Over the top of the parabola, the pilot pushes the stick forward to hold the acceleration to zero. The pilot continues to pitch over until the aircraft is 45 degree nose down. Wind from the nose or tail varies the parabola somewhat. During a flight, which lasts about two hours, total, we usually fly 40 parabolas. In this aircraft, tail number NASA 930, we've done as many as 101, depending on fuel and gross weight limitations.
More parabolas mean more flexing of the airframe and more stress.
We could fly 200 maneuvers, but we'd use the airplane up. After the flight, we fly back to EFD, usually arriving around 12. We change out of our flight suits, and we talk about how our experiments went. The KC-135 parked in front of the NASA LeRC Hanger. Some flights include astronauts participating in crew training so that they can have low-g experience with experiment hardware prior to shuttle missions.