NMEA output to autopilot

[plaviator]

I am considering fitting a Trutrak autopilot to my aircraft. This AP requires an NMEA input from my GPS to be able to fly a flightplan.
As I am using Skydemon with a tablet, there is no direct RS232 data output.
However, the Pilotaware unit has access to this information by wireless connection which is used for an ADSB output from my transponder.
So is it possible for an NMEA output from the Raspberry with the relevant GPS data for my autopilot?
Looking through the AP installation setup manual, the data required is as follows:
GPS RS232 -- Primary serial input
GPS ARINC -- A 429
GPS ARINC -- B 429
Baud Rate -- 4800
Refresh at least 1/sec

I would welcome any information

[Admin]

Hi,

PilotAware can indeed supply GPS messages over an RS232 wired interface.
As you point out, this is how we send data to the transponders.

You also mention ARINC, are these optional ?

You will need to check which NMEA messages you require

Thx
Lee

[plaviator]

Thank you for your reply Lee.

The Trutrak Vizion 385 calls for these inputs for flightplan steering control. Is it possible to access this data?

Primary Serial Input. Baud rate selectable 1200, 2400, 4800 or 9600 baud. Automatically decodes NMEA-0183, Garmin Aviation Format, or Apollo/UPSAT MovingMap or GPSS format. Provides directional reference to the autopilot.

ARINC-A   Digital differential signals from Garmin, Sierra, or other panel-mount receiver which provide directional steering
ARINC-B   commands (GPSS, GPSV) to autopilot
       
Regards, Michael

[Ian Melville]

 
Sorry but I have to question the wisdom of guiding an aircraft autopilot with a 20 quid computer with various low cost additions?

[Paul_Sengupta]

A £6 Chinese GPS and a £2 Chinese serial converter, all powered by a £1.30 Chinese lighter adaptor?

What could possibly go wrong?! 

It should work most of the time. If in VMC I wouldn't worry too much about it.

[plaviator]

By your comments, you make the PilotAware sound like a Micky Mouse system. I am sure that Lee and his team do not regard it in this way.
A lot of hard work has gone into the development of this inexpensive system to the benefit of our safety and I think that, as members, to ridicule it is disloyal to the team.

[Ian Melville]

I don't regard it as a Micky Mouse system, but lets not make it into something it isn't.

[SteveHutt]

Hi Michael,

I have Advanced Flight Systems (AFS) kit in the plane I am building, which includes an AFS autopilot, which is a Trutrak AP with slightly customised software to allow control from the AFS EFIS. Basically a GPS feeds data to the EFIS and the EFIS feeds data onward to the AP via an intermediate ARINC module.

The above allows the AP to run in its most advanced modes. There are lower capability modes that the AP can run in where the ARINC input is not used and instead it takes input direct from an NMEA capable GPS and in these modes it just needs a couple of NMEA sentences (as you have mentioned previously).

I suspect your TT AP is relatively close functionality-wise to mine. So, if you only wish to use the lower level modes then those NMEA sentences are probably all you need. A key requirement though is that the update rate is atleast once per second for best flight accuracy.

I have built my system to to allow the AP to run on ARINC data from the EFIS but to be switchable to a direct GPS NMEA feed (utilising a different GPS) for redundancy.

Steve

[Paul_Sengupta]

This is only for outputting GPS NMEA data for the autopilot, so there isn't much to go wrong once it's working, though care should be taken to secure everything so the cables don't come apart and everything's fed with a reliable power supply.

Another way of getting NMEA would be to buy an old air/marine/trekking GPS off e-bay and tie that in somewhere. These will have batteries in so will be backed up in case of power failure, at least for as long as the batteries last.

[plaviator]

Hello Steve, that is very interesting. I built my Bristell NG5 last year here in Poland and as it is registered in the Czech Republic or Czechia as I believe it is now to be called, I am able to register it as an Ultralight. This being said, it is basically the same as the UK LSA version.
Anyway, at 72 I am not a fan of digital instruments but I did fit the Avmap Ultra as the electric AH was too heavy. The ultra has a dedicated GPS input but although the instrument is wired for NMEA output, as yet they are still working on the software for this facility which they hope to have available as a software update within 2 months.
What I don't know is whether this data output will include ARINC data which I understand is required for the AP to fly a flight plan
The Trutrak Vizion comes in two versions, the 380 which is capable of flying a track from the RS232 data input and the 385 which has the capability to follow a flightplan, given the GPS ARINC data.
I asked this question as I was aware that the Pilotaware system extracted the position data for ADSB output to my transponder and am interested to know if the data for the AP was accessible too. 

[SteveHutt]

Hi Michael,

Sounds like you have not yet decided which version of the TT Vizion to buy. Is that correct?
You can upgrade the 380 to a 385 later, if desired.

If you want the AP to be able to fly a pre-planned route, e.g. to automatically execute turns, etc, then there needs to be an element in the system that tells the AP where you want to fly as well as where you are.

On its own, Pilotaware can only provide data on where you are. It has no knowledge of your planned route.

You probably know this already, but without route following capability, the AP will ordinarily, when activated, maintain the current heading and allow you to set a new heading via the AP controls. And if it is a 2-axis AP then you can also hold altitude. Some, including the 385, allow setting of climb/decent rates and even target stop altitudes.

My AP is 2-axis and is capable of automatically executing climbs and decents if you input these into the route plan AND you run the AP in the correct mode.

Regarding the NMEA sentences that Pilotaware outputs, I forget which ones they are but you ought to be able to find confirmation somewhere in this forum or in the Pilotaware documentation.

If you buy the TT Vizion 385 you ought to be able to replicate my redundant input wiring if you have access to both NMEA data and ARINC data.

By the way, if you've not had dealings with them, my experience of support from TT is excellent. Lucas has always been very helpful to me.

Regards,
Steve

[plaviator]

Thank you again for your reply Steve and yes you are correct in assuming that I have not yet decided on the version. Is the upgrade from the 380 to the 385 just a software update?
Thinking about what you have said, I now realize that the Ultra EFIS would not have the flightplan info so would only have current position and track data. At present Skydemon does not have a means of GPS data output at all which is frustrating so for the time being at least, I could use the basic position data from pilotaware until such time as the new Avmap software is available. As for following a flight plan route, I will have to find another way do obtain the data of change my GPS.
I drove down to Friedrichshafen last week and visited the Trutrak stand. I have to say that I was not that impressed with the CEO who tried to persuade me to buy the ECO AP which is still really at the Beta stage. I have to say that it was interesting but would I want to cut holes in my shiny new aircraft, I think not especially with no guarantee of a successful outcome. I think that Lucas Massengale was there too but he didn't say much to me.

Regards, Michael

[SteveHutt]

According to this post on the TT customer forum, you have to return the 380 for upgrade to a 385.
http://trutrakap.com/forum/forum/autopilots-and-instruments/vizion-series/760-vizion-380-or-385-for-my-ctsw

Interestingly, both the TT website and Aircraftspruce are only listing a single price. Did you check with TT that they still do the 380 version?

I agree with you. There are thousands of the Vizion APs and predecessors in use in the field. It will cost more than an Eco but it is proven technology that is relatively straightforward to install.

I know someone that has a TT Vizion installed in an RV-9 and last time I talked to him he was happy with it.

And, if you have space for a 3 ^1/8th inch unit, there is the option of the TT Gemini AP. Does the same as the Vizion with the addition of a builtin digital attitude/ASI/Altitude display but for a bit more money.

Regards,
Steve

[plaviator]

Good morning Steve,
Thank you again for your opinions and observations.
Yes I did consider the Gemini as a direct replacement for my Avmap Ultra but if I take that route then I lose the only direct NMEA data source (When they get the software sorted out) Now if the Gemini had a dedicated GPS antenna and data converter built into it, there would be no contest.
So at the moment it looks like it will be the Vizion. It is just a case of where I can fit it in the panel. Perhaps I can move the MGL fuel computer and fit it in place?
Decisions,decisions!

Kind regards, Michael

[Robski]

Another way of getting NMEA would be to buy an old air/marine/trekking GPS off e-bay and tie that in somewhere. These will have batteries in so will be backed up in case of power failure, at least for as long as the batteries last.

My Dynon EMS requires a GPS input to allow calculation of fuel economy, getting the date & time, and calculating power levels (needs altitude). I use a very old Garmin GPS III Pilot as that can output NMEA sentences, if you set it up to do so!

A friend has just bought one on ebay for £60 to do pretty much the same thing!