I went all Garmin and wanted 2 big screens because I've gotten used to it flying behind the G-1000. I added a G5 because I don't have a vacuum pump and wanted it for IFR redundancy in case of electrical failure or if the G3X system tanked for some reason.
Does Garmin not have an option for installing a second ADAHRS that either screen can use if one ADAHRS goes belly up? If not, then I totally get your setup. I thought I had seen that putting in a second ADAHRS was cheaper than the G5 or smaller Dynon EFIS, but maybe that's just Dynon? Hence my confusion - if adding a second ADAHRS is cheaper, I'm trying to figure out why panels with 2 large glass displays would use a small EFIS over just a second ADAHRS to drive the big screens.
I can already see that designing my panel is likely going to put me one step closer to the psych ward.
Yes - you can easily add a second (or third?) ADAHRS into a Garmin network, and all G3X screens have access to all ADAHRS. People add the G5 for unlike redundancy - the code is all completely different than in the rest of the G3X system - just in case you’re afraid of a common bug taking down the primary screens
“Man with two watches never knows what time it is.”
If you have two adahrs, which one is correct?
You really need a tie breaker…
This would be true if the systems used a voting mechanism all the time. Skyview has a primary and a backup only, and if they disagree the pilot becomes the tie breaker to decide which one is right.
If that happens while in the soup though, having a independent backup (like a G5 with a built in IMU) helps the pilot make that decision.
I can already see that designing my panel is likely going to put me one step closer to the psych ward.
It certainly can make a person a little crazy. I started with mission requirements and mine is hard IFR. I don’t intentionally fly hard IFR in singles anymore, but will be equipped to do so and have a level of redundancy that makes sense to me. A few years ago I knew I would go glass, but would install a mechanical airspeed indicator and a 12v Turn & Bank for last ditch attitude info. Since then my panel has morphed into all glass, dual G3x, G5, GTN 650, GTR 200, 45R, Garmin autopilot ect. For backup electrical power I installed a 8 amp B&C alternator on the empty vacuum pump pad instead of a backup battery. Last ditch attitude info now comes from the G5 and it’s own internal battery.
Don Broussard
RV9 Rebuild in Progress
57 Pacer
You miss my point; I you just have two adahrs and one fails in the soup, which one is correct?
I was listening to a podcast a few years back which featured the Dynon engineer who designed its ADHRS.
ADAHRS failure - in that case it simply self-detects a problem
Ay, there's the rub.
"dual screens" and "dual ADAHRS" are used, somewhat interchangeably in this thread.
Although mentioned several times, I want to be sure we're saying that Dual ADAHRS is have two (or three) GSU-25 units with Garmin setups (I believe the Dynon equipment name is SV-ADAHRS, but the context is the same).
I completely agree that If you have two ADAHRS units, AND a G5, then you have triple redundancy to allow for auctioneering that several folks have discussed.
<<<SNIP, SNIP>>>
Great redundancy opportunities... pity still only one brain on the pilot though.
I like dual ADAHRS on the same system and a totally independent like a G5.
You will feel much better to have a tie breaker.
"dual screens" and "dual ADAHRS" are used, somewhat interchangeably in this thread.
Although mentioned several times, I want to be sure we're saying that Dual ADAHRS is have two (or three) GSU-25 units with Garmin setups (I believe the Dynon equipment name is SV-ADAHRS, but the context is the same).
I completely agree that If you have two ADAHRS units, AND a G5, then you have triple redundancy to allow for auctioneering that several folks have discussed. For my installation, I have one GSU 25 mounted in the "standard" location back aft on the ADAHARS mount that reports to the MFD, then a second one on the back of my PFD and connected via CAN, and RS-232 to the PFD. And then of course the G5 has its own internal ADAHARS.
While Garmin does have some mismatch checking for software, network and database errors, and being able to select which GSU each display uses is a very cool option, it's dependent on the pilot observe and pick the winner(s). The Garmin manual says that the G5 data will be displayed on the GDU's if GSU data is unavailable, which makes me wonder what alerting would tell you that? Experiment time...
Hey Garmin: the manual says "In a system installed with one or more dedicated ADAHRS units and one or more G5 standby flight displays, attitude and air data from the G5 will also be displayed on the GDU displays, in the event that valid data is not available from any dedicated ADAHRS unit." What is your definition of valid data and how do you announce that?
A really good point this thread brought up for me, is "what happens if one of the ADAHRS units doesn't just fail, but 'drifts'?" I haven't experienced this event and I'm not even sure what that event would consist of; I'm thinking about doing an exercise to cause failures and see what happens above and beyond simple unit failure. And what happens with a third GSU 25 installed? And if you're really going "armageddon mode", do you get three GSU 25's (with obviously one connected via RS-232)? I might invest the AMU to find out.
Great redundancy opportunities... pity still only one brain on the pilot though.
To your question about drifting:
My observation is that the Attitude solution can get way out of the "useable" range long before the misbehaving AHRS re-aligns and you get AHRS reversion. So yes you can most definitely have "drift" that looks like one AH pitch 10+ deg different to the other. The CAS will alert to the miscompare before the revert obviously, but you need to have a mechanism to tie break because it can persist for enough time to cause you trouble.
Richard
So in a stressful situation in IMC with a misbehaving/drifting AHRS ideally you would want the autopilot on while trouble shooting but presumably the autopilot would also be misbehaving/drifting before reversion.
Fin 9A
So in a stressful situation in IMC with a misbehaving/drifting AHRS ideally you would want the autopilot on while trouble shooting but presumably the autopilot would also be misbehaving/drifting before reversion.
Fin 9A
Not if you have a stand alone autopilot. Interestingly, the added cost of a Trio/TruTrak over an efis-integrated AP is about the same as an extra air data attitude box.