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jbDC9
10-25-2017, 12:52 AM
A few months ago I finally installed a used Vizion 385 a/p in my RV-8. It. Is. Awesome. Why didn't I install one years ago?? I have it connected to my 496 GPS (RS232 wire) for nav tracking.

But, here's my issue with it; when navigating to a fix, I usually point the plane in the general direction of the fix with the Track selector, enter "Direct to" in the GPS and then select "Nav" mode on the a/p. The a/p then starts to drift a bit left, very slowly... I monitor the drift on the GPS cross track data block. It usually drifts left to show 200' cross track error, then will hold that steady as a rock. Weird! If I re-enter "Direct to", it does it again, drifts left and holds steady at 200' left of the course line. It also tracks left when on a multi-leg flight plan, so it's not just a "Direct to" glitch.

Any ideas as to what's going on here? Is there a setting in the a/p or maybe the GPS that I've missed? Has anyone else seen this? I'm glad to have basic nav tracking capability, but the offset has me puzzled...

Thanks!

rleffler
10-25-2017, 07:45 AM
A few months ago I finally installed a used Vizion 385 a/p in my RV-8. It. Is. Awesome. Why didn't I install one years ago?? I have it connected to my 496 GPS (RS232 wire) for nav tracking.

But, here's my issue with it; when navigating to a fix, I usually point the plane in the general direction of the fix with the Track selector, enter "Direct to" in the GPS and then select "Nav" mode on the a/p. The a/p then starts to drift a bit left, very slowly... I monitor the drift on the GPS cross track data block. It usually drifts left to show 200' cross track error, then will hold that steady as a rock. Weird! If I re-enter "Direct to", it does it again, drifts left and holds steady at 200' left of the course line. It also tracks left when on a multi-leg flight plan, so it's not just a "Direct to" glitch.

Any ideas as to what's going on here? Is there a setting in the a/p or maybe the GPS that I've missed? Has anyone else seen this? I'm glad to have basic nav tracking capability, but the offset has me puzzled...

Thanks!

What are you looking at to determine that it's 200' left of course? Your EFIS? If so, I suspect the source of the issue is that you EFIS map may be using your ADAHRS/Magnetometer as a position source, which is off slightly from your GPS. If you change the position source to the GPS, the variance should go away.

jbDC9
10-25-2017, 08:58 AM
What are you looking at to determine that it's 200' left of course? Your EFIS? If so, I suspect the source of the issue is that you EFIS map may be using your ADAHRS/Magnetometer as a position source, which is off slightly from your GPS. If you change the position source to the GPS, the variance should go away.

EFIS? I wish! I guess I should have mentioned the rest of my panel... it's steam gauges; no EFIS, ADHARS, magnetometers. Nothing but a Garmin 496 feeding RS232 data to the Vizion 385 and a Trutrak ADI. I'm reading the cross track error directly on the 496.

DarylT
10-25-2017, 09:22 AM
HEY JB

Time to upgrade that old 496 for an Aera 660. Works perfect.

Crosscheck 0.0.

:D

rleffler
10-25-2017, 09:40 AM
EFIS? I wish! I guess I should have mentioned the rest of my panel... it's steam gauges; no EFIS, ADHARS, magnetometers. Nothing but a Garmin 496 feeding RS232 data to the Vizion 385 and a Trutrak ADI. I'm reading the cross track error directly on the 496.

Sounds like a good time to call Lucas or Zach at Trutrak.

Jesse
10-25-2017, 08:41 PM
Lucas isn’t there anymore. Zach should be able to help. It may need to go back, but I have seen that before.

JCSmith
10-25-2017, 09:41 PM
It sounds like it may be an issue with the GPS not the autopilot. Check your GPS to see if it is set up to utilize the offset navigation feature. This feature can set up a parallel track course either left or right of the track when in the navigation mode. This is the way my Garmin GNC300XL works with my Trutrak Digiflight 200VS.
Jim

TruTrakAndrew
10-26-2017, 09:05 AM
Before you send the unit back to TruTrak, please do the following:

Perform a Long Gyro Set:
Power up the autopilot
Press and hold the Knob for about 45 seconds
The screen will show Gyro Set after a few seconds

This will reset the long term center point on the gyros.

Does the autopilot fly with an offset when flying a selected track? It sounds like a slight azimuth gyro offset. It should not be flying with an offset.

I am trying to get the new sales / support guy up to speed on watching this site for autopilot related questions, his name is Corey, and while he doesn't have a lot of autopilot knowledge yet, he is a pilot that is VERY enthusiastic about flying and loves working in the aviation world.

thanks!

Tankerpilot75
10-26-2017, 02:37 PM
Lucas isn’t there anymore.

What happened to Lucas? Where did he go?