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AHRS Mount angle

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toaster73(at)embarqmail.c
Guest

Posted: Thu Jan 27, 2011 9:04 am Post subject: AHRS Mount angle

I have my AHRS (GRT) mounted behind the baggage bay on the two angles which lay on top of the angle longerons .  I see many people have this set up.  Best I can tell this does not result in a pitch for the AHRSl which is the same as the door sill (door sill being the level called out for leveling the aircraft). How is this handled ? Do I need to shim it?  

Thanks   

Chris Lucas  

#40072  

Approaching painting and other “minor” tidbits  

       [quote][b]

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Bob Turner

Joined: 03 Jan 2009
Posts: 885
Location: Castro Valley, CA

Posted: Sat Jan 29, 2011 12:25 pm Post subject: Re: AHRS Mount angle

Any real world input? I'd also like to know the answer. 



The GRT instructions say to put the AHRS parallel to the longitudinal axis. But there is also a software adjustment to move the vertical bars up/down, "...just as in a conventional AI...".  So I don't know how critical this is.



By my measurement (same location, a shelf built off the longitudinal aluminum angles behind the battery) I will need to shim the forward end up by 0.15" for every 7" of length, which is 1.2 degrees. Anyone else get or use these numbers?

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_________________
Bob Turner
RV-10 QB

jesse(at)saintaviation.co
Guest

Posted: Mon Jan 31, 2011 4:50 am Post subject: AHRS Mount angle

I didn't see any replies.  I haven't done a lot with GRT, but with Dynon and AFS they are quite adamant about getting it as close as you possibly can.  In my experience, if it also has a magnetometer in it, it is critical to have it as far away from ferrous metal, especially moving ferrous metal, as possible, but the angle of installation is supposedly very important.  I haven't tried installing it other ways, but I'd try to get it as close as possible.  If I remember correctly, mounting a 90-degree bracket onto the bulkhead gets it pretty darn close.



do not archive



Jesse Saint

Saint Aviation, Inc.

jesse(at)saintaviation.com

C: 352-427-0285

F: 815-377-3694



On Jan 29, 2011, at 3:25 PM, Bob Turner wrote:



 	  Quote: 	
		   

 

 Any real world input? I'd also like to know the answer. 

 

 The GRT instructions say to put the AHRS parallel to the longitudinal axis. But there is also a software adjustment to move the vertical bars up/down, "...just as in a conventional AI...".  So I don't know how critical this is.

 

 By my measurement (same location, a shelf built off the longitudinal aluminum angles behind the battery) I will need to shim the forward end up by 0.15" for every 7" of length, which is 1.2 degrees. Anyone else get or use these numbers?

 

 --------

 Bob Turner

 RV-10 QB

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=328932#328932

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dlm34077(at)q.com
Guest

Posted: Mon Jan 31, 2011 5:39 am Post subject: AHRS Mount angle

my backup is a GRT sport with integrated AHRS and external magnetometer. 

There is a slight error when mounting the Sport box in the panel but the 

pitch adjustment in the software solves that problem. My magnetometer is 

mounted on a shelf attached to the longeron in the tailcone. It is off 

centerline but parallel to the Crossbow AHRS on the centerline. BTW, the 

XBOW is shimmed to match the window sill angle.

---

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bcondrey

Joined: 03 Apr 2006
Posts: 580

Posted: Mon Jan 31, 2011 7:50 am Post subject: Re: AHRS Mount angle

The non-Sport versions of GRT have a separate AHRS and magnetometer to consider.  The AHRS must be very close in roll and yaw alignment.  While you want it to be close in pitch as well, however there is a pitch offset adjustment in 1 degree increments.  If you need to make minor adjustments after your mount is fabricated, shims can be used.  Van's sells an AHRS mount that goes behind the baggage bulkhead that guarantees alignment and has attach holes prepunched for several different AHRS units.



The magnetometer also needs to be in alignment, especially with the yaw axis.  Typical locations for that are either high in the tailcone or outboard in a wingtip.  There's an alignment procedure for the magnetometer that can take out some of the effects from nearby ferrous materials but keep in mind that battery contactors, autopilot servos and trim servos are all little electromagnets that will potentially cause problems.  When I installed my magnetometer I found that the level of the longerons was unacceptable because of the battery contactor.  I wound up putting it on a small shelf attached to the top J-channels.  The center J-channel gives a nice longitudinal reference for alignment.



Bob

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dlm34077(at)q.com
Guest

Posted: Mon Jan 31, 2011 8:56 am Post subject: AHRS Mount angle

Since my install was in 2005 I established the plate on two angles across 

the longeron and then ran a fish line from the aft center of the tail cone 

to the front center of the tail cone. See before and after pictures

---

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toaster73(at)embarqmail.c
Guest

Posted: Tue Feb 01, 2011 7:55 pm Post subject: AHRS Mount angle

Thanks for the replies, looks like there is somewhat of a consensus to align

with the same plane as the door sill so I will shim under the twin ahrs box

as required. My mount is already a done deal I just wanted to make sure I

should just go ahead and shim it level to the sill.

-Chris

#40072



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