my Jett 90LX is having a hell of a time with sucking small bubbles and leaning out due to the fuel vibration at the high RPMs it turns, i currently use a 2oz hopper tank but as soon as it gets a small bubble trapped in it, the fuel soon starts to 'foam' and suck air as well. I've had no luck at all finding good information on a felt clunk and even less luck finding a felt clunk so i was looking at the UAT but it's quoted as a pumped system only setup. anyone tried it with a non pumped glow system? I'll be running 22% oil (20% synthetic 2% Castor) nitro fuel, any recommendations are a welcome.

I've looked at the tettra bubbless tanks but they seam to be a bit more of a PITA then they are worth when you get up to the 18oz size that I'd need. seams the 'tankers' only hold about 10 oz and would require multiple fills of the tanker just to fill the tank.

thanks in advance
kc

Your hopper tank should have a rigid pickup tube located in the geographical center of the tank, with no clunk. That way, the pickup tube is always submerged ion fuel.
No chance for air to get inhaled.
The hopper tank stays full, as it draws it's fuel from the main tank clunk line, through the air trap vent.
The BVM UAT uses 6mm feed lines, and I seriously doubt that your engine could draw fuel through that large a diameter.

Harley Condra
BVM REP
JetCat REP

the hopper tank when it gets air in it from the main tank also starts to vibrate to the point the fuel is a 'foam' and air is getting sucked in regardless, do you happen to know anything about the UAT, that is my question. downsizing the feed line isnt a problem, i need to know if a non pumped engine can draw fuel with 22% oil through the 'sock' in the UAT.

kc

Go to the Jett engineering website...if you click on accessories they have bubbless tanks ranging from $12-20.

Mike

and as mentioned above about the tettra's the jett tanker is only 10 oz, takes two fillings to get a full tank, allot of hassle for a 10 min flight.

kc

Have you tried using the dubro centered clunk? It will filtter out foam in the fuel tank. The other thing you can try is what we did for .049 racing which is a tsp of armorall in your gallon of fuel.

I think you need to be addressing the real problem first!! Your plane is trying to tell you there is a reason your setup is vibrating badly enough to foam the tanks. Your fan is most likely out of balance, or the shroud is not isolated from the mounting rails etc. I ran D/F for years, and never had foaming problems. That much vibration will kill your servo's and the rest of your electronics in short order also. I truly beleive that if you get to the real root of the vibration and fix that first, your foaming problem will be gone. That said, Harley's discription of the header tank setup with the "clunkline dead center and no clunk" is exactly the same thing i used to do also. It worked perfectly.

I'm sure that a UAT has too much flow restriction to work on a non-pumped application.

Why are your tanks vibrating so much? Sounds like you need to balance your prop., or maybe there is a problem with your engine. Try mounting both your main tank and hopper in foam rubber.

Are you sure that you don't have an air leak somewhere in the system? Usually the easiest thing to do is just replace all of the fuel lines and tubing.

What diameter fuel line are you using? You should be using at least large (1/8"), or better yet extra large (5/32"). If you are not using 5/32" try up-sizing the flexible tubing AND the brass tubing in your tanks. Also drill out your clunks to 5/32".

Good luck,
Joe

it's a prop plane, prop/spinner/etc.. are all perfectly in balance, the vibration is simply from 16,300 RPM high resonance and the design of the plane makes it impossible to mount the tank anywhere that allows more then a marginal amount of foam between the tank and formers. the only way to get room for foam is to move the tank away from the engine a good 18" which is unacceptable due to limited access in those areas or spray the canopy and remove the cockpit which I'd rather avoid if possible. none of my old ducted fans had these problems because i was always able to get at least 1/2" of foam around the tank, on this setup the formers are only slightly larger then the tank so to keep the stock location and have foam, I'd have to remove the former completely.

Joe, thanks for the comment on the UAT seams nobody else had that answer.

kc

ordered two of the Dubro 'bronze' in tank clunk/filters, one for the main tank and one for the header tank, I'll try the one in the header tank mounted rigid in the center of the tank.

kc

Ok, i get it, it's a prop plane, thats cool,

But, you still should not have that much vibration. If your prop/spinner are perfectly balanced, and the engine is presumably factory balanced, then you might be overreving the engine. You could experement with more pitch and or diameter to lower your RPM. Concentrate on lowering your vibration levels. Because, even if you do get your fuel to stop foaming with padding or some other bandaid, your electronics will be the next thing to fail, and it won't take long.

it's a Jett 90LX, it has to turn a minimum of 14-15 grand on the ground. if you overprop it, it will run hot and lean out.

kc