Matching SkyView Fuel Level to Moeller Gauge

[N74846]

I have occasions on start-up where the SV shows less than the Moeller gauge. It appears the only match or adjustment is to what sender says, not what the gauge indicates. (I hope this is clear). They should be the same at all times but are not. Therefore SV will show less than the tank has in it. Is there a way to manually tick up the SV level without having to re-calibrate?

 

[tomkk]

Is your Moeller gauge really more accurate than the calibrated SV readout? My SV readout is VERY accurate, unlike my Moeller gauge ... did I misunderstand your post?

 

[N74846]

As I add fuel manually, I believe the Moeller to be more accurate. The SV may show 13 gallons while the Moeller is right on the 9 o'clock tick. And there is no way to add gallons to the SV, only delete, as I recall.

 

[mmarien]

I'm assuming SV and the gauge are using the same sender. When you calibrated was the gauge showing the same as what you were adding? If it's a problem you needed sorted out, it's probably worth re calibrating and keeping track of what the gauge is showing. Especially if the tank in not a regular shape. 

 

[Dynon]

So first, when you say "SkyView shows", are you talking about the fuel computer values or the actual SkyView fuel level readings? The per-tank fuel level values will show as accurate as your senders were calibrated, subject to not being able to read above where ever the sender tops out. So it's possible for you to have 15 gallon tanks, but if SkyView could only see 13 of that when you calibrated each tank, you'd see "13+" for the first few gallons when you're filled up.

But, the fuel computer adjustment will take any number you give it. The "MATCH" button is useful for synchronizing it to your tank sensors when you're mid-tank, although once your fuel flow sensor is well-calibrated this won't be necessary. The fuel computer also has the ability to remember "FULL" and "PRESET" values, so that when you fill-up, you can just tell the fuel computer so.

Real world example: My Sportsman has two 15 gallon main tanks, and two 10 gallon outboards that we usually don't fill but for long trips. When we fill up the mains, both quantity gauges say 13+, because the in-tank sensors can't see the last two gallons. After a trip to the fuel pump, SkyView will pipe-up that the computer doesn't match the in-tank sensors (because a bunch of fuel was just added). So our PRESET button sets the fuel computer to 30 gallons, which is just the mains filled. If I were going cross country, and filled everything, I'd press the FULL button, which sets the fuel computer to 50 gallons.

If, after landing and not refueling for some reason, I noticed that my in-tank sensors said said 10 and 7 gallons, but my fuel computer said 20 gallons (which is 3 gallons too many), I'd press the "MATCH" button to drag the fuel computer value to the measured quantity. Practically speaking, this doesn't happen in our airplane because our fuel flow is well-calibrated to the actual flow of the fuel that gets into the engine and turned into noise.

 

[N74846]

Thanks to all for your input. For clarification, I have an RV-12 with a 19.8 gallon tank. The referenced SV fuel is the amount displayed on the screen. The plane has a fuel return line from the carburetor if the pump sends too much fuel. Could that be the problem, if fuel level is reported based on flow?

 

[Dynon]

If you're using the RV-12 pre-sets (or have an S-LSA), your screen should look something like the below. Are we talking about the vertical fuel bar with the number above it?

 

[Dynon]

If you're using the RV-12 pre-sets (or have an S-LSA), your screen should look something like the below. Are we talking about the vertical fuel bar with the number above it (it says "cal?" in this picture)?

 

[Dynon]

And if not, can you post a picture of your display and which value you're talking about?

In short, the fuel flow computer (which is nominally a number that is labeled GALS REM) can be affected by return flow that is not counted by the flow sensor, if installed. You can improve flow accuracy by installing a second return flow sensor that subtracts that flow. That's not really done in the RV-12 though (to my knowledge). In the RV-12, you can improve things to large degree by by using the procedure in the SkyView system installation manual to tune the fuel flow calibration number.

Now, if we're talking about the bar with the number above it, that's from the in-tank sensor. It's as good as the calibration that was performed, which is essentially demonstrating to the system what the sensor looks like after a series of pours. This system is extremely accurate, subject to it being well-calibrated.

Can you post or email a picture of the value you're talking about?

 

[N74846]

I've been unsuccessful in uploading photos from today's flight. Send your email and I'll try to send directly to you. Thx.