What are the keys to success for using a multi tank fuel system that does not include a UAT?

I have a new installation in an older pre-UAT jet that really doesn't have space for the UAT without replacing current fuel tank and therefore reducing total capacity.

I know there are lots of guys out there that don't use one so a little help, Please!

David S

On my last 2 models I haven't used a UAT (or similar).

One uses a felt clunk in a one litre tank (Wren 44) & the other BVM Sabre
(P-60) uses a small fuel tank (2 oz I think) with the pick up tube fixed in the middle
of the tank, after the normal kevlar tank.

You could probably squeeze a similar small tank crossways in front of your 4 existing. - John.

Dave, I remember The General (Lewis) mentioning he skips UAT's on all his builds. May be worth a PM to him.
Shaz

Looking at that pic you could easily fit a small UAT such as a MAP small one in that installation. I know a few people dont use a UAT but for $45 I think the added security and peace of mind is well worth it.

There was a poll on here some time ago and the people using UAT'S far outweighed those that did not

Hi,

I've been using a 2 ounce Dubro tank with the pleated paper deal. No purging, no bubbles, and perfect flights since the switch.

David, not sure on the turbines you are using but for reference the CAT-M (which Todd stocks your side of the pond) measures 46mm in diameter by 83mm long (101mm to barb tops) and is cylindrical in shape and can be used vertical.

Looking at your picture it seems there might be room in-front of the tanks for this unit(s) to sit stood up.

marcs

David

Very simple you should use a pleated paper filter pickup and make sure that it will swing from side to side without getting hung up. Locate the pump as near to the tank as you can and preferably use one or 2 tanks. The more tanks you use the better the chances of an air leak. The yellow Tygon supplied with Chinese models can very hard, don't use it. 'Proper' Tygon can be very flexible and cause problems with the heavy clunk being hung up at the front. I now use a short length of brass pipe and 2 lengths of Tygon inside the tank so this does not happen. I fit the tanks so they are propped up at the front slightly so when taxiing and flying at low speed for landing the clunk sits in the fuel. If you have more than one tank you can get away with just having a pleated paper filter in the tank the pump draws from, but I usually put pleated filters in all tanks.
In my experience header tanks are completely unnecessary and just add weight and more junctions that can leak. I tried one before going to the filter in the large tank.

They are available nor from GBR-jet

http://www.gbr-jet.com/catalog/produ...44vk6q8qqme577

John

David

I just looked out some photos of a small FEJ Rafale I fitted out originally for a Jetcat P60

As you can see it has a pleated paper filter in the tank, no UAT and a very simple installation. This was done in March 08. The engine was changed to a K80 and has flown for about 100 flights. I cannot recall there being a flameout with it.

Hope this helps

John

UAT is absolutely not neccesary. A felt clunk or similar in a centre tank or twin tanks is OK. Less flow restriction, less complexity, fewer leaks, no purge. In fact UAT's induce probably more problems than what they solve.
Andre

Andre, whilst clunks in tanks often provide a reliable bubble free fuel flow to state that UAT's probably induce more problems is a tad rich.

In a tank you have a large mass of fuel flying around (even small movement makes one hell of a swirl - try holding a shallow tray of water and walking about ;-)) so yes a good clunk will follow the fuel within reason but as the fuel draws down the time the clunk spends in air increases and this will result in a greater chance of air being drawn in.

In a well made and properly plumbed UAT product the volume of fuel is small in comparison to the main tanks and the filter/pickup is fixed and not whooshing about, this as a device is going to provide a better chance of not drawing air in with fuel.

There will always be those who use UAT's and those who don't, choice is great.

Just one small note, I was asked to make 4 large custom CAT products for a very well known American aerospace company to use in a large three turbine powered experimental aircraft, the turbines are 400N units and the fuel system has worked flawlessly, so if at the cutting edge of technology the use of UAT type products is considered important then I would suspect they have done some homework

marcs

The UAT came about in the early days when causes of intermittent flameouts were not certain, the header/bubble trap gave more reliability and was so adopted as the norm.
Modern turbines and ECU's are much better and even if the odd bubble does appear it will not always make them stop.

Air bubbles get blamed alot, the pump, fuel valve, plus all those and other connections at ECU can cause it to stop suddenly, do a test while the turbine is running, pull the fuel valve plug out of the ECU and it will stop instantly, with guys having to add extensions to this lead, it is one unlooked at area, that a poor connection can cause more bother than any air bubble.
I have fitted new RJ12 plugs to the black telephone type lead used on Jetcats because of damaged pins, a bad connection here will also cause a turbine to stop intermittently.

My Old Boomerang has a BVM UAT and it always has air in the top corner, now I only use homemade centre pickup tanks which never have any air in it, so which is better?

From my view there is more benefit of having a header tank to provide a constant fuel source (as the heli guys do) than being fitted purely for use as an air trap.

Many have proven that a felt, orbit or similar clunks work well with no additional tank, so if it is proven to work and you have no room for a header tank then why not use this system.

Thanks for all the responses! I knew I could count on you guys for good info!

This is a twin turbine installation using JetCentral Super Eagle turbines in a BVM Rafale. The two silicone tanks shown are the header tanks in front of two additional tanks per turbine. Those header tanks are Dubro 16 oz center pickup, and I have currently installed the large Walbro felt clunks for pickup. I've used a UAT on every other jet I've ever had, so, I just want to be sure that I'm on the right track for this install, if I decide to go with no UAT.

Unless I plan on doing extended negative G maneuvers, wouldn't a higher or top mounted pickup tank work just as well? Felt or pleated paper, same effectiveness? i checked Dreamworks site didn't find pleated paper pickups.

David S

Just went throught myself,home this helps

http://www.rcuniverse.com/forum/m_11...m.htm#11045742

As air bubbles always want to go to the top, the UAT/air trap/last tank before pump should always be the lower than the vent, so any air will always try and go up and out a pipe into the higher fuel level.

For an example if you had a UAT on top of the main tank then any air will always try to flow into the UAT from the main tank where you dont want it. So good practice in installs to keep the UAT/header that feeds the pump as low as possible.

i got this in a Turbine that was shipped to me from the Netherlands kind of like Dubro,s i guess but that is what they use over there

In my CAI Raptor with a Pegasus there is no UAT nor header tank nor pleated paper clunk. Just large size fuel lines, 2 saddle tanks feed into a center tank directly into the pump. The center tank is at least a liter. In all honesty, I have never had a flameout on that, or any jet that I couldn't figure out the reason and it's never been air bubbles. Failed EGT probes, battery died, or ran out of fuel all together, but never air bubbles. Just lucky I suppose.

There was once a time when the UAT didn't even exist (It's true, it's true).

I flew my first two turbine powered models with three 40oz tanks in series (one was an operational drop tank) with no special air trap of any kind. Worked great, I put several hundred flights on each one of those airplanes without any problems.

I do have UAT's installed in two of my models today simply because it is cheap insurance (and they are BVM airplanes so they came with the kits). In my little PMP Gripen there was not room for a UAT, so I installed a Sullivan 3oz round tank with a pleated paper clunk. It cost a fraction of what a UAT does and works just as well.

Hi David,
I would feel comfortable with a walbro felt clunk in each of the 16oz header tanks and no UAT.
Vin...

Do UATs have a lifespan?

On the note of air bubbles, I'm new to turbines, and I ran my k80 up. I messed up and I had a lot of air bubbles, some 1 inch long go into to the turbine. Expecting it flame out, nothing happened. It ate a long stream of bubbles. kept going.

I was using a 2 liter bottle and I pulled the fuel tubintout too far for about 5 seconds, it sucked air but still got fuel. Wierd.</p>

Marcs,
I am sure that for some type of installs a UAT would help, especially if the rest of the system is not up to the job. Problem I have with UAT 's( I used them as far back as 1980's in Pulse jets) is that during maneuvers the fuel is always going to go to the outside perimeter of the tank and the centre will be just air if the tank becomes too much of an airtrap. On pulsejets this was an instant flameout if you made any roll with some negative G's. This is where bladder tanks came in. A moving felt type clunk as described by John in the final tank is thus preferred. On my UAV systems we had 8 wing tanks feeding a 1 litre tank with felt clunk. I managed to get it certified as an airworthy military craft authorized to fly in mil airspace.
That said if someone thinks they need a UAT for a given install they probably do.....
What could be really usefull is a UAT that would constantly purge itself from air.
I would buy one....
Andre

Andre, is tests the CAT would only start to draw air when the fuel was depleted to around 1/3 full, that's an awful lot of air to be inside before it gets into the fuel lines.

marcs

I am no turbine expert, but my two most reliable installations - not a single flameout in flight with fuel in the tank - were my CARF Rookie and my O/D jet trainer both of which had home made 2 litre cider bottle fuel tanks with pleated paper pickups (from Mick Reeves) feeding straight to the pump as John Wright described.

My two most troublesome models of late have been my CARF Eurosport and Lightning (both boughtS/H) which have the factory tanks and a UAT. I am not blaming the UAT itself, but they do not cure faults elsewhere in the plumbing. I now wonder if they cure anything at all as, like essyou35, I have seen bubbles in the fuel line cause no problem in testbench running