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CIRRUS SR22 G2 & G1 Fuel Level Sender Retrofit Update 

 Cirrus SR22 G1 & G2 RETROFIT NEWS

       Kit Price $2,950.00  or  approx,  $5,000 installed 

 We had been supplying OEM Fuel Quantity Indication Systems to Cirrus Aircraft G3 and G5 
aircraft for a year with great success and we had obtained a Supplemental Type Certificate
​ to retrofit this system to legacy Cirrus G3 Aircraft.

As we had the STC for the Cirrus it was only a small change to include the G1 and G2 model aircraft into the mix. The FAA had indicated
 that to insure we were matching the original aircraft, we needed to put our floats in the same location as the original installations. We obtained several original sets and proceeded to design a CiES retrofit

​ Generally Cirrus Owners had indicated that the G1 / G2 aircraft had better fuel reporting than the G3 brethren,

However we knew that the technology used in these early fuel sensors would eventually fail and without an OEM business and obligation, the prior vendor was free to raise pricing to support this limited production.  

​ We smelled an opportunity. So we jumped feet first in retrofitting early Cirrus Aircraft.  

The first indication that something was amiss was from the first retrofit owner, he reported that the system looked good, but no comment on the accuracy of fuel level information.  This report stood in stark contrast to our experience on the retrofitted Cirrus G3 and new Cirrus G5 aircraft, where fuel level reporting was deemed to be a notable highlight.  We had another customer install - same result - "Gee it looks great, but no comment on accuracy in reporting".

I had heard about issues with the original G1 / G2 fuel level, but I had attributed them to the potentiometer technology used in those aircraft. I fell into a trap - potentiometer float sensors are not very good - therefore you won't get good results.

We have had amazing success
with every aircraft/helicopter platform we have been applied to and we still felt we had the best system out there for aviation fuel level reporting. We have this proven every day on many aircraft and aircraft platforms.

We also knew the CiES fuel level indicators were reporting accurate information about what was happening in the fuel tank.

Interpreting those responses in relation to fuel level indication needed to be performed.

So a little background on the Cirrus G1 & G2 fuel level

So we set up the test tank with his calibration data, and started to run tests - the system performed flawlessly for us - it reported the same volume going up or down as we had initially found with calibration.

So what gives -  We had notated that aircraft structure prevented the Inboard fuel sensor from reaching it's full travel , there are two fuel sensors in each wing for this aircraft , Inbd and Outbd. We set this limit up with a plexiglass box and tried the recalibration again.  Same result - nearly flawless recording, however we did notice one thing - when we depressed the Inboard sensor slightly by 1/4 inch or so we saw a 5 gallon decrease in fuel volume on the display. 

Now we have "a Smoking Gun" so we delved a little further - the sensors are actually located in separate tanks - one Inboard of the other -
 the Inboard tank (Collector) being much smaller connect to the Outboard tank (Main) with fuel lines.

The Collector Tank
​ - Holds ~3 gallons
- Contains the Inbd fuel level
- The Inbd fuel level sender measures the first 12 to 14 gallons of fuel

The Main Tank
- Holds ~37.5 gallons
- Contains the Outbd fuel level sender
- The Outbd fuel level sender measures the last 26.5 to 28.5 gallons of fuel

So with fuel being drawn out of the Inboard tank the level in that tank must go down 1/4 inch.   Well was this true in the aircraft - we had reports for our system and the prior vendors loosing 5 gallons when that wing tank was selected.  We knew that it was consistent - if you depress the Outboard sensor - the change is progressively smaller and not uniform.  Depressing the Inboard sensor  invariably gave a 5 gallon decrease each and every time, as long as some amount of measurable fuel was present in the main tank.  We asked the question "Could this tank level be effected by fuel pump suction"

When the Inboard fuel level sender goes down due to:
- A local level change caused by the fuel pump suction
- Lower tank volume.
- The Inbd fuel level sender measures more fuel than is in the actual collector tank

Therefore this slight depression in local collector tank fuel volume is subtracted from the larger main tanks -  a quarter inch in a 3 gallon tank is peanuts - a 1/4 inch in a ~40 gallon wing tank is well - 5 gallons.