Fly-away and crash at 30mph...

[Fracapouille]

Hello to all of you experimented P4 users...


I've had quite a bad day, as my P4Pro went crazy and crashed in a cliff at 80 mph (yup...).
I'm looking for some clues about what happened and if, as a pilot, I had anything to do with this.

A little bit of context below, but feel free to ask me anything that could help:

- I was doing a surveying mission in a remote area along a cliff. No GPS signal here, so I had to launch the mission in OPTI mode. I disconnected the ground sensors in order to reach 30m, then reactivated them while in flight. Maybe a bit clumsy, but it seemed to work perfectly fine for the first flight, quite sporty though when shifting from OPTI to ATTI, but everything went well. Absolutely no wind, calibration done before each flight.

- During the second flight, I totally lost control over the UAV. It made its own decision (no warnings or so before, except regarding the fact that I had reached the max altitude), and it was a very poor one. It decided to accelerate with no limit whatsoever until it hit a cliff at almost 80mph, and falled along the cliff to hit the ground 30 meters below. No need to say it is now in very bad condition...

- I've got no video recording to show, as I'm only using it as a camera. I was using it (and fully aware about that) with no GPS positionning: it seems that phantomhelp doesn't manage files without GPS positions (maybe I'm wrong here?), so there's no viewer available. Anayway the txt flight log is atttached. There's also a video of the last minute of flight as viewed by the DJI Go log viewer available here: Dropbox - 20170809_150206.mp4
I can send any other document if required for a better understanding.


Any clue about what happened would be really appreciated, and sorry about english mistakes, frenchman pilot here...

Thanks by advance for any help.

Cheers

 

[Fly Dawg]

Upload that file to Airdata and download it as a .csv file. Then try uploading to Phantom Help again.

 

[msinger]

Upload that file to Airdata and download it as a .csv file. Then try uploading to Phantom Help again.

My log viewer cannot read Airdata files.

 

[macoman]

Just to let you know in the future when you get another phantom. These aircrafts don't need to be calibrate every time you want to fly. If you calibrated once and went successful, do not do it again until it tells you to do it. You was calibrating the machine in every flight and that can cause issues if a bad calibration is performed.

 

[sar104]

Some very fierce stick inputs towards the end. Were those deliberate? That would certainly have the potential to get it moving fast in ATTI.

 

[Fracapouille]

Just to let you know in the future when you get another phantom. These aircrafts don't need to be calibrate every time you want to fly. If you calibrated once and went successful, do not do it again until it tells you to do it. You was calibrating the machine in every flight and that can cause issues if a bad calibration is performed.

OK! I thought it was mandatory at least eveytime the environment changes (Home altitude, barometric conditions, and so on...). Thanks for the advice!

 

[Fracapouille]

Some very fierce stick inputs towards the end. Were those deliberate? That would certainly have the potential to get it moving fast in ATTI.

View attachment 86601

Thanks for this data! Yup, those were deliberate, and in opposite direction the drone was going to... If you look at the video, you can see I push the stick mainly to the right, and a little bit to the front. I was surveying the cliff I was walking on, so the drone was looking towards my direction. It went very fast to my right, but by pushing right on the stick, it should have gone to my left...

 

[Fracapouille]

In the video, you can also see that the UAV shifts between, GPS, OPTI and ATTI multiple times at the end. Could it be a hint?

 

[Fly Dawg]

My log viewer cannot read Airdata files.

That's why I said to convert to .csv and then try to re-upload. It does read .csv file's right? Or does airdata format their .csv's differently? Confused???

 

[Fracapouille]

Thanks for your replies.
For the moment, no explanation about what happened?

 

[sar104]

Thanks for your replies.
For the moment, no explanation about what happened?

There is some strange stuff going on in the log file. The PhantomHelp viewer shows the aircraft in ATTI for the entire flight after takeoff, but the AirData equivalent shows it going in and out of GPS mode several times, complete with warning messages. However, the AirData log also shows zero satellites for the entire flight and no lat/long recorded, even when it shows GPS mode. The PhantomHelp log file shows up to 7 satellites at times, but also no lat/long.

That said, it looks to me from the stick inputs and inertial velocity data that you became confused at the end and actually applied the opposite stick inputs than you intended and simply flew it into the cliff. The graph below shows the final few seconds before impact at 833.1 s, and both elevator and aileron were accelerating, not decelerating, the aircraft. As a check on the flight behavior, the second graph shows the same data for the entire flight, from which it is clear that the aileron and elevator behavior were consistent through the flight. Does that seem like a possibility?

 

[Fracapouille]

Thanks a lot for your analysis and your comments.
Regarding the possibility that I may have been confused, it remains a possibility.
Is it possible for you to check on the log file some information (compass, yaw, or other...) about the orientation of the UAV in the seconds before the crash? Could it be possible for it to have rotated full 180°?

If so, my mistake. However, is it possible to check if the sensors were on, and in that case, shouldn't they do their job? How is it possible for th UAV to have been so fast?

Thanks again!

 

[Meta4]

How is it possible for th UAV to have been so fast?

Without data we can only guess.
One thing that that can cause what you described is launching from on top of steel or reinforced concrete.
I'd also be concerned about calibrating the compass before the flight.

 

[sar104]

Thanks a lot for your analysis and your comments.
Regarding the possibility that I may have been confused, it remains a possibility.
Is it possible for you to check on the log file some information (compass, yaw, or other...) about the orientation of the UAV in the seconds before the crash? Could it be possible for it to have rotated full 180°?

If so, my mistake. However, is it possible to check if the sensors were on, and in that case, shouldn't they do their job? How is it possible for th UAV to have been so fast?

Thanks again!

Yes - the yaw/compass heading data are good. It did not rotate and was reacting correctly to rudder input right up until it crashed. It was on a heading of approximately 72° until about 10 seconds before the crash, when you rotated it counterclockwise to a heading of approximately 27°, which it held until it crashed.

 

[sar104]

In terms of speed, it was travelling at just under 80 mph (36 m/s) at impact according to its inertial sensors, which it can integrate with respect to time to get velocity. But it was in ATTI mode and had no absolute position data, and hence no absolute speed data (i.e. instantaneous differentiated position). I don't think the FC is really able to control speed at all in ATTI mode - it is only holding alitude and attitude.

 

[sar104]

Without data we can only guess.
One thing that that can cause what you described is launching from on top of steel or reinforced concrete.
I'd also be concerned about calibrating the compass before the flight.

There is no obvious evidence of any compass issues until after it crashed. Those data look good.

 

[msinger]

That's why I said to convert to .csv and then try to re-upload. It does read .csv file's right?

My log viewer is only able to read DJI TXT logs and Litchi CSV logs.

 

[sar104]

My log viewer is only able to read DJI TXT logs and Litchi CSV logs.

And it reads the OP's file just fine - it just doesn't produce a map or position data table because there are no position data. It does, however, interpret and convert the file properly to a CSV for viewing in other applications, as does AirData, which is what I did above.

 

[Fly Dawg]

And it reads the OP's file just fine - it just doesn't produce a map or position data table because there are no position data. It does, however, interpret and convert the file properly to a CSV for viewing in other applications, as does AirData, which is what I did above.

Thanks for clarifying that. I converted the file on AirData to .csv and just read through it in Excel. I was confused as to why the Phantom Help viewer would not interpret the AirData .csv as I thought it should do.

 

[Bakersfield Quad]

Thanks a lot for your analysis and your comments.
Regarding the possibility that I may have been confused, it remains a possibility.
Is it possible for you to check on the log file some information (compass, yaw, or other...) about the orientation of the UAV in the seconds before the crash? Could it be possible for it to have rotated full 180°?

If so, my mistake. However, is it possible to check if the sensors were on, and in that case, shouldn't they do their job? How is it possible for th UAV to have been so fast?

Thanks again!

In ATTI mode, the sensors do nothing, above 22 mph, the sensors also do nothing to avoid obstacles, if that is what you are referring to. ATTI has only a barometric sensor for navigation, it will attempt to hold altitude, but that is all. Without GPS data, it would not know how fast is was moving, there is no air speed sensor. In a slip, a plane will accelerate if no opposing input is made, this will result in a high speed slipping movement that can raise the speed significantly in a very short time.