The Three Fundamental Truths About Aircraft Fuel Level

We have a unique perspective to aircraft fuel level,  in that CiES works daily on these systems.  We see the good, the bad and the downright ugly.

What we have observed and are sharing here is what CiES has determined to be the

Three Fundamental Truths about Aircraft Fuel Level Systems. 

Here they are:

If the technology of fuel level measurement can find the surface of the fuel reliably. 

• Floats that actually float or are allowed to float.
• A set capacitance based on fuel level in a tube (ignoring temperature & other fuel dielectric effects).
• Ultrasonics tend to get messed up with foaming fuel. 

If the basic sensor system can output a lot of data related to fuel level. 

• A capacitance fuel level system can output a theoretically infinite number of data points - but realistically in an actual fuel level device -  potentially 10,000 to 30,000 data points 
• Our Magnetic Field Technology has 10,000 to 12,000 data points.
• A legacy potentiometer system that provides maybe 50 or 60 data points (wiper and trace size controlling the data point size) 

If your fuel level display system can capture the complexities of a fuel tank curve  

• a non linearly marked fuel gauge or an Multi Function Display with a calibration feature

Then if these three criteria are met - you will have an excellent aircraft fuel level system - meet a few of them and your fuel level system will be functional. 

As we know the world isn’t perfect -  

To make a old aircraft fuel level system work well -  You need to make a unique potentiometer, carefully assemble it to reduce internal friction, maintain wiper contact and hope it all holds together and doesn’t corrode.  

Now combine the above with a non linear and an easy to calibrate gauge.  This is fussy work at best.

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Here is  our real world challenge  - 

• Say for example you have a simple fuel gauge marked with the same distance from Empty to 1/2 tank, & from 1/2 tank to full 
• We are all very familiar how long it takes to go from Full to 1/2 Tank and that it takes a fraction of the time to go from 1/2 Tank to Empty.
• The above is a fundamental universal truth. 
• Therefore because CiES can  - we load a tank table with a characteristic curve onto internal memory on the sender.
• Log, Sine, 3rd order, 4th order, 5th order, Non Linear - You name it - We can do it - challenge us.
• Of course we need the tank function and a simple gauge to get it right.
• Unlike a potentiometer - we don’t have to cram all that onto a circuit card by physically making the small steps with variably positioned traces, or onto a carefully delineated gauge.
• We have 10,000 reliable data points with our sensor technology - we just do it in software - easy peasy. 

Just don’t tell me that fuel gauges only have to be accurate at empty - we get all apoleptic.