Author Rich Pickett fuels his Cessna T206H which has CiES fuel senders.
As pilots know, accurate fuel level determination has eluded pilots of many aircraft for decades, especially lighter piston-engine airplanes. Many of us would either top off the tanks or insert a “calibrated” stick into the tanks of aircraft before flight rather than rely on the accuracy of the fuel quantity depicted on the gauges. Some of us also believe the old myth that the only FAA requirement of a fuel gauge was to be accurate when it was empty. Perhaps it was one way for us to be comfortable when they didn’t work very well.
The issue is not so much the fuel gauge but the accuracy of the fuel senders. With the exception of capacitance-type fuel probes in some turboprops and virtually all jets, the design of the fuel senders in most aircraft is extremely simple – they simply float. The float is attached to an arm that moves across a variable resistor, and the fuel gauge uses the resulting change in resistance to measure fuel quantity. Over time, and even from initial installation, the components deteriorate and are notorious for causing inaccurate readings. I’ve owned some piston aircraft, including my 2005 SR22, that read very accurately for over 5,000 hours, while other airplanes were notoriously inaccurate. The variability could be frustrating, and a potential safety issue for pilots. Scott Philiben and his team at CiES in Bend, Oregon, sought to change that.
Scott, president of CiES and engineer by training, has former experience designing aircraft oxygen systems and other components. He was approached by Cirrus Aircraft in 2010 to see if he could develop a “better mousetrap” – in this case, fuel senders. Cirrus, being very technically focused, wanted to provide more accurate fuel level information since many owners were noticing annoying quantity variations similarly seen in other piston aircraft.
CiES worked on a very novel design that, while it may appear simple, actually involves a significant amount of engineering innovation. Scott believed that one of the design problems was using a resistive element sloshing around in the fuel (at extremely low voltages and not a fire hazard) that was prone to errors. The new sender design they created has no electrical components within the tank. CiES has developed a magnetic-resistive fuel sender with the sensor external to the fluid it is measuring. As the float moves with the fuel level, a corresponding change in the magnetic field is sensed by an external electronic circuit. This extremely slight change in the magnetic field as the float arm changes position can be used to indirectly sense the fuel level.
Cirrus implemented the new design from CiES in its 2012 aircraft, and soon after, it was available as a popular retrofit for the existing SR20 and SR22 fleet. Scott didn’t stop there. He then expanded to other OEMs in 2014 when Tecnam and Vulcan Air used the senders in their production aircraft. One of their next projects was the Piper Malibu and Mirage aircraft, which have a float placement design that complicates even the traditional inaccurate senders. Piper Malibu and Mirage owners would occasionally cringe at the inaccurate fuel readings, sometimes trying to solve the problem by replacing the senders with new ones of the same design. This solution often didn’t work well. The CiES engineers came up with a design, working with several aircraft owners, to offer a better solution. It took several attempts, however, the resulting fuel sender design has proven to be an effective alternative to the previous design.
Now available on over 600 airframes, more than 100,000 fuel senders have been produced. I have them in one of my aircraft, a Cessna T206H, and I can attest to their accuracy compared with the original factory probes. While I also have a fuel totalizer in the Garmin G1000 NXi, it is important for me to also have accurate fuel tank information. The totalizer will tell you how much fuel you have burned and indirectly what you have remaining. Fuel gauges inform the pilot of the actual fuel in the tanks, which can be very important in the case of a potential fuel leak or inaccurate initial information provided to the totalizer at engine start. The CiES fuel senders are extremely accurate, showing accuracy in level flight easily within the smallest resolution I can detect on the MFD.
I had a chance to talk with Scott at the recent NBAA event in Orlando. Scott and the CiES engineers are now working on a solution for the fuel level inaccuracies with the inevitable aircraft attitude changes during flight and turbulence. While not revealing too much of their new design, when they solve this issue, they will be providing aircraft operators with fuel level indications that will rival, or even surpass, the capacitance-type fuel probes used in turbine aircraft. Imagine being in turbulence or a climb or turn and having accurate fuel information upon which you can confidently make your flight decisions. The increase in safety and reduction in concomitant risk will be significant for aviation.
CiES, a 20-employee company, has designed a very nice product. And it was clear after talking with Scott they will continue to innovate, not only on the advanced fuel sender they are developing but also on other aircraft products. Scott also believes in the importance of developing their staff and encouraging the love of flight. Employees can enjoy the use of their Diamond Katana for lessons and personal flights. When Scott told me about some of the employees’ flight success stories, you could tell he was just as proud of those accomplishments as the products they produce.
