Hmmm....Unless you're operating under a fairly-high power level, I sincerely doubt that the model is accelerating at 9.8 M/s/s, which is standard Earth gravitational acceleration. Drag will make it less than that amount. Even so, if the model only fell at that speed, the fuel would be in "free fall" and would just vibrate around the tank. In order to make the fuel move to the back of the tank, and stay there, the acceleration would have to be MORE than 9.8 M/s/s. This can be done momentarily, and is well-exceeded in turning maneuvers for the duration they are held (loops can also be considered "turning" maneuvers for the purpose of this discussion). However, in a dive, with a constant line, most models will stabilize rather quickly...and if it's coming down at less than 9.8 M/s/s, then the fuel will run to the front of the tank.

9.8 M/s/s come out to 32 F/s/s. This means that you'll fall about 480 feet in 5 seconds, and 1,760 feet in 10 seconds. This is assuming there is no drag of any kind. As soon as the model encounters drag, that is, ALL the time, then it is accelerating at LESS than gravitational acceleration. The fuel in the tank, though, is not so restrained, and tries to accelerate at the 32 F/s/s. It moves to the front of the tank, as a result.

So, sorry, regular physics shows that the fuel won't stay in the back of the tank unless the model is acclerating faster than 32 F/s/s. If you're diving from only a few hundred feet, and are taking 10 seconds, the model is NOT accelerating faster than gravitational acceleration, and the fuel in the tank will slosh to the front of the tank.