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nuckolls.bob(at)aeroelect
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 Posted: Fri Aug 29, 2014 9:54 am Post subject: The cost/benefit ratio for automation |
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At 03:36 PM 8/28/2014, you wrote:
| Quote: |
I was wondering about automatic fire extinguishers and whether or
not this philosophy might be applied to them.
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Good question . . . for which there are no pat
answers. One first needs to detect the presence of
fire. Not an easy task. Worked on a fire detection
system some years back that seemed pretty well thought
out. The 'detector' was a length of what you might call
semi-rigid coax. It was about 1/8" diameter. The dielectric
material was a semi-conductor with a large temperature
coefficient of resistance. A length of this 'cable' was
routed about the engine compartment not unlike a piece
of plumbing. The installer was encouraged to route into
areas most likely to be a location for fire.
Under normal ops, the TOTAL resistance of this 8-foot
long resistor would assume some nominal value but
if any portion of its length were exposed to flame, resistance
in that area would drop sharply.
The 'trick' was to detect that drop. With modern software,
that task would be much easier . . . we did it with
op-amps.
This was a warning system . . . all it did was flash
a light. We built a working prototype but got out-bid by
another supplier . . . never got any history on the
effectiveness of this technology.
Numerous approaches have been devised for the
detection of fire. Do a search on "fire detection"
on http://www.freepatents.com for a sampling of
the proposed technologies.
I look back with fondness on the long-thermistor
detection system for its simplicity. To be sure,
there are lots of complex ways to watch for fire.
The problem to be approached for the decision to
automate is rooted in the complexities. A fire
detection system brings new preventative maintenance
issues . . . others come with risk for false
warning. Depending on the fire suppression physics,
the cleanup after dumping the bottles can range
from benign to severe and all are no doubt expensive.
One is further tasked with identifying the high
risk sources for fire. In air transport category
aircraft, the risks run all over the airplane
with a constellation of potential events ranging
from smoking in the john to lithium batteries
in the hold to compromised wiring setting
insulation on fire. In the OBAM aircraft, we're
pretty much limited to fluid fed fires under
the cowl.
The idea that split-second decision to actuate
the fire suppression system will somehow "save
the day" doesn't offer much comfort.
It's sorta like putting boots on the leading
edges for ice-removal. Boots are useful over a
very narrow range of circumstances . . . better
to apply greater diligence in avoiding and/or
escaping icing conditions. Similarly, one's
return on investment for keeping fluids under
the cowl properly contained will go a lot
further to reducing risk than adding a fire
suppression system - automated or not. It's
much easier to prevent fire than to deal with
it after it starts.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Fri Aug 29, 2014 12:44 pm Post subject: The cost/benefit ratio for automation |
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At 07:28 AM 8/29/2014, you wrote:
| Quote: | --> AeroElectric-List message posted by: "racerjerry" <gki(at)suffolk.lib.ny.us>
> I had been through the drill many times to simulate an engine out emergency but I know for me when it actually happened, I did not perform as well as I could/should have.
After flying an ultralight for 300 hours, I was certain that I wanted to continue flying and bought an older 172 with hopes of quickly obtaining my private pilots license. Immediately, I proceeded to plaster any available blank panel space with ‘cheat sheets’ or reminders and checklists to help me along. It worked well. Each list was laminated and stuck to the panel with a dab of Velcro so I could easily modify them as needed. Most of those early reminders have since disappeared, but many still remain. One list still worthy of retention is an ENGINE OUT CHECKLIST, because it is so little used, escapes memory and you usually don’t have time to fiddle with the manual. |
But how much is there to diagnose engine
stoppage in a 172. One flies on BOTH tanks,
BOTH mags and it's a gravity feed fuel
system to the strainer sump. If the engine
starts to fade, the elapsed time from when
your hand starts to move toward the boost pump
switch (while glancing at fuel pressure gage)
is but a second or two . . .
[img]cid:.0[/img]
That airplane is a fine example of risk reduction through
simplicity. Short of catastrophic failures from which
there is no engine recovery, likelihood of failure due
to anything but dry tanks is vanishingly small.
Critical systems management needs to be as automatic
as the practiced flare looking for a greaser. This
system offers not the slightest risk of needing
to fiddle with the manual . . . or sift through
post-it notes on the panel.
Critical systems management needs to be as automatic
as the practiced flare looking for a greaser.
Bob . . .
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