Difficult AHRS-ectomy

So my old GRT AHRS has developed the leans. After some attempted fixes based on advice from GRT, it looks like it's flown west for good. I've decided to upgrade it to their new Adaptive AHRS. I'm also going to replace my trusty but aging Horizon WS with their Horizon EX.

So I need to send my old AHRS in to them for the upgrade. However, it looks like the aircraft was sort of built around the AHRS.

Here's a photo I stole from the original builder's website, looking toward the pilot seat from the front of the airplane. There's now painted fuselage skin riveted over the top of this area, and of course the "easily" accessed avionics are largely behind this, closer to the pilot:

https://www.icloud.com/photos/#0OUXlCZSijnp074nC2H8MDaQA

From what I can tell in the archives, this was not an uncommon place to mount the AHRS, although some people apparently installed an access panel in the fuselage skin above it.

It looks like maybe I can do some serious panel spelunking and remove the tray that the AHRS sits on, allowing it to drop down for access. But before embarking on that adventure, I thought I would ping the crowd here to see if anyone with a similar setup can offer any tips for access.

I'm tempted to just leave it in there as a time capsule and put the new Adaptive AHRS somewhere else (it has much more lenient mounting requirements), but the $ difference between a new AHRS and an upgrade is significant.

Thanks for any suggestions!

Mine is mounted the same way. Four screws are inserted from the bottom. They are relatively easy to remove from below once you are under the panel. Take the seats out and place something in the foot well for your head to rest on, get good lighting and someone to hand you tools and it should be out in no time.

Martin Sutter
Building and flying RV?s since 1988 for +4000hrs
EAA Technical Councilor

Re: Difficult AHRS mounting location

From the picture you posted, the shelf that the AHRS is mounted on is removable. I see nut plates on the aft end of the shelf so if the forward end is the same and has nut plates also, your job won?t be as bad as you think. Getting in their to drop the shelf will be no fun but looks doable. Take the seats out and put some pads on the floor to protect your back. If the right side control stick is removable that will help with getting yourself in to do the work.

The good news is the Adaptive AHRS can be mounted upside down with the connector and pitot static ports facing aft. That will make installing the new AHRS a bit easier. Add some plate nuts to the top of the mounting shelf for the new AHRS while you have it out. Use the existing AHRS mounting holes for the new AHRS if you can, reinstall the shelf and the new Adaptive AHRS will have a home. I have mine mounted this way between the ins panel and the sub panel behind the ins panel, so am confident the upside down mounting will work for you.

I would try and keep the old mounting location as it has proven to be rigid and free of vibration problems with the old AHRS.

Thanks

Martin Sutter said:

Mine is mounted the same way. Four screws are inserted from the bottom. They are relatively easy to remove from below once you are under the panel. Take the seats out and place something in the foot well for your head to rest on, get good lighting and someone to hand you tools and it should be out in no time.

Click to expand...

Just the kind of info I needed, many thanks.

Trying to picture this

Isaac said:

The good news is the Adaptive AHRS can be mounted upside down with the connector and pitot static ports facing aft. That will make installing the new AHRS a bit easier. Add some plate nuts to the top of the mounting shelf for the new AHRS while you have it out. Use the existing AHRS mounting holes for the new AHRS if you can, reinstall the shelf and the new Adaptive AHRS will have a home. I have mine mounted this way between the ins panel and the sub panel behind the ins panel, so am confident the upside down mounting will work for you.

Click to expand...

So you're saying to use the same shelf, but to have the replacement (Adaptive) AHRS hang from that shelf, rather than sit on top of it?

If I understand what you're getting at, this strikes me as fiendishly clever.

Yes, that was what I though would be a good solution. I think the Adaptive AHRS is 2 3/4 inches high and your existing shelf looks to be high enough so you should not have a problem clearing the rudder pedal bars with it mounted upside down. The AHRS will still be in a awkward location but more accessible that it is currently.

Hopefully, the existing wiring harness has enough length to reach the connector location. The old AHRS vs. new version wiring might require moving pins in the connector.

AHRS-ectomy complete!

Well it took some doing, but a combination of passenger stick & seat removal let me wriggle in there and extract the ancient AHRS?albeit at some length and with copious cursing appropriate to avionics upgrades.

In all seriousness, I once again came away from tinkering with 9JA with an increased appreciation for the guy who built it. He did nice work.

Thanks again for the help.