Help can't stop the Bubbles and Sucking in of the UAT
 

This is like my 6th jet and I have never had issues like this.

I got 1 1/2 flights on my new JL 1/5 L39 gen 2. With K180

Madden flight was great only used full power on take off the rest of the flight at 1/2 - 3/4 no issues

2nd flight after takeoff go to do full power low fly by and at the end it barely did the vertical, it felt like full power was 1/2 stick. Then flame out.
Got it down no issues, the UAT
http://www.dreamworksrc.com/catalog/High-Flow-Air-Trap

Was full and the Kingteck said max pump voltage reached

Went to drain the system and the UAT suck in on the round paper element and was putting air bubbles in the 5g fuel jug

so I think kinked 6 festo line from the tanks Y to the UAT so I pull it out from under the receiver mounting plate and run directly.

Then disconnected the line from the motor and ran it to my fuel jug and used the KT program box to test pump. At max fuel pump voltage I was getting a stream of air bubbles from UAT to pump and from tanks to UAT and UAT was sucked all the way in.
I clamped off the left the right tank to see if there was a different with no luck.

Also disconnected each vent line incase the vent line was two small
I used all brass adapters for the UAT from Dreamworks with metal wire twist ties in all connection.

Im lost. Is this a big motor thing were I need a composite UAT?

what kind of vent setup do you have?

I think the bubble are coming from the rubber that holds the brass fuel tub into the tank. It comes out with 6 size festo tubeing into a 6 size festo Y the straight to the UAT were there is a 6 to 8 size festo brass adapter

The vent is all 6 size festo with a T, ( the second purple T in the vent is for the Smoke tank above) one drain port on the bottom.

I was thinking vent restrictions too and pulled all hose off the tank and the UST still sucked all the way in against the round paper filter

Thanks

Sounds like the paper filter is the culprit. How old is the the fuel and what type, any slime? Did you try pulling fuel from the UAT without the main tank and vent lines connected?

Keith

If the bubbles are already showing in the tubing right after the tank, you may want to try these:
http://www.dreamworksrc.com/catalog/Fuel-Line-Barb-532

It seems from the pictures you have a brass tube and PU hose on it, without any kind of barb.
The problem could be there, or inside the tank on the pickup line.

If the UAT is sucked in, then you probably need a more rigid one

Cavitation, Mike.
something is creating too much suction drag upstream the air trap.

1. Connect your air trap to a simple jug with a large bore tube. If the air trap still sucks in, its filter is the culprit.
2. If the air trap does not suck in any more, then your tanks have a problem. Could be coming from the clunk lines or the fuel stopper. In that case, you could try one tank after the other to see how much restriction you get with only one connected.

Please report here with pictures and we'll try to help you.

The picture appears to show all 3 tank lines connected to the same vent line. I'm betting you are pumping fuel out faster than the vent line can keep up with.

Mike take Olis advice he is 100% right. What you are seeing is cavitation. When under high suction the fuel will get air bubbles all through it. Something is causing a restriction someplace.

http://www.rcuniverse.com/forum/atta...7&d=1469419768

Why have you plumbed the three tanks like that?
It looks like you have extra tube and T's

Mike, it seems like you are using the correct hardware. Have you tried bypassing the UAT? You can fly without it if you want to isolate it.

Check your pump fittings. On most pumps, the barbed fittings are pressed fit (into a plastic pump casing which makes absolutely no sense!). They can loosen over time, or if you pull on a line hard enough during assembly. It's very difficult to notice, but it will draw air pretty bad. Solution is to hysol in place, being careful not to obstruct ID. Went through several UATs before finding this problem.

Good luck,
David

Principals of cavitation


https://www.youtube.com/watch?v=ON_irzFAU9c

Thanks guys, Cavitation is a new one for me, air leaks yes, LOL

I'm currently only using the 2 main plastic tanks, there is a 30oz dubro tank on top, but that is the smoke tank, My boy told me that the smoke vent line had little pressure and there would be no issue tying into the main tanks vent line so there is only one vent whole on the bottom of the jet. But at this point I don't want any extra issues so I will make it separate.

I hope its not the filter as its a new UAT, with only 4 test starts and 1.5 flights, but I did have a huge issue with algae in my diesel last year so I will do your test when I get home from work.

Thanks guys, Its crazy, this is the most simple fuel lay out of any of my jets and its the one that causing me issues.

change the 4mm to at least 6mm on suction from tanks to uat this might be the problem + eliminate all the reductors connections 4to6 and 6to4 make all one larger size at least 6mm .

Thanks, that did help on a skymaster F15 I was having a hard time getting max rpm with.

This UAT I have never had before, it has a huge 8 size nipples on pump and suction side, instead of putting the 8-6 adapter so close to the UAT I will put size 8 line to the tank, then put the adapter.

Its crazy to me, I have a AMT 450 at 48 pounds of thrust just using plane 4 size line with no issues, but it dose have a huge pump!

I know this jet and I know this is not the original fuel setup ,I have the same jet all with large Tygon lines ,vents,and fuel supply to the uat ,this is good working uat I never have a problems with this type uat ,usually it's the vent and fuel supply lanes .

Well the results. My K180 had a hart attack!!!

So I'm going to call my self out here. So when I ordered this bigger UAT I was unaware of the fact it had 2 8 size festo lines and only come with one adapter. So I did the old put CA on the 6 size line and jammed it in the 8 size line.

Well i tested it and had a few air bubbles so I spent another $40 at Dreamworks for the correct adapters and a few feet of 8 size line. I replaced the hack and all seemed good.

Well when I pulled the main line from the UAT to the y on the tanks and found a 1/2in chunk of CA sitting in the line like someone waiting on a hart attack.

Upgraded the line with 8 size from the UAT to the main tanks since I was there.

Crazy right

Never seen, now I know.

How did CA get into the lines? Seems odd..

User error. I know right who ever admits that. The clear tube peace I had I thought was size 8 was not. And I had little air bubbles during my testing so I added more ca around the tubeing trying to get it to seal.

Im glad I wisely chose to get the right parts.

In the picture, it looks like the same size bottle as a standard UAT, just bigger fittings. If so, I would not trust this with a 180 engine. The element surface area is simply too small for the fuel flow of the engine, and its size is limited by the bottle's size, and made worse by the flexible sides, which can suck in under vacuum, further reducing the working area. Keep in mind the UAT itself can cause cavitation under the right circumstances. That is clearly not what happened here, but I would definitely go to a larger hard sided unit like the Intairco, JMP, or the GBR ( my favorite) that are designed for these larger engines. Don't get me wrong- i have 2UATs, I just use them on my 100 and smaller engines.

Also, on this unit, neck sealing with teflon in the threads is critical.

Your air bubbles may be coming from your safety wires. Always give a double wrap around tubing before twisting due to the wire pinching the tubing right at the start of the twist.

He said he had a fuel restriction from a chunk of CA in the line........

His problem is solved

I thought so, I got 3 flights yesterday. First flight was mild flight and I had a lot of air inside of my UAT once on ground with 1/4 fuel left in both main tanks,

2nd flight was more aggressive and it the UAT was almost 1/2 empty but not sucked in like before. Could not find any leaks or restrictions

So 3rd flight was very boarding, Flew flat and level for the whole flight no loops or splits S and only went to Full power 2 times for a few sec, and it was 1/4 full of air.

I don't see air bubbles when defueling, or when using the pump with the controller.

I pulled the UAT apart last night and the filter is very clean, I did add a bigger vent adapter that goes throw the bottom of the fuse for more vent airflow so I'm not sure if that will help things I'm gong to fly it again today to see.

I was thinking of Connecting an air compressor to the fill line and fill the whole fuel system at 10psi or so and spray with Windex to look for leeks, What do you think? The main tanks are plastic, so Im not so worried about blowing up a tank.

What are you sealing the fill line on the bubble trap with? Biggest cause is air leaking there.

Might I suggest that you use a bit of soapy water rather than Windex? May I also suggest that you get yourself a couple of syringes with say 18G needles, sand the points off and use that to apply the soapy water exactly where you want it?

Just suggestions for leak checking.

Just the aluminum stopper that came with the UAT.. I look into it. Thanks