After burning off the four gallons in the right tank, I calibrated it in the SkyView system. I’m using a scale that has 1 gram accuracy, and I’m measuring roughly 1 gallon at a time. Given the accuracy of the scale, I should be able to measure the fuel capacity within one-tenth of a gallon over the 21 gallon capacity of the tank.
I added two gallons at a time up through 20 gallons, hitting the add button at each point on the SkyView. I used the opportunity to calibrate my dip-stick at the same time. Finally, I filled the tank to the very top and measured the amount of additional fuel I added. I ended up with 20.43 gallons of usable fuel. The claimed fuel capacity is 21 gallons, so there’s only a little over 1/2 gallon of unusable fuel. That’s more than I was expecting, but the flop tube pickups may leave a little more fuel in the tank than the standard pickups. I still need to do some in-flight checks to determine unusable fuel in all normal flight attitudes including full slips.
Unfortunately, I almost completely drained my battery in the process. I was down to 10.2 volts before I shut everything down and hooked the plane back up to the trickle charger. I’m planning on flying again in a couple of days, so I hope the battery is charged enough. I’m thinking I might need to replace the battery anyway since I killed it at least twice during the build (so dead that the trickle charger wouldn’t bring it back).