Sudden MM descent into pond...

[FleetPhil]

Short flight in my garden with my 3 week old MM - no damage or issues on the previous 20 or so flights. On this flight I started a descent but when I tried to level out it failed to respond to left stick input until it hit my pond...

Details are in the attached TXT, but in summary:

9m 17s: I had 55% batteries holding at 31ft altitude and commanded a descent
9m 20s: Altitude 21ft and left stick back to neutral
9m 21s: Altitude 14ft and descending rapidly with stick still neutral
9m 22s: Left stick full up as I realise what is happening but MM still descending at ~8ft/sec
9m 23s: Altitude negative as the MM hits the pond

In hindsight I should be careful about descending over water, but I don't understand why there was no response to my input at 9m 22s... is there any other analysis I can do to try and understand why?

Thanks, Phil

 

[sar104]

And another one. It had nothing to do with the water - it appears to be a design fault. The props deform and fail to produce enough lift to control descent. Can you see if you can retrieve the mobile device DAT file ending FLY019.DAT from your phone before the DJI Fly app deletes it?

 

[FleetPhil]

it doesn't look like I have that - is it in the MCDatFlightRecords folder? If so it's empty so it seems the DAT files are not being recorded?

 

[sar104]

it doesn't look like I have that - is it in the MCDatFlightRecords folder? If so it's empty so it seems the DAT files are not being recorded?

They are recorded but then appear to be deleted by the DJI Fly app when it syncs the records. I'll look at the txt log later, but in the meantime you can check out a number of other similar reports:

Search results for query: mini uncommanded descent

mavicpilots.com

 

[slup]

And another one...

Jeez, this have become epidemic, new cases every day

 

[RodPad]

Wow, another one.
I was just about to order a MM, to play with on a 3 day vacation, Friday-Sunday.

@sar104,
"The props deform and fail to produce enough lift to control descent."
It appears your stating it is a problem with the design of the props?

Rod

Update:
I found my answer.

Aircraft Max Power Reached?

 

[slup]

You were rather quick there to get airborne, didn't have enough strong sats ... got the HP eventually, but on the other side of the house along side with the driveway.
The Mini were then later battered in harder winds on it's highest altitude above the trees, this produced alot of wind warnings & messages about max power load reached.

Messages:



It was an uncommanded descent in the end though ... but this time without the characteristic up pitch. I sincerely get a picture of a tired & exhausted Mini no longer wanting to fly
After the negative throttle at 559sec it continues to descent even though both positive throttle & elevator are applied. Would have been nice to see the DAT log also ...

 

[sar104]

You were rather quick there to get airborne, didn't have enough strong sats ... got the HP eventually, but on the other side of the house along side with the driveway.
The Mini were then later battered in harder winds on it's highest altitude above the trees, this produced alot of wind warnings & messages about max power load reached.

Messages:

View attachment 93613

It was an uncommanded descent in the end though ... but this time without the characteristic up pitch. I sincerely get a picture of a tired & exhausted Mini no longer wanting to fly
After the negative throttle at 559sec it continues to descent even though both positive throttle & elevator are applied. Would have been nice to see the DAT log also ...

View attachment 93614

I think the instabilities are the defining feature on descent, rather than the lack of pitch which occurs during attempted forward motion. Same cause though - insufficient power.

 

[slup]

I think the instabilities are the defining feature on descent, rather than the lack of pitch which occurs during attempted forward motion. Same cause though - insufficient power.

Yeah ... the whole flight looks by the pitch & roll to have been unstable, even more above the trees fighting the wind.

 

[sar104]

Yeah ... the whole flight looks by the pitch & roll to have been unstable, even more above the trees fighting the wind.

I ignored the windy part of the flight, although I was a little surprised that the aircraft didn't blow away.

 

[le_wib]

Jeez, this have become epidemic, new cases every day

does it look like what happened with my flight ?

 

[slup]

does it look like what happened with my flight ?

Yep ... pretty much the same.

 

[Zeke]

View attachment 93614

Can I ask what program you're using to generate this graph? Airdata extracts a ton of good information but the tabular form isn't nearly as impressive as this visual.

 

[slup]

Can I ask what program you're using to generate this graph? Airdata extracts a ton of good information but the tabular form isn't nearly as impressive as this visual.

I use CsvView ... get it here --> CsvView Downloads

 

[Zeke]

I use CsvView ... get it here --> CsvView Downloads

Thanks I'm going to try that. I downloaded a CSV Viewer but it gives me the same information in tabular form (spreadsheet). No graph.

 

[slup]

Not any Csv viewer will do ... "CsvView" is a program, follow my provided link & you will find installers both for PC & Mac.
Furthermore ... this program will not provide finalized predefined charts, you load either a TXT or DAT log file & start with an empty chart & fill in "signals" you want to study to support a theory.

 

[Zeke]

Not any Csv viewer will do ... "CsvView" is a program, follow my provided link & you will find installers both for PC & Mac.
Furthermore ... this program will not provide finalized predefined charts, you load either a TXT or DAT log file & start with an empty chart & fill in "signals" you want to study to support a theory.

Thanks! I installed it but for some reason it's not finding Java on my computer... Go figure.

 

[netsonic]

it's not finding Java on my computer... Go figure.

Because you have Java 32 bit and it needs 64 bit! Go to the java download page and manually and install Windows Offline (64-bit) , then retry.

 

[bigswifty]

<SNIP>
The props deform and fail to produce enough lift to control descent.
<SNIP>

I ask this in a spirit of pure ignorance and enquiry. If the aircraft manages to achieve initial takeoff and climb, then the props are presumably undeformed. So is the deformation something which occurs during flight, exacerbated by sustained high rotational speeds making the prop blades deform to a finer pitch due to air pressure against the lower surface from leading to trailing edge?

I'm thinking along the lines of minimising full throttle operations - could that mitigate or delay the onset of deformation?

Does the plastic the props are made of have any "memory"? I know nothing about plastics, do they fatigue like some metals? Would some sort of periodic replacement schedule?

I guess the initial deformation would be at the tips where the pressure is highest and the material the thinnest? Do the motors have enough headroom (sorry, don't know the technical term) in terms of RPM to allow, say, snipping a few mills off the prop ends?

As a personal anecdote, years ago I used to race Control Line model planes. We used to make our own CF props by using a commercial, inferior-materials, plastic prop to make a mold. Our shed-made props were turning well over 30,000 rpm in flight. It can't be too hard.

Mike

 

[FleetPhil]

Thanks for the replies and analysis. It looks like I was a little too keen to get flying that day - I knew it was going to be windy for the MM and saw the wind and power warnings when it was above the trees. When the warnings stopped i though it was coping with the wind but i can see that it’s possible that it was still struggling and eventually gave up. A warning to respect the conditions I think...