raron455

My Feedback: (38)

looking for a little more advice fellas,
I am replumbing this jet that I got, putting all new lines on everything,, I drew up a diagram on MS showing how the lines are routed,, I wanted some experienced fellas to check this over and make sure I have it right. If its not right please let me know what to do to make it right,, I have no experience with multiple tanks,

I have a few questions, as this is my first turbine and still learning

1.It looks like all the line is still the yellow tygon I use on my gassers,, Looks like the larger line though, not the 3/32 is this the correct line?
2. the vent lines on the three tanks are all tied together, do I run the last vent line out of the plane Like on my gassers?
3.I will filter the fuel while filling, but I have read that I need to run a fuel filter in the jet also,, Where does the filter go,, I would assume to put it in the line leaving the UAT before the fuel enters the pump?
as always thanks for the help and advice,,

CraigG

My Feedback: (40)

That's not a good way to plumb 3 tanks. The UAT will draw fuel out of all three tanks simultaneously and start sucking air when the first/smallest tank runs dry. Instead, feed the center tank from the saddle tanks by taking the two saddle tank pickups (red in your drawing), "T" them together and attach the single line from that "T" to the vent line on your center tank. Plumb the pickup on the center tank directly to your UAT. Plumb the two vent lines on your saddle tanks together and run the vent to an open fitting somewhere on the bottom of the jet.

Craig

raron455

My Feedback: (38)

Thanks Craig,, That's why I ask,, I did another diagram,, So Does this look like how the system should be?

DiscoWings

My Feedback: (76)

See,

You could also "T" the vent lines form the 2 tanks to make 1 vent for the main tanks, I keep the seperate, allows for more air to fill the tanks and makes it easier for the fuel system to breath.

basimpsn

My Feedback: (5)

Your first setup will only work if all three tanks is the same capacity and fuel lines the same size.

CraigG

My Feedback: (40)

Yep, looks good. You could use individual vent lines for the saddle tanks like DW suggested but if you use large diameter fittings and vent lines the T method will work just fine. A single fuel vent line also makes it easier to hook up an overflow/taxi tank, which you will need to use if you plan to attend any jet events.

Craig

raron455

My Feedback: (38)

Thanks fellas,I am grateful for the time and help you give
The saddle tanks are the same size, the center tank is smaller,,I will stick with the last setup I drew up and use a T in the vent lines that way I only have to run 1 exit line if I need to hook it to a catch tank.

Is the fuel tubing used the Yellow Tygon, the same I use on my gassers,, and what size line should I be using, I am guessing to use 5/32 which is the larger size?
and where should I put the fuel filter in the system? right before the pump?
Thanks guys you are helping me learn a lot and I do appreciate it.

rcjets_63

My Feedback: (4)

Here's a generic fuel system diagram for a plane with three tanks plus a UAT. It was done for a Jetcat P-120SE with a keroplug and includes recommended tubing sizes. Please note that the tubing length between the T's and the Left/Right tank should be identical so that the fuel is drawn equally from both tanks. (The shape of the tubing inside the left and right tanks is a bit "funky" because the stopper hole in the tanks was drilled at the factory at the top rear of the tank. If your tanks are drilled at the front or top front of the tank, you can just do standard shaped tubing.)

Note that the diagram shows the manual shut off valve on the output side (not the suction side) of the pump. If you put the valve on the suction side of the pump, you should use a large bore valve (such as a 6mm 1/4 turn ball valve) to help prevent cavitation due to pressure drop through the valve. Also, the valve has to seal well in a suction/vacuum application or you might pull air into your UAT. I put the valve on the outlet side of the pump because I use the supplied JetCat small bore valve.

Regards,

Jim

Note: Use the 2nd diagram. RCU won't let me delete the first.

bcovish

My Feedback: (8)

Ron, what plane and turbine are you working on?

raron455

My Feedback: (38)

The 1/8 scale fej advanced f-16, don't have the turbine yet, was gonna get a little more advice when I see ya guys on friday.

PHall

So somebody explain to me why in the first diagram the UAT will suck air and in the following diagrams the center tank will not suck air. No matter what you call the tanks, a tank is a tank and air is thinner than fuel so what will the header tank suck first. Air or fuel??

Air.

I think all the tanks should be in series.

rcjets_63

My Feedback: (4)

In the first diagram (also pasted below), an "X" connector is used to connect the clunk line from all three tanks to the feed line to the UAT. The pump draws fuel out of the UAT which is replenished by fuel drawn from the three tanks. In theory, fuel is drawn at the same rate from all three tanks. In practice, this will vary depending on the length of tubing between the X-connector and each tank. However, if all three tanks are not the same volume, the smallest tank will empty first and then air will be drawn past the X-connector and into the UAT because, as you said, air is thinner than fuel.

In the second diagram (also pasted below), a T-connector is used to connect the clunk line from two saddle tanks to the vent line of the center tank. The clunk line from the center tank is connected to the UAT. In this arrangement, the pump draws fuel from the UAT which is replenished by fuel from the center tank. The center tank is replenished by fuel arriving from the saddle tanks through the center tank vent line. The saddle tanks which are assumed to be the same size) both contribute fuel equally (provided that the lines between the saddle tanks and the T-connector are the same length) to keep the center tank full. Once the saddle tanks are empty, air is drawn through the saddle tanks and into the center tank which continues to feed fuel to the UAT.

Installing the tanks in series as you suggest will also work. The downside of that is that it can lead to a high vacuum level required to pull the fuel through a single path (electrical analogy: resistance series circuit is Rtotal = R1 + R2 + R3 whereas resistance in a parallel circuit is 1/Rtotal = 1/R1 + 1/R2 + 1/R3).

Regards,

Jim

CraigG

My Feedback: (40)

Good explanation Jim. Using a center/header tank is also helpful in that it minimizes the opportunity for getting air into the system. The clunk/pickup line can pickup air during maneuvering as the tank gets closer to empty. Since the center tank stays full until the saddle tanks empty, it pretty much guarantees air-free fuel to the UAT until the center tank itself starts to run low. By that time, you should be landing anyway.

It's probably not an issue with most jets but I had to go with this setup on my CompArf Eurosport with thrust vectoring. The two standard saddle tanks fed directly to the UAT through a T but I was getting air during 3-D maneuvers. Adding a center tank solved the problem.

Craig

PHall

Thanks Jim! And I 100% agree.

But.........we assume that both saddle tanks will empty at the same time. If the first saddle tank empties before the second, then the remaining fuel in the second tank will not be drawn to the center tank.

joeflyer

My Feedback: (48)

I do mine like the second diagram above except that I install two vent lines in the center tank and plumb each saddle clunk directly to the center tank. This eliminates the tee and reduces system restriction. Also I plumb each saddle tank and up to the center tank vents with 1/8" Tygon. The center tank clunk to the UAT is then plumbed with 5/32" Tygon.

DO NOT USE SEPARATE VENTS FOR THE SADDLE TANKS. They need to be teed to a single atmospheric vent. A friend used two vents and after he filled up fuel started dribbling out one of the vents. As the plane sat while he was getting ready to fly most of the fuel syphoned out. He took off and about one minute into the flight he ran out of fuel and crashed.

Joe

bcovish

My Feedback: (8)

I may a little thick here, but I don't see how having separate vents on saddle tanks will syphon since the vent line is in the top of the tank. Sounds to me like the pilot forgot to fill the tanks.

joeflyer

My Feedback: (48)

I saw him fill the tanks. Initially I didn't think it could happen but it did. The vent probably wasn't quite all the way to the top so that it had some fuel above it. As fuel was drawn out that vent it was replaced with fuel from the other saddle tank through the clunk line. When he took off he had one saddle tank full and one empty.

bcovish

My Feedback: (8)

Wouldn't someone have noticed a puddle under the plane.

Silent now but not convinced

AMA 74894

My Feedback: (1)

+1, I'm having a hard time figuring out how a vent line (which should terminate internally near the TOP of it's tank) can siphon the entire tank out.
or how the second saddle tank could siphon... especially considering in this example that it does not share that same (siphoning) vent line...

joeflyer

My Feedback: (48)

The funny thing was that several of us did notice and mentioned it to him. He ignored our warnings, assuming that it was due to the tanks ballooning during fill, and too0k off anyway.

AMA 74894

My Feedback: (1)

yep, I'm not convinced either... 1 full tank +1 empty tank = 1 minute of flying time?
sooooo 2 full tanks = two minutes of flying time?
I'm sure there was a reason for running out of fuel, but I don't think it was from having used separate vents on the saddle tanks.

I DO see the logic of having separate feeds from the saddle tanks into the center thank though.

bcovish

My Feedback: (8)

Let me share what happened to me.
I was filling my plane when someone came over and asked for some help. When the tank got full, I shut off fill pump but I did not disconnect it from the fill line in the plane. Came back about 20 minutes later, disconnected the fuel filler, took off and the turbine shut down on climb out. What happened was the fuel was syphoned back into the jersey modeler thru the fill line. This was a single tank install, not saddle tanks
BTW, I got the plane down with no damage.

Now I'm silent and still not convinced

joeflyer

My Feedback: (48)

Re-read post #18. The vent was through the rubber bung and did not go all the way to the top. When the tanks are filled until fuel runs out of one of the vent it starts to syphon. The only connection between the two tanks is the clunk lines that are teed together. As fuel is drawn out of the one tank it is replaced with fuel from the other drawn through the clunk line. It will continue to syphon until the other saddle tank is empty and the fuel level drops below the vent tube.

When saddle tanks are plumbed in parallel they will stop drawing fuel when one tank is empty. So obviously he had some fuel in the low tank when he took off.

Boomerang1

That would be my way of doing it, unless the saddle tanks were
wing tanks & the large imbalance would upset the side to side
balance of the model excessively.

After seeing what happens to a tank if you leave the vent tube plugged
I'd say there's PLENTY of vacuum available from the pump!

John.

757Driver

My Feedback: (90)

What turbine are you planning?
I had a bad experience with a runaway turbine fuel pump in a friends YA F-22. BobO you may have witnessed it. We were starting up and the ECU failed somehow and commanded full power from the pump. The pump responded and halfway through the start the non turbine went to max rpm plus some more I'm guessing. So imagine there you are and this thing is a: trying to blast off across the ramp and B: scaring the heck out of you.
The pilot commanded the turbine to shut down with the TX. No response.
The pilot turned off the airplane RX power in hopes of telling the ECU to power down. No response.
Next was the manual fuel shutoff valve. That worked and we went from WFO to engine off in a matter of a second.
Result: now we had a very hot turbine and pipe. Within three seconds fuel started to spray and fill the inside of the airplane.
Big fire hazard to say the least. Within one minute the entire bottom of the jet, to include the area under the engine, had about 1/4" of fuel in it.
The pump was still delivering fuel! The fuel line between the discharge side of the pump and the shutoff valve blew up like a balloon and ruptured. The reason for this is the fact that these pumps are gear type, positive displacement pumps. In short, they MOVE fluid when they turn, provided they have access to it.

So with the airplane continuing to fill up with 220oz available onboard the pilot began to try and unplug the power to the pump or the ECU whichever he could grab. In the meantime I continued to cool the turbine with shots of CO2. He was able to get the power pulled along with several other wires.

After that I set up every jet I build differently. Yes, contrary most all MFG's recommendations.
The first thing I do is to install the fuel filter at the end of the line. I keep it downstream of everything, including the pump. The reason is if the pump wears or worse, chips a tooth, the filter will catch it. The small passages inside the engine will not tolerate any contamination. It's far better to starve an engine of fuel with a blocked filter than to plug up its internals ( = overhaul).

Festos, any push type Festo is designed to be used in a pressurized line. Only barbed fittings are designed for use on the suction side. Now that said, many of us use the push type, with success, on the suction side.
I recommend putting a -6 shutoff valve before the pump. This will allow you to starve the pump of fuel should you need to such as during the runaway I experienced above.

Mount the the fuel pump and the shutoff valve (if on pressure side) in an area that will drain if the discharge line between the pump and valve rupture. Gear wells areas work well for this. Pun intended.

Route the power wires to the pump so that it can be unplugged during an emergency! If your install is buried you can setup a remote pull using zip ties to break the plug apart. I did this on an F-15 as absolutely everything was crammed in the nose.

I recommend using 5/32 line on everything. If you are unable then try and use the Festo-6 line. (6mm). I like using the anti-static line also, especially over barbed fittings. Be sure to put barbs on every connection and safety wire or zip tie them.

Locate your vent line on the fuselage where it will not be crushed, damaged or pick up debris during transportation. Also be sure this line is easy to reach for you or ground crew. This helps easy removal of the taxi tank.

Filter your fuel as it goes into your fuel jug. Auto parts stores sell a neat water/sediment funnel for about 5 bucks. Filter your fuel at the pickup in the tank. I like to get the large, see through, pleated paper filter that's also available at the auto stores. Filter again, I the line leaving the fuel jug pump. Usually these two filters will plug up before ever letting anything get to the jet. Most often the filter inside the tank will be the only one that needs replacing. Filter filter filter before fuel touches the airplane. Then just one filter (supplied by the MFG) right before the engine. Most UAT's also act as a fuel filter.

Don't try and fill your jet fast! Fast fueling creates excess pressure in the fuel system of the airplane and can damage tanks, ect.
Time your normal refuel times. When this time begins to take longer its a sign that the filter in the fueling jug is getting dirty, all else being equal.

Great question and fly safe!