Digital Fuel Gauge Fuel Level Heads Up

[Bob - S50]

We have Cies floats and an Aerospace Logic fuel gauge.  A couple weeks ago we thought we had problems with fuel level accuracy for the right wing.  What we think happened could happen to you too so I thought I would post it here.

We had about 13 - 15 gallons remaining in the right wing and were flying through turbulence.  The left wing only had about 10 gallons remaining.  What we noticed was the right tank fuel level indication varying from about 13 to 18 gallons.  That would be pretty disappointing considering we installed Cies floats.

What we think happened is a result of how the floats and gauge interact.  I believe that the gauge takes an average reading over a period of about a minute or so.  It does this to prevent the indicated fuel level from rapidly changing during turbulence or short periods of uncoordinated flight.  Normally this works.  During turbulence the floats will spend a little time above the actual fuel level and a little time below the actual fuel level which results in an average fuel level that is pretty close to correct.

However, in our case, we had just enough fuel in the right tank so that our outboard float was sitting on the tank bottom.  When turbulence sloshed fuel out to that float, the float would rise and give a false high reading.  When the fuel sloshed back inboard, the float would bottom out.  It could never give a false low reading to offset the false high reading so the overall average reading was too high.

The left tank was far enough below that fuel level that turbulence did not cause the outboard float to rise so fuel indications for that tank were normal.

So, if you are able to figure out when the outboard float bottoms out, do not be surprised if you get false high fuel level readings in turbulence when you are at about that fuel remaining state.  It should self correct after you burn off a few more gallons.

[kortopates]

Interesting, thanks for sharing. Have you talked to Scott at CIES to see if his senders do the averaging or if it's done by your Aerospace logic fuel gauge and if the averaging period is a minute? 

[carusoam]

Scott is a pretty technical tech sales guy...

See if we can bring Him into the conversation...

@fuellevel

Hey Scott, got your ears on?

Another opportunity for a digital gauge to be more reliable than a mechanical...

Best regards,

-a-

[fuellevel]

I am here.    

So the Aerospace Logic unit averages over 10 second intervals and the average of the reporting is output is updated on the display 

This is just simple averaging of the input values over time  -  I will ask Shane but I believe it is 100 or so data points but it could easily be 1000.

When I operate the Aerospace Logic gauge in our test and display setup - we don't see wild changes even with gross movement of the sender around a singular virtual level point.  And that is moving a sender pair like the Mooney.    However each aircraft due to arm length and travel  presents  unique challenges 

We have thousands of aircraft flying with a similar configuration due to the nearly universal use of our system by most of the OEM manufacturers and this reporting is new.   

Yes owners find the system to be more sensitive - that is a true statement 

Lately - in the last day or two I am seeing a few of these show up in aftermarket installations  - customers with issues in turbulence - Navajo and this Mooney  

Our testing is all computerized so I checked to see if something had changed, thankfully no joy.   On the Navajo, I called a fleet operator to check in to see if they had seen similar issues with their aircraft.   Thankfully the single owner operator was unique. 

We are looking into momentary losses of power to the sensor - which can produce a wilder set of outputs 

It is interesting to get field data as aircraft are notoriously individualized - and if we can prevent the anomalies to our best effort as it is best to get KUDU's vs disappointment.

What we have created is a very large and accurate turn and bank indicator - so lateral acceleration  or a little boogie action reaction to turbulence in the air can move the fuel outbd - yes that happens.   So will putting a little pressure on the rudder. 

We are flying several aircraft with dataloggers onboard to capture real aircraft information - and we do get a large number of Garmin G1000 data dumps (a 1 second interval reporting) 

Internally we have our own damping algorithm or actually sets of algorithms,  that for most production senders we turn off.   This damping can be up to 16 seconds so that we can customize a fuel sending solution for any opportunity or anomalies that exist in any aircraft fuel system.   Other than turbine helicopters,  the Cessna TTx and a few military projects we have not turned this on.  

So Bob's observation can happen in a number of ways,  but it is unusual -  let us simulate that configuration and report back

 

 

[Bob_Belville]

I'll take this new thread as an opportunity to make a preliminary report on the installation of CiES senders in my M20E with new 64 (2 x 32) gallon bladders. The O&N (now Griggs) STC only allows for 1 sender per wing so with the 4th cell installed outboard of the 3 cells in each wing, and consider the wing dihedral I expected that the sensor, which is in the cell nearest the cabin, would not sense the top gallons. In fact it appears that on the first flight since installation the sensor reported "full" until about 6 gallons had been used.

I'm interested in gathering more data but if that holds up and it turn out that the senders are accurate from empty up to 26 gallons per side I will be well satisfied. 

For those of you using a JPI EDM 930 (900?) I'll report that I was pleasantly surprised that the updated EDM now displays "Fuel Remaining" which is based upon FF data. That is right beside the fuel quantity display which is based on sensor data. Nice.  (My EDM is now firmware rev 1.20.532.001)

[Marauder]

You must have been using a real old version of the firmware. Mine always showed fuel remaining. What I like now, is that the fuel gauges are always close to the fuel remaining number.




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[Bob_Belville]

6 minutes ago, Marauder said:

You must have been using a real old version of the firmware. Mine always showed fuel remaining. What I like now, is that the fuel gauges are always close to the fuel remaining number.




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My 930 is 5 years old. It had been back to the factory once, about 3 years ago?

[fuellevel]

I am not dismissing Bob's issue or complaint - the plane is relatively local to us.

If his mechanics can't figure out the issue,  we surely can 

[Bob - S50]

Scott,

I don't consider it an issue, just a knowledge point to store away for future use.  The gauge did not fluctuate wildly, it just slowly drifted up and down between about 15 and 18 gallons.  As you are probably aware, turbulence not only causes up and down movement but yawing as well.  I suspect it is the yawing in turbulence that slings the fuel about in the tank.  In smooth air the gauges are still deadly accurate.  Did a couple flights last week and the gauges and fuel counter stayed within 1 gallon of the initial spread the entire time.  That was during about 3.5 hours of flying.

I will just keep in mind that if I have about 15 gallons left in the tank and hit turbulence, I won't be surprised if I see fuel level vary a little.  By the time actual fuel level becomes important (less than 10 gallons in the tank) it won't be an issue.

[MIm20c]

4 hours ago, Marauder said:

You must have been using a real old version of the firmware. Mine always showed fuel remaining. What I like now, is that the fuel gauges are always close to the fuel remaining number.

I think JPI originally had the numerical fuel remaining but took it off for a couple of years(?) however customer demand pushed them to bring it back.