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-   -   Single ADAHARS, Single big Screen and IFR (https://vansairforce.net/community/showthread.php?t=145091)

BobTurner 12-23-2016 03:00 PM

Quote:

Originally Posted by Walt (Post 1136361)
Just my opinion but honestly I don't think there's any real comparison between an inexpensive 'gyro' found is some AP's and a true ADAHRS such as the Garmin GSU25/73.

I respectfully disagree, sort of... If you have electric power my Trio Pro will fully control the airplane, with no reference to any other attitude source (like an EFIS), it will not allow the airplane to stall (if the pitot system is functional), and if your GPS is working it will fly an LPV right down until you hit the runway, and do it all better than 90% of the pilots who are hand-flying "real" ADAHRS systems.
OTOH, the digital altitude display and "bunch of dots" turn coordinator display make hand-flying using just the Trio display fairly difficult in all but calm weather. But if just used as a "tie breaker" between two EFIS boxes (one says wings level, one says turning), it easily tells you if you're turning, or not.

GalinHdz 12-26-2016 10:26 AM

Quote:

Originally Posted by N804RV (Post 1136185)
Seriously thinking about foregoing the double redundancy for PFD.

My thinking is, I'd have a single large screen (with a single ADAHARS and an EMS), a GTN650, and a small, inexpensive, self contained basic EFIS as a backup and maybe save a few dollars and some panel space.

Is anyone else doing this?

IMHO if you are going to enter actual IMC (even if it is only "light" IMC) DON'T DO THIS! As a matter of fact you really need TRIPLE redundant so if two disagree you have something to refer to as a tie-breaker. Your life is worth more than "a few dollars and some panel space". As been noted in other posts, even the old airplanes you refer to have multiple redundant systems and sources. Even back then they didn't go with one single source.

Think of it as insurance. It is better to have it and not need it than need it and not have it. I can't stress enough; Your life is worth more than "a few dollars and some panel space"

:cool:

RV8iator 12-26-2016 11:18 AM

It was easy for me.
 
I NEEDED a tie breaker. To me it's just another cost of safely flying IFR. 3 independent ADHRS was what I felt comfortable in the clouds with.

Sure it cost's a bit more, but me and my wife are worth every penny..

I'm sure there are any number of ways to do it.

Just always leave yourself an out when, not if, but when things go south.


skylor 12-26-2016 12:01 PM

Tie Breakers
 
Much discussion in this thread seems to imply that we need 3 fully independent AHRS/ADAHRS to have a "tie breaker'. However, just like a traditional 6 pack has adequate information to "tie break" in the event of instrument failure, so do glass panels with only 2 attitude systems. In my RV for example, I have a single AHRS dual display EFIS as well as analog airspeed, altimeter, artificial horizon, and vertical card compass for back up. I also have a Truetrak Vizion AP. In my case, a disagreement in bank between the iron gyro and efis can be resolved by observing GPS (GNS430W) track or the compass. Pitch information disagreement can be resolved by air speed and altitude trends. Heck, I learned to fly a Citabria "under the hood" including unusual attitude recoveries with only "needle, ball, and airspeed". And as others have stated, an independently functioning autopilot (Truetrak in my case) can also be used to stabilize the aircraft to determine which attitude source is correct. And yes, my plane has periodically been flown hard IFR, as well as many hours under the hood.

Skylor
RV-8

terrykohler 12-26-2016 12:41 PM

I'm Just Spit Ballin Here,
 
but it seems like most posters are talking about completing an Instrument flight after they lose a primary instrument. BAD CHOICE.
In the "old days", when we lost our sole vacuum source, we advised ATC (sometimes declaring an emergency) and looked for an exit out of IMC or a quick landing using our turn coordinator, compass and pitot static instruments. You don't need three or four or five independent ADAHARS sources to safely fly instruments, but you do need to know what to do if the dominos start falling, and from my experience, it's seldom to "carry on".
Terry, CFI
RV9A N323TP

RV8iator 12-26-2016 04:43 PM

Both absolutely correct
 
Both Skylor and Terry above are correct. It's a comfort level and what you are trained proficient too. In any emergncy or abnormal, fly the plane and work yourself out of it.

We had all rather be on the ground wishing we were up there than vice versa in a bad situation.

GalinHdz 12-26-2016 05:37 PM

Quote:

Originally Posted by terrykohler (Post 1136860)
but it seems like most posters are talking about completing an Instrument flight after they lose a primary instrument. BAD CHOICE.

I personally was talking about figuring out which instrument to trust before using any of them to get you back on the ground ASAP. Without at least a third instrument you are taking a 50/50 chance of getting it right. Not odds I want to risk my life on. YMMV

:cool:

RV7A Flyer 12-26-2016 05:55 PM

Quote:

Originally Posted by N804RV (Post 1136276)
I'm planning for an IFR "capable" system. It seems like all the glass sales promotions are aimed at dual and triple redundancy. Yet, most IFR "capable" C-172s with vacuum systems do not have all this redundancy. And, they've trained how many thousands of instrument pilots?

I know this is an old debate. But, I'm really curios to know if there are any others out there flying IFR behind behind a big single display, instead of the airliner style full redundancy.

I know with the steam gauges, you've got some redundancy with the fact that each gauge is independent and discreet. Whereas, if the EFIS display fails, you lose everything. That's why I would put a small basic self-contained unit, maybe a used D6, as a back up.

This is what I have...a Dynon SV1000T (with its own ADAHRS and backup battery), and a Dynon D6 (again, with its own ADAHRS and backup battery).

Seems to me that we should look at the most likely failure mode of an electronic/MIMS/whatever ADAHRS, which I suspect is probably a complete failure (which would show as a failed component/red X/etc. on the corresponding display). Second most likely might be a complete failure of a sensor in one axis, which perhaps would be caught by the EFIS or the ADAHRS and flagged (I dunno...maybe not, but it seems if a sensor is out and not providing data, the Kalman filter can't operate properly and find a solution?). Third, and probably least likely, is an *incorrect* reading from a sensor...which is what all the "tie-breaker" discussion has really centered on.

So I'd be interested in real-world data on failure modes and likelihoods, and then one could do a proper FMEA to figure out how to mitigate those risks. Just saying "failure" is not specific enough.

In the case of an incorrect attitude, I should be able to first see the difference between the two systems, then resolve it by comparing it to GPS track, airspeed, altimeter, ROC indicator, etc. Just as an example...sort of like how it has always been done in the case of a failed mechanical gyro or vacuum pump for a "traditional" AI, right?

BobTurner 12-26-2016 07:25 PM

Quote:

Originally Posted by RV7A Flyer (Post 1136917)
This is what I have...a Dynon SV1000T (with its own ADAHRS and backup battery), and a Dynon D6 (again, with its own ADAHRS and backup battery).

So I'd be interested in real-world data on failure modes and likelihoods, and then one could do a proper FMEA to figure out how to mitigate those risks. Just saying "failure" is not specific enough.

In the case of an incorrect attitude, I should be able to first see the difference between the two systems, then resolve it by comparing it to GPS track, airspeed, altimeter, ROC indicator, etc. Just as an example...sort of like how it has always been done in the case of a failed mechanical gyro or vacuum pump for a "traditional" AI, right?

Since you have an all-Dynon system, I'd be curious as to how it reacts to a partial pitot clog - bad enough to lose attitude reference, not bad enough to auto-switch to GPS (a failure like this has been reported here on VAF). Would both instruments look exactly the same (but both incorrect)?

RV7A Flyer 12-26-2016 07:33 PM

Quote:

Originally Posted by BobTurner (Post 1136931)
Since you have an all-Dynon system, I'd be curious as to how it reacts to a partial pitot clog - bad enough to lose attitude reference, not bad enough to auto-switch to GPS (a failure like this has been reported here on VAF). Would both instruments look exactly the same (but both incorrect)?

That's probably a question for Dynon...a *partial* blockage? Dunno.

If airspeed is unavailable, the SV manual says that GPS groundspeed is used as an attitude aid ("GPS Assist" is displayed). But with a partial blockage, I suppose that both of them would show the same incorrect value.

Better install a 2nd pitot tube to avoid this SPF. :eek:


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