@alanfernandes said in Bug? Fuel Burn.:
Although fuel flows by gravity from the forward to the aft compartment within the main system during refueling, there is no gravity transfer between the auxiliary and main tanks. In flight, this transfer relies exclusively on jet pumps operated by engine motive flow, which renders the fuel in the auxiliary tanks unusable should the pump system fail.
I recall discussing this in one of my videos. Here is what I said in the manual:
"Most of the fuel in the aft tanks will transfer to the main tanks by gravity, and the rest can be transferred by the aft tank transfer jet pumps. Should the aft tank transfer jet pumps fail, the total usable fuel may be reduced."
Here is what the Flight Safety manual says:
"Although a small amount of fuel may gravity-feed from the aft tank without the motive-flow system, the pilot should consider all fuel in the aft tank as unusable and plan the flight accordingly."
Without looking right now (sorry, I'm leaving to record sound from the Twin Commanders in a few hours), I recall that I assumed this statement was made out of abundance of caution, and implemented the system such that it would slowly equalize to a certain point, so long as the jet pumps had not failed (emulating a blockage). Given the arrangement of the jet pumps and their no-moving-part nature, I assumed that there would be flow through them, so long as the pressure on the auxiliary tank side is high enough.