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.

----------------------------------------------------------------------------------------------------------------------------------------

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.

Cessna Cardinal 177 & 177 RG Fuel Level Sensor

Well we produced another configuration of our fuel level sender for a very popular Cessna Aircraft model with a rabid and enthusiastic following.

---- Yes the Cessna Cardinal 177 ----

We had sought out common aviation fuel level sensors to copy into our format and we had a few mixed results, for example owners of Cessna 177's would send in the sensors per our request,  but the part numbers of the units supplied only matched up to another model Cessna Aircraft and did not match any of the Cessna Fuel Level drawings we have on hand.  

Finally, last year we got what we were looking for - Senders from an aircraft that matched the P/N for the aircraft. 

Note:  When you get involved in this small segment of aviation - It becomes very clear why fuel level in aviation has a very low reputation.

A Cardinal Aircraft owner tells a better story: 

Anyway, I saw the mention of CiES on one of the Cardinal Flyers Digests and gave them a call.  I spoke with Scott Philiben, who said that they could build them for me, and it would interface correctly with the JPI.  JPI confirmed this.  This was last FEB 2014 when I initially purchased the JPI, based on that answer.  

I had to wait till July 1 to start install, both due to the cold weather here, and because that was my annual date  (I also wanted to install an Oilamatic Pre-oiler and an Alpha Systems AOA Gauge).  

What Scott didn't tell me initially, was that I was to be the guinea pig for them getting a TSO sender for Cardinals as this minor variation needed to be sent to the FAA and approved - they had predicted an October delivery.

Scott & company finally came thru with fully TSO'd senders in late Nov, but I then encountered the passing of my Mom, which has led to further down time - anyway, FINALLY got the senders installed last Saturday.

CiES Above - Competitor Below

I was quite impressed on the substantial difference internally between CiES senders and the Electronics International ones.  The electronics in CiES look great, and based on the digital freq meter I have, they work VERY smoothly. I am also impressed with the machining on the fuel senders.

For JPI's part, their wire harness to the wing has three wires - +5V, Ground, and Signal. The JPI diagram says NOT to connect the +5V for CiES, but what they didnt say, and I didnt know until early Nov (when I mentioned that to Scott at CiES) is that the CiES units need +12V!! Turned out not to be an issue - the JPI harness has a "Y" connection in the harness shortly after the harness leaves the JPI box enroute to the wings - I unpinned the +5 wire that comes from the JPI and capped it off, and instead ran a +12 supply from one of the Circuit Breakers (dont remember which at the moment) into the same pin spot. (There is NO interface box as there is with some other senders. Not sure if my JPI is any different internally - JPI could answer though.) Works great (again, on my digital freq meter out at the sender)

One thing I particularly like about the CiES is that the float arm wire is 3x as thick as the one from Cessna, BUT the CiES float arm easily disconnects from the sender, making installation MUCH MUCH MUCH easier. I placed a long tie wrap on the fuel sender arm (in case I dropped the float/arm combination into the tank while working the sender into position) and then after the sender was connected and small cotter pin inserted, the tie wrap was removed. The senders come with a new rubber gasket, and there is no chance of leakage in the middle (like Cessna supplied Rochester, Stewart Warner, or Leigh senders) as there is no pass-thru screw terminal.  CiES uses a 3-pin connector with a twist lock shield. VERY easy to plug in.

At first, Scott and his engineers were concerned about MIN/MAX settings, but they had an epiphany one night and realized that all measurements are relative. They were worried about setting hard "stops" these are the little metal tabs on Cessna original equipment fuel senders that limit the float arm travel.   Turns out the CIES senders have the capability to move thru-out an almost 180 degree range from straight down to straight up.  The original equipment Cessna fuel sender contained a 60 degree potentiometer which limited the angle range allowed by these senders.   The calibration in the JPI is what establishes the fuel level limits and the physical limits of the fuel tank are the physical limits of the sender.

Scott Philiben's phone number is 541-408-1095 - they are in Oregon, so there is a 3hr time difference for me. His email is scott.philiben@ciescorp.com I still have the prototype sender/float combination that we used for testing and verification that this new simpler configuration would not hit any internal ribs/structure. Can't see internally, but externally it looks exactly like the ones with the TSO labels on them!

Update - Installed and calibrated - first impressions are good