Ok, so I've probably got a great big "Told ya so..." coming for this, and I'll take my lumps as required.
During my build of my fuel tanks, capacitive senders were all the new tech, everyone was talking about them like they were just absolutely gonna be the berries, and I drank the Koolaid. I built my tanks with capacitive senders, and in a wave of unsubstantiated enthusiasm, I did not include the standard float senders as a backup, though they would have happily co-existed in the tank.
The capacitive senders operate by means of an AC voltage applied to a couple of plates in the tank that are insulated from the tank itself, and this forms a capacitor that charges and discharges according to known electrical rules. The fuel is a dielectric between the plates that has a different value from air between the plates, and thus the computer can calculate the level of fuel in the tank from the capacitance characteristics of the plates.
This would probably work fine for most people - but I set my airplane up to run 91E10 autofuel, and it has a different dielectric than 100LL. No problem, I thought - I calibrated them for 100LL, and again for 91E10, and I'll just switch back and forth as needed when I change fuels. Well, as it turns out in practice, I nearly always have some mix of 100LL (due to long trips and fueling enroute) and 91E10 (which I have in the hangar and always top off the tanks with when I shutdown). The result is that I very rarely have a nearly-pure concentration of either 100LL or 91E10 in the tanks, and the capacitive senders are almost always inaccurate to some degree. This has caused me to rely on the fuel flow sender and fuel computer almost entirely, which has fortunately turned out to be incredibly accurate, within 0.5% from my observations over the last 135 hours.
Finally enough was enough - everything else works like it's supposed to on the airplane, and this should too. I ordered replacement access plates, nutplates, and float senders, and then proceeded with surgery this afternoon. I'm going to abandon the capacitive plates in place, no point in trying to remove them, I'm just putting the standard floats in place. They will respond the same no matter what fuel, or mix of fuel, I have in the tanks. Lesson learned and shared for others playing with autofuel.
For the record - it's right at 3 hours to pull a single tank.
During my build of my fuel tanks, capacitive senders were all the new tech, everyone was talking about them like they were just absolutely gonna be the berries, and I drank the Koolaid. I built my tanks with capacitive senders, and in a wave of unsubstantiated enthusiasm, I did not include the standard float senders as a backup, though they would have happily co-existed in the tank.
The capacitive senders operate by means of an AC voltage applied to a couple of plates in the tank that are insulated from the tank itself, and this forms a capacitor that charges and discharges according to known electrical rules. The fuel is a dielectric between the plates that has a different value from air between the plates, and thus the computer can calculate the level of fuel in the tank from the capacitance characteristics of the plates.
This would probably work fine for most people - but I set my airplane up to run 91E10 autofuel, and it has a different dielectric than 100LL. No problem, I thought - I calibrated them for 100LL, and again for 91E10, and I'll just switch back and forth as needed when I change fuels. Well, as it turns out in practice, I nearly always have some mix of 100LL (due to long trips and fueling enroute) and 91E10 (which I have in the hangar and always top off the tanks with when I shutdown). The result is that I very rarely have a nearly-pure concentration of either 100LL or 91E10 in the tanks, and the capacitive senders are almost always inaccurate to some degree. This has caused me to rely on the fuel flow sender and fuel computer almost entirely, which has fortunately turned out to be incredibly accurate, within 0.5% from my observations over the last 135 hours.
Finally enough was enough - everything else works like it's supposed to on the airplane, and this should too. I ordered replacement access plates, nutplates, and float senders, and then proceeded with surgery this afternoon. I'm going to abandon the capacitive plates in place, no point in trying to remove them, I'm just putting the standard floats in place. They will respond the same no matter what fuel, or mix of fuel, I have in the tanks. Lesson learned and shared for others playing with autofuel.
For the record - it's right at 3 hours to pull a single tank.
Last edited: