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AUTOPILOT AWRY



 
 
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  #1  
Old February 12th 06, 08:45 PM posted to rec.aviation.owning
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Default AUTOPILOT AWRY

I have a piper Arrow and out of the blue...(no pun intended)... the
Autopilot banked hard left (30 deg.) for no apparent reason. It was on Hdg
Mode and the bug was centered.

Each time it was shut off and re-engaged it continued to bank hard left.

I have a long trip to FL planned over the school break and sure would like
to have the Autopilot working.

Does anyone know why this would happen?

Thank You All.
Bill Snow


  #2  
Old February 12th 06, 09:00 PM posted to rec.aviation.owning
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Default AUTOPILOT AWRY

First, what is the make and model of the autopilot?
For my respsonse, I'll assume you have a Piper autopilot,
which is based on the Edo-Aire / Mitchelle designs.

In general, a hard bank to one side indicates that that
roll servo is being driven that direction by the amplifier. (Obvious,
uh?). The question is why.

In my Piper Altimatic II, the roll servo is a motor that is driven by
an H-Bridge type of amplifier. This input to the final motor
driver amplifier is a left / right signal which is derived from the
difference in the heading bug and indicated heading, and if in
NAV, OMNI, LOC or REV LOC mode also the left / right
signal from the nav output. Therefore, your trouble could be in
the console amplifier itself or the input(s) to the amplifier.

If the alierons are driven to their mechanical limits, I'd suspect
a bad transistor in the console amplifier output stage (H-Bridge).

If the alierons are driven to their maximum bank position but not
the their mechanical limits, (usually about 30 degrees of bank), then
I'd suspect a stage before the final amplifier.

Since this happens in heading mode, the problem could the the
resolver in the DG, or any of the electronics in the autopilot console
amplifier or the radio coupler.

Ronnie


"William Snow" wrote in message
...
I have a piper Arrow and out of the blue...(no pun intended)... the
Autopilot banked hard left (30 deg.) for no apparent reason. It was on Hdg
Mode and the bug was centered.

Each time it was shut off and re-engaged it continued to bank hard left.

I have a long trip to FL planned over the school break and sure would like
to have the Autopilot working.

Does anyone know why this would happen?

Thank You All.
Bill Snow



  #3  
Old February 12th 06, 09:46 PM posted to rec.aviation.owning
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Posts: n/a
Default AUTOPILOT AWRY

Sorry if this is too obvious, but you are sure it is not actually in
wing-leveler mode with the wing trim turned off to the left?

--
Best Regards,
Mike
http://photoshow.comcast.net/mikenoel
"William Snow" wrote in message
...
I have a piper Arrow and out of the blue...(no pun intended)... the
Autopilot banked hard left (30 deg.) for no apparent reason. It was on Hdg
Mode and the bug was centered.

Each time it was shut off and re-engaged it continued to bank hard left.

I have a long trip to FL planned over the school break and sure would like
to have the Autopilot working.

Does anyone know why this would happen?

Thank You All.
Bill Snow



  #4  
Old February 12th 06, 09:48 PM posted to rec.aviation.owning
external usenet poster
 
Posts: n/a
Default AUTOPILOT AWRY

Autopilot banked hard left (30 deg.) for no apparent reason. It was on Hdg
Mode and the bug was centered.

Each time it was shut off and re-engaged it continued to bank hard left.


Does it keep the wings level when NOT in heading mode?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"


  #5  
Old February 12th 06, 10:52 PM posted to rec.aviation.owning
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Posts: n/a
Default AUTOPILOT AWRY

Ronnie
It is an Autocontrol II B with HSI. I only tested it in the Hdg mode sine I
had a passenger and did not want to alarm him. When the weather clears I
will give it a test in the other modes to try and isolate the problems/mode.
Thanks for the tips.
Bill

"Ronnie" wrote in message
. com...
First, what is the make and model of the autopilot?
For my respsonse, I'll assume you have a Piper autopilot,
which is based on the Edo-Aire / Mitchelle designs.

In general, a hard bank to one side indicates that that
roll servo is being driven that direction by the amplifier. (Obvious,
uh?). The question is why.

In my Piper Altimatic II, the roll servo is a motor that is driven by
an H-Bridge type of amplifier. This input to the final motor
driver amplifier is a left / right signal which is derived from the
difference in the heading bug and indicated heading, and if in
NAV, OMNI, LOC or REV LOC mode also the left / right
signal from the nav output. Therefore, your trouble could be in
the console amplifier itself or the input(s) to the amplifier.

If the alierons are driven to their mechanical limits, I'd suspect
a bad transistor in the console amplifier output stage (H-Bridge).

If the alierons are driven to their maximum bank position but not
the their mechanical limits, (usually about 30 degrees of bank), then
I'd suspect a stage before the final amplifier.

Since this happens in heading mode, the problem could the the
resolver in the DG, or any of the electronics in the autopilot console
amplifier or the radio coupler.

Ronnie


"William Snow" wrote in message
...
I have a piper Arrow and out of the blue...(no pun intended)... the
Autopilot banked hard left (30 deg.) for no apparent reason. It was on Hdg
Mode and the bug was centered.

Each time it was shut off and re-engaged it continued to bank hard left.

I have a long trip to FL planned over the school break and sure would
like to have the Autopilot working.

Does anyone know why this would happen?

Thank You All.
Bill Snow





  #6  
Old February 13th 06, 03:39 PM posted to rec.aviation.owning
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Posts: n/a
Default AUTOPILOT AWRY

As you've been told, lots of things in the path between what's
happening and where it may have started. To isolate some of them out:


1. First try it in ROLL mode. If it still fails, then it's almost
certainly in the "computer" (the black box with the ROLL knob on it).
See if you can get the ROLL knob to have ANY effect in this mode.

2. If it works in ROLL mode, but not in HDG, then try bypassing your
NAV coupler. [This just requires unplugging two cables and plugging
one back in.] You also likely have an HSI - NAV adapter that could be
bad.

3. If the info from your AH is bad, then it will roll no matter what
(but you might be able to offset it, or at least slow it down, with the
ROLL knob in ROLL mode). Those Tyco (AMP) connectors are not very
reliable. Try plugging and unplugging the one between your AH and your
"computer" several times (and make sure it is plugged in good and
locked).

After all that, if even in ROLL mode it insists in rolling
oncontrollably, then you've got a bad computer. You might check for
broken wires on the rear connector housing, or even removing and
re-inserting it a time or to - but most likely it needs to go back in
for service. Century no longer services them, but several other places
do. It's just some simple analog transistor discrete stuff... nothing
high tech.

  #7  
Old February 13th 06, 04:19 PM posted to rec.aviation.owning
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Posts: n/a
Default AUTOPILOT AWRY

I had a failure like this. It wasn't the computer but one of two
transistors in the location of the servo. The avionics guy told me they
each process (?) turning signals and sort of balance each other out for
level flight. If one goes, the other is free to bank the plane without a
signal from the broken one to bring it back. Now his explaination wasn't
the best and this was many years ago.....but that was my experience. In
my situation, it would bank and never level out, I imagine I punched it
off about 30 degrees or so, but it would have kept going. On the ground
you can demonstrate the failure with the heading bug.

But I have a seneca with a king autopilot and the parts were under the
seats, computer in the tailcone.

In case it helps..

John

William Snow wrote:
I have a piper Arrow and out of the blue...(no pun intended)... the
Autopilot banked hard left (30 deg.) for no apparent reason. It was on Hdg
Mode and the bug was centered.

Each time it was shut off and re-engaged it continued to bank hard left.

I have a long trip to FL planned over the school break and sure would like
to have the Autopilot working.

Does anyone know why this would happen?

Thank You All.
Bill Snow



  #8  
Old February 13th 06, 04:22 PM posted to rec.aviation.owning
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Posts: n/a
Default AUTOPILOT AWRY

William,

The Autocontrol II is equivalent to my Altimatic II, the difference
being the altitude control in the later. I'm not sure how the Autocontrol
II B
differs from the orginal Autocontrol II, so some of this information may not
be correct.

The roll circuit is picks off bank information from the attitude
gyro via a RF pickup coil. This pickup is a small coil which
helps to determine the resonant frequency of an RF oscillator in
the roll amplifier. There is a "follow-up" capacitor on the roll
servo that indicates the position of the alierons. The turn trim or
roll knob on the console is another reactive component in this
circuit. With the wings level, attitude indicator level, and turn tirm
centered, all these reactive compoents are centered up and the circuit
is operating at it center frequency. If any one moves, the resonant
frequency of the roll circuit changes. There is a frequency discriminator
in the console amplifier that produces a DC output when the frequency
moves above or below the normal operating frequency. This DC output
is amplified and used to drive the roll servo motor left or right.

In heading mode, the radio coupler takes information from the resolver
(heading bug) in the DG and feeds that into the console amplifer as
a DC signal between the discriminator and the output amplifier stage.
When in NAV, OMNI, LOC, or REV LOC modes, the radio coupler
mixes in a left / right signal from a nav radio source. If the uncommanded
roll happens in heading mode, then none of the radio nav modes are going
to be any better. They will have the problem too.

Therefore, an uncommanded roll could be caused by:

1. Bad pick up in the attitude gyro.
2. Bad resolver in the DG
3. Bad radio coupler (yes, even in HEADING mode).
4. Bad console amplifier
5. Lack of feedback or "follow-up" signal from the roll servo
6. A loose connection between any of these components.

As others have suggested, check all the connectors by reseating
them a couple of times. If that does not work, you'll need to determine
which component has failed. Without a means to substitute a known
good unit or test signal for each of these, isolating which component has
failed bad may not be easy.

When I posted a query about my old autopoilot, the kinds folks on the
net had these recommendations for shops:

"Contact the folks at http://www.bevanrabell.com
Not sure about now, but they used to work on ALL the old stuff...

No longer works some of the older stuff, but may be able to point
you to a shop that does: Bob Ferguson, Autopilots Central at Sparks
Aviation, Tulsa, OK "


Good luck and let us know what you find out.

Ronnie

"William Snow" wrote in message
news
Ronnie
It is an Autocontrol II B with HSI. I only tested it in the Hdg mode sine
I had a passenger and did not want to alarm him. When the weather clears I
will give it a test in the other modes to try and isolate the
problems/mode.
Thanks for the tips.
Bill

"Ronnie" wrote in message
. com...
First, what is the make and model of the autopilot?
For my respsonse, I'll assume you have a Piper autopilot,
which is based on the Edo-Aire / Mitchelle designs.

In general, a hard bank to one side indicates that that
roll servo is being driven that direction by the amplifier. (Obvious,
uh?). The question is why.

In my Piper Altimatic II, the roll servo is a motor that is driven by
an H-Bridge type of amplifier. This input to the final motor
driver amplifier is a left / right signal which is derived from the
difference in the heading bug and indicated heading, and if in
NAV, OMNI, LOC or REV LOC mode also the left / right
signal from the nav output. Therefore, your trouble could be in
the console amplifier itself or the input(s) to the amplifier.

If the alierons are driven to their mechanical limits, I'd suspect
a bad transistor in the console amplifier output stage (H-Bridge).

If the alierons are driven to their maximum bank position but not
the their mechanical limits, (usually about 30 degrees of bank), then
I'd suspect a stage before the final amplifier.

Since this happens in heading mode, the problem could the the
resolver in the DG, or any of the electronics in the autopilot console
amplifier or the radio coupler.

Ronnie


"William Snow" wrote in message
...
I have a piper Arrow and out of the blue...(no pun intended)... the
Autopilot banked hard left (30 deg.) for no apparent reason. It was on
Hdg Mode and the bug was centered.

Each time it was shut off and re-engaged it continued to bank hard left.

I have a long trip to FL planned over the school break and sure would
like to have the Autopilot working.

Does anyone know why this would happen?

Thank You All.
Bill Snow







  #9  
Old February 13th 06, 08:51 PM posted to rec.aviation.owning
external usenet poster
 
Posts: n/a
Default AUTOPILOT AWRY

Thanks for the help!!

I am going to do some detective work and will report back.

Bill Snow


"William Snow" wrote in message
...
I have a piper Arrow and out of the blue...(no pun intended)... the
Autopilot banked hard left (30 deg.) for no apparent reason. It was on Hdg
Mode and the bug was centered.

Each time it was shut off and re-engaged it continued to bank hard left.

I have a long trip to FL planned over the school break and sure would like
to have the Autopilot working.

Does anyone know why this would happen?

Thank You All.
Bill Snow



  #10  
Old February 14th 06, 06:52 PM posted to rec.aviation.owning
external usenet poster
 
Posts: n/a
Default AUTOPILOT AWRY

Hmmm... I have to admit, that's quite a bit different than a standard
Autocontrol (aka Century) for a normal Piper system - and I would ask
if you are sure of your information? The standard "wing level"
indication from the AH is indeed off a pickup coil, but it's about 5
KHz, no RF. And there is no frequency shift - the inside of the
Century AH/AI just has two coils and a metal plate behind them (looks
like an iron butterfly). As the thing shifts from one side to the
other you get a shift in amplitude, either in phase or out of phase
(180 degrees) with respect to the ROLL EXCITATION signal. [Or the HDG
EXCITATION signal, if it goes through the nav coupler.] With the AH
centered in roll, the amplitutde is zero. There is no frequency shift
regardless. It would be great if there was some sensor back from the
ailerons, but there isn't - so it has no way of knowing their position.

Having said all the above, your "list of the usual suspects" is the
same one I would come up with. #3 is the one that surprises most
folks, but if you have a nav coupler then it uses HDG EXCITATION to
drive the ROLL coils, so lose of HDG signal affects just operating in
the WINGS LEVEL mode. You can move the ROLL cable that goes from the
computer to the NAV Coupler to go to the AI instead and restore use of
ROLL EXCITATION for a test.

 




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