/I too have wondered about the statement "Designed with Nuisance Breakers."
/I will wait with you for the explanation.
I think I said, "with breaker installations designed to nuisance trip."
Here's the rational behind that statment:
Dozens of folk who've attended my forums and seminars have attested to the
same experience I've had with contemporary power distribution systems
in light airplanes. Master switch left on and battery is flat on a cold
morning and you start the airplane with ground power. You're ready to
lauch into the clouds so EVERYTHING gets turned on for departure. A cold
alterntor will put out MUCH more . . . as much as 10-15% more than a hot
one so as you take off, the alternator is willing to power up the whole
airplane -AND- try to recharge a flat battery. A 60 amp breaker may carry
70 amps for some time . . . or if it's an old breaker and drifted down a
little, it trips some time after departure. I've never flown a stock
production airplane with a low bus volts warning light so the flight
generally proceeds "normally" until things start dying . . . which isn't
very long after because the battery never got fully recharged.
Sometimes, resetting the breaker gets things back up and running and if
you've punched into the clear above the clouds, this flight and subsequent
flights don't experience the problem again . . . for awhile.
/I do however have most of the facts concerning the 50 amp breakers used in
/many Cessna and Piper Aircraft.There were a lot of problems with these
breakers
/tripping for no apparent reason.I have personally verified this condition
/on dozens of aircraft.
/The one main reason that a lot of folks were upset is the fact that neither
/Cessna,Piper,or the manufacturer of the breaker would not accept the
/responcibility for the defect and had to pay for the replacement.
This is the down-side of regulation. If, for example, under part 43 rules
we were automatically allowed to upsize any circuit in the airplane as
long as the wire and breaker size rules were observed, a larger circuit
installation would fix the problem. Some breakers are indeed on the "weak"
side and tend to become nuisance trippers . . . especially the larger sizes.
Fortunately, they seem to drift downward instead of upward although I've
heard tales on Beech's piston line that they've discovered breakers that
refused to trip. I've asked to receive such a breaker for evaulation but
haven't seen one yet . . . this may be legend.
But consider the manufacturer's dilemma. The rules of conduct under
Parts Manufacturing Authority requires a manufacturer to report and
describe corrective action for any defects in design and manufacturing
of it's products or componenents used in it's products. If the breaker
problem can be classified random failure or end-of-service-life there's
no reason to react. If a manufacturer were to acknowlege the "defect"
then flags go up all over the place. Many times, they're unnoticed but even
trivial problems can become mountains of paperwork and associated expense
if some rule-book wielding do-gooder in the FAA really wants to look good
for his boss.
The very rules that were set in place to "protect" the unwary flying
consumer are the very rules that guarantee the same consumer has to
put up with problems that were literally designed into the airplane.
/OK Bob, you've got my attention. I agree that a properly designed electrical
/system should not cause fuses, or breakers, to trip unless a fault condition
/arose . . . . <snip>. . . Now, I give you the opportunity to educate us! HOW
/(so we won't do the same thing), and WHY (to expand our understanding and
convince
/us not to do it), would a commercial aircraft manufacturer DESIGN nuisance
/tripping of breakers into an aircraft electrical system?
Well, they didn't do it on purpose. It's interesting to have observed the
evolution of light plane systems design from close range . . . in many cases
I've worked directly with the people who made many of those decisions.
I hope it's VERY CLEAR that the reason these conditions exist on
certified ships is that our crystal ball wasn't all that good 30 years
ago and in hindsight, it would most likely be different today. But the
consequences of bringing such problems and their solutions to light in
today's economic conditions in our litigious society have ramifications
far beyond the effort required to simply fix the problem.
As builders of the finest, most modern single engine aircraft ever flown,
we are able to enjoy and take advantage of our hindsight; both in current
designs and from experiences past. If a problem hops up, we can fix it
right now and freely share the knowlege with others without having to
run it past the engineering, marketing, finance and legal departments or be
harrassed by government for any reason. So, it's not a matter of of
convincing anyone how NOT to do it, it's more a task of convincing people
that no matter what proplems are presented, it can be fixed with no fanfare
or great expense. The difficult part is evaluating our collective
experiences with certified ships for applicability to the experimental
airplane. The overwhelming experience base in the former can make us
unjustifiably fearful of the latter.
Regards,
Bob . . .
AeroElectric Connection
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