Autopilot install.

[Jimmy B.]

Hey all, I'm getting quotes to put an autopilot in the bug smasher. Of
course S-Tec is the big dog in the field. I was looking at their units
that fill one of the 3" holes.

My bird has a plastic panel to cover the instrument cluster.

One shop recommended against 50/60 unit because they said that its
really not round and they would have to cut away the plastic panel to
fit it in. Because the panel is molded to bevel down to the instrument
face, they said that there would be a gap between the panel and the AP.
The shop said that some people consider it unsightly.

Now, I've seen aircraft with the overlay panels and S-TEC APs and don't
remember seeing a gap. (But I don't remember not seeing a gap either.)
I mentioned this to the manager and he said that some people wouldn't
notice it.

He is kind of hinting that the unit 30, which replaces the TC would be a
better option.

Does anyone remember seeing a aircraft with this style setup and
noticing a gap? Was it really unsightly?

Is there a source for a fresh cover panel that I could specify where the
AP is going to be and they could fabricate a nice cutout for it?

[Doug]

One thing I can tell you is there is a major advantage to having an all
electric autopilot. Now you can couple it to the VOR head and the GPS
(if you have one). But not the DG. If you couple it to the DG and the
vacuum fails then it goes into failure mode. Some people say that they
wouldn't have an autopilot without coupling to the DG, and it is nice.
But consider this. You are flying along in IMC. You loose your vacuum.
You still have your autopilot, fully functional. Works like it always
did. Most all of the all electric autopilots have an "uncouple" feature
where it just flies wings level (off of the TC). Sort of poor mans
couple to the DG, as you just turn the airplane to that heading. It
tracks the heading pretty well. So if you need to track a heading just
use it uncoupled in wing leveler mode.

If you must couple to the DG, go ahead. Just make sure it is all
electric otherwise. No coupling to the AI or using vacuum to power any
of the autopilot features. But really, you don't need DG coupling. It
makes failure modes MUCH more complicated.

Having an autopilot coupled to a GPS is the cat's pajamas. Right on
track and it's an accurate track from anywhere to anywhere. If you
don't have a GPS that it can couple to now, just make sure it can in
the future if you upgrade to a GPS. Usually it's an IFR GPS that it
couples to. I've never seen coupling to a VFR GPS, though I suppose
it's possible.

I think most of us would do just fine with a coupled autopilot and
altitude hold. Anything more in a small GA plane is overkill, IMO. The
times you need it is on long cruise. No problem flying climbouts and
approaches by hand. If you can couple to the VOR head, then you can let
the autopilot fly the ILS right to left and you manage the descent
rate. That is what I do. Works well, though I never use it in IMC as I
always need the practice.

Anyway that is my take. I have a Century I coupled to either my VOR
head or my IFR GPS. No altitude hold in my bird though I would like
that. The plane flies pretty well with just the trim, not a lot of
altitude adjustments necessary, at least in calm air. But altitude hold
would be nice, if I were putting one in now, I'd get it.

But even just a simple wing leveler setup works pretty good (no
coupling at all). There are lots of options. But if you fly in IMC
consider making everything electric. Vacuum failures are fairly common.
Electric failures, at least in fairly new airplanes are rare from what
I have seen.

[Guy Byars]

Hard to beat a round S-Tec 30 in a round plastic hole:

http://www.gfbyars.com/skylane/P5230032s.JPG

The STEC was an easy direct replacement for my old T/C. The old AutoPilot
was vaccume powered. It was a bummer when the vaccume pump failed .... I
lost everything..... glad I was in good VFR at the time.. Now with the
STEC, losing the vaccum would not effect it. I also have the standby backup
vaccum system from the intake manifold.

My A/P installation also has tracking coupled to the GPS. Very nice. Just
select your destination and.... ENGAGE....!!!!

More photos of the plane & pilot at:

http://www.gfbyars.com/skylane/

Guy Byars


"Jimmy B." > wrote in message
hlink.net...
> Hey all, I'm getting quotes to put an autopilot in the bug smasher. Of
> course S-Tec is the big dog in the field. I was looking at their units
> that fill one of the 3" holes.
>
> My bird has a plastic panel to cover the instrument cluster.
>
> One shop recommended against 50/60 unit because they said that its
> really not round and they would have to cut away the plastic panel to
> fit it in. Because the panel is molded to bevel down to the instrument
> face, they said that there would be a gap between the panel and the AP.
> The shop said that some people consider it unsightly.
>
> Now, I've seen aircraft with the overlay panels and S-TEC APs and don't
> remember seeing a gap. (But I don't remember not seeing a gap either.)
> I mentioned this to the manager and he said that some people wouldn't
> notice it.
>
> He is kind of hinting that the unit 30, which replaces the TC would be a
> better option.
>
> Does anyone remember seeing a aircraft with this style setup and
> noticing a gap? Was it really unsightly?
>
> Is there a source for a fresh cover panel that I could specify where the
> AP is going to be and they could fabricate a nice cutout for it?

[Jim Burns]

We've got a 60-2 in our Aztec. Says it takes a round hole, but it's really
a square with rounded corners. The plastic overlay panel that covers our
aluminum panel was trimmed a bit but it really isn't noticeable. I wouldn't
let appearance be a very large determining factor in which autopilot I'd
buy.
Jim

[Jon Kraus]

We are having a S-TEC30 installed in a couple of weeks in our '79 Mooney
201. We have a Garmin 430 so we went with the GPS Steer option that will
couple to the 430 and fly your flight plan. If you are anywhere close to
Georgia (we are in Indianapolis) then call Tim Matheson in in Lafayette
GA. This is all he does for a living and noone can come within several
thousand of his quotes. He can install a S-TEC30 in 3 days not the 2
weeks I was getting quoted for around here. This must be where all the
savings come from. All those hours at $60 or so an hour add up quick.
You can email me offline and I'll give you his # and what he quoted us.
I kid you not he is one of the best.

Jon Kraus
PP-ASEL-IA
'79 Mooney 201
4443H @ TYQ

Jimmy B. wrote:
> Hey all, I'm getting quotes to put an autopilot in the bug smasher. Of
> course S-Tec is the big dog in the field. I was looking at their units
> that fill one of the 3" holes.
>
> My bird has a plastic panel to cover the instrument cluster.
>
> One shop recommended against 50/60 unit because they said that its
> really not round and they would have to cut away the plastic panel to
> fit it in. Because the panel is molded to bevel down to the instrument
> face, they said that there would be a gap between the panel and the AP.
> The shop said that some people consider it unsightly.
>
> Now, I've seen aircraft with the overlay panels and S-TEC APs and don't
> remember seeing a gap. (But I don't remember not seeing a gap either.)
> I mentioned this to the manager and he said that some people wouldn't
> notice it.
>
> He is kind of hinting that the unit 30, which replaces the TC would be a
> better option.
>
> Does anyone remember seeing a aircraft with this style setup and
> noticing a gap? Was it really unsightly?
>
> Is there a source for a fresh cover panel that I could specify where the
> AP is going to be and they could fabricate a nice cutout for it?

[Jimmy B.]

Jim Burns wrote:
> We've got a 60-2 in our Aztec. Says it takes a round hole, but it's really
> a square with rounded corners. The plastic overlay panel that covers our
> aluminum panel was trimmed a bit but it really isn't noticeable. I wouldn't
> let appearance be a very large determining factor in which autopilot I'd
> buy.
> Jim
>
>
Thanks for the information , Jim. How do you like the 60-2 unit?

Any thing you don't like about it?

[[email protected]]

Matheson is simply the best. The paperwork is approved before
he even sees the airplane. Most of the wiring is done too.

Bill Hale A-36

[Jim Burns]

Hmmm.... so far we like it. AFTER discovering that two wires on the pitch
servo were reversed, causing a pitch down while reducing power/airspeed in
altitude hold mode rather than a pitch up. Talk about dangerous... scared
the crap out of us. Think about it... reduce throttles in altitude hold
mode on an approach to slow down.... as the aircraft slows, it starts
pitching down, building airspeed, so you reduce throttles... now you're not
at the altitude the autopilot wants to hold, so it increased the pitch trim
speed, increasing your decent... runaway down trim... very spooky. How the
previous owner never discovered this is beyond me. All it was doing was
turning the servo motor the opposite direction, swapped the wires and bingo,
fixed.

In cold weather our roll servo weaves back and forth, presumably due to
stiff oil? cables? pulleys? requiring the servo to draw more "correcting
voltage" and over compensating. In warm weather it doesn't do it.

We've got electric trim and the flight director options installed also.
Because we have a KLN94 gps, S-Tec's GPPS steering option is not available
to us, so that kind of sucks, but other than that, we're pretty happy with
it. One thing I don't like about it is the ability to manually enter the
approach mode, or precision mode. The newer S-Tecs are capable of this.
Ours will only go into approach mode when triggered by the GPS or a
localizer.
Jim

[Paul kgyy]

I went with the model 30 because panel holes are always scarce - maybe
I want an electric AI some day.

I also installed the GPS steering with my Garmin 430. I programmed a
flight plan a while back with a 160 degree turn, and it was just
awesome to see the system handle that with maybe only 40 ft of altitude
adjustment.

I also have the DG connection, but the GPS connection is just the best
thing ever.

The Model 30 also requires that you be within 10 degrees of the
localizer heading before you engage it. It's absolutely solid on track.

[Andrew Gideon]

Doug wrote:

> But really, you don't need DG coupling. It
> makes failure modes MUCH more complicated.
>
> Having an autopilot coupled to a GPS is the cat's pajamas.

At least around here, I spend a nontrivial amount of time on vectors.
That's much easier with an AP connected to the DG.

A vacuum failure that goes unnoticed while one is still on HDG mode would
mean either circles or a bad heading. Not a good thing, but still not the
same as had the AP been using the (now failed) AI.

Can an AP get heading information from the GPS? It can get track; is that
close enough?

At least at this moment, I cannot figure out how I'd tell the GPS to fly a
particular heading from the current position. Anyone know how to do that
in a Garmin 430?

- Andrew

[Tauno Voipio]

Andrew Gideon wrote:
> Doug wrote:
>
>
>> But really, you don't need DG coupling. It
>>makes failure modes MUCH more complicated.
>>
>>Having an autopilot coupled to a GPS is the cat's pajamas.
>
>
> At least around here, I spend a nontrivial amount of time on vectors.
> That's much easier with an AP connected to the DG.
>
> A vacuum failure that goes unnoticed while one is still on HDG mode would
> mean either circles or a bad heading. Not a good thing, but still not the
> same as had the AP been using the (now failed) AI.
>
> Can an AP get heading information from the GPS? It can get track; is that
> close enough?

The GPS heading information is taken as differences
of position fixes. It is prone to pretty bad errors,
and probably of too low quality for AP reference.

--

Tauno Voipio
tauno voipio (at) iki fi

[Dave S]

Tauno Voipio wrote:


> The GPS heading information is taken as differences
> of position fixes. It is prone to pretty bad errors,
> and probably of too low quality for AP reference.
>

I have flown AP equipped planes that take their steering from the CDI...
which in some cases is driven by a VOR/LOC and in some cases driven by a
GPS. Direct heading info, no.. deviation from desired course... yes.

Same succeptibility to GPS errors.. of course.

Dave

[Tauno Voipio]

Dave S wrote:
>
>
> Tauno Voipio wrote:
>
>
>> The GPS heading information is taken as differences
>> of position fixes. It is prone to pretty bad errors,
>> and probably of too low quality for AP reference.
>>
>
> I have flown AP equipped planes that take their steering from the CDI...
> which in some cases is driven by a VOR/LOC and in some cases driven by a
> GPS. Direct heading info, no.. deviation from desired course... yes.


The radial / GPS track following in an autopilot has
three control loops:

- innermost loop controls roll with ailerons and
taking reference from horizon gyro,

- next loop controls heading taking reference from
heading gyro,

- outermost loop tracks the navaid course difference.

The outermost loop sets the required heading for the
middle loop, and the middle loop sets the required
roll angle for the innermost loop.

The GPS heading is ill suited to the middle loop
due to the inherent noise enhancing property of
a differencing method. The noise may be attenuated
by filtering, but then the heading reference is
too slow for acceptable control loop stability
and speed.

--

Tauno Voipio
tauno voipio (at) iki fi

[Jon Kraus]

< snip >

- innermost loop controls roll with ailerons and
> taking reference from horizon gyro,

Wrong....

S-tec AP's do not take any info from the AI. They are rate based not
attitude based and get their roll info from the Turn Coordinator.

The GPS Steer function is a true wonder to behold. Both in simplicity
and accuracy. You know not of which you speak... No offense... :-)

Jon Kraus
'79 Mooney 201
4443H @ TYQ



Tauno Voipio wrote:

> Dave S wrote:
>
>>
>>
>> Tauno Voipio wrote:
>>
>>
>>> The GPS heading information is taken as differences
>>> of position fixes. It is prone to pretty bad errors,
>>> and probably of too low quality for AP reference.
>>>
>>
>> I have flown AP equipped planes that take their steering from the
>> CDI... which in some cases is driven by a VOR/LOC and in some cases
>> driven by a GPS. Direct heading info, no.. deviation from desired
>> course... yes.
>
>
>
> The radial / GPS track following in an autopilot has
> three control loops:
>
> - innermost loop controls roll with ailerons and
> taking reference from horizon gyro,
>
> - next loop controls heading taking reference from
> heading gyro,
>
> - outermost loop tracks the navaid course difference.
>
> The outermost loop sets the required heading for the
> middle loop, and the middle loop sets the required
> roll angle for the innermost loop.
>
> The GPS heading is ill suited to the middle loop
> due to the inherent noise enhancing property of
> a differencing method. The noise may be attenuated
> by filtering, but then the heading reference is
> too slow for acceptable control loop stability
> and speed.
>

[Doug]

My autopilot can be coupled to the GPS. It gets it's left and right
from the GPS's OBS (sort of a VOR head for a GPS). In calm air it is
PERFECT. The track lines are straight as they can be. Outflies any VOR,
NDB coupling or anything else. GPS is accurate to a few feet right and
left. In over 2000 hours of flying behind my GPS, it has never failed
on me for any length of time. (A very few lockups and lost signals due
to military jamming, but VERY FEW and never for more than 5 minutes).
GPS coupled autopilot is the way to go. Nothing else even comes close.
Couple your autopilot to the GPS if you can couple to anything. It's
phenmenal.

[Tauno Voipio]

Jon Kraus wrote:
> < snip >
>
> - innermost loop controls roll with ailerons and
> > taking reference from horizon gyro,
>
> Wrong....
>
> S-tec AP's do not take any info from the AI. They are rate based not
> attitude based and get their roll info from the Turn Coordinator.
>
> The GPS Steer function is a true wonder to behold. Both in simplicity
> and accuracy. You know not of which you speak... No offense... :-)
>

It still does not take the short-term heading reference from the GPS,
but it uses the turn coordinator as a replacement for the horizon
roll axis. As is well known, the TC data is part roll speed and part
heading rate, and it can be integrated to create a rudimentary
replacement for the roll reference.

The GPS steering then functions as a setpoint value for the
roll servo. The basic flight dynamics are still there.

The digital signal processing gives an advantage over
the older analog units in thyet it is possible to create
stable long-term (over a couple of seconds) integrators
with the digital way.

--

Tauno Voipio
tauno voipio (at) iki fi

[Andrew Gideon]

I don't understand GPSS. Why is this better than simply setting a GPS to
follow a CDI, and then setting that CDI to take GPS data?

- Andrew

[Tauno Voipio]

Andrew Gideon wrote:
> I don't understand GPSS. Why is this better than simply setting a GPS to
> follow a CDI, and then setting that CDI to take GPS data?

They belong to different layers:

- bottom layer is to keep wings level (or properly banked),
- middle level is to fly a heading,
- top level is to follow a track.

The track following uses heading flying as the tool.
The heading flying uses suitable banking as the tool.

The autopilot can directly control the ailerons
to get the proper bank. For setting a required
banka angle several aileron movements are needed.

The flying of a heading needs several bank angles
to get and keep the heading.

The flying of a track/radial needs several headings
to follow the track.

In control engineering terms, the order of a control
system to directly follow a track with aileron
control will be too high to be realizable.

The CDI difference is what requests heading
changes to follow the track, but to do it
properly, the lower layers (heading control
and roll control) are needed.

HTH

--

Tauno Voipio (MSEE, avionics specialist, CFII)
tauno voipio (at) iki fi

[Ron Natalie]

Jon Kraus wrote:
> < snip >
>
> - innermost loop controls roll with ailerons and
> > taking reference from horizon gyro,
>
> Wrong....
>
> S-tec AP's do not take any info from the AI. They are rate based not
> attitude based and get their roll info from the Turn Coordinator.
>
> The GPS Steer function is a true wonder to behold. Both in simplicity
> and accuracy. You know not of which you speak... No offense... :-)
>

Yep, watching the STEC track the GNS480 in the GPSS is a true wonder.

[Ron Natalie]

Doug wrote:
> My autopilot can be coupled to the GPS. It gets it's left and right
> from the GPS's OBS (sort of a VOR head for a GPS).

The GPS CDI you mean. The OBS is largely unused in the GPS.

In calm air it is
> PERFECT. The track lines are straight as they can be. Outflies any VOR,
> NDB coupling or anything else. GPS is accurate to a few feet right and
> left. In over 2000 hours of flying behind my GPS, it has never failed
> on me for any length of time. (A very few lockups and lost signals due
> to military jamming, but VERY FEW and never for more than 5 minutes).
> GPS coupled autopilot is the way to go. Nothing else even comes close.
> Couple your autopilot to the GPS if you can couple to anything. It's
> phenmenal.
>
The GPSS will track turns in the GPS track better than just following
the CDI deflection.