How far could a failed drone drift when falling?

[aerialimagery]

Presume a drone is flying at 400 feet in calm winds. If the battery fails, how far could it drift from the point directly below it upon impact? If in another scenario say in the case of a phantom 4 drone, one of the propellers fails, would the other spinning propellers move it laterally? Just trying to determine how much of a safety zone there needs to be directly below the drone. Thanks.

 

[BigAl07]

LOTS of variables but starting at 400' is going to give the most potential "Drift". If it goes "Dead Stick" during a hover it's going to tumble some but will mostly be pushed by the wind (if any).

Few of us hover very often to the more momentum when it goes Dead Stick the more it's going to travel.

If it's a lost prop scenario it's going to be an erratic flight/fall and all bets are off.

 

[Meta4]

Presume a drone is flying at 400 feet in calm winds. If the battery fails, how far could it drift from the point directly below it upon impact?

Not far

If in another scenario say in the case of a phantom 4 drone, one of the propellers fails, would the other spinning propellers move it laterally?

With three props the drone cannot maintain altitude and it will spiral to the ground.

 

[SanCap]

Although this is not 400 feet, this was a commanded shut down by me when the Phantom 1 went to an uncommanded full throttle takeoff. It did have vertical and horizontal momentum before I shut it down and It pretty much fell straight down. If you listen I almost got it started before it hit the ground

 

[aerialimagery]

Once again from a different perspective--presume hovering at 400 feet with no wind and near a busy freeway. How close can you be to the highway and still be safe if there is a failure?

 

[MapMaker53]

From 400 ft and no wind I would guess 50-75 yards from the highway might be my comfort zone. But you can never be sure there is no wind at any given moment. If there is even slight breeze at ground level, I would make sure I was hovering on the downwind side of the busy highway - though there is no guarantee that the winds aloft are traveling in the same direction. In any case, I wouldn't want to be hovering very long near a busy highway. If viewing the highway from 400 ft, there really is no need to be vertically close to it IMO.

 

[aerialimagery]

From 400 ft and no wind I would guess 50-75 yards from the highway might be my comfort zone. But you can never be sure there is no wind at any given moment. If there is even slight breeze at ground level, I would make sure I was hovering on the downwind side of the busy highway - though there is no guarantee that the winds aloft are traveling in the same direction. In any case, I wouldn't want to be hovering very long near a busy highway. If viewing the highway from 400 ft, there really is no need to be vertically close to it IMO.

I don't mean viewing the highway. I mean if there is a subject close to the highway that is to be photographed.

 

[SanCap]

I don't mean viewing the highway. I mean if there is a subject close to the highway that is to be photographed.

Just curious why you are this concerned about loosing a prop or battery failure. Have you had some? I have flown hundreds of flights around structures within close proximity to highways without a failure. My suggestion would be to follow FAA guidelines avoiding flying over people and moving vehicles and you will most likely be fine should a failure arise. Some things are simply out of our control, I do respect your concerns and questions.

 

[aerialimagery]

I already know I shouldn't be "over" people or moving cars. I'm just trying to determine to what distance. I could be hovering directly over the shoulder of a highway and wouldn't technically be flying over any moving vehicles, but that might be too close. I'm just trying to get an idea for a rule of thumb or what others are doing, besides the fact that I don't really know how far a drone could move horizontally during a fall.

 

[aerialimagery]

Not far

With three props the drone cannot maintain altitude and it will spiral to the ground.

Thanks for your response. So if there are three props it's going to spiral and not just keep going in one direction, so in that situation also it should not go very far from the vertical?

 

[SanCap]

I already know I shouldn't be "over" people or moving cars. I'm just trying to determine to what distance. I could be hovering directly over the shoulder of a highway and wouldn't technically be flying over any moving vehicles, but that might be too close. I'm just trying to get an idea for a rule of thumb or what others are doing, besides the fact that I don't really know how far a drone could move horizontally during a fall.

As others have said any specific distances would be a guess depending on environmental conditions. Myself and many others have flown over the shoulder of a road avoiding traffic lanes. Most of who do have to get that close can mitigate safety issues by climbing a bit higher and getting a different angle that allows you to stay closer to the structure. This discussion of these type of potential issues need to be discussed with the end client. Most of us are allowed to deviate flight profiles to maintain safety.

 

[SanCap]

Thanks for your response. So if there are three props it's going to spiral and not just keep going in one direction, so in that situation also it should not go very far from the vertical?

Correct but no guarantees.

 

[Meta4]

Thanks for your response. So if there are three props it's going to spiral and not just keep going in one direction, so in that situation also it should not go very far from the vertical?

1. If your quadcopter loses a prop or motor it starts to spin because of the unbalanced torque of two spinning clockwise and one anti-clockwise or vice versa.
2. And it's unable to hold itself in the air against gravity with only 3 props.
The recorded flight data from numerous cases of loss of a prop or motor always shows the drone spinning almost straight downwards +/- whatever momentum it has from immediately before losing the prop.

 

[Norstar]

Lost a prop once on a Phantom, in calm wind about 200 ft, the drone spiralled almost straight down. They act just like a rock. Lol

 

[adm_geomatics]

In our experience with Phantom 4 Pro's, all at about 200-250ft and 10-15mph winds.

Shorted battery - almost straight down
Lost prop - expanding spiral of no more than 50ft
Failed Compass - 150ft

 

[SWA Pilot]

Taking photos for an insurance litigation involving a truck/car accident on the interstate. Trying to get the required videos/pictures while complying with 107. Constantly thinking about contingencies. So I can understand your concerns. However I think the previous comments have highlighted there is no “one stop shop answer”. Some things that I constantly evaluated (Pretty obvious I would think)...forward vector, speed and wind. If you stop flying....how far is your dead bird going to go and in which direction. Preferably keep the horizontal vectors parallel with the road....try to use slow deliberate speeds (maybe tripod mode on phantom). In my case, the customer didn’t need impressive visuals...just detailed pictures/videos. So eye catching cinematic shots were not necessary. No shots were higher than 200 feet.

 

[Earthman]

Once again from a different perspective--presume hovering at 400 feet with no wind and near a busy freeway. How close can you be to the highway and still be safe if there is a failure?

It depends on the type of failure.

If it’s a flyaway, the UAV may fly as far as the remaining battery power will carry it.

If it’s hovering and loses all power in calm air, it will fall essentially straight down.

If it is flying in calm air, but has some forward velocity when it loses all power, it should follow a parabolic path to impact with the ground.

If it loses all power while hovering in a moving air mass without position hold engaged, it will travel laterally an amount that is approximately equal to the speed of the moving air mass relative to the ground (a.k.a. the wind speed) times how long it takes the UAV to hit the ground (Distance = Velocity of the Wind X Time to Fall). Wind speed varies with elevation AGL, so use the averaged wind speed between the altitude at which the UAV lost power and the ground. The UAV’s air speed (relative the the air mass) may be zero (it’s hovering), but since it’s drifting with the moving air mass, it’s ground speed will be equal to the wind speed. An aircraft’s ground speed is the vector sum of its air speed and the wind speed. This is a long-winded way of saying an object in a moving air mass drifts with the air mass (unless something like position hold is countering the affect of the wind), so the UAV will drift with the wind until it hits the ground.

Of course, there are any number of other emergency scenarios that would cause the UAV to travel laterally an amount that is different than those described here.

In any case, you don’t know how far the UAV may travel in an emergency, but you as PIC are still responsible for any damage caused by your decision to fly and your operation of the UAV. Therefore, always fly with liability insurance and don’t do anything that might be considered reckless.

Good luck.

 

[R.Perry]

When I was flying at UC Merced most flights were around 200 feet other than mapping. I had to deal with the professor at the college that taught 107 and aeronautics. I wasn't allowed to get within 100 feet of the active campus when doing panos. When doing panos the drone is hovering. One of the panos I had to do was very close to the active campus and had constant student traffic. Also when approaching that area to do the pano, he didn't want my forward speed to be over 10 mph within 200 feet of where I would shoot the pano.
I don't know how he came up with those numbers, but they seemed to make sense to me.
To me if you go dead stick your drone is going to fall like a rock, there is no glide ratio unless you have some kind of forward movement or wind factor.

I think the question is a very good one and should be considered whenever we fly close to people.

 

[adm_geomatics]

When I was flying at UC Merced most flights were around 200 feet other than mapping. I had to deal with the professor at the college that taught 107 and aeronautics. I wasn't allowed to get within 100 feet of the active campus when doing panos. When doing panos the drone is hovering. One of the panos I had to do was very close to the active campus and had constant student traffic. Also when approaching that area to do the pano, he didn't want my forward speed to be over 10 mph within 200 feet of where I would shoot the pano.
I don't know how he came up with those numbers, but they seemed to make sense to me.
To me if you go dead stick your drone is going to fall like a rock, there is no glide ratio unless you have some kind of forward movement or wind factor.

I think the question is a very good one and should be considered whenever we fly close to people.

Those are not truly 107 regulations as they are enforced. They were more related to his comfort level and perception of the regulations so they are guidelines, but obviously a campus official (which he is not being a professor) has the right to direct activities. The list of officials you should coordinate with.

• Maintenance and construction of campus buildings and grounds (the physical plant);
• Safety and security of people and property on the campus (often organized as an office of public safety or campus police);
• Public affairs (including relations with the media, the community, and local, state, and federal governments)

I agree with not flying directly over an active campus, but in the terms of while students are switching classes. There are times when the campuses are no more populated by foot traffic than a typically city of even subdivision and flight plans can be configured to mitigate risk of that foot traffic and active roads. Our approach with Texas State University was to devise a plan, coordinate that plan with them and actually close specific areas during the time of flight. Of course the Limits of Construction were always off limits to all non-construction persons.

 

[adm_geomatics]

A little further guidance from a Drone Law Attorney.

Part 107.19(c) (The Rarely Understood Regulation & Brother of 107.39)​

So if I don’t fly over people and moving vehicles, I’m good right?

It’s not as simple as that.

Section 107.19 applies which says:

(c) The remote pilot in command must ensure that the small unmanned aircraft will pose no undue hazard to other people, other aircraft, or other property in the event of a loss of control of the small unmanned aircraft for any reason. (Emphasis mine)

Here is what this graphically looks like.

107.39 prevents you from flying directly over (red) non-participating people while 107.19(c) (yellow) requires you to “pose no undue hazard . . . in the event of a loss of control of the small unmanned aircraft for any reason.” Any reason like a propeller breaking (you are logging the time on those right to switch them out regularly?) an autopilot going nuts, GPS interference testing happening or GPS multipathing in an urban environment, etc. The FAA did charge a guy recently with this regulation for flying over downtown Philadelphia.

Notice 107.19(c) requires you to pose no undue hazard. It’s exposure, not being over. Keep this in mind when doing your operations near people. See my section 107.19 article for a more in-depth discussion. Or maybe take my Part 107 regulations course over at www.rupprechtdrones.com?

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Issues Surrounding Over People Operations​

The two big issues are transferring kinetic energy and lacerations.

1. Transferring Kinetic Energy​

This is an area that is currently being researched to understand how unmanned aircraft transfer energy. All sorts of things go into decreasing the energy transfer such as shape of the aircraft, the material it is made of, the positioning of certain parts, the size to create a greater distance between the aircraft’s center of gravity and the most outer edge of the aircraft, etc.

Basically, an aircraft has an overall amount of energy while in flight and you have to figure out how to manage the kinetic energy levels and/or decrease the amount of transfer upon impact.

To keep energy levels low, you could fly slowly, low in altitude, into the wind, or decrease the mass of the aircraft. You could also install some type of flight termination system (parachute) which slows the aircraft down to a low kinetic energy level. Here is an impact calculator I built. Just plug in your drone and altitude to see what is your kinetic energy.

Drone Kinetic Energy Calculator​

Unless you have a solid steel rod, you are NOT going to transfer all the energy into the object. All sorts of energy is dissipated by the aircraft moving, warping, rotating, compressing, etc. This is where it gets tricky in calculating things because you basically have to launch the drone into some crash test dummies (in different realistic configuration) to see what happens.

This is why in the FAA’s over people proposed regulations, they came up with a simplified method. It’s basically assuming all the energy is being transferred and you are just doing energy management with speed, altitude, wind, mass, etc.

And here is another wrinkle in calculating things, when you distance the center of gravity of the aircraft from the center of gravity of the object being impacted, there is decrease in energy transfer because the CG of the aircraft tends to glance off and not transfer all the energy through. Imagine this. Which will transfer more energy into the object? (1) an arrow with the CG close to the back of the arrow near the feathers or (2) near the tip. (1) would result in glancing and rotating around which means it’s even less probable of nailing the target dead on where the energy would go down through the arrow shaft into the target.

Even when you have figured out calculating things (typically things are static like the aircraft’s energy transferring properties., CG, and mass) the other big hurdle is proving that the energy levels you are at are indeed safe. Is 50 foot-pounds ok? What about 100 foot-pounds? What does that do to the neck or the skull?

There has literally been hundreds and hundreds of pages published on this one point. How much energy can a person really receive and what energy levels will result in what levels of injury where?

Basically, prove a “safe” level of energy and prove your aircraft will be at the safe energy level or lower during impact.

2. Lacerations​

The other concern is that these flying lawnmowers might come into contact with people and cause further injuries on top of the blunt injury. The propellers could also break and stab the person.

There needs to be a mitigation for this hazard. One is to stop the propellers if there is an emergency and another is to install prop guards/bumpers.

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What Aircraft Have Been Approved to Fly Over People?​

It’s really important you understand this. There are two sections here: (1) what was approved from (2016-2020) and then (2) what has been approved under the new regulations.

Some aircraft are approved by their design. Some are approved because they have a parachute system.

(2016-2020 )Aircraft & Parachute Systems​

Here are some of the ones that have been approved that you can purchase today:

• eBee Classic
• Prox Dynamic’s (Owned by FLIR) PD-100 Black Hornet
• Mavic 2 with Parazero Safeair
• Phantom 4 with Parazero SafeAir
• DJI Inspire 2 with Indemnis Parachute
• Fotokite Pro 1

Here’s a list of ASTM compliant parachute systems you can purchase today that were used to obtain waivers from 2016-2020:

• AVSS parachute for the DJI Matrice 200 Series (Matrice 200 V1, Matrice 200 V2, Matrice 210 V1, Matrice 210 V2, Matrice 210 RTK V1, and M210 RTK V2)
• Parazero SafeAir
  • Phantom 4 Series (non RTK)
  • Mavic 2 Series (Pro, Zoom, & Enterprise).
• Indemnis parachute for:
  • DJI Inspire 2
  • DJI Mavic 2
  • DJI Matrice 210

Coupon Codes for Parachute Systems:

• AVSS for $50 off. “AVSSRUPPRECHT50”
• Parazero for $50 off. “RUPPRECHT50”

(2021 and Onwards)Aircraft & Parachute Systems​

As of the time of this writing, there have been none approved under the new regulations.