Autocontrol IIIB

Both my old cherokee 180 and my current 1978 Turbo Arrow do the same as yours is
doing. I have to put the heading bug a couple of drgrees to the left of my
heading. I think thats just the way the heading bug is, when I turn the AP to NAV
or LOC, it reads my HSI and is right on the money.

Jeff

PaulaJay1 wrote:

In article , Jeff writes:

Are you in GPS or NAV mode?
GPS - the CDI would be reading the GPS course
NAV - it would be reading what you had your OBS set to and your NAV receiver
set to
the freq of the navaid
what GPS/ NAV do you have, the garmin 430 and the NAV that you can get with
it?

I know that when I am having my auto pilot track a VOR it may be off by a dot
sometimes, this is basically because the VOR is not that sensitive when your
a ways
from it. But when I shoot a localizer, the AP tracks it perfect. Have you
tried
tracking a localizer with your AP ?

When I am flying a GPS course (with the garmin 430) straight and narrow, the
CDI is constantly about one dot to the left. Same for an ILS, though the
Garmin goes into approach mode and the full scale CDI is 0.2 nm. Thus the
"error" is only a couple hundred feet. I generally fly the last part of the
approach so, no problem at all.

I've decided to take the advice of several and leave it alone and say that it
is the nature of the beast. Thanks to all for the comments.

Chuck

(Michael) wrote in
om:

(PaulaJay1) wrote
If you have a burning desire to fix this, there is an adjustment on
your nav converter (the box that has the multiposition switch with
labels like Omni, Loc, Loc Rev, Hdg, and Nav). Personally, I wouldn't
mess with it.

There's left and right intercept (R13 and R20), plus radio gain. I don't
think any of those would affect the situation he is seeing (since it is
consistent, not wandering around within a window). There are two more that
are only internally adjustable, mostly setting the hysterisis. But since
he doesn't have an alignment rig...

-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------

"Michael" wrote in message
om...
If you have a burning desire to fix this, there is an adjustment on
your nav converter (the box that has the multiposition switch with
labels like Omni, Loc, Loc Rev, Hdg, and Nav). Personally, I wouldn't
mess with it.

If this a/p is anything like the one I had in my prior PA-28, and my current
PA-24 before I installed the Stec system, the adjustments I remember are
behind the faceplate on the a/p head, not at the coupler.

There are two variants of this system, and there will be either 3 or 4
adjustment screws behind that faceplate, depending on whether it has the
push-button switches or the rocker type switches.

As I recall (and my recall is a little fuzzy), two of them are left and
right roll limit adjustments, one sets heading center, and I think the
fourth was for sensitivity of some kind. It's been a long time.

I used to be anal about getting them set right, and I kept a set of
jeweler's screwdrivers in the glove box to use in flight whenever I got
bored.

"CriticalMass" wrote in
:


"Michael" wrote in message
om...
If this a/p is anything like the one I had in my prior PA-28, and my
current PA-24 before I installed the Stec system, the adjustments I
remember are behind the faceplate on the a/p head, not at the coupler.

Both have adjustments. The NAV Coupler basically sits in series with
the DG (HDG) and, if in anything but HDG mode, combines the DG error
with the CDI error (from VOR or LOC receiver, or from GPS) into a single
signal that the AP "computer" sees as a DG heading bug offset.

As I recall (and my recall is a little fuzzy), two of them are left
and right roll limit adjustments, one sets heading center, and I think
the fourth was for sensitivity of some kind. It's been a long time.

Actually, you remember pretty accurately, long time or not. That last
one is the hysterisis adjustment. It sets the "dead band" on the servo
motor (yes, in effect, making the unit more sensitive to error sooner).
Set it too low and the aircraft will wander either side of the course
line. Set it too high and you will get wing rock. In theory, there is
a correct setting in between the two. G

The "B" units have this fourth trimpot. The earlier units just used a
couple of diodes... no adjustment.

-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------