Erratic Airspeed - Dynon HDX

J

Joe

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May 17, 2020
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The airspeed indication on my Dynon HDX, installed in my RV-14A has become very erratic. It is now to the point that I can not shut the system down because it thinks the plane is moving. I am suspicious that the static line could have water in it and plan to check this today. I have done the zero airspeed calibration to no avail. Plane is sitting in my hangar, doors closed, pitot cover installed and the IAS runs up and down about 20 - 30 knots. Occasionally the zero airspeed calibration seems to help, but this does not last long. It has gotten to the point that sometimes the only way to shut the system down is to unplug the display units (2-10" screens) because it switches over to backup battery power when the master/avionics switches are turned off.
Any suggestions?
 
If zero pressure calibration didn't help, AND you've checked for water (that can definitely do it), then we'd probably want to look at your ADAHRS.
 
Joe said:
Sometimes that works and sometimes it does not! You never know. Weird.
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That may be something else you should check then. The system should be able to be shut down when flying. I have done it at times to "reset" things. It has never not done it when I needed to. Is it an assumption that it won't shut down sometimes when it thinks you're flying (i.e. airspeed being indicated), or is that documented somewhere I missed?
 
PilotMelch said:
Is it an assumption that it won't shut down sometimes when it thinks you're flying (i.e. airspeed being indicated), or is that documented somewhere I missed?
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It has been stated by Dynon on a number of threads that the screen(s) will remain on battery (if equipped) if power is lost and airspeed is detected. I don't recall the threshold.
 
Raymo said:
It has been stated by Dynon on a number of threads that the screen(s) will remain on battery (if equipped) if power is lost and airspeed is detected. I don't recall the threshold.
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Indeed, that's precisely *the point* of having a backup battery. Also, note that the general description is in the User's Manual under "Loss of External Power with Backup Battery Connected".
 
Raymo said:
It has been stated by Dynon on a number of threads that the screen(s) will remain on battery (if equipped) if power is lost and airspeed is detected. I don't recall the threshold.
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Yes, but did joe lose external power? Turning the screen off using button one is not the same as losing power. It is a direct command to "turn off", which can also be done if you lose power and are on the backup battery. I can't think of a time when I wasn't able to turn off a screen regardless of the airspeed being indicated, regardless of how it was being powered.

Joe said he was sometimes unable to turn off the screen "because" there was indicated airspeed (erratic), even though you were on the ground. That still seems very odd and is not my understanding of how the system is designed to behave.

You should ALWAYS be able to manually shut the screen off by holding down button 1 for the designated time until it turns off.

Dynon screens with backup batteries are designed to stay on when external power is lost, regardless of the indicated airspeed. What they do with the airspeed when external power is lost is not to then automatically shut off after a countdown on the backup battery power.

Again external power loss is different than holding button 1 down to shut down. To be clear, you can do that to manually shut down at any time, whether under external power or under battery power, in the air, on the ground, ... Literally at any time.

Joe, if you are having trouble manually shutting down your Dynon with button 1, regardless of the circumstances, I think you have a whole 'nother problem too. You should always be able to do that.
 
PilotMelch said:
Yes, but did joe lose external power?
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That's the point of his post. When turning the master off, the screens detect airspeed and remain on battery power. It sounded as though he was unplugging the screens at the back to get them to shut down when all he needed to do was use button 1.
 
One of us is still confused. Joe, are you turning off the screens using button 1, or by removing external power? They are not the same thing.

Nevertheless, using button 1 should ALWAYS turn off the screens.

The issue I was responding to was Joe responding to the question about using button 1 and saying sometimes it works and other times it doesn't (see post #3). That would be another problem because it should ALWAYS work.
 
PilotMelch said:
Dynon screens with backup batteries are designed to stay on when external power is lost, regardless of the indicated airspeed. What they do with the airspeed when external power is lost is not to then automatically shut off after a countdown on the backup battery power.
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No, even with backup batteries, when external power is removed *and the plane is not moving (i.e., zero or very low airspeed), the system will enter a 30-second countdown to shut off. NOT "regardless of indicated airspeed".

Let's not make this more confusing than it already is.
 
swatson999 said:
No, even with backup batteries, when external power is removed *and the plane is not moving (i.e., zero or very low airspeed), the system will enter a 30-second countdown to shut off. NOT "regardless of indicated airspeed".

Let's not make this more confusing than it already is.
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Raymo said (post #7): It has been stated by Dynon on a number of threads that the screen(s) will remain on battery (if equipped) if power is lost and airspeed is detected. I don't recall the threshold.

If the indicated airspeed does not keep the units alive without a countdown when external power is lost, my bad. I actually thought that was the case too. I've just never run into that situation to live it.

I can however, always force a screen off (without any countdown) by holding down button 1 until it turns off. I've had Skyview, Skyview Touch, and HDX, and I know of no exception.

So if this is all true, that if external power is lost you get a 30 second countdown, always; and
If you hold down button 1 you can always force a screen off; then

Joe's system has major issues and his assumptions are likely incorrect. The eratic airspeed isn't keeping his units alive and he should always be able to turn them off, either by removing external power (turn off Master) and waiting 30 seconds (or pressing Pwr Off in this state), or forcing them off by holding down button 1.
 
So if this is all true, that if external power is lost you get a 30 second countdown, always...
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Which it is not. If airspeed > some value (unknown, but not 0), then *the system will remain ON*.

Let's look at the manual (imagine actually reading the manual):

Loss of External Power with Backup Battery Connected
If external power is lost to a display that is connected to a backup battery, it will either stay on for an additional 30 seconds or stay on indefinitely depending on whether or not the aircraft is in flight. This feature minimizes backup battery discharge when on the ground and master/external power is shut off normally. It also reduces pilot workload during an actual in-flight power loss.
If the aircraft is not in flight, SkyView displays the message “POWERING DOWN IN xx SECONDS” while counting down from 30 seconds. During this countdown, the menu displays the buttons STAY ON and PWR OFF at the bottom of the screen. Press PWR OFF to turn off the SkyView display immediately. Press STAY ON to keep the SkyView display on via the connected backup battery. If STAY ON is pressed, the display will continue to use the backup battery to power itself until the battery’s charge is depleted or the display is turned off manually pressing and holding button 1. Finally, if neither button is pressed before the countdown expires; the display will automatically turn off after 30 seconds to conserve the backup battery charge.
If the aircraft is in flight, SkyView displays the message “AIRCRAFT POWER LOST” with no additional count down. This ensures that active pilot action is required to turn off a display when power is lost in-flight and backup battery power is available. The STAY ON and PWR OFF buttons are still offered, but the display will stay on indefinitely unless PWR OFF is pressed.
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swatson999 said:
Which it is not. If airspeed > some value (unknown, but not 0), then *the system will remain ON*.

Let's look at the manual (imagine actually reading the manual):
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Let me clarify a couple of things: When the Master and Avionics switches are turned off the countdown begins at 30 seconds, which is what one would expect. However my indicated airspeed fluctuates anywhere from zero (or less) to 30-40 knots even though the plane is in still air in my hangar. So, the countdown stops and resets to 30 seconds. It may countdown to as low as 5 seconds and then reset to 30 seconds. The POWER OFF button usually works, but not always. I can recall two different occasions where it did not and the only way to shut down was to unplug the units from behind the panel. I still believe the problem may be in the ADAHRS unit.
 
Joe said:
Let me clarify a couple of things: When the Master and Avionics switches are turned off the countdown begins at 30 seconds, which is what one would expect. However my indicated airspeed fluctuates anywhere from zero (or less) to 30-40 knots even though the plane is in still air in my hangar. So, the countdown stops and resets to 30 seconds. It may countdown to as low as 5 seconds and then reset to 30 seconds. The POWER OFF button usually works, but not always. I can recall two different occasions where it did not and the only way to shut down was to unplug the units from behind the panel. I still believe the problem may be in the ADAHRS unit.
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Ok, this has gotten a bit out of control. My original point was, and still is your (Joe)'s comment that he sometimes is unable to power off the units with button 1. In his clarifying here he says the POWER OFF button. I'm assuming that means he's attempting to hold down button 1 for a long time, long enough to shut down that screen, and it is not turning off.

This is the issue that seems odd to me. You should ALWAYS be able to turn a screen off with holding button 1 down. This "ALWAYS" is meant to be literal. I.e. it shouldn't matter if you have indicated airspeed or not. It shouldn't matter if the external (Master) is on or not. It shouldn't matter if you are on backup battery or not. Hold button 1 down and the system should turn off. If it doesn't there is something else wrong, perhaps additionally wrong.

Somehow this point got jumbled up with the airspeed keeping the units on, or what external power loss meant, or whatever. None of that matters to my point, which again is simply: If Joe is unable to turn off a screen at any point in time, regardless of the situation, then he has possibly another problem.
 
PilotMelch said:
Ok, this has gotten a bit out of control. My original point was, and still is your (Joe)'s comment that he sometimes is unable to power off the units with button 1. In his clarifying here he says the POWER OFF button. I'm assuming that means he's attempting to hold down button 1 for a long time, long enough to shut down that screen, and it is not turning off.

This is the issue that seems odd to me. You should ALWAYS be able to turn a screen off with holding button 1 down. This "ALWAYS" is meant to be literal. I.e. it shouldn't matter if you have indicated airspeed or not. It shouldn't matter if the external (Master) is on or not. It shouldn't matter if you are on backup battery or not. Hold button 1 down and the system should turn off. If it doesn't there is something else wrong, perhaps additionally wrong.

Somehow this point got jumbled up with the airspeed keeping the units on, or what external power loss meant, or whatever. None of that matters to my point, which again is simply: If Joe is unable to turn off a screen at any point in time, regardless of the situation, then he has possibly another problem.
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OK. I believe we have drifted away from the root cause of my problems. Let's assume, for discussion purposes, that I can always shut the screen off with the POWER OFF button. Lately I have been successful with this function. However, this does not explain why my airspeed fluctuates from -10 to 30 knots very rapidly even though the plane is inside my hangar, doors closed, pitot cover on. This is clearly the reason why the screen fails to shut down when the master switch and avionics switch are turned off. It thinks the plane is still moving and switches to backup battery power. Also, the horizon indicator also moves around.
On takeoff the indicated airspeed begins to settle down upon reaching about 50 knots and behaves more of less normally during flight. I have developed such a distrust of this system that I have mounted my iPhone on my panel with the GPS app activated during takeoff and landings. I know, GPS is not IAS, but knowing the wind speed I can compensate, thus avoiding a stall and falling out of the sky during maneuvering for a landing.
I have checked the static lines for leaks and water and all appears normal. All tubing appears to be connected correctly to the ADAHRS device. At this point I am at a total loss as to what I should check.
 
I'd suggest then that indeed you have checked everything you can check. Your problem sounds like an issue with the ADAHRS unit itself then. It's not unheard of that the ADAHRS unit fails or malfunctions. One of the planes I used to work on had an ADAHRS failure that appeared erratic at first, then total failure. This was about 3 or 4 years ago. We took the unit out, sent it to Dynon and they sent back a new unit. It was beyond its warranty period, so kudos to them (it's far from the first time they've done this by the way). Replacing the unit solved that problem. I'm not saying it is the same issue, but if you've checked everything else that you can check, then perhaps it's time to let Dynon check what they can check.
 
PilotMelch said:
I'd suggest then that indeed you have checked everything you can check. Your problem sounds like an issue with the ADAHRS unit itself then. It's not unheard of that the ADAHRS unit fails or malfunctions. One of the planes I used to work on had an ADAHRS failure that appeared erratic at first, then total failure. This was about 3 or 4 years ago. We took the unit out, sent it to Dynon and they sent back a new unit. It was beyond its warranty period, so kudos to them (it's far from the first time they've done this by the way). Replacing the unit solved that problem. I'm not saying it is the same issue, but if you've checked everything else that you can check, then perhaps it's time to let Dynon check what they can check.
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My thanks to everyone for their comments. I, too, had come to the same conclusion that the problem almost had to be with the ADAHRS. Do any of you have any experience with the turn-around time with Dynon if I were to send the unit in? I plan to fly my RV14 to Oshkosh in about a month and would really like to have a fully funtioning unit.
 
My experience is that they turn things around quickly. More time has been sent shipping than in their shop. I haven't had to send in anything for a couple of years though, and now they are full speed ahead on certified installs, so perhaps things have changed. I know they've hired others, so I'd call their support and ask about it.
 
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