Merlinspop wrote:Isn't UNusable fuel determined by "worst case"? Possibly a climb or a climbing turn? In which case, Andy's proposed method may leave less fuel in the tank(s) than what was deemed UNusable by the manufacturer?
How are you going to simulate "the worst case" on the ground? Assuming you can't, how are you going to drain the last bit of fuel out of the tanks so that you can then add in the factory specified unusable fuel?
Being perfectly accurate is great, but there are considerations that make that nearly impossible in some cases. In this case I think my method is "close enough", will be accepted by FAA representatives, and doesn't compromise safety.
Since we are talking about W&B here, consider my airplane as an example. Each tank has unsusable fuel of 0.5 gallons, according to the factory. Let's say that in flat attitude on the ground, the unusable fuel is really 0.3 gallons. So we're talking about a total difference between the two tanks of 0.4 gallons, or 6x0.4 = 2.4 pounds. Which is right over the center of lift and center of gravity, which are the same in a CT.
What kind of engineering and mathematical shenanigans are we willing to go through over 2.4lb that has zero CG effect that the FAA considers to not be an issue (by virtue of them accepting this method for W&B purposes)?