Dual ADAHARS installations

[rjones560]

I have a Skyview 3 screen setup in my RV10. I have a 10” screen on each side set up as PFD’s and a 7” screen in the middle for engine instruments. When I originally installed the ADAHARS I did what the Dynon manual said and used a splitter to join the the ADAHARS together and run one cable forward to the rest of my network. I think this is the wrong thing to do. That 1 cable, and especially the D9 connectors at each end, represents a single point of failure for both ADAHARS. Not only that but the network cable going from a 5 port hub on the right side to the co-pilots EFIS is also another possible failure point that would also leave the system with no attitude or air data.
I just ordered another cable to correct this issue. I have two 5 port hubs in my system, one on each side of the cockpit. The current cable is connected to the right side and I am going to connect the new cable to the left side 5 port hub. The rest of the units are daisy chained between these 2 hubs. This way a failure on either side, or somewhere in the middle with a failed network cable, would still leave me with at least one good ADAHARS on at least one screen. This might not be important for a VFR only aircraft. However for even an occasional IFR aircraft this is really important.
I am not running another standalone attitude indicator. With 2 ADAHARS and 3 screens to see the data I have far better redundancy than any of the other light aircraft I have ever flown. I have the standby batteries for all 3 screens and I have 2 B&C alternators.
If I flew this aircraft in IMC all the time I would have probably figured out a way to put in a third attitude indicator. However I am not flying jets in all kinds of dastardly weather anymore and I have more brains than to fly my RV10 into possible icing conditions. I have the skill to fly approaches down to minimums and even land without seeing the runway, but I sure don’t plan on using those skills in the RV10.

 

[jakej]

Mr Jones - IMO you're overthinking it, an aircraft has many other points of failure that have the potential to worry me more.
BTW - the network cable has 2 x data pairs for redundancy in case 1 goes mia. I'd be concentrating more on the security of the joining of the 9 pin dsub connectors - make sure they are tight

 

[rjones560]

Mr Jones - IMO you're overthinking it, an aircraft has many other points of failure that have the potential to worry me more.
BTW - the network cable has 2 x data pairs for redundancy in case 1 goes mia. I'd be concentrating more on the security of the joining of the 9 pin dsub connectors - make sure they are tight

The D9 connectors are what I am most worried about. The chances of a break in the wire is quite remote. With my installation, any one of 4 D9 connectors coming loose would result in no ADAHARS information being available anywhere. The connections that would fail everything are either end of the harness from the ADAHARS to the 5 port hub, and either end of the network cable from the 5 port hub to the left EFIS.
I started flying late in life, about 35. I accumulated about 15,000 hours, most of it in jets. You would be amazed at the number avionics failures I experienced over the years. Backups for failures are important in IMC. In VMC everything can fail but the engine and you will be fine.

Mr Jones - IMO you're overthinking it, an aircraft has many other points of failure that have the potential to worry me more.
BTW - the network cable has 2 x data pairs for redundancy in case 1 goes mia. I'd be concentrating more on the security of the joining of the 9 pin dsub connectors - make sure they are tight

 

[Rhino]

And there'd still be numerous points of failure. His point was that you can't get them all. Your engine is also a single point of failure. Obviously you aren't trying to mount a new one somehow for redundancy. There's nothing wrong with having backups, and obviously it's your aircraft and decision. But you aren't going to eliminate all such points of failure. It simply isn't possible. You can certainly try, and soon you'll be at gross weight before even adding any fuel. At some point you have to decide the break even point. I worked avionics for 20 years and saw numerous failures, but I can't recall any of them being due to a DB-9 connector falling off. That's because we safety wired them. I did see cannon plug connectors come off a couple of times, but that's because they weren't installed properly and weren't safety wired. So if you're really worried about a DB-9 coming loose, you could simply safety wire it. Would be much simpler and save weight.

 

[swatson999]

And there'd still be numerous points of failure. His point was that you can't get them all. Your engine is also a single point of failure. Obviously you aren't trying to mount a new one somehow for redundancy. There's nothing wrong with having backups, and obviously it's your aircraft and decision. But you aren't going to eliminate all such points of failure. It simply isn't possible. You can certainly try, and soon you'll be at gross weight before even adding any fuel. At some point you have to decide the break even point. I worked avionics for 20 years and saw numerous failures, but I can't recall any of them being due to a DB-9 connector falling off. That's because we safety wired them. I did see cannon plug connectors come off a couple of times, but that's because they weren't installed properly and weren't safety wired. So if you're really worried about a DB-9 coming loose, you could simply safety wire it. Would be much simpler and save weight.

How do you do this? I'm thinking of the DB connectors with the knurled knobs (or worse, the little bitty screws) that go into things like the EMS, servos, ADAHRS, ADS-B, etc. I check the knobs at each annual and have never found any loose, but I'd be curious about how they can be safety wired in place...where do you attach the wire, etc.?

FWIW, I've never liked the screws/knobs for DB connectors, and always thought that something like the spring clips we used to see on things like parallel printer connectors and such would be much better, but nobody makes DBs with those.

 

[rjones560]

Electronic equipment is fairly notorious for suddenly quitting without warning. I can’t imagine flying IFR with one radio. Lost com in that situation denies you the ability to get current weather and other information that may be useful. It also requires ATC to lock up large portions of airspace for you. Yes there are procedures for it, but they are not pretty.
I have had AHARS fail on jets in IFR weather. I have had EFIS screens fail, air data computers fail, and com failures.
Yes you can’t back everything, especially the engine unless you are flying a twin that can actually fly on one engine. Most light twins can’t. However a lot of things can be backed up without much weight penalty. That’s why I have 3 GPS receivers, 1 VOR for the ILS, 2 coms, three EFIS screens, 2 ADAHARS and 2 ignition systems for my engine. Engine sensors are not backed up, but the engine will run fine without them. I have had those fail on jets also and they did not concern me too much. The electrical equipment was always the least reliable. Some of my avionics problems were solved by pulling the equipment and putting it back in the rack. Obviously there was a problem with contact on one or more pins in the connectors in the back. For a VFR only aircraft I would not worry about any of this. Because I fly IFR occasionally yet I want the really important things to have backup. Attitude and air data are more important than the engine when you are IFR. I have a friend who had engine failure over the Central Valley in California in a Mooney. The low fog was on the ground with ceiling less than 100 and less than 1/4 mile vis. He survived because he still had flight instruments and flew it all the way until the trees caught it. Without flight instruments he would have got into a steep spiral even if the engine was running fine.

I have over 15,000 hours in the air in everything from ultralights to heavy corporate jets. I have seen a lot of electrical failures and very few mechanical failures.

 

[Rhino]

How do you do this? I'm thinking of the DB connectors with the knurled knobs (or worse, the little bitty screws) that go into things like the EMS, servos, ADAHRS, ADS-B, etc. I check the knobs at each annual and have never found any loose, but I'd be curious about how they can be safety wired in place...where do you attach the wire, etc.?

FWIW, I've never liked the screws/knobs for DB connectors, and always thought that something like the spring clips we used to see on things like parallel printer connectors and such would be much better, but nobody makes DBs with those.

That's a very good question. Your 'standard' DB9 connector doesn't typically come with an option to do that. I suppose you could research mil-spec connectors and come up with what we used, or just do what I've seen some other homebuilders do. I've seen this done two ways so far. One method was to drill a hole through the knurled knob to allow it to be safety wired, duplicating what we did in the military. Another was to safety wire the connector in a criss-cross pattern directly to the unit chassis so it couldn't fall off if the knobs came loose. I haven't yet decided what method I might use, but I lean toward drilling the knobs. I imagine I'd look for connectors with thick, relatively stiff knobs to facilitate this method. I can always fall back on the chassis method if needed. I've done that before on other stuff, but it's kind of a pain.

 

[CanardMulti]

A much simpler solution to your attitude worries: Move your knob panel to beneath your left screen. Move your autopilot panel to the hole left by knob panel. Mount a Garmin G5 to the left of your left screen. Under $1500 including a 4 hour backup battery. No network vulnerabilities.

 

[jakej]

DB connections to devices eg EFIS, EMS & ADAHRS etc are much better/easier now with the newer black backshells supplied with most Dynon equipment. They have much bigger ends on the thumbscrews to give more 'leverage'. If those connectors come off inflight then they were not secured properly in the first place - ie, it doesn't happen.
The simple 'silver' DB backshells - I have seen many of theses not secured properly because the much thinner thumbscrew shaft can be difficult to do up especially in awkward limited access spaces & with fat fingers.
Inline joining & 'securing' the silver DB connectors can be done very simply & better with -
1. (best method IMO) do not use the thumbscrews at all (on the silver backshells), just use 6" cable ties ( I only use the Thomas & Betts ones with the stainless steel locking barb) diagonally across the 'ears' of both connectors - that way you know visually that they are joined securely (its like using torque seal on hardware) & that there is no doubt they are done up.
2. Silver backshells -Use screw jacks on one DB connector & the thumbscrews on the mating DB & use pliers to tighten them up if you wish - simple.
3. The above 2 are the simplest, easiest & most cost effective method - that's what we all want

 

[Rhino]

A much simpler solution to your attitude worries: Move your knob panel to beneath your left screen. Move your autopilot panel to the hole left by knob panel. Mount a Garmin G5 to the left of your left screen. Under $1500 including a 4 hour backup battery. No network vulnerabilities.

If you're going to go that route, just get a Dynon D3. Cheaper, and doesn't require a total panel redesign.

 

[rjones560]

If you're going to go that route, just get a Dynon D3. Cheaper, and doesn't require a total panel redesign.

I have 2 ADAHARS and 3 screens capable of displaying flight instruments. The object was to prevent one failure from killing all my attitude and air data. The way it is wired now, no single connection failure can kill my Attitude/air data. This is better than having 4 D9 connectors in series, any of which could kill all attitude and air data. All you really have to do is start going through your network and looking at the impact on your system if each one failed by itself. If you think that any network connection you have failing will have minimum impact on safe flight you are probably fine. I considered another attitude indicator. I thought it wasn’t necessary as long as one point of failure could not stop data from both ADAHARS. Then I really do have a backup for any possible single failure.

 

[Rhino]

Didn't mean it would be suitable for what you want. I meant it would be much simpler and cheaper than the scenario jakej laid out.

 

[JoshT]

I use to work on Fly By Wire systems for the biggest jets out there, so this is an area of interest for me. Even though I probably will never fly the plane in thick soup, I wanted more than 2 sensors from the same manufacturer. I like the D3, but its going to share some or many of the software and hardware components as our skyview ADAHRS, making it susceptible to the same software bugs or common mode failures.

Don't jump on me for over analyzing - this level of scrutiny isn't conducive to finishing an airplane kit

I found a nice simple 3rd sensor at Oshkosh that looks to be popular for gliders. Probably will be the solution to my "problem".

 

[rjones560]

I do fly IFR part of the time. I don’t plan on shooting the ILS down to 200 and 1/2 anymore. My weather minimums are higher than when I was flying jets for a living. However I wanted enough reduncy to keep me out of trouble. I also installed 2 alternators since the aircraft is all electric. I am fairly comfortable with my current installation. I can easily deal with any individual failure, and even many multiple failures in an IFR environment. If I had a primary alternator failure away from home I would feel comfortable flying home VFR with the backup alternator. I would also feel comfortable flying home with one screen failure in VFR conditions.