916 Fuel Flow

The injected Rotax engines do not have a sensor.  Fuel consumption is a calculated value only and as such not a replacement for a fuel tank gauge.  If you have an ancutaal sensor this would be a question for the sensor manufacturer. Is this part of the Garmin G3X?

Cheers

Thanks.  It was an assumption on my part that since fuel flow was a provided parameter there must be some type of transducer.  But I understand if the flow figures are based on some type of algorithm.  I wasn’t interested in using fuel flow as an alternative to fuel tank monitoring.  But it is nice to have multiple sources of fuel management.  I am using a G3X.  Fuel flow is a selection based on Rotax FADEC input.

Richard McBride wrote:

Thanks.  It was an assumption on my part that since fuel flow was a provided parameter there must be some type of transducer.  But I understand if the flow figures are based on some type of algorithm.  I wasn’t interested in using fuel flow as an alternative to fuel tank monitoring.  But it is nice to have multiple sources of fuel management.  I am using a G3X.  Fuel flow is a selection based on Rotax FADEC input.

I have personally never managed this issue, but I know that the "K Factor" can be adjusted within the G3X configuration setting. This is the excerpt I found in the Install Manual. Hope it helps.

"24.3.10 Fuel Flow
Fuel flow in the G3X system is sensed via a mechanical transducer which converts the movement of fuel to
a series of digital pulses.
For engines with a fuel return line, a second flow sensor must be used to measure the quantity of unused
fuel that is returned from the engine to the fuel tank. Connect the return fuel flow sensor to the GEA 24/
GSU 73 FUEL FLOW 2 input (see Figure 30-2.1). The value displayed on the fuel flow gauge will be the
difference between the main (supply) fuel flow and secondary (return) fuel flow measurements.

24.3.10.1 K-Factor Adjustment
The number of electrical pulses sensed per gallon of fuel flow is referred to as the K-Factor. The G3X
system uses the configured K-Factor to convert pulse frequency to fuel flow. When installing the fuel flow
sensor, the installer should take note of number on the tag attached to the sensor (if applicable). This
number is the calibrated K-Factor of the sensor. For sensors that are not supplied with a specific calibration
value, use the default K-Factor value provided.
Although each fuel flow sensor has a default K-Factor value, aspects unique to each installation will affect
the accuracy of the initial K-Factor, and as a result the K-Factor must generally be adjusted up or down for
accurate fuel flow measurement.
If the fuel usage reported by the G3X system differs from the actual fuel usage, as measured at the fuel
pump (or other trusted method of measurement), use the following formula to calculate a corrected
K-Factor, which can then be used to calibrate the fuel flow.
Corrected K-Factor = ( [G3X reported fuel used] x [previous K-factor] ) / [actual fuel used]
Refer to the K-Factor portion of Section 34.4.19.4 for (GDU 37X) or Section 35.4.32.13 (for GDU 4XX)
for information on entering K-Factor calibration."

Thanks!  I was familiar with adjusting the K-Factor on my RV-8.  That system uses a Red Cube transducer that physically measures fuel flow.  I thought the 916 might be similar.  I checked the G3X this morning and if you choose Rotax FADEC as fuel flow the system doesn’t provide any means of calibration.  After reading Rotax Wizard’s response, I double checked the 916 wiring diagram and confirmed that there is no sensor that physically measures flow.  Accordingly, he’s correct that flow is a calculated value based on other engine parameters.  Oh well, it’s not the end of the world.  I’ll know now, after multiple tests, that the Rotax number reads 9% less consumption than actual.  Thanks again for the input!

Richard McBride wrote:

Thanks!  I was familiar with adjusting the K-Factor on my RV-8.  That system uses a Red Cube transducer that physically measures fuel flow.  I thought the 916 might be similar.  I checked the G3X this morning and if you choose Rotax FADEC as fuel flow the system doesn’t provide any means of calibration.  After reading Rotax Wizard’s response, I double checked the 916 wiring diagram and confirmed that there is no sensor that physically measures flow.  Accordingly, he’s correct that flow is a calculated value based on other engine parameters.  Oh well, it’s not the end of the world.  I’ll know now, after multiple tests, that the Rotax number reads 9% less consumption than actual.  Thanks again for the input!

Thats great! Thanks to you and Rotax Wizard for clearing that up for me as well. I hope to run a 916iS one day in the future!