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From: yzarn@lhdsy1.chevron.com (Philip Yzarn de Louraille)
Newsgroups: rec.skydiving
Subject: Re: Skydiving at supersonic airspeeds
Message-ID: <996@lhdsy1.chevron.com>
Date: 24 Jun 91 17:06:13 GMT
References: <1991Jun24.135815.8781@cc.curtin.edu.au>
Organization: Chevron Oil Field Research, La Habra, CA.
Lines: 59

In article <1991Jun24.135815.8781@cc.curtin.edu.au> tcliftonr@cc.curtin.edu.au writes:
>In the discussions arising from
>GRAPH OF OSC'N DUE TO HIGH WINDFORCE
>
>Walter@cayman.AMD.COM (Walter Butler) writes:
>
>
>>It is possible that the jumper ( at 750 mph and 1.6 gees of
>>drag after a 120 000 ft exit) will have stability problems
>>from the supersonic airflow.
Don't let the term "supersonic" affect you too much. If a skydiver was
going supersonic at low altitude, *that* would be something to write
about, but going supersonic at high altitude is nothing to scream
about.
>
>Because of the soft impact with the atmosphere there will be
>an extended period of 30 seconds or so of deceleration, where
>much more wind force is available to induce "rocking" in a
>normally utterly stable skydiver.  (A non skydiver is likely
>to go further, into a tumble, and a spin is also likely)
Intuitively, I disagree.
>
>
>>I am no expert, but believe that the shockwaves can cause
>>very localized areas of high stress and drag.
The skydiver will go fast but the atmosphere will be tenuous, so why
shockwaves? Airplanes experience shockwaves but they have *engines*,
skydivers don't.
>
>It sure would.  Perhaps some of your NASA colleagues - the re-
>entry people - might know enough of the physics.  Perhaps they
>already have a re-entry simulator.  As it stands, this
>(subsonic) simulator is extrapolated out of its proven valid
>range.
Ha! As it stands, what is the range of the simulator? (what is its
maximum altitude?)
>
>In particular, we need to know how the drag coefficient (for
>us brick-shapes) changes for low supersonic flight.  Then we
>need to know the effect of temperature on the drag
>coefficient.  Certainly the stratospheric cold of -56 degrees
>affects viscosity and reduces drag.
>
>For vibrations and oscillations, we need to know the effect of
>the compression cones on the extremities and how long they
>take to build up.

Vibrations, vibrations? Hey, we are made of soft (living) tissue, not
rigid metal. Nor are we hollow, unlike most airplanes.
>
>Let's salute their first exploration of impact.  Whatever
>they find out for us, it is going to be interesting.

Agreed.
-- 
  Philip Yzarn de Louraille                 Internet: yzarn@chevron.com
  Research Support Division                 Unix & Open Systems
  Chevron Information & Technology Co.      Tel: (213) 694-9232
  P.O. Box 446, La Habra, CA 90633-0446     Fax: (213) 694-7709