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Stacy

Left tank dry, right tank 12 gallons left

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Friday my wife and I flew from North central Missouri to a Dallas suburb. In a little over 4 hours of flying, the left tank had 3 gallons left and the right tank had 13 gallons remaining. On our return trip yesterday, fuel remaining per tank was about the same as it had been on Friday.

 

I,ve only owned the plane about a month. The day I bought it, I flew it home 2.5 hours. Tanks were equal when I arrived at my home airport. Without looking at my log book, I think I've put about 15 hours on the plane on local flights. Except for the Dallas flights, the tanks have always stayed equal.

 

Shortly before we arrived home, we learned that my elderly mother had been missing for a little over a day . After speaking to folks on the ground, I put 5 gallons in the low tank, giving me a total of 21 gallons. We flew for a couple hours, looking for her car at places we thought she might go.

The engine ran rough for a very few seconds, the quit running. I advanced the throttle full, and leveled the wings. At 500 AGL, we were going to land very soon. I had started to trim the plane when the engine restarted.

When we landed at the nearest airport, the left tank was dry, the right tank had over ten gallons in it.

Soooo, what do you think is causing the uneven fuel feed.

BTW, a lady saw a post that our daughter had put on Facebook, and called to tell us that my mother was at her home. Credit card charges, to my mom's card, showed that she had driven at least 100 miles. She was found just a few miles away.

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Most CTs have one tank that tends to drain faster, probably due to the tanks not having perfectly equal level on assembly (or inclinometer tilt as Corey mentioned).  Also, it's *very* easy to fly these airplanes with one wing lower than the other, and fuel will preferentially flow from the higher wing as that tank develops higher head pressure.

 

A lot of us compensate for this by flying the airplane in a slight slip.  Usually having the ball half to one ball out is sufficient.  Charlie Tango likes to say "the fuel follows the ball", but it's easier for me to visualize that the higher wing flows more fuel to the engine.  Using the rudder trim it's easy to fly with a wing high.  Just look at the wingtips in relation to the horizon as your level indicator.  If the left tank is more empty than the right, adjust so the right wingtip is higher above the horizon than the left.  Usually 10-20min is enough to balance things out on a longer flight.  Because of the T in the fuel lines, you can actually transfer fuel between tanks using this method.

 

No judgment here, but I have a question:  Did you not notice one of your fuel tanks was empty or approaching empty, or did you not think it was an issue since you had fuel in the other tank?  In the CT this can be a bad condition because of the simple on/off fuel valve and how the tanks are configured.  If you have a dry tank and fuel below a certain threshold in the other tank, then during a turn toward the full tank (or flying with the empty tank wing higher than the other) the fuel can slosh away from the pickup at the wing root.  Since there is no fuel in the other tank and its pickup is also dry, you can get a fuel starvation situation.  It sounds like that is what happened to you in this case.

 

If you periodically check and balance the tanks as I described, you will avoid this problem in the future.  They don't have to be perfectly balanced all the time, but you should at the minimum  be able to see fuel in both sight tubes.

 

Also check the tank vents to make sure they are both clear.  If one is clogged it will keep that tank from flowing fuel normally.

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My CT will currently drain right dry left 10 remaining if I flew with the ball centered.  It is not currently calibrated correctly and you can not perceive this slight slip visually but your fuel flow can.

 

I'm currently flying 3-4 days / week and have my flow nailed with my ball on the right side of the cage.

 

Uneven flow rates and even tank level have little to nothing to do with the flow balance.  Its all about where your nose is pointed or how level your wings are, however you want to look at it.

 

The potential flow rates far exceed usage so as long as you are level / coordinated your flow is balanced.  When you are truly level there is a single vector, flow towards the engine.  When you move the nose even a very small amount, due to our flat tanks, you quickly introduce a 2nd flow vector, towards the trailing wingtip.  As long as you have both vectors you will drain forward wing first.

 

Note: you are not really draining one tank faster than the other instead your are doing a combination of feeding the engine and transferring fuel.

 

Your ball calibration is easily checked using your sight tubes.

 

This flow correction works even if I fly someone else's CT, it also works if I'm a passenger and I point out the calibration error and the needed adjustment.

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Friday my wife and I flew from North central Missouri to a Dallas suburb. In a little over 4 hours of flying, the left tank had 3 gallons left and the right tank had 13 gallons remaining. On our return trip yesterday, fuel remaining per tank was about the same as it had been on Friday.

 

 

 

Which model CT?  There is a big difference between the older plane with the 912ULS and the newer ones with the 912iS engine in regard to fuel system design.

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Yup, and if you over correct you can transfer more fuel into a tank.   I can takeoff with Left 10gals, Right 10gals and Land with Left 5gals Right 12 gals.  I agree if the ball is centered on the CT (mine is a CTSW) you will have uneven drain.   Ball slightly to the right is the 'sweet spot' 

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It depends on the plane, the mounting of the Dynon and the mushroom. I have seen this corrected by a re mounting of the display, but flying in a cross wind will also cause one tank to drain faster tha the other. Trim to correct it. The sight tubes will verify it.

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I can't say this as precisely as some of the previous commentators have done, but let me explain it my way.  I was having the same problem with my 2008 CTLS.  My mechanic decided to place the aircraft on a (nearly) perfectly level piece of concrete.  Then he took a six-foot bar level and placed it as level as possible, spread between each wing root.  The bubble was centered in the level.  Then we turned on the Master switch and observed the ball in the EFIS; It was NOT centered.

 

He concluded that the entire instrument panel and housing was not installed level.  With a precise digital level he concluded that the EFIS screen was not level by about (I think I remember correctly) 2.5 degrees.  Instead of trying to re-level the entire instrument housing, he merely leveled the EFIS screen.  The finished project shows the EFIS tilting so little you can just barely notice, but the ball was then centered on level ground.

 

This all implied that the aircraft, with the ball centered, was previously flying slightly sideways causing the fuel vents on one side to be a bit more pressurized than on the other wing (so I was told.)

 

Anyway, since that time both fuel tanks keep about the same levels; problem solved.

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Guys, thanks for your help. My plane is a 2006 CTSW. I had already blown on both fuel camps, and they seemed fine. The plane was flown ball centered, except while we were looking for my mother's car. While looking for the car, I flew right wing low, so two of us could see out the right side. But, I had commented to my wife, on the trip from Dallas, that the ball didn't seem right to me.

 

In the past, I've always paid close attention to fuel levels in flight. The site tubes on this plane are fairly dark, dark enough that I have not been able to read them. I mentioned this fact to a guy; he said I didn't need to worry about it, since the tanks always drained the same. He also said that the plane would fly with an empty tank. When I heard the second statement, I wondered how it could continue to run if it was sucking air. Well, dumb on my part, because I should have got the book out.

 

I had also wondered if a small flashlight would help when trying to read the tubes. I tried it today with a flashlight and I could read them easily.

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The sight tubes should be replaced. Over time they become brittle. There's a new material being used now that stays pretty clear for a long time.

 

Also, to build on previous posts: the engine is incapable of sucking fuel once air is in the line; it relies on head pressure to displace the air, which is simple enough to do, being a high wing. Even if you unport fuel for a moment, in normal circumstances the air will just get pushed through the system and vent out via the carb vent ports.

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I was with DocRon and it is his plane I was speaking of. Thanks Ron for filling in the details. Still miss having you around here.

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I had also wondered if a small flashlight would help when trying to read the tubes. I tried it today with a flashlight and I could read them easily.

 

oh gosh - change the tubes.   Mine are medium brown, enough to read but i already caught myself making a mistake due to the 'low' readability of the site tubes.  I am scheduled for a change once parts get in. 

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Crosswinds cannot effect your fuel flow balance.  The plane doesn't 'know' its in a crosswind it drifts along with the air mass.

 

They can if you are using the autopilot to maintain a course.

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No special tubing is needed. FD used to use just clear polypropylene tubing. When I did a research project on this in 2008 I called several tubing MFG's. They all said that tubing is just porous enough that all will stain when using auto fuel with the brown dye. Several people have tried different tubings and it starts out life not clear and then just gets worse. Some have come in here with different tubings and you couldn't see a level to save your life. 

 

You are supposed to do a wing pull/inspection every 2 years or 600 hours whichever comes first. This is the perfect time to change tubing. The poly tubing that can come from Ace Aviation is dirt cheap. It should cost you around $2 for the two lengths you need. It WILL NOT break.  Like most tubings it will get stiff, but I have tested every single tube that I have taken off planes by bending them in half and not a single one has ever broken. Not even the ones that are over 4 years old. When I do a wing pull which has been 2 in the last 4 days I put the nice perfectly clear poly tubing on and when the wings are reinstalled I pour 5 gals. back in each wing and then mark the tube so it is accurate. For the most part that's just half way down the tube. Tubings that others have tried start out hazy or yellow.

 

Poly tubing is fine, perfectly clear, should stay good for viewing for your 2 years and makes seeing a fuel level easy. Sometimes trying to do better than than an older proven way is worse.

 

 

I'm pulling John-Olav's wings this morning and poly tubing is on them and going back on. You can see his level just fine in the old poly tubing.

 

 

p.s.

If anyone in the world has ever SEEN a poly tube on a FD plane wing break while it was just sitting there speak up.

 

p.s.s.

There isn't any.

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They can if you are using the autopilot to maintain a course.

 

The AP changes nothing.  True the AP can drain one tank first but its for the same reason, the nose isn't into the wind.  Rudder trim fixes it and referencing the sight tubes can confirm you are at the correct trim.

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The idea that crosswinds can effect fuel flow (except when using a side slip in the landing phase) is a good Stick and Rudder Moment.  I'm sure Fast Eddie would have pointed that out. :)

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The AP changes nothing.  True the AP can drain one tank first but its for the same reason, the nose isn't into the wind.  Rudder trim fixes it and referencing the sight tubes can confirm you are at the correct trim.

 

The AP changes how the airplane is being flown. You said, "The plane doesn't 'know' its in a crosswind it drifts along with the air mass." If you are just drifting in the air mass then this is true.

 

When flying with an AP like we have you are trying to hold position to a geographical point by means of the GPS. Older AP's would let a pilot set up a crab in a crosswind just like the pilot would do himself. The airplane is flying in a crabbed, but coordinated condition. The heading was controlled by the DG, and was not in reference to a geographical location.

 

With Our AP it tries to hold a course instead of a heading. If the wind blows the airplane off course it banks and tries to turn back to the course. There is no way to maintain the course in a crosswind in coordinated flight while using the AP. To get even fuel drainage from the tanks you have to trim the rudder so the airplane tries to yaw into the crosswind and the AP will try to turn away from it and the balance between the two will maintain the course and provide even fuel flow from the tanks.

 

This has nothing to do with the ball being out of calibration.

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There is no way to maintain the course in a crosswind in coordinated flight while using the AP.

 

You make a good point about flying in a 'course' mode vs 'heading' mode but your conclusion is wrong.  When wind shear occurs and a correction is required and there is no rudder input and the speed is slow enough for adverse yaw, your right, un-even flow will result but only for a matter of seconds.  After the adjusting turn and back to strait and level then the AP in course mode is no different than the AP in heading mode.  Even an AP in heading mode can loose coordination from shear.

 

BTW  my AP allows me to fly various modes, some track course some track heading.

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So, what does the AP do after it intercepts the desired course line?  Does it turn directly toward the GPS fix again?  Is there no logic built in to maintain some heading other than directly toward the GPS fix?  I guess if the GPS and AP are sensitive enough, there would be a constant series of small uncoordinated (slipping) turns toward the course line.  Therefore, the wing tank away from the course line would constantly feed fuel to the other tank.

 

All APs use logic.  Tom is implying all CTs track a course (mine tracks headings too) and that this sets up a slip or skid in a crosswind.  Actually there can be some slipping or skidding when shear is encountered and a correcting turns happen with no rudder input but once back 'on course or heading' fuel flow is even if trim is correct.

 

There is no constant AP induced slip or skid to cause continuous uneven flow when flying a course that is cross to the wind.

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The AP in both the CT and the plane I fly now flys a wind correction angle when encountering a cross wind in cruise..  The plane crabs wings level...The heading will be where the nose is pointing right or left of the course line.  The course will be the plane moving over the ground on a track necessary to arrive at the waypoint as specified in the flight plan or as set using Direct feature.

 

If the AP used a forward or side slip to get this done it would cause a loss of altitude.   So I question the uneven fuel feed if the AP is flying the plane, even if it's only a 2-axis AP.  The ball may be out a bit but it won't be extreme.

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Tom is saying there is.  I don't know.  It would be a slip, not a skid.  The only way Tom's assessment would be wrong would be if the AP can determine a cross-wind correction and hold that heading in wings level, coordinated flight.  If the AP is merely trying to keep the airplane on a course line, the plane would turn toward the target, drift downwind, then turn back toward the course line, over and over.  Since there is no rudder input, each turn would be a slip.  If the GPS and AP were very sensitive, the turns back and forth would be almost instantaneous.  The result would essentially be a crab into the wind with no rudder input, therefore a constant wing low slip.  I don't know if this is correct because I don't know if these AP's can determine and hold a heading or not.  I guess the pilot could correct this by dialing in some rudder trim on the up wind side.

 

 

When the cross-wind is constant state the 2-axis AP will fly the planes trim which should be for strait and level in cruise.  Only when shear occurs and during the following correcting turn(s) will it be uncoordinated (assuming it was trim for coordinated cruise)  Shear might move the tail feathers and therefore the nose in either direction.  Overshoot corrections could cause transition from slip to skid.

 

Blaming these grossly unbalanced flights on maneuvering is missing the point, it takes time, quite a bit of it to get the big imbalance and that happens from cruising.

 

When you talk about the AP setting up for a crosswind correction we're back to the Stick and Rudder moment, the plane doesn't know its in a crosswind it only knows if its nose is in the relative wind or not.  If not fuel transfer begins.

 

Big issues are, 1) you can't see the nose; 2) wings are short and a small amount off level isn't seen; 3) the slip skid balls are not mounted at 90* and are not reliable mounted in a binacle.

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The AP in both the CT and the plane I fly now flys a wind correction angle when encountering a cross wind in cruise..  The plane crabs wings level...The heading will be where the nose is pointing right or left of the course line.  The course will be the plane moving over the ground on a track necessary to arrive at the waypoint as specified in the flight plan or as set using Direct feature.

 

If the AP used a forward or side slip to get this done it would cause a loss of altitude.   So I question the uneven fuel feed if the AP is flying the plane, even if it's only a 2-axis AP.  The ball may be out a bit but it won't be extreme.

 

 

In my plane the imbalance is large with the ball centered and the AP flying.  Why?  Because the ball isn't calibrated and isn't correct and when centered actually represents a slight slip.  The Cirrus has precise/accurate instruments and the pilot isn't mislead into a slip, plus the Cirrus has longer wings and a visible nose so the slight slip would look wrong and the pilot would likely adjust the rudder or aileron trim till wings were level.

 

In the CT the using AP can result in un-even flow but its not the AP's fault its the pilot that failed to trim the nose into the relative wind. Only a 3-axis AP could compensate for such a pilot but we fly with 1 and 2 axis APs.  Prolly the big iron has all 3.

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Forget wind shear or gust.  That is not the issues being discussed.  The issue is do the AP's in a CT hold a heading when flying a GPS course line?  If they do, then Tom's assessment is incorrect.  If they merely fly back and forth across the course line, then he is correct.  Maybe, even if he is correct, each subsequent turn back and forth across the course line becomes smaller and smaller until the AP "finds" the correct wind correction angle and heading to fly to maintain that course line.  At that point, it would be flying wings level in coordinated flight.

 

 

Forget the shear?  Okay that puts us squarely in stick and rudder land, where a plane doesn't know its in a crosswind.

 

Without shear there is no difference between course and heading, once established they are and remain the same.

 

You say forget shear then you talk about turns back and forth across the course line?  Think about it, without shear there is no need for correcting turns. Without shear both course and heading remain the same all the way to the waypoint.

 

12 to zero imbalances don't happen because of the AP looking for the course.  Turns at cruise speed have much less adverse yaw.  12 to zero imbalances happen because of fuel flowing towards the trailing wingtip for a sustained period of times, cruise flight.

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