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Phantom 4 inverted from 240m, came down full power into the ground.
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fansfcb70189
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Hello, First post. I was hoping for it to be a more plesent one but its not.

Heres the story.

   Being long weekend here in canada, I went up to my cottage. Took the drone with me. After unloading the truck i took out my drone. Battery fully charged. remote fully charged. i popped in the battery. powered on the remote, powered on the drone. opened the dji go app. calabrated the compass. ready to fly.

I take off the drone and i ascend up pretty quickly. i stop at a height just above the treeline for a few seconds just to see the drone is staying stable and not drifting. everything seems ok.

I continue to ascend to 240m up. The drone is literally above my head 240m up. I pan around the camera to view the area from a birds eye view of the area for the first time.

Then..................

i wanted to decend again to bring the drone to a lower level then go foward over the trees. press down on the left stick for maybe 3 secconds. the drone was always in view. i take a quick look down on my screen and notice the horrizon is inverted? the sky is now on the bottom of my screen? the drone still stable, i notice the drone decending at a very quick rate. i am watching my drone coming straight down toward me. i figured it was RTH for whatever reason. Once it got closer i realize it is upside down propellers full power. propelling itself towards earth. then BOOM hits the floor perfectly on its back literally a few m away from me.

1 it was not a bird strike. all pieces of the propellers were there on the floor at the crash site.
2 the footage on the sd card stopped before the flip.
3 the footage on my phone recorded right up until just before the impact
4 the flight data on my phone stopped right before the flip
5 the drone stayed horozontally stable throught the decent so all props were intact.

i will post the video here that i have from my phone.
can someone please explain to me what happened?
i already contacted DJI today and they want me to send it in for analysis. I just want to know what happened. This could of killed someone. and it literally fell 2m from 2 vehicles parked. im sure if this would of hit the roof or hood of the vehicle it would of caused major damage.

here is the flight log
[backcolor=rgba(249, 249, 249, 0.3)]http://app.airdata.com/main?share=ioAVwz

2017-5-22
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fansfcb70189
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video is here..
2017-5-22
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fansfcb70189
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video is here..  
Damage, Case is scuffed up pretty bad. even though falling on its back, the camera popped off the gimble, camera no longer works, all props broken, the battery has 2 small dents on it from the impact. not sure internal damage but drone powers up and i can access it threw the computer and remote app.
2017-5-22
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Labroides
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Phantoms don't flip and fall in any normal flight.
It's most likely some sort of malfunction.
DJI will be able to get a lot of info from the internal memory.
Airdata is not very good for understanding incidents.
You'd see a lot more if you go to http://www.phantomhelp.com/LogViewer/Upload/
Follow the instructions to upload your flight record.
Come back and post a link to the report it provides
2017-5-22
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fansfcb70189
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Labroides Posted at 2017-5-22 18:02
Phantoms don't flip and fall in any normal flight.
It's most likely some sort of malfunction.
DJI will be able to get a lot of info from the internal memory.

http://www.phantomhelp.com/LogViewer/PVNWLOVIK6GMKDF85340/
2017-5-22
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fansfcb70189
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i noticed the VPS is showing altitude even tho its way up in the air. Is this a normal thing?
2017-5-22
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blackcrusader
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fansfcb70189 Posted at 2017-5-22 18:46
i noticed the VPS is showing altitude even tho its way up in the air. Is this a normal thing?

I guess this is one for  DJI nothing in the flight log I can see.  I fly in remote areas and try to stay away from people houses etc when I can.  

PS I guess you are up to date on drone laws in Canada.   Might not want everyone to see your video.  
2017-5-22
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Nigel_
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Clearly a P4 Pro, standard P4s don't do this!
2017-5-23
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Mabou2
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The P4 flipped in its own prop wash vortex as it was descending.  Early on after I got my P4, I had one experience where my P4 bucked really hard while descending quickly.  We all know that the P4 has a rough ride while descending and our video footage reveals this.  Turns out this is a somewhat known possibility for any drone.   The prop wash creates havoc in the air, when the drone is descending, it is constantly dropping into its own unstable chaos.... add the side wind from an abrupt gust and your drone could flip.  Now I make sure to move in a slow crawl forward while descending quickly.

it actually works against us that this problem isn't more widespread.  If this problem wasn't so rare, DJI would find a way (whether using its existing sensors or adding a new sensor) to know if the drone had inverted and could program a rapid auto-response for the drone to right itself (for example, by briefly killing power to the props on one side of the craft, causing the drone to flip back from being inverted).
2017-5-23
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fansfcb70189
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Mabou2 Posted at 2017-5-23 03:28
The P4 flipped in its own prop wash vortex as it was descending.  Early on after I got my P4, I had one experience where my P4 bucked really hard while descending quickly.  We all know that the P4 has a rough ride while descending and our video footage reveals this.  Turns out this is a somewhat known possibility for any drone.   The prop wash creates havoc in the air, when the drone is descending, it is constantly dropping into its own unstable chaos.... add the side wind from an abrupt gust and your drone could flip.  Now I make sure to move in a slow crawl forward while descending quickly.

it actually works against us that this problem isn't more widespread.  If this problem wasn't so rare, DJI would find a way (whether using its existing sensors or adding a new sensor) to know if the drone had inverted and could program a rapid auto-response for the drone to right itself (for example, by briefly killing power to the props on one side of the craft, causing the drone to flip back from being inverted).

I agree with the vortex.. but number 1 why would the data stop once it flipped? The video on the sd stops once flipped. The video on my device kept recording. Also I seen videos of people flipping their drone 6ft off the ground and it recovers it self before hitting the ground. At 800+ ft I'm sure it had time to fix itself. Another thing is I have read that if the phantom is upside down for x amount of time the motors power down.. in my case you can hear in the video it accelerated upside down toward earth like a bat out of hell.
2017-5-23
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Labroides
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Mabou2 Posted at 2017-5-23 03:28
The P4 flipped in its own prop wash vortex as it was descending.  Early on after I got my P4, I had one experience where my P4 bucked really hard while descending quickly.  We all know that the P4 has a rough ride while descending and our video footage reveals this.  Turns out this is a somewhat known possibility for any drone.   The prop wash creates havoc in the air, when the drone is descending, it is constantly dropping into its own unstable chaos.... add the side wind from an abrupt gust and your drone could flip.  Now I make sure to move in a slow crawl forward while descending quickly.

it actually works against us that this problem isn't more widespread.  If this problem wasn't so rare, DJI would find a way (whether using its existing sensors or adding a new sensor) to know if the drone had inverted and could program a rapid auto-response for the drone to right itself (for example, by briefly killing power to the props on one side of the craft, causing the drone to flip back from being inverted).

This suggestion is most unlikely and what evidence we have does not support it.
Since the P3 series, Phantoms are not susceptible to VRS.
And if VRS was involved, we would be seeing lots of descent in the flight record and would expect to see flight data continuing and giving a record of the fall.

The flight record shows that at 2:44.9 the left stick was pulled back to start the descent.
The flight data ends 1.6 secs later with the Phantom having descended 2.9 metres.
The Phantom limits descent speed to 3 metres/sec and this together with the canted motors is what prevents VRS.
During the last 0.5 seconds of data, the descent speed recorded is 2.3 metres/sec which would not be enough to cause VRS.

I've not heard of the Phantom switching off if it is upside down and this sounds unlikely.
But I have heard of people that were unable to shut down Phantoms that had crash landed upside down.

I can't see any evidence of the Phantom flipping in the data we have and the pitch, roll and yaw figures are not out of the expected range.
There are no other clues in the recorded data.

So the mystery is why the data stopped and why the Phantom fell.
There being no answers in the data we have, this is a case for DJI to investigate the internal data recorder to see what it shows.
2017-5-23
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Nigel_
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Labroides Posted at 2017-5-23 05:11
There being no answers in the data we have, this is a case for DJI to investigate the internal data recorder to see what it shows.


Agree, and since it is not the first P4 Pro to come down upside down, although still very rare, DJI need to take it seriously and find out what is causing this issue that has never existed on the P4 standard.
2017-5-23
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PartsGuy
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There are only a couple of things that can get a P4 inverted. It is not the "vortex" effect. The programming limits the descent speed to prevent this effect. The most sure way to get it upside down is total power loss. The other way is a bird strike or motor obstruction.  From your heavily edited video, it's clear that you have mixed the video from the P4 with the sound from a mobile device. Since the flight log and the video from the drone stop at the same time, I'd have to lean towards power failure of some kind. A bird strike would not necessarily stop the the power and you could have a flight record to the ground. Try this. Post the flight record from the record saved to your device. Set it to overlay the stick commands. It will also show any error or warning messages. If your flight record stops at the same time as the others, the only plausible explanations are power failure or CSC.
2017-5-23
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Mabou2
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Labroides Posted at 2017-5-23 05:11
This suggestion is most unlikely and what evidence we have does not support it.
Since the P3 series, Phantoms are not susceptible to VRS.
And if VRS was involved, we would be seeing lots of descent in the flight record and would expect to see flight data continuing and giving a record of the fall.

Hi Labroids!  You rock.
Well, I didn't research the data, I only know of my own experiences, coupled with the obvious fact that descending with the P4 is clearly a rougher flight than ascending.  It makes sense to me that the rough descent on any flight indicates that the prop wash is a player in the stability of the craft... and given the delicate stability of a small 4-prop craft being buffeted by its own prop wash, that it might not be too difficult to go outside of spec to disastrous effect.

In the video, you can hear some or all of the props (powered) at high speed after it flipped and sped to the ground, so the motors were still running (at least some of them).  If only two (or maybe three) motors were running, I would imagine the bird would have been tumbling in the air on its way down, not driving itself quickly and evenly toward the ground.

OBVIOUSLY, I don't really know what actually happened, just sharing my own experiences of having a near flip while descending.  Keep in mind that sometimes the data only gives part of the story, especially if something occurs that goes outside of spec that can cause the data to be misleading.  

Question in support of the data... does the data show what the status of the motors were at any given point?  Just curious (and I don't know how to read the data myself) if there was a momentary power-down of one or more motors that might have initiated the flip..  

Labroids, you are greatly appreciated in this forum buddy.
2017-5-23
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Mabou2
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I was just watching the video again.
I notice that just before the flip, the p4 pitches hard to the left (which looks to me like a wind gust?), then flips to the right (which looks to me like an overcorrection of the pitch to the left?).  
While the abrupt pitches are occurring, the camera records something attached to the legs, appearing to be a large white ball on each leg with something black (some sort of lock?)... I'm curious what is attached to the bird?  

I'm also curious if whatever is attached could cause an out-of-spec condition that could affect the stability of the P4?  Possibly causing the bird to be more vulnerable to VRS?  
If nothing else, the attachments to the legs could cause (?):
-- the bird to be more vulnerable to a side wind, simply because of greater "bulk" and surface area?
-- less able to maintain balance in a near-out-of-spec roll axis event since there is greater weight that the P4 isn't programmed to handle?

Just brainstorming.







2017-5-23
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Labroides
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Mabou2 Posted at 2017-5-23 05:49
Hi Labroids!  You rock.
Well, I didn't research the data, I only know of my own experiences, coupled with the obvious fact that descending with the P4 is clearly a rougher flight than ascending.  It makes sense to me that the rough descent on any flight indicates that the prop wash is a player in the stability of the craft... and given the delicate stability of a small 4-prop craft being buffeted by its own prop wash, that it might not be too difficult to go outside of spec to disastrous effect.

"Question in support of the data... does the data show what the status of the motors were at any given point? "

This data is in the internal memory of the Phantom and is part of the big picture that DJI will be able to extract.
2017-5-23
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Labroides
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Mabou2 Posted at 2017-5-23 05:59
I was just watching the video again.
I notice that just before the flip, the p4 pitches hard to the left (which looks to me like a wind gust?), then flips to the right (which looks to me like an overcorrection of the pitch to the left?).  
While the abrupt pitches are occurring, the camera records something attached to the legs, appearing to be a large white ball on each leg with something black (some sort of lock?)... I'm curious what is attached to the bird?  

Good spotting.
I can't work out what it is but it sure doesn't look like anything that's standard equipment on a DJI Phantom.
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Looks to me like it powered off intentionally because it believed that it had landed, the phone video continues because phone video does continue after landing.

What I don't understand is why it came down upside down, the standard P4 never does that.

The props where still spinning at high speed simply because they had not been shut down by the pilot so where still at idle, but since it was upside down where also being driven by the air passing due to the fall.
2017-5-23
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fansfcb70189
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PartsGuy Posted at 2017-5-23 05:37
There are only a couple of things that can get a P4 inverted. It is not the "vortex" effect. The programming limits the descent speed to prevent this effect. The most sure way to get it upside down is total power loss. The other way is a bird strike or motor obstruction.  From your heavily edited video, it's clear that you have mixed the video from the P4 with the sound from a mobile device. Since the flight log and the video from the drone stop at the same time, I'd have to lean towards power failure of some kind. A bird strike would not necessarily stop the the power and you could have a flight record to the ground. Try this. Post the flight record from the record saved to your device. Set it to overlay the stick commands. It will also show any error or warning messages. If your flight record stops at the same time as the others, the only plausible explanations are power failure or CSC.

It is raw video from my device. Not mixed .. it's the full flight from after takeoff only the take off was not being recorded
2017-5-23
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Nigel_ Posted at 2017-5-23 06:26
Looks to me like it powered off intentionally because it believed that it had landed, the phone video continues because phone video does continue after landing.

What I don't understand is why it came down upside down, the standard P4 never does that.

All that is attached to the drone is landing gear extensions. That clip to the edge of the stock landing gear and give it a extra 1.5" lift off the ground when landed. It's literally just 4 spikes on each corner of the landing gear. Doubt this would catch any air. Plus the wind was very low at most times none at all. Obviously I can't be certain at that height but ground winds were next to nothing.
2017-5-23
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StephenGSY
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In assistant on a computer you can view the data. And each motor has a data window. You can pick through it and see if you can work out what happened.
2017-5-23
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Nigel_
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fansfcb70189 Posted at 2017-5-23 06:35
All that is attached to the drone is landing gear extensions. That clip to the edge of the stock landing gear and give it a extra 1.5" lift off the ground when landed. It's literally just 4 spikes on each corner of the landing gear. Doubt this would catch any air. Plus the wind was very low at most times none at all. Obviously I can't be certain at that height but ground winds were next to nothing.

Unfortunately, looking at the log file in detail, I think your landing gear extensions were seen by the ultrasonic sensors and it thought they were the ground so it landed and cut the power.  I guess the reason it came down upside down was due to the extra drag from the landing gear extensions working as a parachute which pulled it over, I've never seen a standard P4 do that before.

I suspect this will not be covered by warrantee.
2017-5-23
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Nigel_ Posted at 2017-5-23 06:45
Unfortunately, looking at the log file in detail, I think your landing gear extensions were seen by the ultrasonic sensors and it thought they were the ground so it landed and cut the power.  I guess the reason it came down upside down was due to the extra drag from the landing gear extensions working as a parachute which pulled it over, I've never seen a standard P4 do that before.

I suspect this will not be covered by warrantee.

The power was not cut at any point. The drone came down with all props spinning full speed. You can hear them in the audio in the video. This also dosent explain why the sd card footage stopped recording. Also dosent explain why there was no data beyond that point
2017-5-23
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Mabou2
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Hi Nigel,
Sure did sound to me like the motors were working hard as the bird raced itself into the ground.  I really don't think it lost power during the upside-down descent.  Also, the bird dips hard to the left, then immediately flips to the right.  Just doesn't seem like a power loss problem.

Fan,
You are right in that there can be no wind at ground level but have sharp winds even a few hundred feet up.  I have experienced this way too many times.  In fact, the near-flip that I described above was one of those times (no wind at ground level, sharp wind at altitude).   On the same day of  the near-flip I experienced, I have a lot of video footage which included the landing gear because the bird was tilting and compensating dramatically for the steady wind at altitude.  When I flew directly into that wind, my gimbal wasn't strong enough and the camera kept pitching downward.  I really didn't think I was going to get my drone back that day.  I had to switch to sport mode and at full throttle, was only able to fly 13 miles per hour into the wind... and there was no wind on the ground at all.
2017-5-23
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Mabou2
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Also, fan, what is the big white ball on the landing gear?  I've seen gear extenders (the black part) but I haven't seen the big white ball before.
AND, I'm just curious, it sounds like you are inside the building or on a covered porch?  Not that this necessarily applies to the flip and crash, but it confuses me.

Regarding the SD card stopping recording video just before impact, I can EASILY understand this one.  Although I don't know how DJI manages the visual data stream, it is entirely possible that the video footage goes into a buffer and is fed to the card from the buffer.  The impact with the ground was likely pretty dramatic and caused the buffer to not be able to write to the card.  So you only see what the final footage is that made it from the buffer to the card.
2017-5-23
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Mobilcams
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The fact that the VPS see's something while it is high up in the air shows that the landing gear were something that it thought was the ground.. This is the cause for the strange behavior..  I would put all my money into the landing gear.. The reason data stopped being recorded is because it thought the flight was complete.. The props were still spinning because they were being pushed by the wind like a windmill..  They may have still had idle power going to them but it did think that it landed so it idled the motors..
2017-5-23
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Nigel_
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fansfcb70189 Posted at 2017-5-23 07:02
The power was not cut at any point. The drone came down with all props spinning full speed. You can hear them in the audio in the video. This also dosent explain why the sd card footage stopped recording. Also dosent explain why there was no data beyond that point

The props were being driven by the wind rushing through them due to the fall, normally when it falls they turn backwards, but as it was upside down they were being forced forwards so made the normal high speed prop noise.

SD card footage stopped because the last bit got corrupted when it crashed, the file wasn't closed properly. The flight log data always stops when the flight ends, it does not continue after landing.
2017-5-23
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Nigel_
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Mabou2 Posted at 2017-5-23 07:15
Also, fan, what is the big white ball on the landing gear?  I've see gear extenders (the black part) but I haven't see the big white ball before.
AND, I'm just curious, it sounds like you are inside the building or on a covered porch?  Not that this necessarily applies to the flip and crash, but it confuses me.

I think that is a bit of the white landing gear that is in sun instead of shadow?
2017-5-23
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Mabou2 Posted at 2017-5-23 07:15
Also, fan, what is the big white ball on the landing gear?  I've see gear extenders (the black part) but I haven't see the big white ball before.
AND, I'm just curious, it sounds like you are inside the building or on a covered porch?  Not that this necessarily applies to the flip and crash, but it confuses me.

What big white ball? There is nothing else attached. I think what ur seeing if from the drone rolling the gimble pitched soo much u saw the light under one of the motors. Can u send a screenshot?  Also I am standing on the steps of the porch to shelter the sun from my screen. But the antennas are away from me pointed at the drone. I could visually see the drone at all times. In the first report I sent it shows that the signal was excellent threwought the flight. And my video downlink always was coming in strong. So I doubt it was any transmission issue. Again my drone is set to RTH in any event. I guess it did return to home... only really fast ... and upside down.

As for the landing gear.. the extensions go out toward the outside... I doubt that would cause the drone to think it was on the ground via the sensors..dosent explain the ad to stop recording video. I have landed many times with props off and forgot to stop recording and the sd continues to record even me picking up my drone. also dosent explain the speed of the props spinning on its was down.. should they not be on idle  if it thought it landed?
2017-5-23
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Mabou2 Posted at 2017-5-23 07:13
Hi Nigel,
Sure did sound to me like the motors were working hard as the bird raced itself into the ground.  I really don't think it lost power during the upside-down descent.  Also, the bird dips hard to the left, then immediately flips to the right.  Just doesn't seem like a power loss problem.

I guess the dip to the left was it falling over due to the extra drag from the extensions, the flip to the right was it trying not to fall over landing on uneven ground, it then cut power to avoid the props hitting the ground under power, although there was no ground there.
2017-5-23
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fansfcb70189 Posted at 2017-5-23 07:30
What big white ball? There is nothing else attached. I think what ur seeing if from the drone rolling the gimble pitched soo much u saw the light under one of the motors. Can u send a screenshot?  Also I am standing on the steps of the porch to shelter the sun from my screen. But the antennas are away from me pointed at the drone. I could visually see the drone at all times. In the first report I sent it shows that the signal was excellent threwought the flight. And my video downlink always was coming in strong. So I doubt it was any transmission issue. Again my drone is set to RTH in any event. I guess it did return to home... only really fast ... and upside down.

As for the landing gear.. the extensions go out toward the outside... I doubt that would cause the drone to think it was on the ground via the sensors..dosent explain the ad to stop recording video. I have landed many times with props off and forgot to stop recording and the sd continues to record even me picking up my drone. also dosent explain the speed of the props spinning on its was down.. should they not be on idle  if it thought it landed?

Hi Fan,  you can see some of the "ball" in the screenshot that Labroids posted above.  Also, take a look at my assessment (just above) as to why the video quit recording at the last second.
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We can see from the VPS height that it thought it was on the ground the entire flight.
We can see from the power consumption that it put the motors back to idle power for the last second of the log.
We can see from the vertical speed  figure that it is believing the ultrasonic sensors during the last second and thinks it has stopped falling, thus has landed.
We can see from the barometer that it is actually still falling fast.
Everything is in place for it to end the flight, then the log ends as it should and the video feed to the RC continues as it should.
2017-5-23
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Mabou2
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Nicely done Nigel.  The VPS thing certainly does make one think that the aftermarket landing gear could be the issue... or maybe the VPS just had a problem in general.  Since the landing gear extension falls outside of the actual landing gear, it is a little hard to believe that they affected the VPS, but ya never know.

Any idea (from the data) how fast the p4 was falling when it hit the ground?  I think it would be interesting to see if it was falling faster than terminal velocity, which would mean that the props were pulling it down.
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Mabou2 Posted at 2017-5-23 07:47
Nicely done Nigel.  The VPS thing certainly does make one think that the aftermarket landing gear could be the issue... or maybe the VPS just had a problem in general.  Since the landing gear extension falls outside of the actual landing gear, it is a little hard to believe that they affected the VPS, but ya never know.

Any idea (from the data) how fast the p4 was falling when it hit the ground?  I think it would be interesting to see if it was falling faster than terminal velocity, which would mean that the props were pulling it down.

Not sure if anyone can time the footage from flip to impact and calculate the time from the last known height .. I'm not that smart
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Mabou2 Posted at 2017-5-23 07:47
Nicely done Nigel.  The VPS thing certainly does make one think that the aftermarket landing gear could be the issue... or maybe the VPS just had a problem in general.  Since the landing gear extension falls outside of the actual landing gear, it is a little hard to believe that they affected the VPS, but ya never know.

Any idea (from the data) how fast the p4 was falling when it hit the ground?  I think it would be interesting to see if it was falling faster than terminal velocity, which would mean that the props were pulling it down.

We don't have any data for when it was about to hit the ground, I guess that is not even in the aircraft logs since it wasn't flying at the time.

Can't even guess from past experience, presumably when the props are turning the correct direction they provide a lot less drag than they normally would on a fall, plus there wont be much lift as they are upside down!  I'll make a guess at 50mph - if the landing gear extensions really are the cause then they are very dangerous extensions!
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fansfcb70189 Posted at 2017-5-23 07:59
Not sure if anyone can time the footage from flip to impact and calculate the time from the last known height .. I'm not that smart

heh... you were smart enough to come up with that idea!  (which is a good one).

So, what WAS the height when it flipped?
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Mabou2 Posted at 2017-5-23 08:07
heh... you were smart enough to come up with that idea!  (which is a good one).

So, what WAS the height when it flipped?


146 meters in 10 seconds = 14.6m per second average, probably about 40mph when it hit the ground, a bit faster than coming down the right way up and enough to make it dangerous, but not an indication of being under power.
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Nigel_ Posted at 2017-5-23 08:39
146 meters in 10 seconds = 14.6m per second average, probably about 40mph when it hit the ground, a bit faster than coming down the right way up and enough to make it dangerous, but not an indication of being under power.

Pretty sure 807ft is 245m in 10 seconds making it 24m per second.. correct me if I'm wrong
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fansfcb70189 Posted at 2017-5-23 08:55
Pretty sure 807ft is 245m in 10 seconds making it 24m per second.. correct me if I'm wrong

Opps, yes, well that is quite fast then!

200m+ is illegal here, not used to that sort of height.
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ok so i just checked my logs from another flight(without landing gear)....  it also shows that vps is 0ft when im at high altitude.  so why when i pressed down on the left stick did it not shut down? can anyone please confirm this on their drone logs?
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