Author Topic: Inverted engine Uni-Flow fuel tank position (Read 2882 times)

Jim Treace · « **on:** October 13, 2008, 10:40:10 AM »

I have a J.D Falcon, RoJett .40 RE powered and have been having fuel flow/tank problems using a standard vent fuel tank. I am planning on trying a Uni-Flow tank. Will this set up work as I have diagrammed. I appreciate any help.
Thanks,
Jim

John Miller · « **Reply #1 on:** October 13, 2008, 11:31:14 AM »

Jim, where the uniflow enters the tank isn't as important as where it's placed inside the tank. Since the fuel system becomes a closed loop when the engine is running, with the overflow capped off, and the uniflow left open to the airstream, or connected to the muffler pressure tap, it becomes the only place that air can enter to replace the fuel that's being used.

I personally have switched to RC style plastic tanks set up for uniflow. Less weight, easy to set up, and in my experience, dead reliable. Search the archives for a post I made that shows how to set up this type of tank.

Jim Treace · « **Reply #2 on:** October 13, 2008, 02:17:49 PM »

John:
I found your earlier post (August '07), on this topic and this was very helpful. Since my tank is metal, I can not be certain where inside the tank the uniflow line terminates. Hence my concern when I flip the tank to keep the pick up line on the outboard side. I also have width space limitation, 2" is max, so plastic clunk may offer more options and easier to determine location of uniflow line. I will give this a try.
Thanks,
Jim

johnbyrne · « **Reply #3 on:** October 14, 2008, 08:14:41 AM »

Have you read the excellent tank building How To by Al Rabe on Stuka Stunt called something like "Tanks, tanks, tanks"? Really good thread and documents as said that it doesn't matter where tubing enters/exits. I copied this thread and have made several nice tanks that have "unusual" exits for my ARF Nobler. Pictures of it are on Stuka. I was faced with a similar situation with respect to size constraints. The final version holds a full 4 oz, has bottom exit tubing, and requires almost no mods to the ARF Nobler to install. While the tubes exit the bottom, the uniflo and fuel pickup are dead center on a 1" tall tank placing it in the same plane as the spray bar on the inverted engine. Gives consistent runs on the LA 40 and 11x4 prop.

I've used plastic tanks with very good success but I really like metal. When done right the metal tank is NOT heavy and will last the life of the plane.

By the way, your pics are for where the tubes will exit the tank correct? I'm assuming that the Uniflo line will cross over to the pickup and terminate just short of the fuel pickup, correct?

Jim Treace · « **Reply #4 on:** October 14, 2008, 11:30:50 AM »

Quote from: johnbyrne on October 14, 2008, 08:14:41 AM

Have you read the excellent tank building How To by Al Rabe on Stuka Stunt called something like "Tanks, tanks, tanks"?

By the way, your pics are for where the tubes will exit the tank correct? I'm assuming that the Uniflo line will cross over to the pickup and terminate just short of the fuel pickup, correct?

John:
I will look up the post on SS. Also, yes, you are correct as to tube placements in my uniflow tank. I would prefer to keep the metal tank, but I just want the system to work. With the standard vent tank, been having difficulties with hard starts and inconsistent runs. Engine will finally run on the ground, but once in the air goes very, very rich. System works perfectly on the bench, but once installed...problems. So, I want to try uniflow. I will keep at this until I get it!!
Jim

johnbyrne · « **Reply #5 on:** October 14, 2008, 11:43:15 AM »

Hope it is ok to post a link to Stunt Hanger. The first link is to my thread with pics of my Nobler tank including inside. As said this tanks works perfect in the air so where tubing exits the tanks doesn't seem to matter too much.

http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=316094&mesg_id=316094&listing_type=search

This link is to Al Rabe's really excellent tank building How To. He is a master.

http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=314440&mesg_id=314440&listing_type=search

johnbyrne · « **Reply #6 on:** October 14, 2008, 11:56:20 AM »

Quote from: Jim Treace on October 14, 2008, 11:30:50 AM

John:
I will look up the post on SS. Also, yes, you are correct as to tube placements in my uniflow tank. I would prefer to keep the metal tank, but I just want the system to work. With the standard vent tank, been having difficulties with hard starts and inconsistent runs. Engine will finally run on the ground, but once in the air goes very, very rich. System works perfectly on the bench, but once installed...problems. So, I want to try uniflow. I will keep at this until I get it!!
Jim

On a side note have you checked for a leaking back plate? I had a loose back plate on the LA 40 in the Nobler and it was a bear to start and gave inconsistent runs. I fixed the leak and it was instantly better.

Granted you are not running uniflo but uniflo tanks with a leak can experience mixture changes. In particular if the leak is "below the fuel level" on the ground and then opens in the air it can really change thangs. You basically will go from uniflo to vented. Given uniflo has a slight negative pressure, when it goes vented the mixture can go rich if I understand this correctly. I had a tank that would do that part way through the flight as the fuel was used. Again, FWIW given you are not running Uniflo yet.

Jim Treace · « **Reply #7 on:** October 14, 2008, 02:21:09 PM »

Quote from: johnbyrne on October 14, 2008, 11:56:20 AM

On a side note have you checked for a leaking back plate? I had a loose back plate on the LA 40 in the Nobler and it was a bear to start and gave inconsistent runs. I fixed the leak and it was instantly better.

John:
Engine starts ,1-2 flips, and runs fine on the bench even with the standard vent tank (I pressure tested it OK). I have checked all engine and tank fittings and nothing loose.
However, once installed in plane with the standard vent tank, I get very difficult starts and once running, I get fine ground RPM's, but then immediately after take off engine goes rich, I mean really rich. Last time after 4-5 laps I just landed "under power" in slow flight conditions. Little down and ground to prop stopped the engine. Current tank's center line is aligned with the NV fuel bib. Engine seems to run a little better when the tank is tilted forward and slanted outboard, but still not to par. Thanks for the links. Excellent information. All of this will help me trouble shoot this problem.
Jim

johnbyrne · « **Reply #8 on:** October 14, 2008, 03:23:06 PM »

No problem with the links. Al's thread and then the posts made in my humble post are very good I think.

I wonder if you could have a harmonic that is causing bubbles? Did you give a shot of Armorall into the fuel? Maybe try a different prop to change the rpm some as a test. Hey, I'm pretty new at this so I'm taking shots in the dark now. Maybe I should shut up lol.

james dean · « **Reply #9 on:** October 14, 2008, 03:46:25 PM »

Jim, have you tried presure testing the tank underwater for minute leaks from seams and plumbing joints? Just a thought. best of luck

james

Jim Treace · « **Reply #10 on:** October 14, 2008, 04:15:48 PM »

Quote from: Jim Treace on October 14, 2008, 02:21:09 PM

John:
Engine starts ,1-2 flips, and runs fine on the bench even with the standard vent tank (I pressure tested it OK). I have checked all engine and tank fittings and nothing loose.

James:
Yes, I pressure tested the tank. No bubbles. And this tank works fine supplying the engine on the test stand...go figure! Seems it works fine as long as it is just sitting still. Think I need a new tank.
Jim

John Miller · « **Reply #11 on:** October 15, 2008, 11:59:05 AM »

Quote from: Jim Treace on October 14, 2008, 02:21:09 PM

John:
Engine starts ,1-2 flips, and runs fine on the bench even with the standard vent tank (I pressure tested it OK). I have checked all engine and tank fittings and nothing loose.
However, once installed in plane with the standard vent tank, I get very difficult starts and once running, I get fine ground RPM's, but then immediately after take off engine goes rich, I mean really rich. Last time after 4-5 laps I just landed "under power" in slow flight conditions. Little down and ground to prop stopped the engine. Current tank's center line is aligned with the NV fuel bib. Engine seems to run a little better when the tank is tilted forward and slanted outboard, but still not to par. Thanks for the links. Excellent information. All of this will help me trouble shoot this problem.
Jim

What you've just described makes it sound like once the centipudal force begins acting on the fuel head, the fuel flow is increased. If this happens in upright level flight, you can try lowering the tank to decrease the "fuel head" seen at the engine. If this helps, and the engine remains running well enough, inverted flight will tell us the rest of the story. Best to do this over soft surface. If the engine floods off, runs rich, then the tank is mounted too low when upright.

I believe using a uniflow may help a lot, butI'm still left wonderring, from this distance, why this is happening.

Jim Thomerson · « **Reply #12 on:** October 15, 2008, 03:06:41 PM »

Based on years of experience with the old Perfect tanks, which had the tubes going somewhere, who knows where, I would not fly a tank without opening it up and taking a look inside. Taking the back off a standard metal tank is easy. Just set it on the stove until the solder melts. Pick the tank up with an oven mitt while holding the back down with needlenose pliers. Reverse process to put it back together. Always check your uniflow tanks for leaks. If it leaks, it is not going to run right.

Jim Treace · « **Reply #13 on:** October 16, 2008, 07:43:08 AM »

OK, when I can get to it, in the shop plane level (engine inverted), I will try lowering the tank so pickup/center line, is slightly 1/8" or so, below the NV bib. But I am going to do this with the uniflow tank. I just think the standard vent tank has internal issues (may do an autopsy to confirm). If I can get flight speed, then to inverted flight to confirm functioning tank system. I do fly over grass/ soft sand substrate. I am still learning stunt, so I do have experience with ground impact and with the soft ground I usually get minimal destruction , messy to clean sand out, though.
I appreciate all the good information and help in trouble shooting my problem. I know this is hard to do at a distance. Once I get the above completed, I'll report back with results.
Jim

johnbyrne · « **Reply #14 on:** October 16, 2008, 02:05:46 PM »

I'm not an expert but if you switch the tank to a new uniflo tank I'd put the pickup at the same elevation as the NVA to start and then move it from there if needed. Keep variables to a minimum. If you change too much you won't know what helped and what didn't.

don Burke · « **Reply #15 on:** October 16, 2008, 02:20:19 PM »

That's the old testing axiom, "Change one thing at time, otherwise you don't really know the effect of the change."

Jim Treace · « **Reply #16 on:** October 16, 2008, 07:26:03 PM »

Keep variables to a minimum. If you change too much you won't know what helped and what didn't.
[/quote]

Ah..OK, good idea and smart problem solving technique, whatever, I will do this. No sense in making more problems that are too difficult to trace down.

Tom Niebuhr · « **Reply #17 on:** October 18, 2008, 08:29:24 AM »

Jim,

I wish you had contacted me.

My "JD Falcon" with a RoJet .40, uses a standard Brodak uniflo tank with forward vents. The plumbing is very simple. I will send you pictures of the set up in a few days, since I am working horrible 16 hr days for a few days in a row. There is room to shim the tank if required, I use 1/16" pads under the engine, so my tank is shimmed 1/16". I have had absoluely no problems with the tanki set up.

I had early problems with the engine going lean about half way through the flight. This was traced to a fuel line filter that was leaking a little air.

Manuel Cortes · « **Reply #18 on:** October 18, 2008, 09:07:55 AM »

My Merco 49 likes 1/16" diference between the tank mid line and the spraybar, the tank "closer to the glow plug height".

Hope it helps.

Regards.

Jim Treace · « **Reply #19 on:** October 18, 2008, 09:39:39 AM »

Quote from: Tom Niebuhr on October 18, 2008, 08:29:24 AM

Jim,

My "JD Falcon" with a RoJet .40, uses a standard Brodak uniflo tank with forward vents. The plumbing is very simple. I will send you pictures of the set up in a few days, since I am working horrible 16 hr days for a few days in a row. There is room to shim the tank if required, I use 1/16" pads under the engine, so my tank is shimmed 1/16". I have had absolutely no problems with the tank set up.

Tom:
My tank was a Brodak but not uniflo. I now have a GRW uniflo with all forward vents. At 2", it's a little wider than the Brodak, but it fits. So, your pickup is level with the NV fuel bib/spray bar? Or shimmed 1/16" above? And yes, there is plenty of room to shim tank. I would appreciate your diagram. No rush. Whenever you can, I thank you.
Jim

johnbyrne · « **Reply #20 on:** November 02, 2008, 07:19:33 PM »

Hey Jim,

Any updates?

Jim Treace · « **Reply #21 on:** November 05, 2008, 08:30:56 AM »

No updates. Unfortunately, I have been too busy to get this worked out. So, far I have only prepared the tank compartment. Had to remove prior glued in shimming to accept the wider new tank. So now I can install the GRW uniflow tank, but haven't completed it. I will post my results later.
Jim