Jay Honeck wrote:

rambunctious thing we ever do are "Up-Downs" (as the kids call them), which
is a firm pull up with a steady push-over at the top that induces negative
Gs in the back seat.

As others have sait: If there's no dirt floating around, you don't even
hit zero G, let alone negatives. I think you should go and take some
real acro lessons. (Actually, I think every pilot should!) It's fun and
it definitely makes you a better pilot. And you'll learn something about
the flight envelope. If I recollect correctly, your average spam can is
certified for something like +5.3 and -2.5 G at Va. Ask your acro
instructor to demonstrate those loads. You'll be surprized! (Not sure
whether you'll like it.)

Stefan