>Bob, why do you recommend fuses over circuit breakers for aircraft use?
>With a military aviation background I instinctively expect to array my
>panel with C/Bs for individual equipment, Main Buss A, Main Buss B, and
>Essential Buss.
That's mostly because military airplanes are war machines.
Any form of failure is a distraction to a pilot that could happen
while he's being shot at . . . further, the equipment and
design philosophies prevalent in military aircraft and flowed
down to air transport category airplanes is deeply rooted
in aviation antiquity. Institutional inertia in both military
and commercial aircraft almost assures us that change will
be slow in coming and lag a decade or more behind the
advancements we enjoy in our automobiles and consumer electro-
goodies.
>
>I'm thinking access when something surges, being able to power off
>busses (down to Essential) when electrical fire threatens, power
>removal for maintenance, etc.
Read the articles referenced or reprinted on my website. Look
at downloadable power distribution diagrams from the back
of our book. All of those concerns are easily addressed
with simple, inexpensive and pilot-friendly hardware and
design philosophies . . . breakers, magnetos, carbs, ADFs,
VORs, and iron gyros of the 1950s are replacable with more
reliable, lower cost equipment that place an RV light-years
ahead of a brand new C172 for 1/3 the dollars.
>
>Fuses seem limited for aviation use. Granted _I've_ never had to pop
>or reset a C/B in my civilian flying yet (knock, knock, knock) but...?
What is generally the first clue that a breaker has opened in
flight? Somthing has quit working or you threw a switch and the
expected thing didn't happen. Now, suppose you look at the breaker
panel and a breaker is out . . . what do you know? Something is
sufficiently wrong with the system to warrant disconnection to
avoid fire in the airplane.
Now, suppose something isn't working and NO breakers are popped.
What do you know? The thing that didn't work is STILL not working.
Given that failures which do NOT pop fuses generally outnumber the
ones that do pop fuses by 10:1 and given that resetting an OVERLOADED
circuit in flight may be foolhardy, what then is the value of having
a breaker on the panel? Probability that replacing a fuse or resetting
a breaker will get your equipment back on line SHOULD be slim to
zero . . . granted, there are numerous cases where breakers in
certified iron will NUSIANCE trip . . . a condition tolerated only
in the holy-water sprinkled airplanes 'cause it's so damned difficult
to correct a certfied mistake.
Not so with your home built. If you experience nusiance tripping,
replace the protection and feedline with the next larger size . . .
there is no reason for an amateur built owner to expect anything
but the best performance from his/her airplane and modifications
toward achieving that goal are only a toolbox away. Our brothers
flying the certified iron are not so fortunate. Did you know that
the majority of single engine airplanes have at least one breaker
DESIGNED to nusiance trip? Besides, what single piece of equipment
is going into your airplane that is essential to your comfortable
completion of flight? If you have such equipment, why are you
worried about breakers/fuses? There are LOTS of ways
electro-goodies crap that don't involve breakers/fuses. Therefore
I'll suggest that worrying about how you protect critical circuits
isn't very productive. Planning for BACKUP to critical devices
is much more useful. Does your flight bag have a handheld GPS
and COM radio? Do you have a single-lamp panel-flood feedable
from the hot side of the battery contactor? Do you have ACTIVE
notification of altenrator failure? Are you going to maintain
your battery to the extent that it will support minimum essential
equipment for duration of fuel on board? If you have dual electronic
ignition, are you planning for dual batteries? I'll suggeset
that issues of FLIGHT SYSTEM RELIABILITY have little to do
with what kind of hardware you use rather how you wire it up
and having PLAN B operating procedures that turn ANY failure
into a ho-hum event.
Recall the L-1011 that went into the Florida swamp a few years
back? The whole cockpit crew was busy trying to figure out
why a gear down indicator light wasn't illuminated. Intent
upon mechanic's duties in flight, they ignored a/p disconnect tones
and other warnings while a perfectly good airplane full of people
went into the mud. Never happen to me? I wouldn't bet on it . . .
unless I observe the simple rule that one wears a pilot's hat
in the air and save the mechanic's hat for on the ground. Design
your system to be FAILURE TOLERANT, not in-flight maintainable.
Modern hardware and design philosophies unencumbered by institutional
dogma and government "assistance" allows us to built the best
airplanes ever.
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