Flathead: I think you may be in error here. Unloading the aircraft refers to a 1-G condition. This means your velocity vector is unchanging, and you're going in a straight line. Zero-G on the other hand means you're weightless in the cockpit. The only way to hold this condition is by holding constant forward stick pressure (if you're upright, that is). Even then, you'll only be able to hold this for a short time. Soon, your a/c will reach a vertical decent, then begin the bottom half of an outside loop, where negative G's will occur.
NASA simulates zero-G for astronaut training by taking the trainees up in a large aircraft like a Boeing 707. The airplane is put into a dive to build energy (not too steep of course...it is a bus after all), then zooms into a climb. The pilot then applies steady forward pressure, causing the a/c to inscibe a parabolic arch in its flight path. Over the top of that arch, the aicraft is able to maintain zero-G conditions for the passengers, sometimes for as long as half a minute.
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Rojo (S-2, The Buccaneers)