nuckolls.bob(at)aeroelect
Guest
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 Posted: Fri Dec 12, 2008 6:24 am Post subject: Need for start up protection |
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At 11:05 PM 12/11/2008, you wrote:
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OK, I've read the debate on the need for start-up protection and I
can no longer resist the temptation to weigh in with my 2 cents' worth:
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Mike, when you reply to a digest message, it's really
important that you trim off the non-relevant body of
text that you're speaking to. All of our responses are
archived and poorly or un-trimmed responses can really
load the system with "stuff" that makes it difficult
for historians to retrieve value from the archives
later.
| Quote: | 1) With all due respect to my learned colleagues, I worked in the
aerospace industry for many years and have seen more than one
product pass DO-160 testing and subsequently fail in-service due to
aircraft electrical system issues. There are lots of reasons why
this should not happen, but there are also lots of reasons why it does happen.
2) Many of the tests in DO-160 have a number of test categories with
differing severity based on the anticipated electrical system
characteristics to which the product will be exposed. However, the
"anticipated" characteristics may or may not reflect the actual
characteristics of any given OBAM aircraft. Further, not all
equipment is necessarily tested to the most severe category of DO-160.
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Your first-hand experiences cannot be argued with.
But we do know that there are reasons for everything.
The simple-ideas in physics and practice (repeatable
experiments) are irrefutable.
If you have observed failures attributed to incompatibility
between accessory and power source, what was the feature
that failed to meet design goals and what was done to
correct it?
Part of my livelihood involves investigation into
"unanticipated" characteristics . . . because
such behaviors are considered failure to meet
design goals.
You have alluded to "actual characteristics
of any given OBAM aircraft". Let us hypothesize
what it would take to cause any aircraft to present
stresses that lie outside the test parameters of
the most relaxed DO-160 recommendation for
robustness.
What piece of hardware would you modify to produce
the sought after event? What would be the nature
of the resultant stress? Amplitude? Duration? Total
energy? How would that modification be expected to
occur in practice as one of our brothers puts his
airplane together?
If you're operating under the premise that DO-160/Mil-Std-704
compliance is fraught with risk, then from what deficiency
of specification, design or craftsmanship does the risk
arise?
When I am chartered to deduce root cause of anomalous
behavior, my customers would probably not pay my bill
if my proffered solution was, "turn the thing off
while you crank the engine." My charter is to identify
the deficiency and correct it . . . not craft out
a work-around to live with it. "Living with it" is
a tacit admission that we're probably not qualified
for the job!
| Quote: | 3) My aircraft is day/VFR, so a total electrical failure is a
nuisance, not a crisis. Balancing the mission profile of MY
aircraft and based upon my points above, I would rather deal with
the risk of a single-point failure of the avionics master switch as
opposed to the risk of damage to my avionics.
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| Quote: | The foregoing is, admittedly, a personal choice that may not reflect
others' situations or opinions. I think it best that we concede
that, like politics and religion, reasonable minds may differ on the
need for start-up protection. As Bob has said many times, as
aircraft builders we must each make the choices that we deem
appropriate for our aircraft.
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That's a really broad brush. Most of what passes for
politics and religion requires individuals be persuaded
to adopt a behavior based on goals of others . . .
when both should be matters of precise PERSONAL choice
borne of honorable behavior and understanding.
Let us not drive the art of aircraft fabrication based
on fear of what we do not know (perceived risk) when
conditions driving that fear are not qualified,
quantified, nor accompanied by deduction of root
cause and successful remedy (repeatable experiment).
If you're citing experiences with a notion of enhancing
our knowledge and confidence, then they must be supported
by quality, quantity and remedy. Otherwise, it can
serve only to persuade based on fear of that which is
imagined.
Bob . . .
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