The SOAR Library

JETS MOVE UP AND DOWN LESS THAN AN INCH IN TURBULENCE

WHY?

In a jet, you are going about about 800 feet per second. From goal line to goal line, a
football field is one-hundred yards, or three-hundred feet. So every second, a jet
moves the length - almost - of three football fields. Imagine three football fields lined
up end to end. Let’s figure the air over the first one is going down, the air over the
next one is going up, and the next one down. On a jet, you go up, down, up just for
about one-third of a second, about as quick as you can read that. Then you are over
the second field with its downward-moving air and you move down for about one-
third of a second. Then you are over the third field and move up for one-third of a
second.

There really isn’t much time to go up (or down) before you are into an area where
the direction of the air is the opposite. It all averages out and the plane stays at its
assigned altitude.

That’s it. How much do you go down? Less than an inch in a jet because you go
from down-moving air to up-moving air so quickly that neither down nor up moving
air has time to do much, and you just feel it as a jolt because you are hitting the
bump so fast (think speed bump in your car at ten mph versus 30 mph). In the
slower plane you are in down-moving air longer and go down maybe a foot or two
before the up-moving air moves you up a foot or two.

But ‘what if’? What if the plane did ‘free-fall?’ What if it did go into a zero-gravity
condition for one-third of a second. How far would it ‘free-fall’? Zero gravity is
thirty-two feet per second per second. So, in one-third of a second of free-fall,
the plane would descend a mere ten feet and eight inches. So the next time
someone tells you they were on a plane that feel ten thousand feet, tell them to
check this web site: http://www.nogravity.com/

That is the web site for Zero Gravity Corporation

The terror fearful fliers experience is based only imagination. They imagine falling
weightlessly from 35,000 to the ground. In a dive an airplane can produce weight-
lessness for only a moment. Contrary to what fearful fliers expect - weightlessness
throughout a dive is impossible. For weightlessness to be produced for more than
a moment, an airplane must carefully fly a parabolic profile. Weightlessness is
achieved only while the plane’s nose is being CONTINUOUSLY lowered at a
prescribed rate. Even with a carefully flown parabola, weightlessness can be
achieved for only about thirty seconds.

For a mere $3750, Zero Gravity Corporation provides a zero gravity experience
using a Boeing 727, the interior of which, is padded on all sides. The longest they
can produce a zero-gravity experience is thirty seconds. But for your $3750, you
fifteen experiences of weightlessness of about thirty seconds each.

Zero Gravity Corp starts the parabolic profile at 32,000 feet with the nose of the
plane approximately raised 45 degrees above the horizon. (About three times
higher than on a normal takeoff.) The nose is then continuously lowered at a
prescribed rate to produce a zero-gravity condition for 25 to 30 seconds during
which everything in the plane is weightless. The lowering of the nose is continued
until the plane is diving with the nose approximately 30 below the horizon. (About
ten times steeper than a normal descent.) At that point the pilots start a gentle pull
up to allows the participants to perch themselves on the padded floor. Then, to
recover from the dive, the nose is brought aggressively back to level. As this is
done, the g-force increases to about 1.8 g’s until the aircraft returns to level flight.
(1.8 g’s is more than you will ever experience in turbulence).

Zero Gravity Corporation does this with a forty-some year old 727, and yes, the
wings don’t fall off. The weightlessness experienced inside the airplane is
actually equivalent to the type of “free fall” experiences for the first six seconds
when sky diving or bungee jumping. After six seconds, a person’s downward
speed stabilizes at a fixed speed of around 120 to 150 m.p.h. and one descends
at that speed in a one g condition.

This brings to mind the difference between ‘descending’ and ‘falling’. We expect
the feeling of falling to be a zero-gravity (weightless) experience. Descending can
be a zero-gravity experience or not. An airplane can descend, but it cannot fall
(zero g) for more than a moment (except when intentionally flying the parabola).

The parabolic flight profile is shown at this web page:
http://www.nogravity.com/how.htm

For more information see: http://www.nogravity.com/

The problem really comes because you visually see nothing holding the plane up
and expect it to fall. You need to think about the jello exercise, . . . possibly even
buy some jello and do it for real.

FOR A SCHOLARLY EXPOSITION ON WEIGHTLESSNESS, SEE:

http://galileoandeinstein.physics.virginia.edu/lectures/gal_accn962.htm