GRT Fuel Level Indication

Hey gang, this one is whipping my butt......help. Probably something simple and I'm being a knothead.

Subject is an EIS 4000 and Sport SX EFIS with standard Stewart Warner fuel tank senders.

Initial (and current) EIS configuration settings are AuxSF "100" and AuxOff "0", per the instruction sheet for float senders.

Initial fill saw the fuel level indication get lower with increasing fuel quantity, from 6 gallons empty to 2 gallons when full. Obviously not right. However, an ohmmeter check at the senders read 30 ohms for a full tank and 248 ohms for an empty tank, which I think is correct. So, I changed the Auxiliary Forward/Reverse Sensing Selection to reverse (negative), increasing voltage = decreased value. That immediately gave me a 20 gallon reading for the full tank, which is about right. However, the empty tank indication is still way off.......and I don't seem to be able to find the correct settings.

Yeah, I can ring up GRT on Monday, but hey, this is VAF

There is a specific procedure

to follow, I think Sandy can fax it to you. You have to have the plane in flight attitude and you test different known fuel levels and set the EIS accordingly.

Hans

Maybe here

Have a look here :

http://www.vansairforce.com/community/showpost.php?p=334102&postcount=49

Regards

Thanks guys....posted last night when I came in tired from the airport, and after two cold ones.....shame on me. Reading through the archives now.

Postscript:.....very interesting.....SF and Off values vary widely between builders. Still some good clues, so I'm off to the airport.

.....and the winner of an IOU for a fly-in beer goes to (drum roll please)....

John Dalman
http://www.vansairforce.com/community/showpost.php?p=334211&postcount=51

John's published numbers worked as perfectly as anyone could expect. Tweaking the AuxSF from 286 to 295 gave me an oscillating -0 to 0 at the unusable fuel point and 16 at an actual 16 gallons or more. At levels in between accuracy is reasonable; 5 is 5, about a gallon error at 10, and by 15 it is back on track.

Happy to cheat on this one (thanks John). South Alabama this time of year is too darn hot to sit in the cockpit and fiddle; the OAT readout was 105F in the hangar yesterday.

Dan,

I am presently dealing with the same calibration issue. Using John's numbers as a guide, was your Aux forward / aft sensing still set to negative?

Regards,

Dan - I feel honored that my numbers worked for you. Any time my work gets anywhere close to your standard I feel I have done my very best!
Glad to have helped. I have learned a lot from your posts especially on oil coolers and urethane and composites and your work has inspired me to work to a higher standard.
John

DAGO said:

Dan,I am presently dealing with the same calibration issue. Using John's numbers as a guide, was your Aux forward / aft sensing still set to negative? Regards,

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Sorry Tom, missed your post yesterday....yes, negative.

Additional curve fitting correction

0 at the unusable fuel point and 16 at an actual 16 gallons or more. At levels in between accuracy is reasonable; 5 is 5, about a gallon error at 10, and by 15 it is back on track.

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Dan,
If you are running a GRT display in addition to the EIS, and are showing fuel indication on the graphic display, there is an additional curve fitting tool within the graphic display. I have not done it yet since my flying will be 2011, but this was discussed with GRT at length during SnF.

You have done the first part by optimising the y=mx+b linear curve fitting in the EIS. The display (H1 or sport) has a two column signal mapping table facility that will interpolate between multiple points you specify. Left column is EIS input number and right column is desired display number. So, you can create a curve with some bends in it to correct for the mid filled region error.
Please call GRT for details. I don't remember the specific command tree to get to it.

Engine Limits is

the submenu that has the correction table for the tank readings, last item in the group. I leveled the plane to do the initial adjustments, then on a long cross country in smooth air I compared tank readings to the info from fuel remaining calculated on the Sport to cross check the results. If the slip/skid ball is the slightest off center the readings will be off. My 6a taxies with pitch up of about 1.5 degrees which throws off the readings, understandably. For initial calibration of the EIS numbers it was handy to have one tank full and the other empty. I input the same factors for both tanks to see how they would effect both ends of the spectrum. This way I could experiment without moving fuel so often. I found SF (scale factor) and Offset values that worked well, then I fine tuned them for each tank separately. In my case zero, 6 gallons and 15 gallons were within one tenth. 8 gallons was only off 3 tenths. Then I did the EFIS table. I am not assuming this accuracy in the air, of course.

DanH said:

Sorry Tom, missed your post yesterday....yes, negative.

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Guys,
I need to revisit this post so I hope some of you may help me out here. I have been flying with my EIS4000/HX dual screen setup since July but have never been able to get the fuel quantity read out to display the fuel quantity accurately. I have talked on several occasions with Sandy at GRT. She has given me some settings to run with but I have never trusted them. Sandy has me running with AUXSF 333 AUXOFF 81. These are quite a bit different than what John suggested using.

I have a 9A that has 18 gallon tanks. I really do not run my tanks down a great deal but I have burned them down to 8-10 gallons remaining on several occasions. At the settings Sandy suggested, the quantity still shows close to full. When I run the tanks down to this level the gauge still shows 17.8 or close to the 18 gallons it shows when it is full.

John, I have attempted to use the numbers you mentioned with AUXSF 286 and AUXOFF 839. These numbers return -24.1 on the EIS display when the tank is full up to the neck. In re-reading this post, the above quote's referenced setting struck me. Can anyone confirm that if I run with the settings John mentions I would need to have the +/- configured for negative (------)? I currently have the +/- set to positive (++++++). I am wondering if this would be why my reading with a full tank of gas is giving me the -24.1 reading.

I would also like to know if the settings John used will work with my 18 gallon tank if you guys are using the settings with a 20 gallon tank. Would these settings be different because of the 18 vs 20 gallon difference?

I have been flying all of this time using the fuel flow and totalizer (these settings are very accurate on the EIS) to track my fuel quantity along with my internal clock that is constantly calculating how much fuel is being burned in relation to how long I have been in the air. The truth is that I have not flown on any major long distance flights except one of 3.4 hours. That particular flight was early on in my Phase I flying and I did not have any of the fuel measurement calibrations set at all.

I would like to get this ironed out so there is no question in my mind what is going on with the fuel when taking those long cross country flights.

Any help would be appreciated.

Anybody got a set of numbers for a 10???

bump

Hmmm, no one looking at this thread any longer? Any thoughts on the fuel quantity issues? I am still interested in ideas if anyone has any?

The settings need to be on --- not +++, and after that, it's absolutely best to just do the test yourself instead of relying on someone else's numbers (that may not work for you). This is really not that hard of an exercise, seriously..

Just for a guide line

Radomir said:

The settings need to be on --- not +++, and after that, it's absolutely best to just do the test yourself instead of relying on someone else's numbers (that may not work for you). This is really not that hard of an exercise, seriously..

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I was looking for a place to start from, I know I will have to fine tune the final figures.

Also, having a set of numbers for a reference will help me to know if I am even in the ball park when I do my calcs.

Radomir said:

The settings need to be on --- not +++, and after that, it's absolutely best to just do the test yourself instead of relying on someone else's numbers (that may not work for you). This is really not that hard of an exercise, seriously..

Click to expand...

Radomir, thanks for the post. I have done the "fill the tank" 5 gallons at a time exercise more than twice now without good results. So my post was aimed at getting ideas that I could look at for why I am not getting good readings.

The +/- settings stuck out at me as something I should look at so wanted to get other's ideas on this.

My apologies for asking about something I obviously should know more about than it turns out I actually do.

RVbySDI said:

I have a 9A that has 18 gallon tanks. I really do not run my tanks down a great deal but I have burned them down to 8-10 gallons remaining on several occasions. At the settings Sandy suggested, the quantity still shows close to full. When I run the tanks down to this level the gauge still shows 17.8 or close to the 18 gallons it shows when it is full.

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The shape of the tank and wing dihedral makes it impossible to indicate the entire capacity. For example, the RV-8 20 gallon tank can't be measured above 16 gallons; at 16 the sender arm is raised as high as it can go.

(1) Put a few gallons in each tank. Disconect the fuel line at the carb or FI servo and pipe it into a fuel container. With the tail up in flight position pump each tank dry using the electric fuel pump. You just established the unusable fuel level. This becomes the zero indication.

(2)Add fuel to a single tank, one accurate measured gallon at a time. Initially watch just to see if the tank indication moves up in a positive manner. If not, switch the polarity setting (probably should be --). Keep adding fuel until you add a gallon and the indication does NOT rise. Now you know the max capacity the float arm can measure; record the number of gallons added so far, minus one. Drain the extra gallon.

(3) Ok, you now have zero usable in one tank and the max you can indicate in the other. Play with the settings, changing AUXSF and AUXOFF for both tanks in an identical manner. The correct settings will indicate zero in one and the max (from step 2) in the other. Note: this method assume the senders have similar resistance values, including the sender ground .

(4) After establishing settings, measure more fuel into the loaded tank until it is full to the neck. The total number of gallons added is usable fuel. Burn that number into your brain because you'll need it for your totalizer setting at each fillup.

I have been flying all of this time using the fuel flow and totalizer to track my fuel quantity along with my internal clock that is constantly calculating how much fuel is being burned in relation to how long I have been in the air.

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Same here. The individual tank gauges tell you when one is about to run dry, or which has the most for the landing approach. Put another way, you don't care about their accuracy except for the last 10 gallons or so.

Thanks Dan,
I have talked with Sandy at GRT again this morning. It turns out I did not have a document that details the procedures for calibrating the tanks. She emailed me a copy of that document. I am going to use the document she sent and your steps to see if I can get the instrument calibrated correctly.