Originally Posted by
DaveReidUK
Correct me if I'm wrong, but average vertical acceleration would simply be a function of vertical distance travelled and time (if initial vertical velocity is zero).
6000' in 18 seconds gives a = 37 ft/sē if my maths is correct.
My idea with the "average" value is the same as yours, namely what value of constant G or acceleration would cause the object to travel the required vertical distance in the required time.
6000 feet in 20 sec gives zero G, free fall or approximately 10m/s2, 6000 feet in 18 sec gives your slightly larger value which is a slightly negative G.