Fuel Gauge misreading?

[Europaul]

Hello friends,

I have calibrated my SkyView Classic fuel gauge, and entered the max as 60 litres.

When I fill up and press the [Full] button, it seems to recognise that equals 60 litres, but only displays [50+] on the gauge… and a very confusing Measured Fuel figure of 49.7 - if it has 49.7 in tanks, why display [50+]…?

More importantly, if I’ve entered the max as 60 and synchronised by pressing [Full] - why can’t it display 60 on the gauge (and in the Measured Fuel field)?

I hope the attached photo describes this… many thanks in advance for any advice!

Best regards,

Paul
G-PLPM
Europa XS Mono, Dynon SkyView Classic

 

[maartenversteeg]

The fuel gauge is a completely independent system here and not linked to the fuel computer. It reports the value measured through the resistor in the fuel sensor (during calibration of the fuel gauge, by adding small quantities of fuel and telling the dynon that you have added another quantity, the Dynon creates a table the list for each measured resistance what the total amount of fuel is). In many systems the fuel sensor hits an end stop before the tank is fully filled with fuel, and bbasically measures the same resistance for any total fuel quantity above that level. In your case that point must have been reached at 50 litres. So for just the fuel measurement gauge, the Dynon doesn't know any difference between 50 litres in the tank or say 54 litres in the tank as for both the fuel gauge measures the same (resistance) value. As said the fuel gauge is an independant system it just reports what the fuel gauge reads it doesn't include smarts fromthe fuel computer that tries to calculate how much fuel you have left. In the Dynon this is reported as the 50+, and you don't want the fuel gauge to be any smarter, if the fuel gauge were to report 55 or 60 litres based on the fuel computer then you could be confused as the gauge really can't tell you that.

 

[GKC Aviation]

The Vans RV is similar.
Even with 70 litre tanks, the fuel sender float tops out at about 55 litres, so that's where the fuel quantity system stops seeing a change in the signal during the fuel calibration. In this case, it will read 55+ with full tanks, even though it knows the tank capacity is 70 litres.
Once you burn fuel down under that amount, it will start reading normally, as it can then see the float coming down. Until then, it has no idea how much fuel is in the tanks, only that it is above the (in this case) 55 litres.

 

[jakej]

As indicated above - many aircraft gauges do not read the total fuel quantity for various reasons associated with the sensor placement & type etc. Basically it's the readings in the lower levels that's important & would get my attention. Although regulations in some places require the tank/gauge calibration I'd always prefer to trust the fuel computer anyday - it just needs 'tuning' as per Install manual instructions & is much more accurate than a fuel gauge. My take is trust 1. eyeball, 2. calibrated dipstick, 3. fuel computer & 4. fuel gauge(always last) - YMMV