Accutrak nav source question.

[Browncbr1]

I saw the ilevil2 sw has nmea out. My Aera 510 does also. Does nmea work with Brittain accutrak as nav input source?

[Hank]

I dunno. My AccuTrack is hooked to my G430W.

[Browncbr1]

Yea, I knew the accutrak could couple to panel GPS, but I didn't recall if that is a nmea source or something else.

[N601RX]

The only coupling to the accutrac is through the analog mv signal that feeds the CDI. I'm not aware of a certified converter that will convert the nema output sentences to a voltage, but there is one for experimentals.

[N201MKTurbo]

The experimental one works real good....

[Vance Harral]

The only coupling to the accutrac is through the analog mv signal that feeds the CDI.

 

To elaborate a little, any CDI that can talk to a panel-mount GPS has nav error signal outputs (differential analog voltage).  And any autopilot with nav tracking - including various Brittain units - can receive those signals from the CDI.  So it's possible to "couple" your GPS to a Brittain indrectly.  You put the autopilot in nav mode, and the CDI in GPS mode.  This is the arrangement we have in our airplane with a B-5 and a GTN 650.  Works well for simple intercept and tracking of GPS courses, including approaches.  But it tends to have trouble with course changes.  The main issue with course changes is logic in the autopilot that treats greater than half deflection on the CDI as indicative of VOR station passage.  This triggers a delay in the unit where it stops trying to track course for a minute or so, and just holds wings level, on the expectation the CDI will swing back in on the other side of the VOR.  You can imagine this doesn't work well with dog-legs at waypoints.  And it definitely won't fly a hold for you, because you don't get CDI guidance in the turns of the hold.

 

Roll steering modules fix this by taking output from the GPS (maybe NMEA, I'm not sure), and converting it to heading signals to the autopilot.  i.e. the roll steering module appears like a heading bug to the autopilot, which changes the selected heading as needed to hold course.  My understanding is Brittain has installed GPS roll steering modules in airplanes with their autopilots, but I got that information second hand, not directly from them.  I don't think there is an STC for this.  My guess is they have a good relationship with the FSDO that serves Tulsa, and they get field approvals.  Again, though, that's all second-hand info.

[Browncbr1]

Thank you all for the great input.

Does anyone have a link to that adapter that converts nmea to analog signals? Brittain and others I've heard of have run accutrak from handheld GPS like area 500 series or 795...etc. I was also wondering about doing it with an ilevil2 sw and iPad because it has an nmea output also.

[N601RX]

Here is the link to the non certified one I mentioned earlier. If you don't already have a panel mount GPS the cheapest legal way to couple an autopilot to a GPS is to buy an older non precision GPS like the garmin 150, kln 89 or 90 and do a VFR only install which is relatively inexpensive and not nearly as involved as a IFR install. This will allow you to select an airport or waypoint from the database and hit the direct to button and the autopilot will fly you there.

http://www.porcine.com/gps/sc/sc_frameset.html

[Browncbr1]

Hi mike,

Thanks, yea, that's what I was looking for. Just basic vfr with Aera 510.

Cheers!