`FUEL TANK * QUANTITY` inaccurate? (Longitude Fuel Bug)

I’ve been using the FUEL TANK * QUANTITY to set the fuel loads in the sim from a client I’ve been working on for the last couple of years. Up until recently, I was ignorant to the fact that it doesn’t seem to be accurately setting the fuel loads.

In the Longitude, for example, I send a request to set both tanks to 50 gallons, but I only get 43.8 gallons.

Is there some sort of thing going on within the sim that’s trying to convert volume to weight but doing it poorly?

Is your issue possibly related to unusable fuel?

See these two different SimVars descriptions:

I would think it would go the other way if that were the case, but perhaps.

My assumption is that by setting the quantity will set the total quantity, not some subset of it.

For what it’s worth, the Longitude is pretty consistently at 6.2 gallons off (+/- 0.3). The 172 is spot on. The Caravan is pretty close, only showing a +/- 0.01 difference at times.

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I’ve tested a few others as well and it’s within 0.01 as with the Caravan, so I’m going to call this a Longitude bug.

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Does it help to bump up the capacity?
flight_model.cfg
; – Fuel Tanks
Tank.1 = Name:LeftTank #Capacity:1089 #UnusableCapacity:6.2 #Position:-6.5,-10,0 #Priority:1
Tank.2 = Name:RightTank #Capacity:1089 #UnusableCapacity:6.2 #Position:-6.5,10,0 #Priority:1

IIt might, but I don’t want to poke at that. My goal is support everyone without having to download more than the simple desktop client I’ve built.