Boomerang1

I used to fit a shutoff valve just before the engine, now I fit it BEFORE the pump for exactly the
reason you mentioned.

The Oz turbine rules require both a manual shutoff valve & a radio controlled method of shutting
the engine down independent of the ECU.

Using a servo to drive the valve satisfies both requirements. - John.

kochj

Great info guys....
A pleasure to read...

zonker123

My Feedback: (21)

Hi Craig,
I am finishing up a Eurosport with the vector pipe now. I was going to run the the saddle tanks (2 dubro 80 oz) into the GBR large UAT but your post gives me pause.
What size center tank do you use or is adequate to to plumb the saddle tanks into?

Thanks!
mike

Harley Condra

My Feedback: (4)

By installing an extra vent fitting on your header tank, each main tank feed line can be attached to it's own devoted inlet. This eliminates some feed problems you might encounter at certain power settings.
It removes the tee fitting from the main feed lines to the Kevlar® header tank.

Countryboy

My Feedback: (25)

For all the doubting Thomas's to Joe's statement above about fuel syphoning, let me run this across. My F-4 saddle tanks are plumbed with a vent for each tank and pickups from each tank T'd together going to a JMP accumulator then to the pump. All lines are 3/16 right up to the pump inlet. I use the JMP dual taxi tank ( fitting to each vent). On three separate occasions upon taxi out, when the taxi tank lines were removed one tank continually proceeded to dump fuel out of the vent in very heavy stream. On all three occasions ,this was caught before takeoff. If not there is no doubt that I would have been out of fuel within a couple of minutes. When I tried to defuel using the Jersey, the tank that was dumping fuel from the vent would try to collapse. Any other time when I defuel, everything is normal. Lewis Patton and Keith Yates have both witnessed this. Any ideas ?

mr_matt

My Feedback: (10)

Maybe some vent or feed line getting pinched only when the hatches are on?

Countryboy

My Feedback: (25)

Thanks for taking a shot at it Matt, but not even remotely possible with the way the feed and vent lines are run.






As you can see from the photos, the lines are well below and out of the way of the engine bay hatch.

CraigG

My Feedback: (40)

Mike,

I used a 16oz round tank that I mounted in the top of the fuselage behind the cockpit. I think any size tank 10oz or larger would do the job. I held the tank in place with rubber bands attached to some hooks screwed into hardwood blocks. I cut a hatch in the bottom of the fuse to get a little better access to the tank and the other plumbing in that area. No problems after I added the header tank.

Craig

757Driver

My Feedback: (90)

CB, I understand that your vent lines are Separate since you are using the JMP dual feed taxi tank.

The issue I believe is the slightly higher tank is gravity feeding the lower tank, at a high rate and filling it to the point of overflow. Once this starts it siphon feeds the problem. I love large fuel lines but they make this condition worse.

I believe the solution will be to bring your vent lines to a 3/16" Festo, barbed T fitting, above the intake duct. Position the T so it sits basically on top of the duct. Next run the single vent line from the T to a higher point in the fuselage. Above the smoke tank for example. Then out the bottom through one of the existing fuselage vent holes or bulkhead fitting.

joeflyer

My Feedback: (48)

Countryboy and all the skeptics,

Here's how it's happening. The saddle tanks usually don't fill exactly evenly. Fuel starts running out of the faster filling tank vent, then you stop filling. That fuel starts the syphoning process. As fuel is drawn out of the full 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. See the attached sketch.

I hope this helps clarify the process. The fix is to tee them together for a single vent. Another fix would be not to tee the clunk lines and have two separate feeds to the UAT or third tank.

Joe

gunradd

My Feedback: (9)

Joe I have had that very thing happen to me on my F22.

I have 2 saddle tanks that feed into one header tank then into the UAT. I also have dual vent lines and vents. I topped off the plane then walked away for a while. With the main hatch off the sun was shining directly on to the tanks. The fuel expanded and syphon out of one side and drained almost everything out of one of my main saddle tanks. I like having an extra drain for the bigger engines with no T fitting. But this is something you need to be aware of.

I don't top the tanks to the very top anymore. Since I started that I have not had a problem. This only applies to planes with dual vents. Also Joe even if you have separate feeds into a header tank it will still happen thee same way. The fuel just has to travel a little further to get out.

Country boy something you can try is when taking the taxi tank off pull one line off the plane. Then cover the vent so the other tank that's plugged in still feeds the engine. Then remove that side while you have your finger over the other vent. This would fix your problem. Or just use a single vent with a T. But I like 2 vents myself.

mikes68charger

My Feedback: (34)

So guys I have followed your diagram for 2 saddle tanks and one main tank then the UAT with great success (all 3 tanks are 24oz)

But I find myself in a situation where I need to add one more 16oz main tank to get more capacity

So to do this I just take the fuel line from the main tank to the vent of my new 16oz tank. Then connect the fuel line from the 16oz tank to the UAT. Is this correct?

Thanks

joeflyer

My Feedback: (48)

Mike,

That would work, however with 4 tanks your system restriction may start to become an issue. The fuel pump will have to work harder, might restrict your fuel flow such that you can't achieve full power, and cause your tanks to balloon during fill.

My suggestion is to replace the center tank with a 40 oz. tank. See if the Dubro 40 oz,. tank will fit. Also you can reduce the system restriction by having two vents in the center tank (one from each saddle tank) like Harley suggested above. If you're using 1/8" Tygon it's not big enough for 4 tanks.

Joe

ravill

My Feedback: (11)

Mike, make sure what ever you do, test your fuel system on the ground BEFORE taking off. If your ECU lets you prime your fuel system, ramp the pump voltage to typical full throttle voltage and drain all your tanks through your onboard fuel pump.

This will let you see any airbubbles, cavitation or any other problem you may have in your set up.

FWIW, I'd put all the tanks in series for your F-16 with that AMT you have.

Quandry

I have a twin tank jet in my build queue so this is an interesting topic with my limited experience. It seems to me though that running in series would be easier, with the commonly cited downside being a higher amperage draw at the pump. What I am wondering is has anyone run a test with an amp meter to see what is the real difference between running in parallel and series? - It would be interesting to see if it is neglible or material.

gunradd

My Feedback: (9)

Quandry I have been thinking about running my tanks in series but just hate the thought of one saddle tank being full while the other one is almost empty. Probably would not feel it in flight unless pulling hard Gs not sure.

757Driver

My Feedback: (90)

I tried both setups, series and parallel plumbing of saddle tanks in my Yellow Aircraft F-15. Series sucked, as I'm very sensitive to out of trim airplanes! Here's why...
At takeoff both tanks are obviously full. As you taxi out the lateral (roll) imbalance begins. By the time you takeoff the airplane is out of trim. This is because both sides were empty upon landing and the airplane was trimmed for that balanced lateral configuration. So after takeoff you might need a click of trim. As it burns you need more trim until empty. Now as the opposite saddle burns down you takeout all the trim you just put in. It's a constant work load and nuisance to say the least.

Additionally, flying around with ailerons or tailerons deflected to accommodate the lateral imbalance causes increased load on servos, linkages, hinges and wings. Aerodynamic handling near or at stall speed is dangerous as the airplane will drop the wing that is holding down aileron.

However, airplanes with a long wingspan are not affected as much due to the increased mechanical advantage.

I always reccomend plumbing in parallel and burning that fuel first.

MarkShapiro

My Feedback: (52)

Guys,
I am trying to decide on a plumbing set up for my Airworld Panther. The main tank that comes with the kit is 142 oz. I am using a Rhino, and want a bit more capacity. So I was thinking about adding two 12 oz. tanks, set up in parallel, feeding into the large 142 oz main tank, and then in to the UAT. Question: is it alright to have the two small 12 oz. tanks being used as "saddle" tanks?

CraigG

My Feedback: (40)

It's worth a try. The two saddle tanks would need to be plumbed identically so that they draw evenly. As soon as the first one goes dry the other will stop feeding so it's unlikely all 24 ozs will be used.

Midas D.

Had the one Disco Wings on post #4 describes in my UF.

Worked flawless!!

2 vent lines gives you the opportunity to see if something goes wrong/blocked cause if all is working fine during filling up the system the fuel should come out both vents at the same time when full.

Quandry

I know this is an old thread, sorry for bumping... but I was re-reading it recently and came across a question I posted. I went on to test this theory and wanted to update with my results in case other folks were facing the same challenge.

After writing this question, I went on to do some of my own testing using an F86D model with fues/saddle tanks and a header tank. There was really two things to test amp draw (at the pump), and air draw to the UAT.The difference in amp draw at the pump was only slight between parallel and series draw, with the draw being higher in series (not surprisingly). From my recollection is was less than 50ma - verified in real time on a volt meter. The difference in air draw was also marginal, but I did find that the UAT had less air in it when the tanks were plumbed in series. Overall the differences were smaller than what I expected and there is probably not one absolutely right or wrong way to plumb multiple tanks. It may in the end come down to some level of personal preference and dealing with specifics relating to individual jets. From my own experience (which is still at this stage limited) I prefer to plumb in series rather than parallel. I flew my F86 with series plumbed tanks between 20 to 30 times and then landed up selling it on to another modeller here. If I were building another multi tank model, I would be happy to go with series plumbing.

TTRotary

I am fairly new to jets but series makes the most sense to me for 1-3 tank setups. It flat out works and you don't have to concern yourself with siphoning issues, vent issues, uneven pull from the saddles, etc. And with today's tubing choices, there should be no issue with ecessive pump voltage for setups up to 200N. My JL F-15 was set up in series and I had high voltage, but that is because small tygon was used. Once I replumbed in medium, no issues whatsoever on a 120SX.

The other thing I like about series saddles is that the fuel movement during maneuvers affects CG less, than a parallel setup or big tank single setup. It also increases what I call your air buffer. That is, every time you have 1/2 tank and you go into a vertical or a downline, that clunk will suck air. The next (full) tank acts as a buffer during that time, So you only tap into your header tank towards the end of the flight.

That, BTW is why you were noticing less air in you UAT with the series setup.

SECRET AGENT

My Feedback: (18)

I like and use the series setup as well. Never had a problem.

chopper52

Jet Guys
Help Need to plumb 2 fuel tanks together,,, One is on top,,,,,,,,,, an the other is below it.... Both tanks have air vents Can't the top tank just drain into the bottom tank..If you can help
Please make a drawing,,,,, need all the help guys....Thanks.....

CARS II

My Feedback: (7)

You are correct, drain top tank into bottom tank first, use vent to vent on top tank and drain into vent on bottom's tank then drain of bottom's tank to air trap.

If you like to gain more knowledge regarding rc fuel system the check this page from Ultimate Jets, the video showing how fuel moves around a bottle is very interesting.

https://www.ultimate-jets.net/blogs/...considerations

I hope this helps.