Adrenalin rush

john smith writes:
Then we smelled it. A sharp electrical smell that told us something was
burning and not quite right. Steve quickly turned off the misbehaving #2
radio. The smell got stronger, but there was no visible smoke. A moment
later, when the realization hit home that we might have a serious problem, I
keyed the mike to tell Atlanta Center that we smelled smoke, may have a
developing issue with our #2 radio, [snip]

Another case of the electronic device in the circuit path to protect the
circuit breaker from overload.

How true! :-)

Now, if there are any EEs present, perhaps they can explain
why aircraft radios tend to fail in this manner whereas
nothing much of anything else in the electronic world fails
in a manner to produce heat and smoke. Are avionics units
designed so close to the components' limits to cause this
failure mode? I can understand a transmitter going up in
smoke (while transmitting), but a receiver?

Everett M. Greene wrote:
: Now, if there are any EEs present, perhaps they can explain
: why aircraft radios tend to fail in this manner whereas
: nothing much of anything else in the electronic world fails
: in a manner to produce heat and smoke. Are avionics units
: designed so close to the components' limits to cause this
: failure mode? I can understand a transmitter going up in
: smoke (while transmitting), but a receiver?

I'll take a stab at it... Probably a big reason why avionics fail like
that because they're older than most electronics. They're used for a longer period of
time so they can suffer individual component failures. "Normal" electronics tend to
get toss earlier, so their failures are more likely due to construction flaws.

They're also packaged very tightly, and cannot afford much overdesign that
would cause additional weight. Also, the environment they operate in is extremely
harsh... *huge* temperature/humidity swings, ridiculous vibration exposure, etc.

That's why I was singularly unimpressed with the internal build quality of the
Michel slide-in replacement radios. They're built with standard DIPs, through-hole
components, ribbon cables, and general run-of-the-mill consumer components. Minimal
strain relief and anti-chafing assembly. Makes for a less expensive unit, but I'm
sure they're more likely to wear/chafe than a well-built unit.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Hmmm, maybe they're on to something. When was the last time you had a
"general run-of-the-mill" consumer product start smoking on you?? ;-)

Seriously, another question for you EE folks: are more modern components of
a better quality in that they don't need a robust surrounding support
structure to prevent catastrophic failures?

Marco Leon


wrote in message
...
Everett M. Greene wrote:
: Now, if there are any EEs present, perhaps they can explain
: why aircraft radios tend to fail in this manner whereas
: nothing much of anything else in the electronic world fails
: in a manner to produce heat and smoke. Are avionics units
: designed so close to the components' limits to cause this
: failure mode? I can understand a transmitter going up in
: smoke (while transmitting), but a receiver?

I'll take a stab at it... Probably a big reason why avionics fail like
that because they're older than most electronics. They're used for a
longer period of
time so they can suffer individual component failures. "Normal"
electronics tend to
get toss earlier, so their failures are more likely due to construction
flaws.

They're also packaged very tightly, and cannot afford much overdesign that
would cause additional weight. Also, the environment they operate in is
extremely
harsh... *huge* temperature/humidity swings, ridiculous vibration
exposure, etc.

That's why I was singularly unimpressed with the internal build quality of
the
Michel slide-in replacement radios. They're built with standard DIPs,
through-hole
components, ribbon cables, and general run-of-the-mill consumer
components. Minimal
strain relief and anti-chafing assembly. Makes for a less expensive unit,
but I'm
sure they're more likely to wear/chafe than a well-built unit.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************




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"Marco Leon" mmleon(at)yahoo.com wrote in message
...
Hmmm, maybe they're on to something. When was the last time you had a
"general run-of-the-mill" consumer product start smoking on you?? ;-)

Oh, I've had a couple recently. My dad bought an electric light that
contained a transformer, which did the blue smoke thing, and the CD-ROM
drive in my sister's PC did the same the other week (I've had them fail, but
never in a combusting kind of way!). And I've lost count of the number of
power supplies in computer equipment that have exuded smoke over the years.

D.

"David Cartwright" writes:
"Marco Leon" mmleon(at)yahoo.com wrote
Hmmm, maybe they're on to something. When was the last time you had a
"general run-of-the-mill" consumer product start smoking on you?? ;-)

Oh, I've had a couple recently. My dad bought an electric light that
contained a transformer, which did the blue smoke thing, and the CD-ROM
drive in my sister's PC did the same the other week (I've had them fail, but
never in a combusting kind of way!). And I've lost count of the number of
power supplies in computer equipment that have exuded smoke over the years.

I've had numerous power supply failures in (ground-based)
devices over the years and have never had any smoke from
any of them. They just quit working...

There is a difference between linear and switching power
supplies. The latter are most likely going to fail
quietly whereas the former can very well smoke something
when they fail.

A thought occurs to me regarding avionics failures: The
confined environment of small airplane cabins and the
close proximity to the avionics devices may cause the
even a miniscule amount of odor to be noticed whereas
on the ground nobody may be close at the time of failure
and any odor goes unnoticed.

"Everett M. Greene" wrote:

Now, if there are any EEs present, perhaps they can explain
why aircraft radios tend to fail in this manner whereas
nothing much of anything else in the electronic world fails
in a manner to produce heat and smoke. Are avionics units
designed so close to the components' limits to cause this
failure mode? I can understand a transmitter going up in
smoke (while transmitting), but a receiver?

Receivers still contain amplifiers, power regulating transistors, resistors,
diodes, etc. in their circuitry. Failures at the discrete component level
can produce thermal events without increases in main power loads above
circuit breaker limits.

--
Dan
C-172RG at BFM

Everett M. Greene wrote:
Now, if there are any EEs present, perhaps they can explain
why aircraft radios tend to fail in this manner whereas
nothing much of anything else in the electronic world fails
in a manner to produce heat and smoke. Are avionics units
designed so close to the components' limits to cause this
failure mode? I can understand a transmitter going up in
smoke (while transmitting), but a receiver?

I'm an EE. In my day job I design guitar amplifiers. Let me tell you,
I've made a LOT of unintentional smoke at my workbench. When I was
in school a fellow student explained to me that the smoke contained
inside those little electronic components is what makes them work.
It's magic smoke. If you let out the magic smoke, the electrons stop
doing whatever it is they're designed to do.

Seriously though, maybe the propensity of aircraft radios to fail in
this manner has to do with the fact that on average they're pretty old,
and constructed mostly of discrete components. Modern electronics are
more highly integrated into power- and space- miserly "chips", or ICs
(integrated circuits). ICs also allow for more circuitry in a smaller
space, so thermal protection, over-current protection, and other
similar support circuitry can be incorporated into a design without the
weight and space penalties that made them impractical for aircraft
radios "back in the day". It's a theory, anyway.

-R