The trick is you need to set an actual "eyeball" zoom, and not physically leaning your pilot forward in the seat.
The OP's problem is that the zoom commands that work in A-10C, Huey, P-51D, etc., don't work the same in the FC3 aircraft.
If there is an alternate command that works, I haven't found it either. Leaning forward with TrackIR is the best I've come up with. Works OK for me, although I'd prefer the zoom command.