GAL. GAL. REM. L. FUEL FLOW R. FUEL FLOW USED G P H ADD FULL TEST ENTER GAL TO DESTINATION GAL RESERVE ENDURANCE NM/GAL Figure 14-79.  A modern fuel management gauge uses a  microprocessor to display fuel flow and numerous other fuel  consumption related calculations. An alternating current (AC) synchro system is part of the  mass fuel flowmeter. It is used to position a pointer against  the cockpit indicator scale calibrated in pounds per hour. With accurate fuel flow knowledge, numerous calculations  can be performed to aid the pilot’s situational awareness  and flight planning. Most high-performance aircraft have  a fuel totalizer that electronically calculates and displays  information, such as total fuel used, total fuel remaining  onboard the aircraft, total range and flight time remaining  at the present airspeed, rate of fuel consumption, etc. On  light aircraft, it is common to replace the original analog  fuel indicators with electronic gauges containing similar  capabilities and built-in logic. Some of these fuel computers,  as they are called, integrate global positioning satellite (GPS)  location information.  [Figure 14-79]  Aircraft with fully digital  cockpits process fuel flow data in computers and display a  wide array of fuel flow related information on demand.  Relatively new types of fuel flow sensors/transmitters are  available in new aircraft and for retrofit to older aircraft.  One type of device found in home-built and experimental  aircraft uses a turbine that rotates in the fuel flow. The higher  the flow rate is, the faster the turbine rotates. A Hall effect  transducer is used to convert the speed of the turbine to an  electrical signal to be used by an advanced fuel gauge similar  to a fuel computer to produce a variety of calculated readouts  and warnings. The turbine in this unit is in line with the fuel  flow but is fail safe to allow adequate fuel flow without  interruption should the unit malfunction.  [Figure 14-80] Another fuel flow sensor used primarily on light aircraft also  detects the spinning velocity of a turbine in the fuel path. It  too has a failsafe design should the turbine malfunction. In  this unit, notches in the rotor interrupt an infrared light beam  between an LED and phototransistor that creates a signal  proportional to the amount fuel flow.  [Figure 14-81]  This  type of sensor may be coupled with an electronic indicator. 14-43 Figure 14-80.  A transducer and microprocessor for control functions are located in the base of this turbine fuel flow sensor. The gauge  is menu driven with numerous display options.  Power Fuel FLOW TOTAL This side slightly lower This side slightly higher (allows bubbles to exit) Flow direction