Mavic Mini Flyaway in Adelaide

[ridion]

Hi,
I just wanted to have some other people look at my logs as DJI are just saying it's my fault for losing this drone. Basically I took off and flew around an area I know well in Adelaide. It's in the hills so there are occasional gully winds but they are generally just short gusts or it's really obvious that it's a windy day. I took some Christmas snaps then went for at look at the city from a few hundred meters away and the drone and weather seemed fine. I started to try and come back with 70% battery remaining to no avail, the drone just couldn't fight the wind it seemed. I'm not too convinced though as looking at the RTH path it took it flew in almost the exact opposite direction from the home point. I've had no luck recovering the drone even though it looks like the last telemetry I got was probably where it landed. Does this look like normal RTH behaviour to other pilots?

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[sar104]

That's correct - the wind speed was over 30 mph out of the SE, which was why it ended up moving away, rather than towards, the home point. It was autolanding due to low battery and the end of the recorded flight, but it was still nearly 100 meters above ground level, and so it will have drifted further while descending. If the wind speed were constant down to ground level, that would have resulted in this:



On Google Earth that puts the landing point as follows:



Since the wind speed likely decreased towards the ground it probably came down before that point, somewhere on the red line. I'd start at the estimated landing icon and then work backwards.

 

[bumper]

I know little to nothing about interpreting flight logs, but you were in "tripod mode" until you were about 1/3 of a mile away. My M2P only goes a few miles an hour (i.e. real slow) in tripod mode.
Looks like another Mini blow away . . . sorry.

 

[Simmo]

Welcome aboard mate and sad first post?!
Our resident expert @sar104 I'm sure could decipher for you and perhaps even give you a better guestimate of where it could be?

Beat me to it whilst I was typing @sar104 !!

 

[RayOZ]

Sorry for your loss. DJI would be correct in their assessment that it was pilot error.

 

[ridion]

Thanks everyone for your time and help. I'm just still struggling to come to terms with it. Especially as the largest gusts of wind in Adelaide on that day were supposedly 20-30km/h and I had a sucessful flight less than an hour earlier in the same conditions. As for 8mph seeming fast in tripod mode, that's exactly the same speed it was going heading into the wind in the previous flight. In my mind the only thing that changed between these two flights was the drone firmware update I performed and compass calibration. I went from the .200 to .300 firmware. Here's the flight from the same day, just before.

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Am I really alone in thinking this is unusual?

 

[Simmo]

I think @sar104 has a paid subscription to Airdata??
That has a 'fairly good' indicator of wind speed and direction??
Plus, simple graphs of the pitch and roll versus control input could confirm the wind speed too?

 

[Meta4]

I'm not too convinced though as looking at the RTH path it took it flew in almost the exact opposite direction from the home point. I've had no luck recovering the drone even though it looks like the last telemetry I got was probably where it landed.

To give you some more words to describe what the data is showing ...
At 5:44 you had turned the drone to face home and gave it full stick in Sport Mode at an altitude of 30 metres above launch point (64 metres above ground)
At full stick in Sport Mode the Mini will fly at 13 metres/sec in still air.
But yours was only making 2-4 m/s toward home.
The variation would have been due to gusty winds at that altitude.
However, although the drone was pointing south toward home, its track shows drift toward the west.
The data shows a steady drop in altitude in Sport Mode which you countered by climbing a few times to maintain altitude.
By 7 minutes flight time the drone was still pointing south but being set to the west at 1-3 m/sec despite full stick, Sport Mode and pointing south.
This is clear proof that there was a significant wind that the Mini was incapable of making headway against.
It is now getting further from home and is about 100 metres above ground level.

If we check again at 8 minutes you have turned the drone SSE to face home and are still giving it full stick in Sport Mode.
But the Mini is still being pushed west at 2-4 m/sec and is now 125 metres above the ground and 610 metres from home.

Skip to 10 minutes and the drone is pointing to home in the SE and going backwards (to the NW) at 1-3 M/sec and now 147 metres up and 930 metres from home

Clearly the Mini is never going to get home battling against this headwind.

At 10:25.1, with the battery at 41%, you gave up and let RTH attempt to bring it back.
But RTH will only fly at 8 m/sec in still air so it's going to have no chance.
RTH brings the drone up to 155 metres above ground level.
The wind is very gusty and speed is 1-9 m/sec but the direction is NNW despite the drone pointing SSE.
The drone is blowing away from home and at 12 minutes it's 1230 metres away.
At 18:22, low battery level (13%) forces the drone to autoland.
It's 2400 metres away and still blowing backwards at 7-8 m/s (which is as fast as the drone can fly in still air in P-GPS mode !!!)

Signal is lost at 18:36.6 with the drone another 120 metres further away.
It's almost 200 metres above ground level and 2.6 km away and will have blown further NNE before reaching the ground.

The wind up where the drone was was much stronger than it was close to the ground where friction reduces it.
The data seems to tell a very simple story.

Now .. what were you saying about not being convinced?

Does this look like normal RTH behaviour to other pilots?

It looks perfectly normal for a drone left in a wind that was much too strong for it to fight against.
Drone pilots need to be fully aware of what their drone is doing andwhere it is.
The app gives you all the instrumentation you need to see this.
All the information was visible for you all the time.

 

[Meta4]

I'm just still struggling to come to terms with it. Especially as the largest gusts of wind in Adelaide on that day were supposedly 20-30km/h.

Forecast winds are not always accurate and they are for wind at ground level - not 200 metres up.
The details of how the drone was blown backwards are unambiguous.

In my mind the only thing that changed between these two flights was the drone firmware update I performed and compass calibration. I went from the .200 to .300 firmware. Here's the flight from the same day, just before.

Firmware and compass calibration made no difference at all.
The wind was everything.

Imagine a strong rower who can row his boat at 5 metres/sec (in still water).
He puts his boat a a strongly flowing stream and rows upstream as fast as he can but is surprised to find himself going backwards at 5 metres/sec.

If you like, you can imagine a large waterfall downstream around the bend.
I think you get the idea.

 

[Meta4]

I think @sar104 has a paid subscription to Airdata??
That has a 'fairly good' indicator of wind speed and direction??

Not necessarily
See here: Why I do believe there's a HUGE problem with the Mavic Mini - Flew AWAY the 2nd day
But the data shows pretty clearly what was going on up there.

 

[Simmo]

Not necessarily
See here: Why I do believe there's a HUGE problem with the Mavic Mini - Flew AWAY the 2nd day
But the data shows pretty clearly what was going on up there.

I was aware of that, hence the 66's & 99's!
That is the first time I have ever heard AirData's weather estimator questioned though.
And has been used in the past even by Sar104.

 

[MrYKBQdV]

Forecast winds are not always accurate and they are for wind at ground level - not 200 metres up.

The part were you say "Forecast winds are for wind at ground level" is also not always accurate.
The are very good free apps that will inform you in advance of wind between 0-150 meters AGL (0-400) which is the altitude at which you should be flying in most countries. Also at higher altitude AGL.

One of those apps is UAV Forecast.

For example, right now in Adelaide I would be not flying since gusts at 100 meters (I don't/shouldn't fly higher) are higher than 32 km/s which is the limit that I have self-imposed to my Mavic 2 Zoom.


If instead I was looking at ground level I would be making the very bad decision of flying, because gusts at ground level only reach 18 km/h. That would be a mistake in any case since my RTH altitude is set to 50m, and that is "at least" the altitude I should be checking, not ground level.


Also this app can display an estimation at 200m or higher where for some reason I don't understand many fellow pilots have set as RTH altitude (it's illegal in most G20 countries).


Know your limits.
Know the limits of your UAV.
Plan your mission.
Better safe than sorry.
It's better to not fly one day than not flying ever again.

 

[InspectorGadget]

But RTH will only fly at 8 m/sec in still air so it's going to have no chance.

Gives rth only 1 specific motor speed? I think it would be logic for dji to apply a groundspeed at rth so in windy conditions that's full power.

 

[Meta4]

Gives rth only 1 specific motor speed? I think it would be logic for dji to apply a groundspeed at rth so in windy conditions that's full power.

But it doesn't

 

[Meta4]

The part were you say "Forecast winds are for wind at ground level" is also not always accurate.

The OP was quoting common, ordinary weather forecast information.
Those are always for ground level winds.

The are very good free apps that will inform you in advance of wind between 0-150 meters AGL (0-400) which is the altitude at which you should be flying in most countries.

I know that UAV Forecats is very popular with some members but it is just another forecast.
Just because you see it displaying info on a screen, it is not necessarily any more accurate than other forecasts and cannot take into account local topography etc.

It's safe to assume that winds up high are going to be stronger than down at ground level without any app to tell you.
The app gives you plenty of data to see how the wind is affecting your drone's speed.

 

[ridion]

Now .. what were you saying about not being convinced?

I just found it suspicious that the line away from the home point was so straight and at such a constant speed, so close to the speed it would normally return at. The behaviour looked to me like it just had the direction of home backwards. I would have imagined gusts would knock it about more but as I generally try to avoid flying when it's windy I guess I don't have enough experience to know.

Thanks for all your help and I'll have another go searching for the drone further from where I thought it landed. If I ever recover it I'll also start using that UAV forecast app.

 

[m80116]

I am saddened by all these MM losses, I know how one can feel.

Can I take the opportunity to ask: can it be a good idea in these irrecoverable (wind caused) drift cases to push the height as far as it is reasonable to do so ?

 

[msinger]

I think @sar104 has a paid subscription to Airdata??

Here's what Airdata calculated:

 

[Meta4]

Can I take the opportunity to ask: can it be a good idea in these irrecoverable (wind caused) drift cases to push the height as far as it is reasonable to do so ?

Very often, the real problem is that the pilot is unaware that wind speed is usually stronger up higher.
Going lower will mostly get the drone into weaker winds that it should have less trouble fighting.

Avoiding getting into that situation by consciously flyiing towards the wind rather than with it, and watching the flight data to see what is happening with the drone is the best strategy.

 

[RayOZ]

I just found it suspicious that the line away from the home point was so straight and at such a constant speed, so close to the speed it would normally return at. The behaviour looked to me like it just had the direction of home backwards. I would have imagined gusts would knock it about more but as I generally try to avoid flying when it's windy I guess I don't have enough experience to know.

Thanks for all your help and I'll have another go searching for the drone further from where I thought it landed. If I ever recover it I'll also start using that UAV forecast app.

Unlikely the home direction is reversed. The arrow in the Log Viewer shows the drone is facing the home point. It won't be flying backwards towards home.