[MrNomad]

The mission for my RV9A is cross country, Tucson to Long Beach and back. Therefore, the Dynon Autopilot and the optional AP74 was indicated. It?s great combo minus a couple of issues.
On occasion, my Lowrance 2000c loses the GPS signal (or, the D180 THINKS the signal is lost) and the AutoPilot switches to TRK mode versus NAV mode. Invariably, when the AP loses the GPS signal and switches into TRK mode, the AP relinquishes control of ALT. When the AP relinquishes control of ALT, the nose of my RV pitches up radically.

Dynon?s manual says: ?When the autopilot is flying the Aircraft in Altitude Mode, an out-of-trim indicator can appear to the right of the AP Status Indicator. This alerts you when the pitch servo detects excessive load on the elevator which would result in a large pitch excursion when the AP is disengaged.?

My AP does suggest a trim change and I implement the trim change until the AP no longer requests a trim change. But when the AP disengages due to loss of GPS signal or garbled comm, it results in a large pitch excursion.

When the GPS loses the signal, the AP switches to TRK mode (versus NAV mode) but it also releases control of the horizontal stab. If the airplane is out-of-trim when the AP servo relinquishes control of the horiz stab, the nose of the RV will pitch up.

And that?s exactly what it does.

That brings me to two questions. First, I question why the AP relinquishes control of ALT just because it loses GPS signal and can no longer follow NAV. The default (IMHO) should be TRK and maintain ALT (or the requested ALT) when/if the AP loses comm with the GPS. Perhaps there is such an option, but I haven't found it.

Second, when my AP is engaged, it usually suggests a trim change but how do I know if that requested change is actually req?d? Perhaps the AP's request for a trim change is not actually required. To test the theory that NO trim change is req?d, I plan to fly the airplane to a specific ALT & speed, trim it so there is little to NO stick pressure req?d, and then engage the AP. If the AP STILL requests a trim adjustment, perhaps my test will confirm that the AP is requesting a trim change that the airplane does not require.

Any thoughts and suggestions are welcome.

Second, why does the GPS signal get lost? Perhaps the GPS signal is not getting lost. Perhaps the communication between the GPS and the autopilot is getting scrambled. A tech counselor suggested a change to the baud rate between the GPS and the D180. I reduced the baud rate from 9600 to 4800 but the GPS and AP lost comm two times during yesterday?s x country which is typical.

The Lowrance GPS never reports any signal loss but perhaps that information is not available to the user so it?s unknown what the issue is. Quite frankly, I'd like to have a GPS that does not lose the signal or a GPS that the autopilot will understand 99.9% of the time.

At present, my GPS antenna is the external unit that comes with the Lowrance and it sits on the glare shield. If there is a better choice, please make a suggestion.

As a workaround, I now fly the airplane with the AP in TRK mode instead of NAV mode so when the GPS and the AP no longer communicate (or the data gets scrambled), the airplane does not radically pitch up. Using the AP74 knob, I modify TRK to mimic the route suggested by the GPS. The Lowrance offers BRG and TRK so it?s a simple task to tune TRK and head the airplane in the correct direction. The only time I use NAV to control the AP is when I enter the LAX basin. It gets sooooo busy in that airspace that I prefer to rely upon NAV to guide the airplane and further reduce my workload.

Your thoughts, suggestions, and ideas are quite welcome. If there is something that I missed in the excellent Dynon manuals, I apologize for my oversight. Eventually, I?d like to fly IFR so these issues need to get resolved and I appreciate any thoughts you folks may have.

 

[Brantel]

Dynon's AP has a problem with GPS Nav where it will occassionally lose the GPS.

At first they were saying it was limited to one model handheld GPS but I have seen it reported with all of the X96 series, 430's and now 2000C's

They also said that it was the GPS that was not updating fast enought etc. or was putting out bad data. I find this hard to believe with so many different models and brands having the same issue not to mention the TSO'd panel mount.

It is strange that the competitors do not seem to have an issue with this if it is the GPS's fault.

Dynon has stated that they are looking into it but who knows how high a priority it is for them.


On the servo trim sensing issue, keep us informed on that one. I have not seen anyone complaining of that issue yet.....

Are you talking with Dynon support? If not, please do so they can work on these issues!

 

[647jc]

I have a DYNON D100 / AP and no AP74. I also have an AvMap IV GPS. My DYNON will also intermittently loose the GPS signal as many other people have reported. When I am in AP NAV mode when the GPS signal is lost the AP simply switches to TRK mode and REMAINS in altitude hold mode (I'm pretty sure). Perhaps you loosing the altitude hold mode is related to your AP74 configuration.

Although the D100 / AP does not loose the GPS signal very often, it is an annoyance when it does especially since I may not notice the switch for quite some time, I think there should be an audio annunciation when this happens.

My AP trim sensing logic and display appear to be working normally. I know DYNONs recent code release de-sensitized the trim required notification logic a bit, on the previous code release you could end up chasing the trim quite a bit trying to make the AP happy.

 

[MrNomad]

Loss of GPS signal and pitch issue.

Thank you Brian. If you missed my reply to your EGT sensor question, I pulled two of my sensors when I changed my oil in June and both of them appeared to be in great shape. I use auto gas primarily so my results with those sensors may be different. I'm not a fuel expert but if fuel has any affect on the life of sensors, I felt it wise to disclose that info.

Yes, I email Dynon and they are most helpful and cooperative. I have not received a response to these recent questions yet, but if the past is any indication of the future, Dynon will respond with helpful suggestions.

My "workaround" for the loss of GPS signal is OK for right now. Dynon told me that Lowrance and other GPS vendors refuse to disclose the exact format of their data and what their software does when abberant conditions occur.

I know there are standards but deviation from standards is a common problem in software development. In my 30 years in that business, the departures from the so-called standards were all too common.

My friend Chet responded and offered the use of his Lowrance so we can determine if the problem is my unit. He also suggested that we tape the antenna to the top of the canopy for a test. Perhaps reception is the issue.

When I was a software developer sitting in an air conditioned office, customer problems were important to me. But when you're flying into Long Beach, ATC is speaking so fast you can barely understand them, LA haze encumbers visibility, ocean crosswinds are present, and then the equipment malfunctions, the pucker factor is a little different than my former desk job.

 

[rvmills]

Barry,

On the loss of your Nav mode: As Brian said, this is an ongoing issue with the Dynon AP. It is discussed (with no solutions identified, as Brian mentioned) in this thread on their Support Forum:

http://dynonavionics.com/cgi-bin/yabb2/YaBB.pl?num=1229344511/0

Brian and I have both posted on that thread, and it may be worth looking at (if you haven't already), and since you also have the odd situation of the AP disengaging followed by the pitch up (very odd and disconcerting indeed), you may want to post there to to see if you get some traction there (or just re-energize the issue so it moves up on their to do list...they seem very responsive, though the issue is still unresolved).

When this issue happens to me in flight, I (and other posters there) get a "NAV Source Lost" indication on the EFIS, and the AP switches to TRK mode. However, my AP does not disengage, it holds TRK, and stays in ALT hold mode. One of the beta testers replied that it is a known issue, and Dynon is working it. He explained that it is due to the GPS getting backed up and sending "stale" NAV data. Not sure exactly what that means in a data sense, but I find that when I get the "NAV Source Lost" error message, I can immediately push the NAV button, and the AP goes right back to tracking NAV. Not sure if the GPS NAV data is no longer stale, but pushing NAV right away always seems to work immediately for me. Rather than having to use the TRK mode and make adjustments, perhaps you can try using NAV, and just reselecting NAV when the AP switches to TRK. Do you get the "NAV source lost" message when this happens to you?

Of course, if you are also getting an AP disengage and a pitch up every time this happens, then you are facing a different situation, and perhaps two simultaneous problems at once. I don't think anyone else has reported a disengage/pitch up when they lose the NAV source, so posting that would be a good add to their data. Another poster in that thread said his AP also goes to TRK, but then starts a rapid turn, which does not happen to me, but if you combine his issue with yours, that gives them more to look at in this situation.

On the trim annunciations and AP disengage, I think you have a good plan with respect to seeing if you get incorrect trim annunciations. I see trim annuciations commensurate with what the manual says to expect...ie, occasional short-lived UP/DN indicators in a yellow box when gusts are present (no need to trim those out if they go away in a second or two), and occasional longer-lasting UP/DN indications if I am actually out of trim (and trimming does make them go away).

It would be interesting to see if you do get longer-term UP/DN indications after trimming to hands-off then engaging the AP. Another test might be to try going from that in-trim state (with the AP on and holding well, with no UP/DN indications shown), then while the AP is still engaged, trim till you just get a solid UP or DN indication, and then carefully disengage the AP to see how the plane reacts. Then compare that to the uncommanded pitch up that you get when the AP disengages on its own when you lose the NAV source.

Your combo of losing NAV source, defaulting to TRK, and the AP disengaging is really an odd one. This may be reaching, but do you have electric trim? And if so, do you see any trimming going on when this all happens to you? I ask, because it almost sounds as though you're getting a spurious trim input when you move from NAV to TRK, thus the AP disengage and pitch up. I can't recall if the Dynon AP currently has an auto trim feature (I have manual trim so it's not on my radar), and like I said, that may be a stretch...but just a thought.

I'll be very interested in how your trimming tests go, and then see if once you nail that piece down, if the AP disengage/pitch up still happens when you lose the NAV source and default to track. Sure concur with you about not wanting to fly IFR or in busy airspace with this stuff going on!

Good luck!

And Joe, your idea about a tone or voice warning when the NAV source is lost would be a nice addition to the "NAV Source Lost" visual warning.

Cheers,
Bob

 

[MrNomad]

Replies and suggestions on NAV loss & D180 reboot

Bob, Brian & Joe:

Earlier in the installation cycle, I offered to send my Lowrance 2000c to Dynon and bought an extra serial cable for them. One of Dynon?s beta testers installed my Lowrance into his RV6 and flew it, accumulating data. He sent that data to Dynon and my guess is that they used his data file to distinguish the format of the Lowrance data so that they could integrate it into their program.

However, I don?t know if the beta tester experienced a data loss during his test. In my retired computer programmer?s mind, until we see the pattern of the aberrant data or condition, it may be impossible to supply a software workaround.

Having been on the other side of software development for 30 years, I would like to help our vendor solve this problem and another post on this website showed one way we can help Dynon even though our brand of GPS is different.

In this post, http://www.vansairforce.com/community/showthread.php?t=45769
Christopher and Jamie Lee wrote some software to intercept the data that comes out of a serial port. Conceptually, this is no different than the data logging our Dynon units perform. With Chris? code and a laptop, I expect I can xmit the data from my Lowrance to my laptop which will be left on to record data during the next flight to SOCAL, and onto the Dynon at the same time. I have never made that flight w/o at least one GPS loss so it?s all but certain to show itself.

Assuming the recorded data is marked with a time stamp, WHEN the Lowrance sends something that causes the Dynon to drop NAV, all I have to do is look at my watch which is synched to the laptop?s time and write down the time it occurred.

Next, send the data to Dynon so they can see what happens when the problem arises. Hopefully, it will be obvious and if there are several occurrences, hopefully they will be similar.

Once they know what?s happening with Lowrance, Garmin or any other GPS, the remedies are many. Dynon?s code can reject the defective sample and advise the pilot via a warning, or re-sample in 5 seconds and if the data looks good at that time, continue in NAV mode. Essentially, this is what we do manually when NAV is dropped. We press the NAV button again and it resumes. It would not surprise me if Dynon is already doing some of this but they may not have seen the defective data causing the mishap.

I posted a message for Christopher and Jamie Lee but understand that work and family may not afford them adequate time to help. My C++ skills are rusty but if anyone on this forum will send me sample C++ code and some assistance with a compiler, I will get back into the software game and implement the data capture myself.

Tomorrow, the wife and I will venture back out into LAX airspace. It would be REALLY nice to have a GPS and AP that can hold hands and help us thread the needle thru this incredibly busy airspace. Until I resolve this along with the large pitch excursion I will likely continue to use TRK and ALT and input changes to TRK manually with the AP74 knob.

Joe said: Perhaps you losing the altitude hold mode is related to your AP74 configuration. I have found no option therein but your comment was positively intuitive, Joe. No kidding. Perhaps the D180 reboot issue is contributing to this or even precipitating this. There is no doubt that the nose pitches up radically when NAV is lost. I press the stick AP button to disengage AP so I don?t have to override the servo.

During the flight from Tucson to Long Beach, I was in TRK and ALT mode and simply followed the HDG suggested by the GPS. I looked at the HSI and noted that NAV was lost. Of course, I was not in NAV mode so nothing occurred. Maybe that tells us something. Maybe Joe inadvertently helped me by triggering the thought that my D180 reboot issue expresses itself in a variety of ways.

Bob suggested: It would be interesting to see if you do get longer-term UP/DN indications after trimming to hands-off then engaging the AP. Another test might be to try going from that in-trim state (with the AP on and holding well, with no UP/DN indications shown), then while the AP is still engaged, trim till you just get a solid UP or DN indication, and then carefully disengage the AP to see how the plane reacts. Then compare that to the uncommanded pitch up that you get when the AP disengages on its own when you lose the NAV source. Great ideas Bob, I will do that during the ride home when we are out of LAX airspace.

Concerning the ?Dynon 180 rebooting itself? problem, Dynon responded that they believe that wiring is the likely culprit so Chet and I will go thru the wiring again when the 9 is back in the hangar. I have two compasses, a Dynon 100 & a D180, so I can swap the wires in the tail and see if the problem travels to the other Dynon

Thanks folks. It?s great to be able to discuss this with others and help ourselves. I checked Dynon?s forum also per Bob?s suggestion. WHEN I solve my problems, I promise to stick with this and continue to help you.

 

[rvmills]

Barry,

I saw your post in that other thread, and it does perhaps open up some additional possibilities. I've not done any datalogging, so am not too familiar with what parameters are recorded. Any idea if GPS serial data is included? If so, you maybe able to capture what you are looking for in terms of bad data from the GPS to the AP/EFIS.

On your pitch up issue, I may have misunderstood what is happening. In your first post, you said the the AP is releases or relinquishes control of the h-stab (elevator). I took that to mean the AP was disengaging, and you were pitching up due to an out of trim condition.

In this last post you said, "There is no doubt that the nose pitches up radically when NAV is lost. I press the stick AP button to disengage AP so I don?t have to override the servo." That sounds more like it is a pitch up commanded by the AP, rather than the AP disengaging due to an out of trim condition. The fact that it is happening when you lose the NAV source (and only when NAV is selected) makes this sound much more complicated, especially when you add in your D180 rebooting issues. My safety spider sense starts tingling when you add all of these different issues, and have an AP that is, as you describe, "pitching up radically".

Although you seemed to have found a mode that works OK (ALT + TRK), I'd be really cautious about testing the envelope, until you have the chance to really check all the wiring and connections (all the stuff you mentioned doing above), and figure out why the reboots, and expecially the pitch-ups, are happening... and get some good test flights in all modes under your belt.

Just trying to be a good wingman! Good luck in the troubleshooting, and look forward to hearing about your progress.

Cheers,
Bob

 

[Jamie]

When I had the Dynon AP I had both of these problems (sort of). My AP would lose the NAV GPS source and switch to TRK mode.

I had the trim pitch issue as well. In my case, the AP trim indication was telling me to trim nose down even when the airplane was in trim. If I trimmed the airplane until the out of trim indicator dissapeard from the EFIS screen and disconnected the AP, the airplane would of course pitch down.

I flew my airplane with three different Dynon servos doing pitch duties. Only one of those servos exhibited that behavior. The problem is with the servo. Go to the servo status screen...then check for the servo force value while engaging, disengaging the AP and applying force on the stick. You will see the servo force is out of whack even when you are applying zero pressure to the stick on the ground. You'll probably have to send your servo back to Dynon. That was their only recourse at that time.

It's almost like dejavu all over again.

 

[N941WR]

...And Joe, your idea about a tone or voice warning when the NAV source is lost would be a nice addition to the "NAV Source Lost" visual warning.

Cheers,
Bob

Funny, but I had this discussion about a voice warning when the nav source is lost with Dynon a few weeks ago so I know that change is on "the list".

As for the ALT hold, your GPS should not let the plane pitch up when switching to TRK. I've had this happen a number of times with my 496 and it never once move, just simply changed to TRK mode. Contact Dynon and ask them what is going on.

BTW, from time to time, I'll take the AP off ALT hold and check the trim. It is never so out as to cause a quick altitude divergence.

Dynon is working on the nav source issue when the GPS signal goes Tango Uniform. They take this problem seriously and are hard at work to resolve it.

 

[MrNomad]

Followup on Thursday's excitement

Dynon is working on the nav source issue when the GPS signal goes Tango Uniform. They take this problem seriously and are hard at work to resolve it.

That's good to hear Bill but I have no idea what Dynon's timeline is so I will continue to actively seek an answer to what's causing the D180 to lose GPS guidance. Ideally, I'll find someone to help me assemble the C++ code and connect my laptop to the GPS as well as the D180. Then I WILL KNOW what the data looks like and WHICH device is the likely culprit. I will make those routines available to anyone else who'd like them and send the data to Dynon to assist them.

Joe, I'd like to speak to you so please give me a call 520-548-6773 (cell) or send an email add so I can get in touch.

I've experienced the loss of GPS that caused the D180 to flash the warning message and go into TRK mode at least twice on every x country, but on occasion, the nose of the airplane also pitches up.

The question is, WHY DOES THE NOSE PITCH UP? I can think of only two reasons. First, the trim was out, the AP relinquished control of ALT, and the out of trim situation caused the plane to pitch up. Or, second, the elev was commanded to pitch up. Of course, all of this occurs pretty quickly and my instant response is to return to level flight given a speed of 140++ kts. I recall sensing servo resistance when this happened on Thurs so I intuitively pressed the AP disconnect button on the stick.

Another post elsewhere on this site claimed he went thru three servos and one servo exhibited the same issue. The AP claimed trim was required only to find out that it wasn't when the pilot disconnected.

Later in the same flight, I disconnected AP to make a quick course correction but no trim error was evident so I can only theorize exactly what happened before. Dynon's response said: "...altitude should not be affected by GPS being lost so please double check that."

Suffice to say, I will check trim frequently via disconnect during today's short flight from LGB to MYF and tear into the compass wiring as soon I get home as Dynon believes that's a likely contributing factor. Until then, it's TRK & ALT using the GPS to suggest a route. I will experiment with NAV after I am OUT OF SOCAL and the wife is not aboard. Anyone whose flown thru here will readily understand why.

Thank you all for your helpful comments and ideas. If you want to form a private users group using email & phone, I'm OK with that. As soon as I learn anything more about these issues, I will make it available to others.

Barry
Tucson

 

[rvmills]

<snip> I will make those routines available to anyone else who'd like them and send the data to Dynon to assist them.

<snip> The question is, WHY DOES THE NOSE PITCH UP? I can think of only two reasons. First, the trim was out, the AP relinquished control of ALT, and the out of trim situation caused the plane to pitch up. Or, second, the elev was commanded to pitch up. Of course, all of this occurs pretty quickly and my instant response is to return to level flight given a speed of 140++ kts. I recall sensing servo resistance when this happened on Thurs so I intuitively pressed the AP disconnect button on the stick.

<snip> Later in the same flight, I disconnected AP to make a quick course correction but no trim error was evident so I can only theorize exactly what happened before. Dynon's response said: "...altitude should not be affected by GPS being lost so please double check that."

Barry
Tucson

Barry,

On the testing piece, I'd be game for collecting the same data when you get the testing program put together. Will need to work with you on how to connect it all up, but if it helps ID the serial data that causes the "NAV Source Lost" error, all the better (and it would be interesting to compare what causes it with my Garmin 396 versus what does it with your Lowrance). If it is indeed "stale" data that is causing the drop from NAV to TRK, it may be a matter of how the EFIS/AP "data aging" tolerances are set, if there is such a parameter in the algorithms (and my gut says that Dynon is working that piece hard). Probably not a simple matter for them though. If a little extra data helps them find the key that unlocks the door, then happy to give it a try. I still want to look at datalogging more closely to see if serial data from the GPS is captured.

On the pitch up, IMHO it sounds more and more like an uncommanded AP input, which is pretty bad juju. That statement (of conjecture, not fact) is based on your description (airplane is in trim when you disengage it under normal circumstances; and you disconnect the AP when the pitch up does occur, to regain control). It will be very interesting to see if your work on the compass (or other) wiring alleviates the pitch up (that would be a very good turn of events!)

One thing I've noted, that may help with your testing and evaluation, is that when either of my pitch or roll modes is disconnected, I get an "Autopilot Disconnect" voice alert from my AP-74. For instance, if I am in ALT/HDG, and I push the ALT button to disconnect just the pitch mode, I get the voice alert, even though the AP is still engaged (in HDG only). Same goes if I am in ALT/NAV, and I reach up and select the NAV button off (now I'm in ALT only, and just the roll servo is disconnected)...I also get the voice alert. I found it to be an interesting methodology, in that I would have expected that alert only if I fully disengaged the AP (all modes), with the AP button or the disconnect switch, or if the AP fully disengaged on it's own. Not necessarily a bad thing, as it does tell you that something has changed...just different than what I've seen in other AP's I've flown behind (and I don't know if that is how TT or Trio do it). My reason for mentioning this is to ask, when you get the pitch up, are you getting an "Autopilot Disconnect" voice alert? If not, I'd say that it is more likely that the pitch up is uncommanded AP input. Just something to look (listen) for when its all happening so quickly.

Happy to talk off line as [email protected].

Good luck with the testing!!

Cheers,
Bob

 

[Mich48041]

Dynon Autopilot switches from NAV to TRK problem

See my posting in the RV-12 forum about this problem.
http://www.vansairforce.com/community/showpost.php?p=590576&postcount=6

 

[MrNomad]

Update from the pilot who started this post

[FONT=&quot]I am the fellow who started this post 5 years ago and during that time I've enjoyed great success with the Lowrance and the AP74.[/FONT]

[FONT=&quot]Yesterday, I used the Lowrance and the AP74 for the entire flight from Tucson to Long Beach CA. I set ALT to 8500, set the throttle to 2450 rpm, and never touched the stick for 3 hours.[/FONT]

[FONT=&quot]The GPS lost the NAV signal 3 times but I just hit NAV and it found the signal & worked immediately. It flops into TRACK mode during the outage which is fine. [/FONT]

[FONT=&quot]I was 30 miles out @ VPLSA and SOCAL told me to fly direct to 25R @ LGB so I punched ZIN ZOUT, toggled to LGB, hit GO TO, and let the GPS find the airport in this hazy, busy mess known as SOCAL. In other words, I abandoned my 14 step pre-programmed route in less than 3 seconds and avoided the regular waypoint known as the 91/605 interchange.[/FONT]

[FONT=&quot]From Banning to LGB which is 70 miles, they changed freq 5 times but I was hands free and able to attend to changes easily. My 9A was descending and zipping along at 160kts and all I had to do was change ALT on the AP74 once I got clearance to descend. Two miles out from LGB, a Jet Blue was landing so they had me execute a 360 and then cleared me to land but I was off AP by that time.
[/FONT]

[FONT=&quot]I don?t care what anyone says, the Lowrance does a GREAT job with the AP74 and when they change the restricted areas, if we cannot get an update, we can put in WAYPOINTS to avoid. The Lowrance will last forever as far as I am concerned for the flying I do. If they change PHX airspace, I will create a custom map using Photoshop and set waypoints with the ALT I need to be at or above.[/FONT]

[FONT=&quot]If someone out there can figure out to apply Jeppersen updates, we can buy the Jepp maps and install them into the Low database. From my limited dissection, all that's required is to embed the serial number. One would hope that the vendor would make that available to the customers when/should he abandon this product.
[/FONT]