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Newsgroups: comp.risks
X-issue: 4.74
Date: Mon, 13 Apr 87 20:18:20 EDT
From: utzoo!
Subject: Re: A different RISK? (in-flight control computers)

> The risk is that a pilot may plan on losing some brain function to
> g-forces, without risking that the plane will go out of control in the
> maneuver. This possibility is entirely due to the presence of the
> flight control computer...

Not very plausible at the current state of the art.  The flight control
computers are *not* capable of preventing the aircraft from going out of
control; they merely prevent one or two specific types of failure (e.g.
breaking the aircraft) that are so clearly undesirable that they can be
unquestionably ruled out.

In fact, because the problem has gotten a lot more visible of late, serious
consideration is now being given to *awarding* the flight-control computers
such powers, to save the aircraft and the pilot!  The tentative intent is
to sense unconsciousness in some manner, signal the pilot that the computer
thinks he is unconscious, and if this brings no response, to take over and
restore (at least) level flight.  Nobody, repeat nobody, is suggesting that
the computer try to continue the maneuver the pilot was attempting.

> ...The F-20 has crashed twice in airshow routines, after the same potential
> 9g pull-up maneuver...

Several other crashes, such as that of the British Aerospace attack-configured
Hawk prototype, have been tentatively attributed to G-LOC (G-induced Loss Of
Consciousness).  And there is considerable suspicion that it may account for
other unexplained crashes of very-high-performance fighters in recent years.

What is new about the recent fighters is that they can get into high-G
situations much more suddenly than older planes could.  In older fighters,
loss of blood flow to the brain was gradual, and symptoms like tunnel vision
could be relied on as warnings.  The new fighters can pile on the Gs so
quickly that blood flow cuts off almost instantaneously, leaving the brain
running on stored oxygen for a moment and then suddenly losing consciousness
when that runs out.

> Were the flight control computer not to assure maneuvering within the
> envelope in the event of an extreme g maneuver, no pilot would risk
> loss of control through impaired function, unless in combat.

"Within the envelope" does not equal "under control", as the F-20 pilots
assuredly knew.  I find it extremely implausible that they deliberately
risked loss of control by relying on the computers; the computers (well,
actually, the programs) aren't that good and the consequences of going
out of control can be too final.

Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,decvax,pyramid}!utzoo!henry

Newsgroups: rec.aviation.military
From: (J.D. Baldwin)
Subject: Re: How to improve G tolerance and prevent g-LOC?
Date: Thu, 3 Jul 1997 18:22:14 GMT

In article <>, José Barahona da
Fonseca <> wrote:
>   Can the the Pilot improve his G tolerance through physical training?
>What type of physical exercises? Jogging?

This is problematic.  High degrees of cardiovascular fitness correlate
with lowered blood pressure and *lower* G-tolerance.  If you run
regularly, and your resting heart rate is 55 or lower, you're probably
not going to make a good fighter pilot.

This doesn't mean that you get to be a slug, though.  (Slugs are
different from fighter pilots in that you can tell something to a
slug.)  You need a reasonable level of CV fitness to maintain a
reasonable level of endurance.

There were a few articles in the Naval Aviation mags in the 1980's
that suggested progressive weight training to build strength and
muscle density/mass were the way to achieve high G-tolerance.  I have
no idea whether this had any clinical basis, or whether it represents
current thinking on the subject, but there was certainly some
anecdotal evidence to back that thesis up.  I personally knew guys
who claimed to have raised their G-tolerance by 1.0 or more by
training 2-3 times per week with weights.

I decided I'd rather ride my bike than lift, so I went S-3's.  Max
G:  4.5.  Even I could handle that.
 From the catapult of J.D. Baldwin  |+| "If anyone disagrees with anything I
   _,_    Finger |+| say, I am quite prepared not only to
 _|70|___:::)=}-  for PGP public    |+| retract it, but also to deny under
 \      /         key information.  |+| oath that I ever said it." --T. Lehrer

From: Lee Green MD <>
Newsgroups: rec.aviation.military
Subject: Re: Red out a myth?
Date: Mon, 14 Jul 1997 22:47:32 -0400

Sean Malloy wrote:

> It's not the capillaries _bursting_, it's the capillaries _swelling_;

What Sean said.  The red you can see in someone's eye after they've
pulled a big negative-G maneuver (and commonly after women give birth,
too, BTW) is a "subconjunctival hemorrhage", from capillaries bursting
under the conjunctiva (the clear layer over the whites of your eyes).
The pressure-regulating mechanism in the eye protects the retinas, but
not the conjuctiva.  You can break the vessels in the latter, and it
makes for a very impressive appearance to others, but does not make your
vision look red.  Bleeding from your retinal vessels won't make your
vision look red, but will give you blind spots.  If you bleed
significantly from your retinal vessels, you probably won't be flying
any more.

Lee Green MD MPH
Associate Professor
Dept Family Medicine
University of Michigan

PGP public key on MIT keyserver at
Verisign public key available from Verisign, Inc.

Newsgroups: sci.military.naval
From: (J.D. Baldwin)
Subject: Re: Pilot's Weight
Date: Fri, 12 Feb 1999 16:38:58 GMT

In article <>, Vince Brannigan
<> wrote:
> > Common side effects of prolonged heavy exercise include a lower
> > pulse rate and blood pressure.  Both of which tend to lower your G
> > resistance
> Why would it "lower" your G resistance.  Its only resting blood
> pressure/ have a far greater ability to increase both under
> stress conditions.

The "get ready here come the G's so start straining hard" scenario is
not the only one in which G-tolerance is important.  Sometimes one is
less than fully prepared for the load.  And, in any case, a lower
baseline blood pressure probably translates to a lower "straining"
blood pressure as well.  You can only constrict those vessels so much,
you know.

The aviation physiologists and flight surgeons I met were unanimous on
this point:  high levels of cardiovascular fitness will hurt your
G-tolerance.  There was even an article in "Approach" or one of those
mags, written by a flight surgeon with a background in sports
medicine, discussing this in detail and offering weight training tips
to increase one's tolerance for G loading.

I had incredibly crappy G-tolerance in training, and so opted for
S-3's.  I would have liked nothing better than fighters or bombers,
but I just decided that the prospect of graying out at 3G, blacking
out at 4G and LOC at not much more than that was inconsistent with
such an ambition.  These figures were *with* G-suit and straining
maneuvers.  On the bright side, I could kick the ass of anyone in
my squadron in distance bicycling!

When I hit the fleet, my cardiovascular training regimen suffered
badly (@#$%& 35-hour work weeks!) and by the time I deployed a year
later, I was handling 4G and a bit more just fine with straining
maneuvers alone (I have never seen or heard of anyone wearing a G-suit
in an S-3).  So in my case at least, the anecdote confirms the wider
 From the catapult of J.D. Baldwin  |+| "If anyone disagrees with anything I
   _,_    Finger |+| say, I am quite prepared not only to
 _|70|___:::)=}-  for PGP public    |+| retract it, but also to deny under
 \      /         key information.  |+| oath that I ever said it." --T. Lehrer

From: (Lee Green MD MPH)
Newsgroups: rec.aviation.military
Subject: Re: Need info on Gz effects
Date: Thu, 28 Dec 1995 01:01:53 -0500
Lines: 31

In article <4brr6t$>,
(Thomas Gee) wrote:

> Books!  What a wonderful thought.  :-)
> Just about any book on aerospace physiology should contain introductory
> material on the effects and issues of high G.  Get thee to a university
> library, and have a go at the file index.  (I know it's ironic: low-tech
> advice from the Great Information Superhighway.)

He might start with the NATO publication, "Man at high sustained + GZ
acceleration", or the Air Force's old standby, "Physiology of Flight". 
Most good libraries will contain at least one.

Lee Green MD MPH        Disclaimer: Information for general interest
Family Practice         and discussion only.  I can't examine you via
University of Michigan  the Internet, so you should ALWAYS consult       your  personal physician.  These posts are my
KF8MO                   personal doings, not a service of nor the
                        responsibility of the University of Michigan.

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