Fuel Flow Explanation Needed

[DonFromTX]

Trying to figure out the fuel flow indicator on the stock RV12. Obviously the sender is on the supply side to the engine, which uses a little of it and returns a lot back to the tank. From this forum, it appears to me that you then set the Dynon with some magic compromise number, which somehow compensates to some low degree of accuracy, for the returned fuel and comes up with al fuel burn (roughly at least).
This would seem to be a crude way of measuring fuel flow USEAGE, would it not be far better to plumb it into the fuel system AFTER the return line for dead accurate fuel use information?

 

[David-aviator]

Trying to figure out the fuel flow indicator on the stock RV12. Obviously the sender is on the supply side to the engine, which uses a little of it and returns a lot back to the tank. From this forum, it appears to me that you then set the Dynon with some magic compromise number, which somehow compensates to some low degree of accuracy, for the returned fuel and comes up with al fuel burn (roughly at least).
This would seem to be a crude way of measuring fuel flow USEAGE, would it not be far better to plumb it into the fuel system AFTER the return line for dead accurate fuel use information?

Don,

In systems that by-pass fuel to control pressure at the engine, it is best to have 2 flow detectors and a instrument system that subtracts one from the other. That's how it was done with the Subby before someone figured out how to convert injection time to fuel flow.

If you have a pressure regulating device upstream from the engine, flow is measured after that device and works since the by-pass fuel occurs before the flow is measured to the engine.

 

[Mich48041]

Two flow transducers would give more accurate results, but add weight and cost and complexity. Most who have successfully calibrated the Dynon are satisfied with the fuel flow display. Below is a schematic of the fuel system.
Joe Gores