slaved ap to gps

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stapler101

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stapler101
I my search for another plane I see a lot of planes with auto pilot and gps, but the ap is not slaved to the gps.
what would be involved in having this done?
I know there will be alot of variables but just some ball park info and price guesses would be helpful.
 
Way too many variables.

I have an STEC 60-2 interfaced to my Garmin 430 in two ways: the GPSS roll steering converter and the regular analog NAV interface. They operate differently - the ILS/VOR nav function won't drive the roll steering, but works fine with the analog NAV interface. But when my second GPS (Trimble) was the only GPS on board, it was wired to use the analog NAV interface.
 
Slaved? hmm my autopilot is hooked up the GPS and will fly a straight line but I do not have GPS steering. To add GPSS would mean a major upgrade to my autopilot and I frankly do not see the cost benefit at this time.
 
There's at least a couple of ways to do this. The easiest, and usually the cheapest, is to slave the AP on the CDI(or HSI) that the GPS is connected. As most have a switch to drive the CDI from the GPS or NAV receiver, this has the added benefit of driving the AP off the VOR or LOC also. However, this is an analog connection. The AP will only react when the needle swings on the CDI.

Another way is GPSS which is a digital connection between the GPS and the autopilot. The advantage to this connection is predictive steering where the groundspeed is taken into consideration and the turn is started such that you roll out pretty close, if not on, the desired course.

My aircraft has both connections, which is quite nice for VOR, LOC, or GPS approaches.
 
smigaldi said:
Slaved? hmm my autopilot is hooked up the GPS and will fly a straight line but I do not have GPS steering. To add GPSS would mean a major upgrade to my autopilot and I frankly do not see the cost benefit at this time.
Click to expand...

What autopilot and GPS do you have? Any GPS with Arinc 429 output can drive a GPSS converter and most GPSS converters will interface with any autopilot that has a Heading mode that follows a bug on a DG.
 
Not to hijack the thread, but -- what would REALLY be nice would be to slave my A/P to my 496. Right now it's slaved to a heading bug on my DG (which, of course, precesses), and it would sure be nice to have it connected to the Garmin.

Is there any way to do this?
 
gismo said:
What autopilot and GPS do you have? Any GPS with Arinc 429 output can drive a GPSS converter and most GPSS converters will interface with any autopilot that has a Heading mode that follows a bug on a DG.
Click to expand...
Piper Autocontrol IIIB. It gets it's signal from a voltage generated by the CDI and the heading bug to keep things on target. No GPS sterring possible according to the avionic technician.
 
Jay Honeck said:
Not to hijack the thread, but -- what would REALLY be nice would be to slave my A/P to my 496. Right now it's slaved to a heading bug on my DG (which, of course, precesses), and it would sure be nice to have it connected to the Garmin.

Is there any way to do this?
Click to expand...

Legally it's only possible if your aircraft is an experimental. Technically it's simple.
 
gismo said:
Legally it's only possible if your aircraft is an experimental. Technically it's simple.
Click to expand...

I'm aware of this bizarre rule, and can only ask: Why? Why is it okay to slave my autopilot to a 1930s directional gyro, but NOT to my 496?
 
Jay Honeck said:
I'm aware of this bizarre rule, and can only ask: Why? Why is it okay to slave my autopilot to a 1930s directional gyro, but NOT to my 496?
Click to expand...

That 1930's DG went through a rigorous certification process (in theory ;-), as did the autopilot and the interface between the two.

The 496, and associated software, did not go through that certification, nor can it under the current rules (as far as I know). Additionally, the interface between the autopilot and 496 would also need to go through the certification.

Certification is not cheap, so unless there's a pretty large market for it, manufacture's aren't interested in spending that kind of money because it may never be recouped.

Trust me, I feel the pain with my Mooney. Just a simple interior refurbishment on a certified aircraft is a pain.

These reasons are the biggest reason I'd like to get into an experimental, I've got my eye on a Sportsman 2+2 ;-)
 
Jay Honeck said:
I'm aware of this bizarre rule, and can only ask: Why? Why is it okay to slave my autopilot to a 1930s directional gyro, but NOT to my 496?
Click to expand...

I can't answer the "why" question from a purely logical perspective because as you apparently also believe, there's no real technical and/or safety issue with that arrangement. But for fairly obvious reasons the certification rules for autopilots are pretty comprehensive and strict and they were written long before anyone contemplated a portable navigator like the 496. More specifically, the rules dictate that what can be connected to any particular autopilot must be listed in the STC (all autopilots not part of the aircraft type cert must have a valid STC for certified aircraft) along with the necessary diagrams and instructions for the connection and and AFaIK any such connected devices must be STC'd themselves. Given that there are no STC'd handheld GPSs available, let alone an STC to connect one to an autopilot we're stuck without any way to make such a setup legal.

On a side note, some of the roll steering converters (GPSSs) on the market aren't STC'd for connection to an autopilot, instead they are STC'd as a modification to the heading source as this apparently has fewer hoops to jump through. It does seem at least remotely possible that a similar dodge could be used to certify a roll steering converter (which would have to be permanently installed) that could legally take it's steering commands from any source including a jack connected handheld GPS, but I'm certain there would be serious resistance at the FAA.
 
ghayes said:
That 1930's DG went through a rigorous certification process (in theory ;-), as did the autopilot and the interface between the two.

The 496, and associated software, did not go through that certification, nor can it under the current rules (as far as I know). Additionally, the interface between the autopilot and 496 would also need to go through the certification.

Certification is not cheap, so unless there's a pretty large market for it, manufacture's aren't interested in spending that kind of money because it may never be recouped.

Trust me, I feel the pain with my Mooney. Just a simple interior refurbishment on a certified aircraft is a pain.

These reasons are the biggest reason I'd like to get into an experimental, I've got my eye on a Sportsman 2+2 ;-)
Click to expand...

I believe that it should be quite feasible to design an interface that could be proven to be safe no matter what erroneous inputs were received from a handheld GPS. Whether or not someone could convince the FAA of this is a different matter though.
 
gismo said:
I believe that it should be quite feasible to design an interface that could be proven to be safe no matter what erroneous inputs were received from a handheld GPS. Whether or not someone could convince the FAA of this is a different matter though.
Click to expand...

I'd agree it's feasible to design it, but as you alluded, testing it for the FAA is the expensive part ... and all the paper work. Working for Lycoming for 10 years in the Configuration Management department, I've seen the crazy certification process for hardware and software. And it's more than just showing it's "safe", you need to provide realiability values on materials, connections, cable routings, etc. etc. You need everything documented, and documented again just for good measure. You don't even want to get me started on DO178 software cetification. ugh
 
smigaldi said:
Piper Autocontrol IIIB. It gets it's signal from a voltage generated by the CDI and the heading bug to keep things on target. No GPS sterring possible according to the avionic technician.
Click to expand...

Your avionics technician is wrong. The Icarus Sam I GPSS will do the job.
 
The Birttan autopilot in my Mooney is slaved to the CDI's only. I have a switch on CDI #2 to slave it to either the NAV/COM or the GPS.

So as far as the autopilot is concerned, it's just stearing to the CDI. But as mentioned in the thread, if the autopilot isn't slaved directly to the GPS, no pre-emptive stearing is possible. But it will still stear to the CDI.
 
I've flown airplanes with fully coupled A/P approaches and have since come to the conclusion that an A/P that can track a heading is less work, and therefore more helpful than a fully coupled approach feature.

After all -- all you have to do is move the heading bug to the desired heading, and adjust to maintain desired course, with adjustments to power to determine descent.

If the A/P fails on the approach, you manually fly heading -- that's it. Power and attitude is already set.

:dunno:

I dunno -- maybe I'm missing something?
 
smigaldi said:
So the Sam I is doing the GPSS? That would mean the tech was correct, I need to upgrade to get GPSS, it cannot be done with just the AP I have and the 430W.
Click to expand...

Since your AutoControl III can follow your CDI it should also be able to track a GPS course simply by selecting GPS (vs VOR) on the 430. This is assuming that your 430 drives the CDI associated with the autopilot although if that's not the case it shouldn't be all that difficult to fix it this way. The SAM roll steering converter replaces the analog connection between the 430 and the autopilot with a digital one, providing the ability to track course changes (waypoints) without having to adjust the CDI or DG and it also can fly some curved tracks like holding patterns and procedure turns. The only "upgrade" you'd need for that would be the SAM itself.
 
gismo said:
Since your AutoControl III can follow your CDI it should also be able to track a GPS course simply by selecting GPS (vs VOR) on the 430. This is assuming that your 430 drives the CDI associated with the autopilot although if that's not the case it shouldn't be all that difficult to fix it this way.
Click to expand...
it already does that. But that is not GPSS. That is tracking a course. What I am refering to is that when you hit a waypoint the AP will go ahead and anticpate the turn based on the data output form the GPS and turn the aircraft to the new heading and track that course.

gismo said:
The SAM roll steering converter replaces the analog connection between the 430 and the autopilot with a digital one, providing the ability to track course changes (waypoints) without having to adjust the CDI or DG and it also can fly some curved tracks like holding patterns and procedure turns. The only "upgrade" you'd need for that would be the SAM itself.
Click to expand...
Right, that is GPSS. Something my AP is not capable of. The interface that you dscribe is doing the GPSS and then just updating the analog signal to the AP to have it track the course that it would have normally gotten from the heading bug and voltage out of the CDI.
 
smigaldi said:
Right, that is GPSS. Something my AP is not capable of.
Click to expand...
Very few autopilots have roll steering (GPSS) built in (S-Tec's 55X is one). For almost anything else an external converter is required.
The interface that you describe is doing the GPSS and then just updating the analog signal to the AP to have it track the course that it would have normally gotten from the heading bug and voltage out of the CDI.
Click to expand...
That's approximately correct, but I think you've got the right idea. Most roll steering converters take a serial digital bank angle command and translate it into an analog signal that is substituted for the output from the DG's heading bug. The CDI signal is not involved in this case.
 
gismo said:
Most roll steering converters take a serial digital bank angle command and translate it into an analog signal that is substituted for the output from the DG's heading bug. The CDI signal is not involved in this case.
Click to expand...
Actually I think we said the same thing. The GPSS generates a signal to the AP. Without the GPSS converter that signal to the AP would have come from the CDI and DG heading bug.
 
smigaldi said:
Actually I think we said the same thing. The GPSS generates a signal to the AP. Without the GPSS converter that signal to the AP would have come from the CDI and DG heading bug.
Click to expand...

Yeah, I'm picking engineering nits.
 
smigaldi said:
So the Sam I is doing the GPSS? That would mean the tech was correct, I need to upgrade to get GPSS, it cannot be done with just the AP I have and the 430W.
Click to expand...

You said your avionics tech said no steering possible, it is possible, but you need to add a converter. You didn't say that the avionics tech was claiming the autopilot did not have a built in GPSS, which would be true.

Until the Sam I, there were 3 GPSS converters, none of which were certified with your autopilot. Since the Sam I is certified as a heading device, it is not restricted by autopilot type. While it is true that your autopilot does not have the GPSS function built in, neither do the vast majority of autopilots installed in our certified aircraft. The very few exceptions where the autopilot has built in roll steering include the Stec 55X and the Bendix King KAP 140 / KFC 225. All the other popular autopilots do not have built in GPSS function. Also, not all autopilots will work with a GPSS adapter, particularly the wing levelers and most of the Brittain autopilots, although the latest Brittain autopilots that support a DG or HSI with a heading bug will.
 
John Collins said:
The very few exceptions where the autopilot has built in roll steering include the Stec 55X and the Bendix King KAP 140
Click to expand...
Just got done with a 10-day IR course involving a KAP 140 in a 2000 C-172S -- no roll steering. Perhaps it's optional.
 
Ron Levy said:
Just got done with a 10-day IR course involving a KAP 140 in a 2000 C-172S -- no roll steering. Perhaps it's optional.
Click to expand...

Ron,

My understanding it is integrated into the autopilot, but that doesn't mean it is hooked up. It may also depend on the software level of the G1000 system.

The KFC225 is somewhat unique in that if it has the roll steering hooked up, it will only track using roll steering when the HSI has GPS as the source. This presented problems when the 430W/530W were certificated, as one could not fly a GPS approach with vertical guidance because the KFC225 required that the CDI be set to the LOC as the source in order to look for, capture, and track a glideslope and switching from roll steering to LOC mode causes the autopilot to disengage all navigation tracking and drop into wings level roll mode. The work around was to fake the autopilot out when flying an LPV etc and send a signal to the KFC225 during final approach that made the autopilot think the CDI source was LOC but in fact was GPS. To trigger the operation, the pilot would get a message as soon as the aircraft was on the leg approaching the FAF to press PROC to enable autopilot outputs, the pilot was expected to press PROC and enter and only then was to press the APR button on the autopilot. The KAP 140 has this same mode of operation and although I have never flown with one using a G1000 WAAS system, I expect it has a similar method to engage the autopilot.

The GNS480 never had equivalent provisions, so with the combination of a KFC225 and a GNS480, the roll steering is not hooked up.
 
Jay Honeck said:
Not to hijack the thread, but -- what would REALLY be nice would be to slave my A/P to my 496. Right now it's slaved to a heading bug on my DG (which, of course, precesses), and it would sure be nice to have it connected to the Garmin.

Is there any way to do this?
Click to expand...

In an experimental? Sure!

In your airplane? no.
 
Ron Levy said:
Just got done with a 10-day IR course involving a KAP 140 in a 2000 C-172S -- no roll steering. Perhaps it's optional.
Click to expand...
What was the GPS - KLN94? or was it an early G1000?

Roll steering was not a feature (nor was WAAS) in the very early G1000s.
 
John Collins said:
My understanding it is integrated into the autopilot, but that doesn't mean it is hooked up. It may also depend on the software level of the G1000 system.
Click to expand...
No G1000 -- this was a 2000 C-172S with the steam gauges and full King stack, including KLN-94 GPS.
 
John Collins said:
OK, that makes sense, the KLN-94 doesn't output Arinc 429 roll steering.
Click to expand...
Not sure what format it has, but the KLN94, as well as the KLN89B do put out a roll steering signal that can be used by the KAP-140. It does not have full GPSS that would allow you to be able to follow a procedure turn or hold for instance.
 
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smigaldi said:
Not sure what format it has, but the KLN94, as well as the KLN89B do put out a roll steering signal that can be used by the KAP-140. It does not have full GPSS that would allow you to be able to follow a procedure turn or hold for instance.
Click to expand...
It's not GPSS that enables the GPS to steer the plane through the PT/HP, it's the software in the GPS. GPSS is the roll steering adapter which allows autopilots which don't read direct roll steering commands to be driven by GPS roll steering outputs. Once you have a GPSS roll steering adapter, the autopilot will follow whatever commands the GPS sends. In the case of the KLN-94 and non-WAAS Garmin 400/500-series GPS's, that does not include steering through HP's and PT's. The S-Tec 55X has GPSS built in; the question here is whether the King KAP-140 does or does not. The one I flew with for the last 10 days does not, and would require a roll steering adapter to properly follow GPS roll steering commands.
 
I'll say it a different way then. The KLN94 and KLN89B do not output commands for procedures turns and holds, they do out put a roll steering command line that can be used by the KAP-140 to roll steer the plane onto a new course when a waypoint is reached.
 
smigaldi said:
I'll say it a different way then. The KLN94 and KLN89B do not output commands for procedures turns and holds, they do out put a roll steering command line that can be used by the KAP-140 to roll steer the plane onto a new course when a waypoint is reached.
Click to expand...
I agree. However, the KAP 140 in the plane we were flying did not have GPSS incorporated, and a roll steering adapter would be required to use those commands.
 
I fly with a KLN 94 GPS and a KAP 140 Auto Pilot W/Alt. Hold. Its a 2001 T182T can anyone tell me is if it's possible to have the auto pilot follow the GPS course on it's own without adjusting the HSI or heading bug when a direction change is needed
 
Ron Levy said:
Just got done with a 10-day IR course involving a KAP 140 in a 2000 C-172S -- no roll steering. Perhaps it's optional.
Click to expand...
KAP140 does support it, but some GPS (89B, early KLN94s) do not.

And it may be that early KAP140s don't either.
 
N182BF said:
I fly with a KLN 94 GPS and a KAP 140 Auto Pilot W/Alt. Hold. Its a 2001 T182T can anyone tell me is if it's possible to have the auto pilot follow the GPS course on it's own without adjusting the HSI or heading bug when a direction change is needed
Click to expand...
You'd need a roll steering adapter. Ask your avionics shop about what is compatible. cost will probably be in the $2-3k area installed.
 
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