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Calibrating Fuel Flow Issue

bill.hutchison

Well Known Member
Neck deep in finishing up a Dynon HDX-based retrofit.

Have gotten to the point of entering data into the Dynon HDX for the fuel flow and K-factor.

Here's the issue:

There is no tag on my fuel flow transducer indicating the number of pulses that I need to enter into the Dynon. The previous owner (or builder, not sure which) had a sheet of paper in the manuals/docs where he had hand-written the K-factor number, but there's nothing on the bench test tag number.

Now, he had an FP-5 fuel computer and transducer package, and, reading those docs leads me to believe that the flow unit is a Floscan 201 based on how it looks and what I can find online. Like I said, I don't have the tag, but I do have the K-factor number. The transducer is the same from legacy and it was pretty darn accurate when it was tied to the old FP-5.

It seems like the K-factor for these is the first three digits of the pulse number, so the K-factor number I have is "850" - which means I should potentially enter 16-85000 into the Dynon config? Would that get me in the ballpark?

I'm not sure what else to do here other than potentially replace it with a known-good-bench-number unit, but I hate to do that since I know the unit works. I just don't have the baseline number to enter into the Dynon HDX.

What would you do?
 
I was in a similar situation. What I did to start is use my best guess K factor. Filled the tanks and flew. When I got back filled the tanks to get the actual fuel use. Compared the actual fuel use to the fuel used based on the dynon. I did the math to calculate what the K factor should have been and updated the Dynon with that new K factor. I did this over the next few flights during my phase 1 testing and I was able to get the Dynon to be within a gallon or less on a 2 hour flight. If you need help with the math send me a PM.
 
Now, he had an FP-5 fuel computer and transducer package, and, reading those docs leads me to believe that the flow unit is a Floscan 201 based on how it looks and what I can find online. Like I said, I don't have the tag, but I do have the K-factor number. The transducer is the same from legacy and it was pretty darn accurate when it was tied to the old FP-5.

It seems like the K-factor for these is the first three digits of the pulse number, so the K-factor number I have is "850" - which means I should potentially enter 16-85000 into the Dynon config? Would that get me in the ballpark?

From the SkyView System Installation Guide – Revision AL, page 7-81:
"If you have the Floscan 201B (Dynon Avionics P/N 100403-001), this number can be found on the tag that came with the transducer. The pulses/gallon value for transducer is 10 times the number shown after the dash. So, if your transducer had the tag that is labeled “16-2959”, you would enter a pulses/gallon value of 29590 in the pulses/gallon section of SETUP MENU > HARDWARE CALIBRATION > EMS CALIBRATION > FUEL FLOW CALIBRATION. If you have lost your tag, a starting pulses/gallon of 30000 will be close enough to begin using the function."​
 
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From the SkyView System Installation Guide – Revision AL, page 7-81:
"If you have the Floscan 201B (Dynon Avionics P/N 100403-001), this number can be found on the tag that came with the transducer. The pulses/gallon value for transducer is 10 times the number shown after the dash. So, if your transducer had the tag that is labeled “16-2959”, you would enter a pulses/gallon value of 29590 in the pulses/gallon section of SETUP MENU > HARDWARE CALIBRATION > EMS CALIBRATION > FUEL FLOW CALIBRATION. If you have lost your tag, a starting pulses/gallon of 30000 will be close enough to begin using the function."​

Carl - thanks. I must have read that paragraph a dozen times in this but that bolded sentence just didn't register with me. I'll try this.
 
Wanted to tie a bow on this and post an update....

Running with the "30000" value gave me some bizarre fuel flow readings, which were not at all close to what the engine was doing.

I thought about this for a while, stuck my head in the manual, and re-read the paragraphs on the fuel flow transducer.

Now, I've been under the impression that I had a Floscan 201 - what's in the plane LOOKS like a Floscan 201. But the previous owner had used an EI FP5 fuel computer, and it looks like he got the flow transducer from them. And according to Dynon:

The approximate pulses/gallon for the Electronics International FT-60 Fuel Flow Transducer (i.e., the red cube) is 68,000. You must configure the fuel flow transducer using this numerical value in the Sensor Setup Menu (SETUP MENU > HARDWARE CALIBRATION > EMS CALIBRATION > FUEL FLOW CALIBRATION).

Now, the transducer I have doesn't look like a current-model Red Cube, but the darn thing is at least 20 years old, so that might not matter.

I set the value to 68000 in the Dynon and PRESTO, I'm getting normal-looking, reasonable fuel flow numbers.

Weird, right?
 
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