Autopilot not following GPS Flightplan.

[K-man]

I think I might already have the answer but I would like to throw this one past the experts.

Firstly, I have recently installed the dual servos with the AP74 and an AVMap GPS. My chest has swollen to breaking point in that I flew for an hour today without having to touch the stick and there were very robust winds.

However, I had an activated flight plan in the GPS which registered the course change at each way point. The problem is, I had a heading bug set that didn't disappear when I engaged Trk. It would seem that I need to manually go into the EFIS and disengage the bug. I'm wondering, if the bug turns on automatically when you touch the control knob, is there any way you can turn it off as easily?

For what it's worth, I just changed the heading to the GPS bearing at each waypoint and it worked perfectly, but that really negates the reason for having a GPS flight plan.

What is my next step?

 

[dynonsupport]

TRK mode is to follow the GPS ground track of whatever your HDG bug is set to.

NAV mode will have the AP fly your flight plan.

I think I might already have the answer but I would like to throw this one past the experts.

Firstly, I have recently installed the dual servos with the AP74 and an AVMap GPS. My chest has swollen to breaking point in that I flew for an hour today without having to touch the stick and there were very robust winds.

However, I had an activated flight plan in the GPS which registered the course change at each way point. The problem is, I had a heading bug set that didn't disappear when I engaged Trk. It would seem that I need to manually go into the EFIS and disengage the bug. I'm wondering, if the bug turns on automatically when you touch the control knob, is there any way you can turn it off as easily?

For what it's worth, I just changed the heading to the GPS bearing at each waypoint and it worked perfectly, but that really negates the reason for having a GPS flight plan.

What is my next step?

 

[K-man]

Thank you for your prompt answer. I hadn't even considered using the Nav button as I had thought it was just for VOR and NDB for which I don't have a need.

 

[K-man]

OK, I flew again today and this time the auto pilot followed the flight plan nicely. The only concern, if concern is the right word, is that the aircraft flies past the waypoint for some time after the GPS heading changes before initiating the turn and then the turn is quite a large arc.

What settings do people find best to get a reasonable turn without it getting too steep?

 

[dynonsupport]

If the Dynon Avionics AP is being driven by a flight plan in an external GPS, when your aircraft reaches the waypoint, the GPS tells the AP: NOW your new heading is X (and you start the turn AFTER the waypoint has passed). Likely your GPS is not supplying the "turn anticipation" sentence that can tell the AP "in anticipation of a waypoint with a new heading, begin a slow turn to heading X".

OK, I flew again today and this time the auto pilot followed the flight plan nicely. The only concern, if concern is the right word, is that the aircraft flies past the waypoint for some time after the GPS heading changes before initiating the turn and then the turn is quite a large arc.

What settings do people find best to get a reasonable turn without it getting too steep?

 

[K-man]

Thank you for this information. I have fine tuned the AP to better manage the turn but I don't think the GPS has the 'turn anticipation' sentence you refer to.

From another Dynon thread ...

"NMEA format GPSs
It does not matter what version of NMEA you are using.
Baud rate must be 4800 or 9600. The baud rate will be auto detected.
Must provide the following sentences.
GPRMB - This sentence is needed always
GPRMC - This sentence is needed always
GPGGA - Only needed if you want GPS altitude
GPBOD or GPAPB - One of the two sentences must be present, but you don't need both. If neither are present, the OBS will always indicate 360.
"

This lists the sentences required but is from nearly nine years back (Jan 2007). Is there a specific sentence for 'approaching waypoint' or should it be included in RMB or RMC?

 

[dynonsupport]

There is not a message for approaching a waypoint. A GPS that does turn anticipation will switch guidance to the next waypoint before it gets to the current waypoint, and will provide a CDI that follows the 2 minute turn arc. It's not in a unique sentence the GPS sends.

All the AP follows is the CDI. It doesn't know or care about waypoints. The GPS needs to start moving the CDI "around the bend" for it to work.

You have to ask AVMap if their product does this, and how to enable it if it does. There are handheld GPS units that do this.

 

[K-man]

Just to finish this thread. The autopilot is working like a dream. It still won't turn until after the waypoint on a flight plan but the turn rate change to '0.0' has reduced the delay considerably.

For what it's worth, AvMap have said they will look in to the 'approaching waypoint' aspect but in all honesty I feel that may be of more benefit to my grandchildren than me.

Again, thank you for your advice.