Re: Piper Altimatic II autopilots - some can be made to work!

Hi Jim,

I do have the service manual. It does not have any setup
information on cable tensions that I'm aware of.

Both the pitch and roll servo motors have a bevel gear which
engages with a bevel gear that is attached to its corresponding axis
of flight control. There are no cable attachment points in this autopilot.
It is hard coupled via gears into the flight controls. The manual override
of the autopilot is provided by a friction clucth mechanism within each
servo. There is a setup procedure for those. At a given amount of
force applied to the yoke in either pitch or roll, the corresponding clucth
must slip which allows the pilot to manually over-power the autopilot.

The pitch servo motor is slid back and forth to engage / dis-engage its
while the roll servo motor is pivoted in its mount to accomplish engagement.
The pitch servo has an over-center latch to hold it in position while the
servo depends only on the push of the cable to hold it engaged.

The control cables push / pull the servo motors much like a throttle
cable on a lawn mower. The cables are moved back and forth by a worm
gear mechanism in the control console when the pilot rotates the roll or
engagement controls. Within the first few degrees of rotation, micro
in the servos activate to control power to the amp (and to disengage manual
trim control) while the gears mesh during the last 10 to 20 degrees of

I can see the potential problem if the engagement cables were not positioned
correctly and/or the cable housings were not securely clampled to the
In that case, the gears would not mesh properly. In fact, that was the
issue with my roll servo. The mounting screws were loose which allowed the
gears to slip rather that stay engaged. The service manual simply
states to set the cables such that the gears fully mesh.

There is a set-up procedure for the trim sensor which consists of
propely centering the trim sensor on the elevator cables, but I don't
recall any cable tension adjustments. I'll have to look at that closer.


"Jim Burns" <jburns3nospam@xxxxxxxxxxxxxxxxxx> wrote in message
Congrats!!! Good for you Ronnie! It's nice to see some news about
actually working rather than another "my xxx is broken" :) If you've got
the service manual, you may want to check the cable tensions also, from
I've heard, if the tension is off just a little it can cause an INOP
condition that is also easily solved.


"Ronnie" <rhughes4-removeme@xxxxxxxxxx> wrote in message
I'll write more later, but I just had to report some sucess.

Long story short, the old Altimatic II is now working and it
works quite well. The wing lever / heading control / NAV &
LOC intercept and tracking all are working great. The pitch
control is working as is the altitude hold, but the altitude pre-select
calibration and its ability to command the airplane to climb or descent
at the correct airspeed to capture the selected altitude still needs some
adjustment. However, based on what I see so far, this should be a simple
matter of following the setup proceedure in the service manual
to make the necessary adjustments.

As it stands, I flew an ILS using only the autopilot controls for
intercepting and tracking the localizer and for controlling pitch
to stay on the glide slope. After living without an autopilot for
almost 6 years, it was a great feeling to see it work. The only real
issues were that the roll servo was loose in its mount allowing the drive
gears to slip and that the mechanical linkage between the pitch servo
the flight controls was loose. With those items tightened up, it came
to life.

Fooey on me for believing the previous owner when he told me
it was INOP and for not investigating it sooner.

Don't disount an old autopilot as being useless just because it is old
someone elese tells you it is not worth messing with as I did for 6
With just a little bit of effort, this one came back to life. Time will
tell how
it holds up, but since it was built in 1964 and is still working, I'm
it will work for a few more years.


"nobody" <rhughes4-removeme@xxxxxxxxxx> wrote in message

I have a Piper Altimatic II autopilot in my '64 C model Aztec which has
been in-op since I bought the airplane. I bought a service manual for
this autopilot with the idea of learning how it was supposed to work,
with the hope of , maybe, just maybe, getting it to work and having it
returned to service. Yes, I know the unit is obsolete. Yes, I know
unit is worthless. Yes, I know that most autopilot shops say the units
are not worth messing with. And yes,

I'm not inclined to spend / waste much money on it.

But, as an engineer and tinker, I am inclined to spend a little time
investigating. If it was good enough to be certified in the airplane,
design once worked and it should still be able to do the job it was
designed for. I'm also inspired by a friend of mine who inherited his
grandfather's 1947 Bonanza. He has been able to get the pneumatic
autopilot (yes, I do mean air controls) in that airplane working and it
works quite well. If his pneumatic analog computer can be made to
surely my germanium transistor analog computer can also be made to

Therefore, I'd be very interesting in getting any information such as:

- A schematic of the console amplifier. The service manual does not
include one.

- Any theory of operation document for the console amplifier and/or the
radio coupler. The service manual has a good overall theory of
for the autopilot system, but does not go into the details for any of
electronic components.

- Any old test equipment / test boxes that were designed to service and
adjust this AP.

The service manual lists some test boxes made by Mitchell.

- Any pieces and parts of any Altimatic II, (or Autocontrol II) such as
the RF gyros, console amplifier, control head, radio coupler, altitude
bellows, and servos (roll, pitch, trim) that you'd like to part with.
you have any pieces and parts that might be useful for spare parts, I'd
like to talk to you.

- Leads to anyone who has experience working on these units, including
component level repair of the electronics. I'd love to find an
experienced technician / engineer that knows these units inside and out
and who would love to see one brought back to life.

- Any "been there, done that", "been there, tried that", type of
positive or negative, from the group.

Again, I know this is a long shot, but I'm willing to invest some time
energy to see what can be done. As a bare minimum, I'll learn a




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