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One thing leads to another...



 
 
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  #1  
Old December 4th 03, 12:04 AM
Jay Honeck
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Default One thing leads to another...

Did you ever notice that fixing one thing often seem to break something else
in the old airplanes most of us fly?

We just had our new Directional Gyro installed today (just six weeks after
our Attitude Indicator failed), and lo and behold, our autopilot works
again! The gyros erect immediately, and no precession of the DG was
noticed in our test flight -- all was right with the world again!

Well, almost. It immediately became obvious that something was amiss with
our Com 1 radio. Depressing the PTT produced a nasty, high-pitched hum that
didn't sound good, and it didn't seem like we were hearing much of anything
on Unicom, despite several planes working the pattern. After a few minutes
of futzing around, we determined that we could just barely receive the AWOS
broadcast, despite being parked right next to the transmitter!

We switched to Com 2, which was working normally, and proceeded with our
test flight.

Since Com1 is our newest radio (the digital Narco 820R), we figured it
couldn't be a problem with the radio itself (although, of course, you never
really know). And, of course, the panel had JUST been ripped apart to
install the new DG (And I had them replace ALL the vacuum tubing from the
vacuum pump back, as long as we had everything open. It was the ORIGINAL
tubing, dated 1975!) So, we pretty much knew that SOMETHING had been
accidentally disconnected during the installation -- but what?

So, it was back to my A&P's shop, where they resignedly (but good-naturedly)
started trouble-shooting the issue. Of course, it meant taking the seats
out again, and climbing up under the panel with a shop light -- no easy task
for two heavy-weight guys approaching 60 years old.

The radios in our plane have probably been replaced six times since 1974.
Worse, every guy that put in a new radio seemed to string new wires, simply
cutting off the old antenna wires. This meant that there are several
"antenna wires to no where" under the panel -- making determining which one
was disconnected an exercise in frustration.

Well, after almost two hours the bugger was found, and reconnected -- but
what a pain, for all concerned! Somehow during the installation of the
instruments, vacuum hoses, filters, and hose clamps, this one wire was
accidentally detached, leading to a long wild goose chase.

This isn't the first time this has happened to me. Anyone else have a
similar experience?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"


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  #2  
Old December 4th 03, 01:58 AM
Neal
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Back when I used to be an electronics tech, we called this phenominon
"repair damage" ;-)
  #3  
Old December 4th 03, 02:06 AM
Aaron Coolidge
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Jay Honeck wrote:
: The radios in our plane have probably been replaced six times since 1974.
: Worse, every guy that put in a new radio seemed to string new wires, simply
: cutting off the old antenna wires. This meant that there are several
: "antenna wires to no where" under the panel -- making determining which one
: was disconnected an exercise in frustration.

My airplane has also gone through many radio installations, from the
original dual narco 2-piece tube units onward.

When I replaced the audio panel in my airplane, I also removed and replaced
all of the radio audio signal wires, and power wires. I removed all of the
"wires to nowhere" that were disconnected at both ends. I retied all of the
wire bundles under the dash. This probably added 4 to 6 hours to the job,
but since I did it during the 9/11 grounding the extra days weren't too
critical. I don't think many people would pay someone to do this, because
it doubled the job time. Since I was working myself (under supervision),
the time was less of a factor.

Net result? Instead of the wire bundles being 3" in diameter, they're now
1" in diameter. The radios don't hum, whistle, or otherwise misbehave.
And, I ended up with a 33 gallon trash bag full of bits of wire! I removed
over 4lbs of unused, disconnected, wiring and a mess of unnecessary
connectors.

--
Aaron Coolidge (N9376J)
  #4  
Old December 4th 03, 02:37 AM
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On 3-Dec-2003, "Jay Honeck" wrote:

Well, after almost two hours the bugger was found, and reconnected -- but
what a pain, for all concerned! Somehow during the installation of the
instruments, vacuum hoses, filters, and hose clamps, this one wire was
accidentally detached, leading to a long wild goose chase.

This isn't the first time this has happened to me. Anyone else have a
similar experience?



In a forum of airplane owners it would be more realistic to ask if there is
anyone who had NOT had a similar experience!

--
-Elliott Drucker
  #5  
Old December 4th 03, 05:33 AM
Dave Stadt
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"Neal" wrote in message
...
Back when I used to be an electronics tech, we called this phenominon
"repair damage" ;-)


Or....take a call, make a call.


  #6  
Old December 4th 03, 05:58 AM
David Lesher
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Jay Honeck wrote:
: The radios in our plane have probably been replaced six times since 1974.
: Worse, every guy that put in a new radio seemed to string new wires, simply
: cutting off the old antenna wires. This meant that there are several
: "antenna wires to no where" under the panel -- making determining which one
: was disconnected an exercise in frustration.

I have often speculated that iffen I were clean-sheet designing a
nav/com; I would do about what ICOM did on at least one series of
VHF amateur transceivers.

There'd be a control panel, with display and controls. It has fiber
fiber back to the box under the rear seat. The control panel is say
1" deep -- it has nothing but the displays, LED's, optical spin
encoders, and a minimum of drive electronics.

This gets all the electronics of import out of the jungle oven known
as "in front of the panel" to where they can be easily wired, seen
and cooled. CG permitting, you could add a adjacent 3AH GelCell as
emergency power.

You could also do the same with GPS, xponder, etc. In fact the
panels might be the same hardware, except for labels.

Yea, I know, that's ~~what the ARINC standard used to do on DC-6
era beasts -- remote everything down to the radio bay. One issue
you add is the interconnecting wiring as failure points. But if we
use flexible fiber jumpers, instead of 18-odd wires, that's a
different kettle of fish. Further, if it loses the fiber connectivity,
the radio can revert to ?121.5? and preset volume, etc.

Now, I don't think anyone will ever do this -- for all the reasons
the GA fleet is what it is. But I still think it is a fun engineering
dream, at least.
--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433
  #7  
Old December 4th 03, 06:44 AM
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Default

David Lesher wrote:

I have often speculated that iffen I were clean-sheet designing a
nav/com; I would do about what ICOM did on at least one series of
VHF amateur transceivers.


There'd be a control panel, with display and controls. It has fiber
fiber back to the box under the rear seat. The control panel is say
1" deep -- it has nothing but the displays, LED's, optical spin
encoders, and a minimum of drive electronics.


This gets all the electronics of import out of the jungle oven known
as "in front of the panel" to where they can be easily wired, seen
and cooled. CG permitting, you could add a adjacent 3AH GelCell as
emergency power.


You could also do the same with GPS, xponder, etc. In fact the
panels might be the same hardware, except for labels.


Yea, I know, that's ~~what the ARINC standard used to do on DC-6
era beasts -- remote everything down to the radio bay. One issue
you add is the interconnecting wiring as failure points. But if we
use flexible fiber jumpers, instead of 18-odd wires, that's a
different kettle of fish. Further, if it loses the fiber connectivity,
the radio can revert to ?121.5? and preset volume, etc.


Now, I don't think anyone will ever do this -- for all the reasons
the GA fleet is what it is. But I still think it is a fun engineering
dream, at least.
--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433


Back in the "good old days" when I was an avionics tech, they HAD to
put things in the back; the equipment was just too big to fit it all
behind the panel.

The equipment rack in the back of your average Cessna/Piper is no
heaven for equipment. It vibrates just as much and it is actually
hotter than behind the panel. Remember, there are no vents back there
while up front you have cabin vents.

Most of the problems with the old MK-12 solid state inverter power
supplies and the AT-5 transponders were due to the heat and vibration
in the back.

Running cables of any kind from the back to behind the panel is also
highly labor intensive when done correctly. Basically, you just about
have to gut the seats and carpets to get under there and make sure
the cables are properly secured and protected so they don't wind up
interfering with control mechanisms or getting chaffed in two where
they run over all the sharp metal edges down there.

Lots of problems turned out to be nothing more than marginal installation
of cables under the floor done by somebody on the cheap. The only solution
was to rip it all out and replace it correctly.

While you could replace a lot of the wiring with a fiber optic data cable,
you still have to run power back there and you still have to keep the
cables protected and out of the workings. Plus splicing and putting
connectors correctly on fiber is a pain in the butt.


--
Jim Pennino

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  #8  
Old December 4th 03, 03:31 PM
Jay Honeck
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In a forum of airplane owners it would be more realistic to ask if there
is
anyone who had NOT had a similar experience!


Yeah, I guess that *was* pretty silly of me... ;-)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"


  #9  
Old December 4th 03, 10:53 PM
JerryK
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Happens all the time. This is one reason I never fly a plane on a trip
right after a repair or inspection.

jerry

This isn't the first time this has happened to me. Anyone else have a
similar experience?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"




  #10  
Old December 4th 03, 11:01 PM
David Lesher
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Default

writes:



Back in the "good old days" when I was an avionics tech, they HAD to
put things in the back; the equipment was just too big to fit it all
behind the panel.


The equipment rack in the back of your average Cessna/Piper is no
heaven for equipment. It vibrates just as much and it is actually
hotter than behind the panel. Remember, there are no vents back there
while up front you have cabin vents.


But you can easily have ventilation. You don't need outside
air; a few boxer fans will help a great deal. The big thing is you
have volume and *access*. The big issue I see is protecting against
cokes spilled on/through the seat.

Most of the problems with the old MK-12 solid state inverter power
supplies and the AT-5 transponders were due to the heat and vibration
in the back.


We're talking an order of magnitude more heat in a MK-12 inverter
than for a current whole stack, I bet... I seem to recall those even
used geranium transistors...

Can't see why vibration is worse under the rear seat; only that the
panel has mounts. So, put stuff on mounts.

Running cables of any kind from the back to behind the panel is also
highly labor intensive when done correctly.


Agreed. But one real plus is fiber, even mil-spec "tank-proof" fiber,
is tiny as compared to the ahem equine reproductive equipment it
replaces here. (I installed LOTS of those in police cars years ago..)

And you end up running coax from each antenna, mike/headphone/etc
up into a very tight location where you work by feel....

Fiber all avoids ground loops as well. I could see a audio panel
with a front panel for control, a knee-level jack panel for
mikes/headphones/PTT/CD player in, and a 2nd in the rear for those
passengers.

While you could replace a lot of the wiring with a fiber optic data cable,
you still have to run power back there and you still have to keep the
cables protected and out of the workings. Plus splicing and putting
connectors correctly on fiber is a pain in the butt.


I'd buy connectorized flexible duplex jumpers. But yes, you'd need to
run power there. Good place for the avionics master contactor.



--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433
 




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