Finding location for ADAHRS

[fellman]

Trying to find a place on my Bearhawk 4place. Working on a location in the back of the fuselage where no significant dynamic magnetic fields and good access through the aft bulkhead. However, the steel frame causes compass deviation of about 20 degrees on a north - south heading and also total magnetic field some 20% weaker than outside.

The manual talks about "significant deviation" but how much is significant? How much can the calibration process absorb?

Any suggestions much appreciated.

Enclosed a pic of present attempt (also same results without the clecos)

 

[jakej]

Lars
Have you contacted the others building Bearhawks ? I know the ADAHRS unit can be installed & working properly on one, a client has done it

Jake J

 

[cubbuilder]

Hi Lars
I encountered the same problem with a cub clone that I recently built. I did contact Dynon a couple of times prior to purchase and afterward, about the "significant deviation" question but the only help I could get was to "just try it", which I did. I wasn't able to get a clean area within their parameters so installed the adahrs in the area with the least interference, hoping for the best. The interference seemed pretty minimal but the result is a nice install of a great product but any compass reference is completely unusable, which I believe makes the autopilot only partially functional too. I have not messed with that yet. There have been numerous requests here to separate the compass to allow for a wing tip installation as in previous dynon products but apparently that is very difficult and apparently there is not enough interest to make if viable for them. It's unfortunate to have a great system with only partial function. Maybe your voice will help.
All the best with your installation.
Ole

 

[swatson999]

Can you degauss the frame around the ADAHRS unit?

 

[fellman]

Thanks guys. I was hoping that the Dynon people would come up with something but nothing heard so far.

I have posted the same thing on the Bearhawk forum and there is one guy who has and older system with the magnetometer in the wing right outside the main tank and he plans to upgrade to Skyview and do the same. The snag is the limitation on CG distance which puts you very close to a steel frame for the flap mechanism but if his experience is that it works it should be OK. Needs to be studied.

Jake, any chance you could put me into contact with your client. Would be much appreciated.

 

[jakej]

Lars, I'll pm you tonight.

Jake J

 

[Dynon]

Steel tube fuselages can be a challenge, and we'd love to be able to offer a remote magnetometer. We don't have anything to announce, but it's a frequent request and challenge for some aircraft.

I can't say I'm familiar enough with the bearhawk's construction to offer any exacting guidance, but is there any prospect that there's a place in the aluminium structure of the wing that can work that's not at the wingtip?

 

[ed.meyer]

I too am building a Bearhawk, the two place Patrol, and have been trying to figure out a good solution to the AHRS placement. Similar placement to the photo has been considered but a hand compass reveals magnetism there. A wing might be an option but not within the six feet of center of the airplane due to fuel tanks and flap mechanism. 7 or 8 feet is probably doable. I emailed to Dynon about this several weeks ago and got back a suggestion that outside the 6 feet would probably work but I am very hesitant to put out several thousand dollars on a probably. Count me as another vote for the remote magnetometer which seems like the ideal solution to me and could be put in a wingtip which would also be more easily accessible than buried in the wing. I would also be interested in knowing more about the one success with a Bearhawk.

 

[mbaerobat]

I too am building a Bearhawk and am at the point of making a final decision on panel/avionics hardware. My past experience with steel tube fuselages and inaccurate whiskey compass indications have been solved by degaussing, (demagnetizing), the airframe and all associated hardware that retains magnetism. I am still old school and this is my first foray into the world of glass. Would degaussing enable the ADAHRS to function as it should? If so, it would be applicable to any tube/fabric aircraft.

 

[n144sh]

Please add me to the list of Bearhawk (4Place) builders that really would like to see a remote magnetometer. I couldn't find a location for the ADAHRS that satisfied the criteria from centerline that was away from disturbances. I ended up mounting behind the baggage compartment - very likely going to be a problem with the magnetometer so am holding out hope for a remote!

 

[Jonas]

which I believe makes the autopilot only partially functional too

The autopilot still works fine... it gets it's info from gps position, and flies on ground track when following a flight plan. If you use "heading" autopilot function, it will be off by an undetermined amount of degrees to the left or right.

If the compass isn't calibrated properly is you will see inaccurate wind direction and wind speed readings on the display, inaccurate aircraft heading readings... the runway on synthetic vision will be crooked compared to the actual runway out the window.
the little plane will be flying crooked on the map page. That's about all that will be wrong.