How many ADAHRS in the system?

[KRviator]

As the title suggests, after 10 years and several hundred hours of flying behind the SkyView in my RV-9, I'm now planning a similar installtion in my Aztec. I want a "Fail operational, Fail safe" design so I can still get home from an away trip no matter what (within reason) single failure I have away from home base.

We obviously need an ADAHRS-200 as the primary, and the manual says the -201 is the backup, but in a 3-screen system, can I install two ADAHRS-201's on the 2nd and 3rd screens or do I need two ADAHRS-200's and a single -201? OOOooorrrr.... will 'the system' only recognize one of each....

EDIT: Why is my post-count only showing 3 posts? Did the post-counts not transfer over from the old forums?

 

[r2brou2]

IIRC, the certified HDX installation does not allow for a backup ADAHRS. If the ADAHRS fails, you'll also lose the autopilot.

 

[KRviator]

IIRC, the certified HDX installation does not allow for a backup ADAHRS. If the ADAHRS fails, you'll also lose the autopilot.

It won't be a certified system, the Aztec is "Experimental - Amateur Built"... Do not ask how that happened! The screens will be 3 x SV-D1000 Classic's, not even the Touch versions.

 

[CanardMulti]

Keep in mind that however you have your multiple ADAHRS hooked up that should the -200 and -201 disagree beyond the programmed amount, you are warned and then asked to pick the one you want to have displayed. For that reason I chose to install - in my 2 screen system - an SAI (standby attitude indicator) to be the tie breaker. I chose a G5, but these days there are plenty of other reasonable choices. The key factor is that whatever SAI you choose is truly independent from your Skyview system in both software and power source. I chose to make mine a small EFIS w/ pitot static information as well; that way if I experience that once-in-a-lifetime system total crash - at night - in the clouds - I still have a chance at survival.

As to your basic original question: If I understand how Skyview 'thinks' - and that is definitely NOT a safe bet - if your 3 screens share data in any way, including network information, there's no way to avoid having them all use the same ADAHRS as their attitude and air data source. If I've misunderstood, I will gladly be pointed at the correct information.

Mostly a thought exercise: I guess if you chose to make your third screen *totally* independent of the two primary screens which have the standard -200 and -201 arrangement, you could provide ADAHRS information to the third screen via its own dedicated (second) -200. If you went even further and installed a second -201 dedicated to the 3rd screen as well ( 4 ADAHRS units total) you could arguably safely do away with the need for the discreet SAI at a bit less cost ( 2 x additional ADAHRS vs an SAI) but the downside would be that all the information, tuning ability, autopilot control, etc., etc., on the primary network would not be available through the 3rd screen. All this supposing can result in getting lost in the weeds…..

 

[BalsaBat]

I am not expert enough to comment on how many ADAHRS you can put on one data bus, but I think the answer is just the single ADAHRS-200 with the optional 201. Otherwise, there would be no need for the 201 -- you could just use 2 (or more) of the primaries, so why would they make 2 different units?

But what I can add, is that for the most robust redundancy, redundant and DIVERSE is better. Your 3rd screen, if on the same data bus, might be good for information display, but not so much for redundancy. For example, if some circumstance (maybe a lightning strike, voltage surge, software glitch, or short to ground, or bad connection) takes out the whole Dynon network, then something not connected to it, and not subject to the same failure modes, is the best protection. So the most diverse redundancy is probably legacy mechanical instruments (although cumbersome, and less reliable if in poor condition, and generally out of favor). But good enough diversity is a separate electronic system (e.g. D10A) like those usually required in new certified installations. That eliminates the most likely common mode failures from resulting in total loss of flight data.