alcmist@ssc-vax.UUCP (Frederick Wamsley) (05/30/84)
<bon appetite>
if anyone actually knows how an fxc works, i would like to hear from
you. if anyone is interested in guesses based on looking at an old model,
see below.
i had a chance to look inside the small box of an fxc 8000 once
(this is the box with the calibration knob on it that mounts on the
harness, not the big box inside the container). it looks like
| | <----air pipe
| |
/\/\/\/\/\ __| | ^ to air hose to big box
alt adj.<--> __ | |
\/\/\/\/\/ | |
<--> | |
aneroid <on-off knob>
where the bellows-like thing, which gets longer or shorter depending on
air pressure, alternately plugs and opens an opening in the pipe that feeds
the air hose. the calibration knob moves the entire bellows left and right.
here's what i think happens (and please set me straight if i am wrong).
when you are up at high altitude, the aneroid is stretched out because of
the low air pressure and it blocks the air hose that goes into your container.
the big box with the spring in it that would actually pull your pins
doesn't get any connection with the outside air. it doesn't know where
you are, and it can't fire.
when you fall down into thick air, the aneroid is squeezed back and it
uncovers the nipple on the air hose. the big box can breathe now.
presumably it checks your rate of descent somehow and pulls the pins
if it gets scared. it didn't fire at altitude because it couldn't tell
how fast you were going.
the calibration knob, by moving the entire aneroid, controls when the
device arms. if the aneroid is pushed toward the air pipe, then it will
take high air pressure (very low altitude) to push it back far enough to
open the air pipe. your fxc is set for low altitude. to set it to go off
higher, you'd move the aneroid back away from the air pipe, making it
easier to open up the pipe.
this leaves several questions even if it's right, like
-how does it sense rate of descent and trigger the spring which
pulls the ripcord pins?
-how come they go off at high altitude?
does anyone have more information?
-frederick wamsley d-8844
--
I am not speaking as a representative of the Boeing Company or any of
its divisions. Opinions expressed are solely my own (if that) and
have nothing to do with company policy or with the opinions of my
coworkers, or those of the staff of the Software Support Center VAX.