On Apr 27, 12:29=A0am, Michael Ash <m...@[EMAIL PROTECTED]
> wrote:
>>: One flight attendant was thrown to the floor and another
>>: one was thrown out of the plane altogether, never to be seen
>>: again.
It would seem odd to start with a single sentence mentioning a person
being "thrown the the floor" and use it as a supporting statement that
the *other* person was "accelerated away be decompression-related
forces". It certainly doesn't rule it out, but it points out the
problems associated with taking news blurbs as starting assumptions.
> I'm doubtful that it's going to be enough to pull anyone
> out, but I could be wrong.
Well, the issue here is that there seem to be two possible mechanisms
for ejecting a person in that situation. And from everything I can
calculate, the pressure differential isn't enough. Not unless she was
right up against the skin of the plane, perhaps.
> The terminal velocity of a human at the lower reaches of the
> atmosphere oriented parallel to the ground is roughly 120mph,
> implying that aerodynamic forces are 1 gee at this speed.
Hmm. That's a very good BotE approach that I didn't think of,
actually. That means that for 54 m/s wind (120 mph), the acceleration
on Callie would be 9.8 m/s^2, more or less. If the exit velocity is
nearly Mach 1, then you'd see this level of wind where the cross-
sectional area perpendicular to the breach was about 6 times greater.
Since that area would be roughly a cylinder, for a 10 cm wide breach
it would be at a distance of about 10-20 cm from the center of the
breach. In other words, to experience roughly an acceleration of 9.8 m/
s^2 you would have to be almost in the breach itself.
By the same method, we can figure that the wind speed at Callie's
location (5 m back, where we can probably assume the cross-sectional
area of the lock is what matters) would be 330 m/s * 0.1 m / 3 m =3D 11
m/s, or 25 mph, about 1/5th of the 120 mph figure you used for a "1 G"
limit. If the drag forces scale as the square of the velocity, then
the acceleration Callie feels at that point would be 1/25th of a "G".
I'm not sure she'll notice.
> A perhaps more convincing example is British Airways 5390. A
> pane of the windshield was improperly installed and blew out at
> 17,000ft. This very nearly ejected the pilot from the aircraft.
What was the distance from the pilot to the window immediately beside
him. and this also has a very significant difference with the original
example: a very very large volume of air relative to the breach. In
other words, the duration of the pressure difference could potentially
be significant. I suspect the reason they couldn't pull him back in
had a lot more to do with a limp human body bent over a metal edge and
most of the way out into a 500 mph splistream than any pressure
differential, incidently.
> In the post which started the thread, the hole was assumed to be
> somewhat small compared to the cross section of the airlock, but
> looking at the media which prompted the post I don't see this shown
> anywhere.
*That* I should explain. the two people disccussing this in a
different newsgroup were debating if Callie would hit the opening
doors before or after they had had enough time to open. Thus why the
"10 cm opening" in my set-up - it came from the original discussion
where one poster was maintaining that Callie would immediately be
slammed into the still-opening doors before they had even opened a
fraction of a meter.
> If the door opens approximately instantaneously it seems
> that the victim will indeed get blown out.
Actually, in that case I think it's even easier to prove it won't
happen. In a "prompt opening" case, the only thing that could push her
is the gas immediately behind her body, moving a about the speed of
sound. There's just not enough energy there to account for a rapid
exit, even if it could all be coupled into her motion.
--
Brian Davis
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