the two might even get tangled. How could this configuration give a consistent run through inside and outside turns? Maybe it does, but I can't see it happening. 

Some guys used two lines with one customized clunk, but these days, most use a rigid uniflow tube inside a clunk tank.    Steve

[Trostle]

My gut feeling is that if the uniflow vent is outboard, then centrifugal force would tend to push fuel out of that vent....so I wouldn't do it.

Steve

My experience with several airplanes is that fuel is not forced out the uniflow vent if the vent is on the outside of the circle.  As explained above one of my earlier posts above, once the vent actually starts to act as a vent to allow air into the tank as the fuel is being used, fuel cannot be forced back out of that tube.

Keith

[Randy Cuberly]

Using a fuel hose to connect the uniflow vent from the tank to the remote actual uniflow inlet tube is fair game. If you look at Randy Cuberly's "G-Nobler" uniflow and overflow vents...that can be avoided IF you wish. I would be concerned with vibration causing a failure in the very long tubes or (more likely) solder joints.

The vent system shown on the tank in my G Nobler is a "Figg" style system and is named for the guy that invented it and used it as I have for many years, on many planes, without problem.  The copper tubes are soldered together in several places and are very, very stiff.  I suspect their fundamental frequency is far above the vibrational frequencies of a single cylinder two stroke engine!  I typically use it because it has proven more reliable than the juncture of a short tube passing through the fuselage wall.  Tanks vented like this have been commercially available (currently from Brodak's) for many years and that makes it a simple solution.

Randy Cuberly

[Christian Chacha]

Picture shows my Gieseke nobler with a Brodak medium wedge 5.0 oz tank with Figg style venting.  This venting places the uniflow vent
(top vent) and the overflow vent (capped bottom) well above the fuel level and prevents siphoning of the fuel into the muffler.  Muffler pressure vent is connected to the uniflow vent to prevent richening of mixture when upwind. This setup gives nice steady runs and is very consistent and easy to plumb!

Randy Cuberly

So if i am no using muffler pressure for example with a brodak 40, do I then leave the uniflow vent open and just cap the overflow?

[Dan McEntee]

So if i am no using muffler pressure for example with a brodak 40, do I then leave the uniflow vent open and just cap the overflow?

   You should have three tubes to deal with. One is the pick up tube that feeds to the needle valve assembly. The other two are the uniflow vent and the over flow. You can do it either way. If you cap the over flow, you can either leave the uniflow open to atmosphere, or dun your muffler pressure line to it. The needle setting will be different for each. You can also cap the uniflow vent and run pressure to the over flow, but then you will get a run similar to an old fashioned standard tank. Some times it is worth trying it both ways!  If you want to leave the over flow open to atmosphere  and cap the uniflow, it will help to fun some fuel line to a tube above the engine centerline, facing into the wind so you do not get any syphoning effect as the wind goes across the over flow tube if it's pointing straight down. I hope this makes sense to you. I never try to leave any tank opening that is 90 degrees to the air flow uncapped as long as there is direct muffler pressure, or air flow into a tube to vent the tank.

  Type at you later,
   Dan McEntee