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Fuel Balance and Potential Starvation


srallen

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Hello Everyone!

 

I'm both new to the forum and new to Flight Design aircraft. However, I have been flying light sport aircraft for awhile now.

 

Recently, I have started renting a CTLS. Love the aircraft thus far. However, I am concerned about what seems to be an unbalanced fuel burn from the wing tanks. For example, a typical fuel load might be 10 gallons per side. However, after a few hours of flying, there might be only 4 or 5 gallons of fuel left in the right tank, but still 8-9 gallons in the left. Is this normal?

 

Several pilots besides myself have reported this situation. That led the mechanic to clamp-off the right tank and fly around on only the left to ensure that the left tank was draining.

 

My primary concern remains, given the differential fuel flow, whether the right tank will be drained dry on a long cross country even though the left tank has plenty of fuel in it. This concern has caused other pilots to put all the fuel they would need for a trip in the right tank, but that is not practical for weight and balance if you want to take two people on a flight over a good distance.

 

Any comments or ideas would be appreciated! Thanks!

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Welcome to the forum,

 

This has been this way for many years. It is a design of the flat fuel tanks. It is in other aircraft as well and isn't particular just to the CT. Most left tanks seem to drain faster, a few have right tank drains and some are actually even. If you know the left wing drains faster then you can fly 1/2 to 1 ball out of trim to the left. The fuel will follow the ball. Usually 1/2 ball is sufficient. If you have fuel in the other wing it should not fuel starve unless you are very very low on fuel and then move that little bit of fuel to the outboard side of that tank by flying out of coordination the other way. That would move the small remaining fuel away from the fuel pick up.

 

Bottom line is it should not be an issue and you have the choice to manage that fuel with flying the ball out some.

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Yeah, that ^

 

Welcome aboard!

There's been plenty written here on the topic... just search for "fuel feed" to find several threads... other theories include having, or not having, the fuel tank vents (on top) positioned wrong. Some claim having them acting as a "ram" (pushing air into tank), or "sucker" (creating negative pressure), can make a difference

BTW... the newest CT has a L/R/B valve...

Tim

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Welcome to the forum,

 

This has been this way for many years. It is a design of the flat fuel tanks. It is in other aircraft as well and isn't particular just to the CT. Most left tanks seem to drain faster, a few have right tank drains and some are actually even. If you know the left wing drains faster then you can fly 1/2 to 1 ball out of trim to the left. The fuel will follow the ball. Usually 1/2 ball is sufficient. If you have fuel in the other wing it should not fuel starve unless you are very very low on fuel and then move that little bit of fuel to the outboard side of that tank by flying out of coordination the other way. That would move the small remaining fuel away from the fuel pick up.

 

Bottom line is it should not be an issue and you have the choice to manage that fuel with flying the ball out some.

 

Thanks! So, if I understand what you are saying, since it drains faster out of the right tank, I should spend some time flying with the ball off to the right? This will then cause more fuel to flow from the left tank??

 

I wouldn't have thought of that as a solution, but then I have never flown a multi-tank aircraft before that did not have a fuel selector valve.

 

Yeah, that ^

 

Welcome aboard!

There's been plenty written here on the topic... just search for "fuel feed" to find several threads... other theories include having, or not having, the fuel tank vents (on top) positioned wrong. Some claim having them acting as a "ram" (pushing air into tank), or "sucker" (creating negative pressure), can make a difference

BTW... the newest CT has a L/R/B valve...

Tim

 

Thank you! I just recently found this forum!

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The tanks are connected to each other at all times (whether the fuel valve is on or off). What is really happening in flight (and when on the ground) is that fuel from the tank in the higher wing is transferring by gravity to the tank in the lower wing. This transfer continues until the fuel levels are equal (not the volumes, but the level of fuel in the tanks with respect to the horizon).

 

Unless there is an obstruction in a fuel line, the flow from the two tanks is equal when the engine is running and the wings are level.

 

If the fuel transfers from one tank to the other during flight with the ball centered, then the calibration of the ball should be checked to be sure that the wings are truly level when the ball is centered (again, the imbalance in fuel in the two tanks is more likely due to gravity transferring fuel from one tank to the other than to differential flow to the engine).

 

Many (I would guess most) CTs that appear to draw fuel from one tank more than the other are actually flying with that wing high and a poorly calibrated ball incorrectly showing center.

 

I am not a mechanic, just an owner who used to have this problem (and doesn't any more, now that my mechanic repositioned my Dynon EFIS to center the ball after establishing truly level wings). Have a mechanic perform or approve of any repair or maintenance made on the basis of my comments.

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Fred G. brought up calibration of the ball which is one of the more relevant issues affecting uneven fuel delivery. There is so much that has been discussed on this in previous posts. Recommend that those who need info on this topic, and probably most any other topic, to search this forum. I know of no other place one can find as much "need to know" information for Flight Design aircraft as right here on this forum.

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Hello Everyone!

 

I'm both new to the forum and new to Flight Design aircraft. However, I have been flying light sport aircraft for awhile now.

 

Recently, I have started renting a CTLS. Love the aircraft thus far. However, I am concerned about what seems to be an unbalanced fuel burn from the wing tanks. For example, a typical fuel load might be 10 gallons per side. However, after a few hours of flying, there might be only 4 or 5 gallons of fuel left in the right tank, but still 8-9 gallons in the left. Is this normal?

 

Several pilots besides myself have reported this situation. That led the mechanic to clamp-off the right tank and fly around on only the left to ensure that the left tank was draining.

 

My primary concern remains, given the differential fuel flow, whether the right tank will be drained dry on a long cross country even though the left tank has plenty of fuel in it. This concern has caused other pilots to put all the fuel they would need for a trip in the right tank, but that is not practical for weight and balance if you want to take two people on a flight over a good distance.

 

Any comments or ideas would be appreciated! Thanks!

 

Srallen: I have had the same "problem" since my CTLS was new (2008) and Roger's solution works fine. I have taken a number of 4+ hour flights and the fuel burn imbalance has not been a problem--in fact in my case I find that the tanks seem to balance out after a while. I personally do not worry about it.

 

See ya, Dr. Ken Nolde, 840KN 50+ hours.

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I notice the CTLSi has a fuel tank selector on the rear bulkhead to help with this issue.

 

The reason for the selector on the CTLSi is because of the fuel return from the fuel injection system. You don't want to be returning fuel to a tank that is already full and dump it overboard.

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I'm having trouble making sense of that Tom. Does the CTLSi always return to one side no matter what the selector is set to? If it returns where the selector is set it should make no difference if the tank is full. I don't know what that would mean when it is set to both.

Doug G.

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In a previous post, Tom said "It needs to go back to where it came from to keep from pumping it overboard."... so I'm guessing that the fuel selector also controls the returning fuel, the excess fuel sent to the engine by the over-producing fuel pumps, presumably directing the returning fuel back to where it came from (L/R/ or Both). It only makes sense that if you allow selection of Left or Right, that the excess fuel would have to be directed back where it came from.

 

To avoid hijacking this thread, I'm going to start a new topic, specifically to cover the new CTLSi fuel selector valve.

Tim

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Maybe this diagram from an SR22 will help:

 

8165118779_68b1041c11_z.jpg

 

Note the extra fuel from the engine driven fuel pump goes back to the selector valve. From there I'm pretty sure it goes back to whatever tank is selected. I would assume the CTLSi setup is similar.

 

I once ferried cropdusters where the hopper was plumbed to carry fuel. In that case I had to take one wing tank down substantially before switching to the hopper - otherwise the fuel returning to the wing tank would overflow. One the hopper (with 150 gals!) was selected, the wing tank would gradually refill with the extra fuel being sent back to it. I had to watch it so as to switch back to the filling tank before it overflowed.

 

I found an old photo of the setup:

 

8165175040_a3c25f92fa_z.jpg

 

Can anyone guess what the bungee is for?

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Great timing on this topic. My right tank has been doing just what has been said here for a while. I was going to search tonight to see how serious this could be.

As usual you guys are great with all of your experience and wisdom. My fuel problem is solved.

Thanks

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Eddie, keep the fuel valve from leaking?

 

Exactly.

 

I was flying along and started to smell fuel. Turned out to be a slow drip...drip...drip from the back of the selector valve.

 

Futzing with it as best I could, I found that upward pressure on the selector stopped the leak. Happened to have a bungee and a tywrap in reach, so, as my mom would say, "Viola!"

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Process of elimination. Was going to say the bungy was there to eliminate a rattle but then figured no one could hear it with headset on and all the noise in that old crop duster. I've actually designed fuel valves like the one in the picture and have seen some leaky ones but never saw a "fix" like yours!

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