Page 10 - Dec22T

Fuel Measurement
When Level is Not Always Level by Rich Pickett
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 de- picted 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
8 • TWIN & TURBINE / December 2022
CiES 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.