Re: Explosive decompression - how fast?

Michael Ash <mike@[EMAIL PROTECTED]
> wrote:
> A bit of BOTE calculations to back it up. The wind should be roughly the

> speed of sound. 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. Aerodynamic drag scales

> as the square of the speed. The speed of sound is about 6 times greater 
> than this, implying a force on the human of around 36 gees. At 700mph
the 
> air will take about 1/10sec to exit a 100 foot aircraft body, and 36
gees 
> over 1/10sec is about 80mph, plenty sufficient to toss an unsecured
person 
> outside. Of course this whole analysis is ridiculously simplistic.
> 
> 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. As it was he wedged halfway 
> and spent the rest of the flight with his upper body outside the plane. 
> While the high speed outside air certainly contributed to the inability
to 
> retrieve him, it didn't seem to pull on the people who had remained
inside 
> the flight deck. It would appear that an explosive decompression can 
> indeed pull people outside the plane in the right circumstances.

I forgot that I left the accident report loading in the background. 
Reading through it, they have some discussion of the decompression forces 
with actual numbers:

"The forces acting upon the commander, to project him through the 
windscreen aperture, were a function of the differential pressure between 
the inside and outside of the cabin and are calculated as having a force 
of approximately 5,357 pounds (depending upon his exact proximity to the 
aperture). This would be quite adequate to drive a person weighing 70kg 
from his seat and through the aperture, whereafter the ram effect of the 
airstream would pin him to the fuselage and seriously impair movement."

Alas they do not show their work. However, this number is remarkably close

to my BOTE calculation of 36 gees, which is weird because this was a 
relatively small hole and at a pretty low altitude.

-- 
Michael Ash
Rogue Amoeba Software