FP-5 Fuel Flow Instrument Adjustment/Calibration

[JeffBe]

So I changed the K Factor setting by mistake and screwed up what was a very accurate instrument. The previous owner had the full setting to 52 gals which I was not comfortable with because 10 gallons of that is unusable in my plane. I reset the K Factor to what the operating manual says for the transducer installed, but it now reports a higher fuel flow than actual.
Is this a simple adjustment an A&P could figure out, or would it be more involved a process? The instructions mention bench test numbers for setting new K Factor.

 

[Stewartb]

There should be a calculation to set your K factor. Fill tanks, fly, refill to measure fuel used, enter the info into the instrument. Repeat to fine tune/validate.

 

[JeffBe]

Damn, I just came across exactly what you wrote in the manual, including a formula. Thanks for your reply Stewart.

 

[Wrench978]

Yep. Just gotta fly and top off a few times. It will recalculate the k factor for you as you enter new data

 

[AA5Bman]

I went through this. If you read the manual it's a pretty straightforward procedure. Be aware that if you enter the K-factor directly, it just uses the k-factor. If you use the re-calibrate feature where you enter how much you burn, it will essentially use the *average* of the old k-factor and the new k-factor, so the fuel flow rate won't adjust as quickly. I'd probably do it initially by calculating the k-factor and entering it directly, and then from there, use the calibrate feature a few times and you should zero in on it pretty quickly.

FWIW, I went through a bunch of these calculations and finally realized that the factory default setting was by far the best for my airplane. You might want to keep that in mind. Once you get it dialed in it's awesome - over a full tank in my plane (80 gallons), it'll only be off by a gallon or so, and most of that is probably entry errors (you can only enter whole gallons, not down to the decimal), or slight changes in pitch or bank on the ramp resulting in more or less gas actually going into the tanks.

By the way, what plane has 10 gallons unusable on a 52 gallon tank? That's 20% of your fuel!

 

[JeffBe]

Thanks for your reply MB. I will reread the re-calibrate feature. I'm bummed because I flew the plane home from Idaho and the instrument was spot on. The plane is a 1960 Cessna 175A. See the table on Pg 1-9 of the attached scan from the owners manual explaining the usable fuel available. Weird design of the tanks. It sucks to have that 60 Lb weight penalty.
Fun airplane though. It has an 0-360 conversion from a Mooney with a constant speed prop.