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AHRS alignment times

Postby rzbill » Wed Oct 02, 2013 10:46 pm

I think this is more an AHRS question than a WS EFIS question but this appears to be the best spot in the Forum to ask since I am a WS owner.

I am curious what influences the alignment times shown on the PFD during boot of the system.
Mine seems to be a random selection that is sometimes 45 seconds and sometimes 2 minutes.

I know of the commentary that it only takes 15 seconds or so and you can move after that, but during Phase 1 last year I had the AHRS tumble on two different occasions because I did not wait long enough. Because of that, I began waiting until it is really finished. I can't afford a tumble in the soup.

SO...My machine was pretty constant at 45 sec unless I accidentally let the brakes slip and then the 2 minute jobber would come up.
I upgraded the AHRS and WS software a few months ago. From v34 to whatever is latest today, and the instances of 2 minute boots really increased.

Therein lies the curiosity. I want to do what is needed to get the boot times back down as a normal course.
Bill Pendergrass
RV7A, EIS, Dual WS H1s, 430W, GRT A/P, Navworx
http://www.grtavionics.com/forum/viewtopic.php?f=19&t=50
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Location: KAVL

Re: AHRS alignment times

Postby GRT_Jeff » Sat Oct 05, 2013 4:16 am

The faster "ground" alignment is 50 seconds. The AHRS can switch to the slower "air" alignment at any time, which extends the time to 140 seconds. The AHRS is very sensitive to changing internal sensor conditions during alignment, and it doesn't take much to trigger the longer alignment. It happens even with the AHRS sitting on a solid bench. Not moving is the best you can do.

If the attitude and heading are correct when the alignment finishes, then the alignment completed successfully. If the AHRS was fine after alignment and then tumbled later, it was not caused by something that happened during alignment.
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Re: AHRS alignment times

Postby rzbill » Sun Oct 06, 2013 9:11 pm

Thanks for the feedback Jeff.
If it happens on the bench, then surely I cannot do any better than I am today.
Sounds like it could be easily upset by the wind moving the craft during boot.
That explains the variability I was curious about.

I do want to be clear about my tumble events. It was my fault, not the GRTs. It was very early in phase 1 when I was still learning the craft.
I am quite certain that I jumped in the plane, hit the go buttons and started taxiing without allowing time for PFD alignment to complete because my nose was stuck in the engine monitor.

The first time, the alignment issue was not evident until I realized the heading was WAY off. I thought it was a magnetometer issue (or my installation of it)
I stopped, got gas, and then did the same thing again (still had my head somewhere dark) but this time after I was in the air, It REALLY tumbled and the horizon did barrel rolls until I got home. That finally made me wake up to what I was doing.

SO.. I had seen some commentary somewhere (VAF or the GRT yahoo probably) about not needing to wait the whole time period.
I do to be SURE now.
Ever since those tumbles 18 months ago, I have waited the whole 50 or 140 seconds and never had another issue.

Again, thanks for the feedback.
Bill Pendergrass
RV7A, EIS, Dual WS H1s, 430W, GRT A/P, Navworx
http://www.grtavionics.com/forum/viewtopic.php?f=19&t=50
rzbill
 
Posts: 14
Joined: Tue Mar 12, 2013 5:19 pm
Location: KAVL

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