How did the Vomit Comet maintain its free-fall trajectory? Careful trimming? Custom autopilot software? Or just good stick and rudder technique?

Wikipedia, citing references but without substantiation, suggests manual control of at least the throttle. To use an automotive analogy, a trained pilot could correct for which direction the fuzzy dice are hanging from the rear view mirror, by playing the throttle and elevator and spoilers. But even a legend like Bob Hoover might lose precision doing that dozens of times in a row.

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    $\begingroup$ I'm not sure about the "Vomit Comet", but the "Zero-G" A310 has a "very simple" device that allows one pilot to control the aircraft vertically, and the other pilot to control it horizontally. This indicates that each parabola is manually flown using a G-meter. $\endgroup$
    – Ron Beyer
    Commented Sep 8, 2020 at 21:55
  • $\begingroup$ And sheer inertia suffices to control it along the direction of flight, I guess, because that isn't mentioned. $\endgroup$ Commented Sep 8, 2020 at 21:58
  • $\begingroup$ I'd think that the horizontal control (i.e. roll) would be pretty straightforward; keeping the pitch control nice & smooth would be the challenge for whoever has the yoke, and precise speed control so that the free-floating folks in the back aren't sailing toward a fore or aft bulkhead as the jet gains or loses speed. I'll be interested to see an authoritative answer to this question! $\endgroup$
    – Ralph J
    Commented Sep 8, 2020 at 23:07
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    $\begingroup$ You can do the same thing in any light plane. It's just that the duration of your 0G ride is only about 3-5 seconds, and the engine will quit during the zero G part unless you have fuel injection. Dive, pull up, push to make the pencil float in front of you until you're back diving at the ground. Push a tiny bit too hard, and all the crud on the floor ends up on the roof. Done that. $\endgroup$
    – John K
    Commented Sep 9, 2020 at 4:23
  • $\begingroup$ Organic Marble's answer says that thrust is modulated, manually. So the A310 would need that too, perhaps automatically. $\endgroup$ Commented Sep 9, 2020 at 4:45

2 Answers 2


The NASA Vomit Comet was flown manually.

From The dynamics of parabolic flight: flight characteristics and passenger percepts

The control inputs required by the pilots of a parabolic flight aircraft are relatively simple, although precision is required to make the 0 g phase as close to freefall as possible, and care is required not to exceed the load limits of the aircraft which at times flies near its maximum rated speed. The pilots modulate lift L with the elevators and wings, which indirectly changes attitude θ, and thrust T with the engines (Figure 5).

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....The pitch angle of the aircraft is not directly controlled by the pilots, but is a secondary result of other control inputs. During level flight the wings produce an upward lift, while the tail-mounted elevators produce a small downward component of lift in order to maintain a desired pitch angle. When flight conditions change, such as when the pilots deflect the elevators down during freefall, the relative forces from these two surfaces change. Since their moment arms are different, this causes a shift in the center of lift so that it no longer coincides with the aircraft center of gravity, resulting in a torque that causes a pitch rotation of the aircraft.

..At approximately 225 KT IAS (360 KT TAS, 185 m/s, Mach 0.61), when the aircraft is pitched nose-up 45°, the pilots commence the 0 g parabola. They push forward on the control yoke ("push over") to lower the angle of attack of the wings, which reduces wing lift, and simultaneously reduce power to a level just sufficient to overcome drag.

...After 25 seconds, at the end of the parabola, when the nose is pitched down 45° and airspeed is close to 350 KT IAS, the pilots pull up (pull back on the control yoke) and increase thrust to change the aircraft’s downward velocity into upward velocity, and restart the cycle.

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    $\begingroup$ "The pitch angle of the aircraft is not directly controlled by the pilots, but is a secondary result of other control inputs." Other control inputs like pushing and pulling the yoke?! From a pilot's perspective you cannot control pitch any more directly than that... $\endgroup$ Commented Sep 9, 2020 at 3:22
  • $\begingroup$ I think what that that statement means is you are using elevator differently - to stay on the ballistic path, not to control attitude in the normal sense ("pitch angle" in the excerpt), with attitude changing continuously while flying the arc. In other words, when flying the arc your pitch control input is directly tied to maintaining zero G, independent of attitude, while in the arc. $\endgroup$
    – John K
    Commented Sep 9, 2020 at 4:20
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    $\begingroup$ Happy to see a familiar face from the Space Exploration site! $\endgroup$ Commented Sep 9, 2020 at 4:43
  • $\begingroup$ Note the orientation of the nose WRT gravity vector changes during the maneuver. Were it not for air drag, one could simply chop power and go "ballistic". $\endgroup$ Commented Sep 9, 2020 at 11:36
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    $\begingroup$ Whatever the author meant to say it was, at best, an odd choice of words. Pitch is defined as rotation about the lateral axis. You control pitch with fore and aft movement of the control column. It doesn’t matter whether your target is attitude, airspeed, AOA, or Gs, that is your primary control for pitch. What “other control inputs” are there? $\endgroup$ Commented Sep 9, 2020 at 16:20

Zero G parabolic flights can be flown "hand flown" manually, as illustrated here:

Parabolic maneuvres piloting technique
Unlike commercial flights, the Airbus A310 Zero G is simultaneously piloted by three members of the flying crew during the parabolic manuevres.
One pilot controls the pitching (nose-up and nose-down angle). A second pilot controls the roll movement (to keep the wings horizontal). A third pilot, sitting behind them, controls the engine speed (he or she also monitors the flight parameters: warnings, temperatures and pressure).
Together, all three pilots maintain a near-zero acceleration level in the three axes to guarantee zero-gravity precision ± 0.02 g
Unlike in a standard aircraft, the pitching and roll control commands are dissociated. The two control column functions are dissociated by the use of an additional control column on one side and two small cables hung from the conventional control column.


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