664KIX

Hi guys. I need some help and opinions here.

I am running two 80ounce Kevlar tanks to a UAT. Each tank has it's own clunk line and vent line. There are two vent lines, one from each tank, that feed to the bottom of the plane (two exits). The clunk lines are equal distance, run to a fuel tee, and then to the UAT.

I am having problems with this setup. The tanks fuel together pretty well. One tank fills ever so slightly faster (less than 8 seconds faster than the other). What is happening is one tank seems to be drawing fuel faster than the other. When one tank empties completely, it is allowing air to enter into the UAT.......obviously causing a flame out. When the one tank is empty, the other has approximately 1/4 tank of fuel.

I have checked and re-checked and am 100% confident all the lines are equal lengths, including the clunk lines, the vent lines, to the tee.

My question, I guess, is this an acceptable way to plumb your tanks / setup.

OR........

Should I have one tank plumbed with a vent to the bottom of the plane and the clunk line to the vent line of the other tank. The clunk line from the other tank to the UAT?

Is one method better than the other? Any help would be greatly apprecaited. I am getting ready to plumb another jet with two tanks now and want to make sure I am doing this the right or preferred way.

Thanks in advance for any help. Much appreciate.

Ryan

jclittle

My Feedback: (99)

I have my 3 planes set up with...2 mains... feeding the same vent line. 2 mains feeding a 10oz header tank, then the header to the UAT. The mains fill and pull about the same. The header prevents any air from getting to the UAT before both mains are nearly empty. Be sure to use the largest possible fuel line to prevent pressure when filling everything.

664KIX

jclittle,

Thanks for sharing your set-up. OK.....so 2 mains with two vents which I assume tee into one vent out the plane. Two clunk lines feeding the 10oz header tank and the header tank to the UAT.

I like the idea of the header tank....didn't think about that. Thanks.

So my question is......are you teeing the clunk lines from the 2 main tanks to the Header tank or are you running each individually into the header tank? Last, the only vents would be the two vents from the main tanks, correct?

Thanks again for the info....very much appreciated.

Ryan

Wayne22

My Feedback: (2)

I had the same problem with identical lenght lines. Some folks suggest making the line to the quick draining tank a bit longer to equallize the draw....but in the end, I just plumbed them in series, and it has worked fine for me ever since...................

664KIX

Wayne22,

Thanks for your reply. When you say "plumbed them in series" I assume you mean one tank feeding into the other tank and finally to a UAT, if you are using one. Is this correct?

Thanks again for your input.

Ryan

KC36330

I've never had two tanks in parallel draw fuel equally regardless of what i tried to do to make it happen, i always ended up connecting them in series (yes one feeds the next and then it feeds the UAT). only thing you need to watch out for is if you use a high voltage on your fill pump you can get allot of swelling from fueling pressure if you're not careful.

kc

jclittle

My Feedback: (99)

So my question is......are you teeing the clunk lines from the 2 main tanks to the Header tank or are you running each individually into the header tank? Last, the only vents would be the two vents from the main tanks, correct?

The two main tanks are t'd together before they go into the header tank. This way the header has only 2 lines, 1 in from the mains and one to the UAT. Try to use a tall header so the feed line from the mains is near the top of the tank to minimize the chance of air getting to the feed line to the UAT. Last, the vents are from the main and also t'd together. This is the way BVM recommended my 1st jet and I've built the last 2 the same way with the same success. Good luck!

664KIX

Thanks guys.......I really appreciate all the help. I think I am going to switch to the series set-up and add the header tank.

Thanks again.

Ryan

joeflyer

My Feedback: (48)

What plane is this? Where are the tanks located relative to each other and relative to the CG?

80 oz. of fuel weighs about 4 lbs. and may give you a noticable change in trim while flying, especially with one tank empty and one full. You need to consider this before deciding on series plumbing.

Having equal length lines is not enough to guarantee that parallel tanks will fill and drain equally. A slight kink in one of the brass tubes or a pinched line will mess it up. Look carefully at the tank internal plumbing including the clunks. Also everthing needs to be equal on the vent side as well as the feed side.

After making sure that everything is equal drain and fill it several times using your fill station. Then in small increments shorten the line to the tank that fills/drains slower until they are equal. You will never get them exactly the same, within a few ounces is good.

Joe

664KIX

joeflyer,

I have a Eurosport. Twin 80ounce tanks. On the CG. The CG is really good, so i am happy with it where it is. I do not notice any trim changes at all in flight from take-off to landing.

I have measured all the lines, they are equal. I am certain of this. I right tank fills faster than the left tank by approximately 1.5 oz. However, it seems the left tank drains faster while running....considerably faster.

If / when I go to a series set-up, I would leave the tanks exactly where they are and simply re-plumb the entire set-up. What are your thoughts?

Ryan

joeflyer

My Feedback: (48)

The only concern would be lateral balance. When one tank is empty and the other full you'll have 4 lbs. more weight on one side of the plane. If the two tanks are touching each other right in the center of the fuse you might be OK. If they are some distance apart then you'll have a noticeable change in flight.

One suggestion is to check the lateral balance with the tanks empty, fill the tank that will be last to empty and recheck it. If it doesn't change too much then give it a try. I personally prefer parallel plumbing to minimize trim changes during flight.

Also you should check to make sure that the clunks in both tanks are the same distance from the bottom. After making sure absolutely everything is equal I usually have to tweek one of the lines to get parallel tanks within an ounce or two of each other.

Joe

664KIX

Very good point. I will check that first. Thanks for mentioning that.

Ryan

icepilot

I fly the SM F16 1/6 with 1 1/2 litres of fuel in each of the saddles tanks
and another 1 1/2 litres in the main tank. They are connected in series
and even though the saddle tanks are quite far apart there is no noticable
lateral balance problem when one tank is empty and the other full, I have
even landed several times with this configuration and had no problem.

I have also flown all my jets with a small header tank with a central pickup,
and have never had a flame-out! (Knock on wood!!)

Tor

KC36330

with the amount of fuel and the very short distance they can be apart inside the fuselage, series setups aren't a lateral balance issue. we're not talking 5 lbs in each wing tip, it's all concentrated at the center of the mass and it would take one helluva drastic change in weight for you to get a trim difference that close to centerline.

kc

joeflyer

My Feedback: (48)

I agree that as far as lateral balance is concerned it all depends on the size of the tanks and the distance from the center of the fuse. In Tor's F-16 his saddle tanks apear to be a few inches from the fuse center and 1 1/2 liters of fuel weighs a little over 2 lbs., so it's not a big deal.

In Ryans Eurosport he has 80 oz. tanks, which will hold about 4 lbs. of fuel each. If they are close to the fuse center he might be OK, if they are a foot away then it may be a problem. Since I have no idea how far his tanks are from the fuse center I suggest that he check it out before flying that way.

Joe