Re: Airbus crash - carbon?

Paul Hovnanian P.E. wrote:
Joerg wrote:
Paul Hovnanian P.E. wrote:
Joerg wrote:
Paul Hovnanian P.E. wrote:
Joerg wrote:
Paul Hovnanian P.E. wrote:
Blarp wrote:
In a certain document I will never be able to retrieve, I noted the
worry of some aviation engineer relating to the growing use of carbon
instead of ye olde iron (aluminium etc) in the construction of
airplanes.

The "Faraday Cage" effect may not be longer in effect, as carbon
constructions have a real electric resistance, and hence disspate
power in a lightning strike.

I have heard of totall loss wind turbine failures due to lightning
strikes in the blades - blade disintegrates - turbine unbalanced -
tears itself up.

Airbus prides itself on using modern composites - anybody knows how
real lightning strikes are tested / simulated?
For aircraft systems, Google RTCA DO-160E. I'm not sure what the state
of the art is for structural integrity, but it is true that composites
are a much greater concern than metal skins were.

Since you seem to be familiar with DO-160 do you know why it is so
strangely silent on creepage and clearance regs?
Because it specifies environmental and test conditions under which
devices must perform. Its up to the engineer to figure out whether their
design will perform under these conditions. Its not a design guide.

True. However, that leaves serious room for error. An engineer can
design, test and pass with creepage paths that would fail under certain
conditions not covered. IOW you could fly under the radar screen. That's
why, for example, EN60601 is very specific about that and mandates exact
minimums.
Or you could design to specified minimums and then encounter conditions
for which they are inadequate. Some people will inevitably apply such
design specs without understanding what the underlying assumptions were
used to create them and then exceed those conditions.

I guess in medical they don't trust design engineers as much as in
aeronautics. Almost every detail is spec'd out to the nitty gritty. So
when the TUEV guy flunks a design and a heated discussion ensues he can
say "Look, it says eight millimeters right there and it ain't eight on
the board".

This assumes that you trust the people who came up with 'eight
millimeters' given the expected operating conditions. And that those
conditions and limitations make their way into the operating manuals'
restrictions section.


Mostly yes but that trust has limits. The rules and regs in medical make sense but I could never understand certain things, like why cardiac contact equipment did not have to be defibrillator-proof until recently. So I always made sure my designs were defibrillator-proof. After all, one cannot simply assume a doctor would would never panic and forget to disconnect before applying the paddles.

Manuals are not useful. I have seen medical equipment that was a decade old and the manuals sat there on a shelf. Still shrink-wrapped ...


The lookup table approach is used heavily in the utility/power industry.
The field engineers don't have the experience or the time to size
everything to suit each installation, so they have a cheat *** of what
size works. Look it up in Table 310.16 and your *** is covered. So it
weights twice what it has to. It doesn't have to fly and the rate payers
pick up the tab for the extra material anyway.


Yeah, the rate payer. Our water district created themselves a new fat cash cow: The right to raise water rates up to wazoo when there is a drought. I knew what was coming and sure enough, right after that "decision" went through stage 1 was declared. All the dams are cresting over, tons of snow in the Sierra, but we are in stage 1 drought.

--
Regards, Joerg

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