R

rjtjrt

Well Known Member
Using a G3X Touch with a Red Cube.
We have no info on k factor for red cube, and have thus set the default value 68000.
Checked fuel use after set k default factor and it is saying we are using much more than we actually used.

Fuel fill 21.18 gals. Fuel computer said I used 33.3 gals.

Calculation
68000 by 33.3 divided by 21.0= 107829 as new k factor.
Does this sound correct? Seems to be a high k factor, but I have no experience of them.
Just hoping for someone to check before I reset k factor in G3X T.
Also, not sure how to reset k factor in G3X Touch (someone else set the k factor in first time, and they are not available to help).
John
 
The setting is done when you are in configuration mode, which you get to by holding down the MENU key before you apply power to the screen - keep holding the key down until you see the message that the unit is in configuration mode.

The detailed instructions are in Section 32.4.25.3 of the G3X install manual.

As a point of reference, my G3X was less than 1 gallon off (after using about 30 gallons fuel) using the default setting of 68000.

Could you have something else going on that would cause your number to be so far off? Like a constant fuel return or electric pump that is running all the time?
 
Rick
Thanks.
It is in an RV-12 so fuel pump is on all the time. There is a fuel return in Rotax in RV-12 as I understand it.
The fuel flow at 5000rpm in flight at 3500ft showed 22.5litre/hour (5.94USG/hr), which is high and clearly not accurate.
(My first post said 21.18 gals, but it should have said litres, just in case anyone is wondering with RV-12).
John
 
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The default K factor assumes no return flow. If you have return flow, your K factor is going to need to be more than the default.

Make the change and test again. It will take 2 or 3 fill ups to get it zoned in but should be very accurate once you find the magic number.
 
The numbers I was referring to in my original reply was for my -7A.

When I had the G3X in the -12, Fuel Flow was NOT used. The explanation from Vans was that it was determined that it was not possible to get an accurate fuel flow in the RV-12 due to the constant return. There is a thread some where on VAF where it was stated that in retrospect, having the red cube in the fuel system was not a great design decision.

The discussion during the prior thread had to due with the Dynon system. The Dynon in the RV-12 did display fuel flow, but people where having a very difficult time getting an accurate flow reading.

The reality is that with a constant return design (like the RV-12) you need 2 red cubes - one for the output and one for the return. The actual flow can then be determined by subtracting the return flow from the output.
 
Here is the excerpt from the G3X manual with respect to this issue:

"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 27-2.1). The value displayed on the fuel flow gauge will be the difference between the main (supply) fuel flow and secondary (return) fuel flow measurements."
 
SMO said:
Here is the excerpt from the G3X manual with respect to this issue:

"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 27-2.1). The value displayed on the fuel flow gauge will be the difference between the main (supply) fuel flow and secondary (return) fuel flow measurements."
Click to expand...

Thanks Mark.
I wonder if anyone has done this for RV-12?
 
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