[pvalovich]

-8A with Garmin 496 and AFS 4500. AHRS mounted on shelf anchored to top fus longerons initially 15 inches behind rear baggage bulkhead. During troubleshooting shelf moved 18 inches further aft to provide greater distance fm Whelan power supply mounted on floor. Numerous conversations with Advanced tech guys. AHRS replaced and recalibrated.

But still get random 30+ degree heading excursions!

I use Hdg Adjust to line up heading indication with runway on takeoff. even at 1000 ft agl and little wind, heading will randomly drift over 30 degrees from GPS ground track. Crosswind indication shows 40-50 kts - actual wind probably less than 5 kts. Turning off strobes doesn't help.

Hours of unsuccessful troubleshooting and flight test. Anyone have any ideas?

 

[F1R]

Possible help from MGL?

Perhaps not the help you need, however the MGL extreme allows GPS track to be displayed in the heading location. It's built in GPS will output to NEMA compatible device.. But I am not sure if the AFS will allow the track data in place of MAG heading. Magnetometers can be a challenging task. One reason I prefer a system that has a pure inertial attitude solution with GPS assist. I have 3 EFIS installed, I don't have a mag heading with any of them by choice.

In an earlier install of a different EFIS a magnetometer worked well located mid span in the right wing(opposite side from the heated pitot EMF) just forward of the aft spar.

I think Tom Martin has an AFS in his rocket. You might check with him on his install.

 

[jjconstant]

Where's the magnetometer? Is it integrated into the AHRS or separate?

Jeremy

 

[kentb]

Paul, you most likely already know this...

After start-up make sure that you don't move the plane until the EFIS is through with it's alignment (the red X goes away).

The only time my 3500 EFIS wanted to go the wrong way was when I didn't understand this.

Hope this helps.

Kent

 

[pvalovich]

Wet Compass?

Heading indication frustration is leading me to consider a glareshield mounted wet compass as a backup. Anyone have any comments on mounting a SIRS Navigator 2400 on an RV-8 glareshield?

To answer previous post - the magnetometer is the AHRS mounted behind the aft baggage bulkhead.

 

[Trevor778]

are you using shielded wires? Sounds like it could be a possible electrical interference problem.

 

[airguy]

Proximity to autopilot elevator servo?

 

[RFazio]

What type of bolts did you use to mount the AHRS

I have read this a number of times and a lot of guys use stanless bolts to mount the AHRS. I had trouble also with my dynon, once I installed brass bolts the problem went away. Most stanless bolts will mess up your AHRS.

 

[N402RH]

Paul,

I don’t remember talking to you about this, give me a call and we can review it.

The AHRS in mounted in the screen, I think you are talking about the remote Magnetometer.

1. Do you have the Magnetometer mounted using brass screws?

2. Are you not moving the airplane until the AHRS alignment is finished and the Red X on the EFIS screen goes away?

3. Is the Magnetometer mounted at the same angle as the EFIS screen? IF your panel is tilted 6 degrees the Magnetometer must also be mounted with the 6 degree tilt.

4. Do you have the canopy open (slid back over the Magnetometer Mounting) when the AHRS is aligning? We have seen RV-8 canopies that are magnetized causing this problem.

5. Send me a picture of your Magnetometer mounting location and the surrounding area.

6. It is not caused by the wire shielding, it is RS-422 differential pairs.

7. What type of GPS are you using and how do you have the magnetic deviation configured? We have seen numerous wind calculation errors being caused by the GPS magnetic deviation set wrong in the GPS. If you are using a Garmin (396, 496, 696, ….) make sure that it is set to auto and that you have the EFIS RS-232 port configured to AF-GPS. If you have the EFIS port set to NMEA 9600 and have the GPS RXD line connected it will mess up the deviation in the GPS.

8. Did you do the Mag Align away from all buildings and aircraft and at a magnetically clean location? You should be at least 250 feet away from everything, better yet do it on a compass rose. We have seen problems with people doing the Mag Align on concrete with magnetized rebar.

You should not be adjusting the magnetic heading offset when you taxi out. When you turn the aircraft the heading is actually being calculated by the gyros in the AHRS and then very slowly updated from the magnetometer. If you have large magnetic errors and turn 90 degrees you will see a 90 degree heading change and then it will slowly drift away. You can easily test for valid mag align by doing the following:

1. Set the Heading Offset to zero.

2. With the engine off and canopy shut point the airplane to North using the EFIS screen. Over the next 2-3 minutes check how far the EFIS Heading moves.

3. Repeat step 2 for East, South, West and record how far the EFIS heading moves.

4. If the heading moves more than a 2-3 degrees you do not have a good mag align and you need to redo the mag align.


If you still can’t get this solved fly the airplane up to Portland (OR40) and I will personally solve your problem in a few hours.

Rob Hickman
Advanced Flight Systems Inc.

 

[DRBuilder]

-8A with Garmin 496 and AFS 4500. AHRS mounted on shelf anchored to top fus longerons initially 15 inches behind rear baggage bulkhead. During troubleshooting shelf moved 18 inches further aft to provide greater distance fm Whelan power supply mounted on floor. Numerous conversations with Advanced tech guys. AHRS replaced and recalibrated.

But still get random 30+ degree heading excursions!

I use Hdg Adjust to line up heading indication with runway on takeoff. even at 1000 ft agl and little wind, heading will randomly drift over 30 degrees from GPS ground track. Crosswind indication shows 40-50 kts - actual wind probably less than 5 kts. Turning off strobes doesn't help.

Hours of unsuccessful troubleshooting and flight test. Anyone have any ideas?

I had the exact same issue with my Skyview ADAHRS/Magnetometer. I installed brass bolts and centered the ADAHRS between the two seatbelt cables. I found that the initial mounting location (RV-7) was closer to one seatbelt cable than the other. This threw off my heading by almost 10 degrees. Once I centered the ADAHRS between the seatbelt cables, recalibrated the ADAHRS by taxiing out to the compass rose at my field, the issue completely resolved itself. Now when I line up with the center line for departure, I have a picture of the runway on my PFD as if I was looking out the windscreen!