RE: RV-List: Exp Bus DC Management Unit
>I have learnt about the above unit and read the various comments on the unit
>by Bob Nuckolls and I would like to add my French Francs worth (perhaps I
>may even make his day).
>The idea of an integrated switching unit no doubt is an easier system to
>wire up than having seperate switches and circuit breakers. Another
>important advantage is that it will use less panel space, which is always at
>a premium.
Less panel space only compared to classic switch-panel and acres-
of-breakers approach. When compared to switch/fuseblock installation
panel space is roughly the same but volume immediately behind the
switches is now dedicated to the ECB assembly . . . I like to see
this area stay more open for access to items above. An offsetting
architecture I've seen discussed is to mount the ExpBus assembly
at the TOP of the instrument panel in the center . . . nothing
above it. I see this trading one maintenance difficult for another.
>The main disadvantage I see with the system is that you can't detect when
>you have an overload condition. With the circuit breaker it will trip out
>and this may be detected sooner or later, as checking the CBs is one of the
>pre flight checks.
In 16 years and 1000+ hours with over 600 logged departures, I've
NEVER climbed into an airplane to find a breaker open. At Beech
we used to do receiving inspections on ALL electronic components.
We paid people to sit at a bench and test every resistor, capacitor,
etc. From a customer relations standpoint, it appeared as though
we were REALLY getting a handle on quality . . . I asked an operator
one day, "How many bad resistors do you find every day?" The reply
was, "Never found a bad one yet!" One might conclude that for all
the pomp and circumstance on display in receiving inspection, no
action taken there was doing anything to IMPROVE our product
quality.
Circuit breaker tripping and fuse blowing is a very RARE event
in airplanes, cars, etc. Further, should some fault occur in
flight, I'm not likely to look at the breaker panel until AFTER
I percieve that some piece of equipment isn't working. THEN,
supposing that I do find a breaker popped . . . whats the
probability that resetting it gets me the system back?????
>It should be possible to overcome the above problem by using an electronic
>circuit which lights a LED when the electronic circuit breaker has gone to
>the high resistance state.
What's the problem to overcome? Adding LED's simply drives parts
count higher, adds another cockpit gizmo to distract a pilot
from his flying duties and only serves to confirm that, yes,
the turn coordinator is indeed crapped out. At that time,
I'll suggest that knowing WHY it's crapped out is close to
useless information; interesting but not helpful in accomplishing
a comfortable completion of flight.
>What I would suggest to Bob is that with his experience of aircraft
>electrical systems that he designs a better system based on his ideas and
>those of us on the RV list. He could then produce and sell us a circuit
>board and components so that we could produce our own at a reasonable cost.
I think I've done that. It's up to you guys to show me where it's
wrong. Let me touch on the features of switch/fuseblock installations.
(1) Fabrication time: Except for installation and labeling of switches,
all components are purchased parts. If breakers are used, both breaker
and switch panels have to be fabricated and bus bars built. The
techniques I propose eliminate all but switch panel fabrication.
(2) Weight: 20 slot fuse block loaded with fuses 260 gms
20 miniature breakers 600 gms + bus bars (estimate 100
gms more)
(3) Cost: 20 slot fuse block loaded with fuses approx $36
20 miniature breakers approx $400
(4) Parts Count: The number of pieces between bus bar and powered
item on a non switched branch . . .
FuseBlock: 3
Breaker: 6 (not counting number of pieces INSIDE breaker!)
Polyswitch (solid state breaker): probably somewhere in between .
. .
(5) Parts Count for switched branch:
FuseBlock/Switch: 6 (not counting number of pieces INSIDE switch!)
Breaker: 9 (not counting number of pieces INSIDE breaker or
switch!)
Polyswitch (solid state breaker): probably somewhere in between .
. .
(6) Wire Installation: For each non switched branch, there is no
difference in the number of wires for any of the
systems being discussed. For switched circuits,
the switch/fuseblock technique adds only one wire
and two terminals for each switch . . . the piece
that runs from fuse block to switch.
(7) Servicability: Toggle switches with fast-on tabs can be replaced in
3-5 minutes sitting in the pilot's seat. Fuses are easily
replaced in the very rare event that replacement is ever needed.
Given that most failures of electrical system components is
mechanical due to environmental stresses and cycles, one might
give consideration to periodic replacement of ALL switches and
fuse blocks at intervals of say . . . every 5 years?
Fuseblock replacement: About 20 minutes and $36
Breaker replacment: 5-10 hours and $400
Polyswitch replacment: probably not necessary
Replace 7 switches: About 30 minutes and $50
>It should be possible to integrate other function such as flashing landing
>lights and a system to select manual or automatic operation of say the fuel
>pump and landing lights so that when in landing and take off configuration
>(ie when flaps are down) they are turned ON. Also current detectors could be
>built into say the fuel pump landing light and pitot heat circuits to detect
>current flow and indicate they are operating.
These functions go more toward issues of annunciation and pilot workload
reductions with addition of automated operations. I've been working
peripherally on the American General Aviation Technology Experiment (AGATE)
program on behalf of Beech/Raytheon. AGATE is an example of how AUTOMATED
some people believe an airplane should be (or become). As an engineer
who also flys what he builds, I gotta tell you that I'm not impressed with
what I've seen proposed so far. Parts counts (another word for system
complexity) are astounding. When counts go up, so does labor and inital
costs while reliability goes down. For my time and effort, I'm inclined
to keep it simple.
>You could even sell it to the fiberglass crowd at a premium of course, as
>they have more money than sense, and make a small fortune.
You gotta cut these guys some slack . . . they're just not in control . .
. . . it's called BUI (building under the influence . . . of epoxy
fumes).
>TGIF, and hope you all have a better weekend than me as I am half way
>through Prosealing my second tank
My condolences . . . ya don't want to breath much of that stuff
either!
Regards,
Bob . . .
AeroElectric Connection
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(o o)
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