Backup flight instruments required?

[rlmarshall]

I would really like to install the SV 10" and 7" in my RV6A but am hesitant because of the backup issue. Does Dynon recommend backups in addition to a two screen, double ADAHRs system?
What info about failure modes can you provide which will give confidence in such a system in IFR conditions, under any forseeable failures?

 

[dynonsupport]

Do we think that that would be enough for a solid IFR configuration? Yes. Will you? We try not to evangelize too much, since you don't have to look far to find contrary opinions. The leading argument against is to never put all of your eggs into one basket. Ie - you want a completely independent system backing up your primary. This is why the space shuttle has 3 redundant computers built by presumably the lowest bidder, and then a 4th that is built to the same end requirement specifications but by another vendor entirely (I think that's right, from memory anyway). Similarly, glass-cockpit airliners usually have a small separate mini pfd that's not part of the integrated system. As you go down the certified line, though, you can find systems that have dual ADAHRS with no other external backup.

So if you have two ADAHRS and two screens, you do have two full potential sets of flight instruments and two screens in the aircraft to rely on, so no single part failure will jeopardize your flight. We have a fleet of customers that fly our current generation with a D180/D100 combination and are happy with the performance, integrity, and reliability of our products.

One caveat - initially, while you can have multiple ADAHRS in a SkyView system, you'll have to manually cross-check them. As we continue development, we'll have automatic cross-checks/voting/averaging and all of that fancy stuff. They will switch from one to another if one completely fails.

 

[RockFLY]

I'm interested in your view on separate pitot/static and AoA lines for redundant ADAHRS modules.

Do you think it is appropriate to run separate pressure lines to avoid a single pipe feeding both modules - after all, if they're bothfed the same wrong information, who would be able to tell?

Cheers, Stu

 

[PhantomPholly]

Search the RV forums on the words "separate" and "pitot" and "static" for some good discussions.

The F-4 Phantom did not have dual pitot systems, and "alternate static" was to break the glass in one of the static instruments. In my homebuilt I have a valve I can turn to use cabin static without breaking glass...

Now that the Dynon unit has backup GPS reference factored into attitude, it seems extraordinarily unlikely that you will be unable to navigate in the rare occurrence where the pitot gets blocked. Just learn the signs of blocked ports and adjust accordingly if it happens.

 

[dynonsupport]

Tough question but a good one. Also one that I'm hesitant to give advice specific on since everyone's missions and opinions on redundancy requirements vary. Our generic advice is to understand the instrument/data sources in your aircraft fully, and then you can decide what level of redundancy you need. For example, most piston singles have just one pitot/static system, but airliners have 3 or 4. This is one of the things that gives transport category increased redundancy, at the cost of expense and complexity. In contrast, most IFR piston singles have just one heated pitot, which means that an electrical failure of that single part means no more airspeed, and partical panel becomes your gyros + engine speed + VSI other "informational only" deviceslike GPSes ground speed. They also usually spend less time in severe conditions, like icing, even when IFR.

I'd say 9X percent of our IFR customers running dual Dynons (with at least one battery backed up, of course) run a single pitot/static system with the pitot heated. There are some "really hard" IFR guys that have gone with dual pitots/static system, with one of them plumbed to each unit/ADAHRS.

So, in conclusion, as you're planning your panel, think about what the partial panel is when EACH component part fails in some way - whether it's s electrical, environmental, mechanical, etc. Then, realize that you're building an aircraft for YOUR mission, and that the level of redundancy that you require might be closer to the typical piston single or your neighborhood airliner.

Our generic recommendation - that you'll find through out threads here - is that that you should equip your aircraft such that no single failure causes an inability for you to get back down safely. You'll find that if you have a dual Dynon, battery backed, up, with GPS failure (so that airspeed going away isn't a critical event for attitude), and a heated pitot, you can start "fail" basically any single system in the aircraft and still have flight instruments that can get you down.

 

[RockFLY]

Thanks guys,

I'm planning two 7" SkyViews (one with backup battery) with two ADAHRS, Dynon GPS, one GNS-430W, one heated pitot, balanced dual static ports, a separate analogue airspeed indicator, altimeter and wet compass.

I guess I'll feel pretty safe in IMC.