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