Riding The Parabolic Curve

© Hal Stoen

May, 2002

NASA trains its astronauts in a modified aircraft affectionately called the "Vomit Comet". The 707's mission is to fly a parabolic curve so that for a portion of the ride the aircraft, and its contents, become weightless.

Before there was a NASA the little flight school that I instructed for came up with our own version. Ours was more simplistic in name and nature. We called it the "Barf bag special."

NASA depends on a powerful four-engine Boeing 707.

We used the single-engine Cessna 150.

Why the 150? Mainly because it was cheap to operate, and we flight instructors could usually take one up to horse around in without raising any flags with the flight school owner. Plus, and it was a big plus for us, the 150, when at the appropriate weight, was certified in the "Utility Category".

It could take negative "g's".

A shallow dive from altitude until the red-line airspeed was reached, then gentle back pressure transistioning to a climb. Then a gentle push-over until you felt that you had entered that magic phase of being weightless. This was no easy task. NASA has a rather complex flight envelope plan that is carefully followed to enter the parabolic curve correctly, and for maximum "linger time" in the curve. We were just dumb pilots experimenting with the effect and doing it by feel. If we missed the "curve", there would be a small negative "g" placed on the little Cessna 150. That's where the Utility Category rating came into play.

How long could we stay weightless? About 3 to 5 seconds maximum. But, if you do the old "one thousand one, one thousand two, ...." you will realize that it is a fair amount of time. Usually, it was less- sometimes only a couple of seconds. My greatest feat was to place a cigarette and a Zippo lighter up on the instrument brow. Once in the parabolic curve, the cigarette would rise along with the lighter and drift toward me. I would mouth the cigarette, grab the lighter as it drifted by, flip it for flame, and then light up. Wonderful show biz, and a needed break from flight instructing.

However, cuteness does catch up with you as one day I attempted my feat in a particularly dirty airplane. Entering the curve, all of the dirt and sand from the floor drifted up to about lap level and hovered there. I knew my fate would arrive in seconds.

I had a devil of a time explaining my badly soiled pants to my wife when I got home that day.

Hal Stoen

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