Well done Timothy, nice presentation of a complex subject, one that often leads to moments of over-excitement in flight when things don't work out as planned. To touch on a couple of your points, I work on a fairly conservative fuel flow rate, that is based on an average hourly consumption somewhat higher than my aircraft actually achieves. I'm sitting behind a Lycoming IO-540, and plan on 15US gph. In reality I cruise at 11.5 - 12 gph when lean of peak. Why so conservative on the planning?... well of course at take off power the engine burns 25 gph, 20 in the climb, and 10 gph or less on descent. So after two years of learning its foibles, including dip-sticking the tanks before and after flight to assess actual usage, I'm happy to plan on 15 gph. My JPI engine monitor (love your description of its hopeless ergonomics!) with fuel burn and fuel remaining figures always starts off showing a different fuel compared to my paper log that I keep in flight, but that error reduces as the flight progresses. My legacy fuel gauges get scanned on each Freda check, but most of the trust is in the pre-flight dipstick and engine consumption data. The big gotcha here though is this wouldn't cater for discovering a fuel leak, and as hopefully rare as an issue this might be, really only comparing planned consumption with actual via an accurate gauge is going to help in this case.... short of visibly identifying the leak. Being of a certain age now, the big saving grace is my own personal endurance is somewhat less than my aircraft's fuel endurance, so assuming full fuel and correct tank management, I'm stopping en route somewhat before the engine does!
Well done Timothy, nice presentation of a complex subject, one that often leads to moments of over-excitement in flight when things don't work out as planned.
To touch on a couple of your points, I work on a fairly conservative fuel flow rate, that is based on an average hourly consumption somewhat higher than my aircraft actually achieves. I'm sitting behind a Lycoming IO-540, and plan on 15US gph. In reality I cruise at 11.5 - 12 gph when lean of peak. Why so conservative on the planning?... well of course at take off power the engine burns 25 gph, 20 in the climb, and 10 gph or less on descent. So after two years of learning its foibles, including dip-sticking the tanks before and after flight to assess actual usage, I'm happy to plan on 15 gph.
My JPI engine monitor (love your description of its hopeless ergonomics!) with fuel burn and fuel remaining figures always starts off showing a different fuel compared to my paper log that I keep in flight, but that error reduces as the flight progresses. My legacy fuel gauges get scanned on each Freda check, but most of the trust is in the pre-flight dipstick and engine consumption data. The big gotcha here though is this wouldn't cater for discovering a fuel leak, and as hopefully rare as an issue this might be, really only comparing planned consumption with actual via an accurate gauge is going to help in this case.... short of visibly identifying the leak.
Being of a certain age now, the big saving grace is my own personal endurance is somewhat less than my aircraft's fuel endurance, so assuming full fuel and correct tank management, I'm stopping en route somewhat before the engine does!