How far could a failed drone drift when falling?

Meta4 · Feb 26, 2021

R.Perry said:
My point was the op wasn't looking for a scientific explanation, but an approximation I assume to insure a safe perimeter. My explanation was an example of how just one factor can effect flight. With aircraft we have proven flight characteristics based on extensive testing and known performance. With non military drones we have no such data so we throw the old book out the window and guess. For me, if my estimation was 147 feet, I would add another 20 to 30 feet to insure I don't end up with a SNAFU.
The pilot that lost the Inspire 1 lost all power, so all four motors shut down simultaneously, there was no wind but he stated the Inspire landed about 35 feet from where it went dead stick. He was doing panos at the time so he was hovering and had GPS data up to the time the power was lost. I'm assuming he he came up with the distance from loss of power to impact area based on aircraft data, but I'm not sure and forgot to ask him.
Based on that experience estimating trajectory or lack of sounds pretty difficult to come up with a formula that could be applied to drones.

Sorry ... I'll have a go at physics any day but I can't work out what you are trying to say or how it relates to the thread topic.

R.Perry · Feb 26, 2021

Meta4 said:
Sorry ... I'll have a go at physics any day but I can't work out what you are trying to say or how it relates to the thread topic.

If that works for you, wonderful. Have a great day.

aerialimagery · Feb 26, 2021

I didn't think air resistance would be as big a factor as it is since everyone was saying they "drop like a rock." Anyway, it's good to know and I now think I have a good idea of how to determine a margin of safety.

Here's a more in-depth discussion of a similar topic:

The Terminal Velocity of a Falling Mavic 2

...seems to be about 70mph. DJI Flight Log Viewer - PhantomHelp.com I have an interesting flight crash log to share. I was definitely pushing the limits in Manual mode (asking for it, I know) but leveled out well before I switched modes back. Either I lost a propeller or the gyro just...

mavicpilots.com

R.Perry · Feb 28, 2021

Looking at that flight log I have no idea what he was trying to do. His pitch was all over the place prior to losing control and is is obvious the thing started tumbling. It does sound like he either broke a prop or lost one. Hope he learned a good lesson, it will be an expensive one.

Air resistance is only one factor, and with a small drone it makes very little difference. An interesting test would be to check your maximum rate of climb on a hot day and above 5000 feet, verses a cold or cool day at sea level. Compare the two flight logs and see if is a measurable distance. In fact I'm going to do that. I can do the cooler temp tests now and when summer hits wait for a nice 100+ degree day and perform the same tests.

Florida Drone Supply · Feb 28, 2021

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dronerdk · Feb 18, 2022

Meta4 said:
Your freefall calculator isn't worth much unless you are interested in objects falling in a vacuum.
In the real world air resistance is a real factor.
DJI drones up to the size of a Phantom reach a terminal velocity of 12-14 metres/sec fairly quickly.
I haven't seen data for an Inspire or Matrice.
If your were looking at a hypothetical Phantom or Mavic falling from that height, it would take about 10 seconds.

Do you have any data for how well the drag from the propellers (windmilling) slow down the velocity compared if the drone had no propeller?

Meta4 · Feb 18, 2022

dronerdk said:
Do you have any data for how well the drag from the propellers (windmilling) slow down the velocity compared if the drone had no propeller?

I've seen recorded data from quite a few drones that fell with props attached, but never for a drone without props.
It's fairly uncommon for them to get into a position from which they can fall unless they have props.

dronerdk · Feb 18, 2022

Meta4 said:
I've seen recorded data from quite a few drones that fell with props attached, but never for a drone without props.
It's fairly uncommon for them to get into a position from which they can fall unless they have props.

Yes, indeed. And thank you for getting back so quickly.
My interest lies on how much drag windmilling props on a drone will reduce the velocity of a free fall.
So your data might have some informations regarding Air resistance coefficient for a falling drone with propellers?
Or some informations for the velocity speed we can expect of a falling drone?

R.Perry · Feb 18, 2022

Dronerdk, I may be wrong but is your question based on helicopter autorotation systems where the rotors can be used reduce the rate before impact?

If so this would not apply to drones since they are fixed pitch. The props could supply a certain amount of drag, but I don't believe it would be enough to keep the drone from reaching terminal V.

One of our people lost an inspire 1 due to complete battery failure. Drone was at 200 feet when failure occurred and the pilot said he was certain it hit terminal long before it hit the ground. The drone and camera were destroyed.

dronerdk · Feb 26, 2022

R.Perry said:
Dronerdk, I may be wrong but is your question based on helicopter autorotation systems where the rotors can be used reduce the rate before impact?

If so this would not apply to drones since they are fixed pitch. The props could supply a certain amount of drag, but I don't believe it would be enough to keep the drone from reaching terminal V.

One of our people lost an inspire 1 due to complete battery failure. Drone was at 200 feet when failure occurred and the pilot said he was certain it hit terminal long before it hit the ground. The drone and camera were destroyed.

Hello

No, not based on autorotation because of the fixed pitch the props have.

My interest is still if any drag will be introduced when the props start spinning when the relative wind will go upwards due to a free fall. I have seen some videos of the effect of a free fall and it seems that the props gains some speed.
But if any data is available of a free fall where the props starts to spin due to windmilling I would be interested to see it.