The Terminal Velocity of a Falling Mavic 2

[Zbip57]

They grossly overestimated the terminal velocity

The entire process was gross.

This was all in response to ever more reports of yet another "near-catastrophic near-miss", or the mounting number of mere drone "sightings". Just imagine what "could have happened if..."

The FAA had to be seen as doing something about this growing menace, and mandatory registration was the magic bullet that would solve everything.

Rather than determining the actual level of risk of fatality in a collision with manned aviation, the Task Force calculated the risk to people on the ground, which wasn't ever at issue.

The only golden nugget of actual usefulness to come out of this Task Force Final Report is this one line at the bottom of page 4:

"The Task Force also sought to define a category of sUAS that should be excluded from the registration requirement because they do not present a significant level of risk to the non-flying public and to users of the NAS."

Sub-250 gram drones do not present a significant level of risk to anyone! (Not even for gutter inspections...)

 

[Meta4]

Using more realistic numbers, they could have gone up to approx 700g to stay below a KE of 80 joules.
Or maybe they were allowing for those incidents where the props to fall off and the arms to fold back?

Actual KE of the 250g Mini would be around 28 Joules.

 

[sar104]

The entire process was gross.

This was all in response to ever more reports of yet another "near-catastrophic near-miss", or the mounting number of mere drone "sightings". Just imagine what "could have happened if..."

The FAA had to be seen as doing something about this growing menace, and mandatory registration was the magic bullet that would solve everything.

Rather than determining the actual level of risk of fatality in a collision with manned aviation, the Task Force calculated the risk to people on the ground, which wasn't ever at issue.

The only golden nugget of actual usefulness to come out of this Task Force Final Report is this one line at the bottom of page 4:

"The Task Force also sought to define a category of sUAS that should be excluded from the registration requirement because they do not present a significant level of risk to the non-flying public and to users of the NAS."

Sub-250 gram drones do not present a significant level of risk to anyone! (Not even for gutter inspections...)

I disagree. The process had flaws, but if they were going to carry out the directive from Congress to figure out how to incorporate sUAS operations into the NAS then they had to address risks to other air traffic and to people and property on the ground. These calculations addressed the latter issue and while some of the assumptions look over-conservative, the basic approach is sound and has precedent.

The didn't ignore the risk of fatality in collisions with manned aircraft - they simply noted the potential level of damage that could arise in impacts, especially non-military helicopters and GA aircraft that are most likely to end up in conflict with sUAS. They concluded that the consequences of collision were not improbably catastrophic and that the probability of such collisions was non-negligible and would need to be mitigated if the rate of increase of sUAS use continued as projected.

 

[Zbip57]

Using more realistic numbers, they could have gone up to approx 700g to stay below a KE of 80 joules.

Even the 80 Joule kinetic energy is a gross over simplification. The shape of the object delivering that energy plays a large role in determining the level of hazard. 80 Joules delivered by a basketball is going to result in an entirely different injury compared to 80 Joules delivered by a golf ball.

Nonetheless, the FAA first came up with this 250 gram number and the rest of the world followed (all except Japan, which chose 200grams).

 

[Zbip57]

I disagree. [...]

The risk to manned aviation was only tackled in much later regulation.

The primary response of the FAA was all about registration, and ONLY registration, as though that was going to cure everything. They wanted to eliminate any exemption for "model aircraft" and pull everything under the umbrella of just plain "aircraft" for which registration was already required.

The Task Force was instructed to look at ONLY registration, and determine to what it should apply and how that would be accomplished. Collisions with manned aviation were not addressed in any form by this Task Force and had no influence on the report.

 

[sar104]

The risk to manned aviation was only tackled in much later regulation.

The primary response of the FAA was all about registration, and ONLY registration, as though that was going to cure everything. They wanted to eliminate any exemption for "model aircraft" and pull everything under the umbrella of just plain "aircraft" for which registration was already required.

The Task Force was instructed to look at ONLY registration, and determine to what it should apply and how that would be accomplished. Collisions with manned aviation were not addressed in any form by this Task Force and had no influence on the report.

I didn't argue that this task force tackled the risk to manned aviation. Is that all you are offended by - that they approached this piecemeal? I really don't understand your almost rabid anti-FAA response to everything they do.

 

[Zbip57]

I didn't argue that this task force tackled the risk to manned aviation. Is that all you are offended by

I'm not offended, and neither should you be.

This thread was discussing terminal velocity. I posted a link to the FAA report wherein they calculated terminal velocity, and used those questionable results to give birth to the now near-universally accepted and copied 250 gram threshold.

I am critical of the methodology used to arrived at that number. The math seems valid enough, but I'm skeptical of the shaky assumptions used as inputs to those equations.

At the time, the FAA held press conferences proudly touting their new drone registration requirements as something that would somehow prevent the bad guys from doing dumb things with drones. And yet there has never been any evidence to demonstrate that registration has ever served any useful purpose whatsoever, other than as a source of taxation.

Sure, the FAA, and Transport Canada, and EASA, and CASA, and everybody else, all later introduced many more restrictions which actually do attempt to influence how UAS can safely co-exist with manned aviation.

But this terminal velocity calculation used by the Registration Task Force was only ever intended to apply to the registration process. And it ONLY addressed the hazard to people on the ground. Instead that number is now used as the Gospel around the world for distinguishing between sub-250 gram drones considered to be safe enough to be ignored, versus 250g-25kg being dangerous enough to require ever stricter regulation.

And the entire time that 250 gram number was generated out of thin air by the Registration Task Force using assumptions pulled out of thin air. No actual test data, no valid risk analysis, nothing at all. It's just become accepted that 250 grams is somehow a sensible threshold.

Based on their numbers, in November 2015 the task force predicted,
"1 ground fatality for every 20,000,000 flight hours of an sUAS"

How many ground fatalities have been caused by 250 gram drones? Or, how many due to drone heavier than 250 grams?

I really don't understand your almost rabid anti-FAA response to everything they do.

I'm equally rabid about many of the things done by Transport Canada. For example, the same 250 gram threshold is used in our regulations, with never an explanation or justification provided for the choice of that number. We simply copied it directly from your FAA. There's no denying where it came from.

 

[jimjunkie]

Well, that was an absolutely fascinating read. I would say pertinent where I am at the moment as well (Australia). CASA is going through the same process of looking into drone registration currently, which seems to initially have been slated for this month but now looks like mid 2023. The same 250g threshold is being used as well, with anything 250g - 2kg falling into the "Excluded Category" (where operator accreditation and registration are required). No decision yet on cost per year to register, but $10 has been mentioned in early consultation.

I ended up here because I was curious about how the risk of a drone like the Air 2S would stack up against other unregulated things you can get your hands on. For example, another hobby of mine on and off is RC cars, where it's entirely possible to buy a 160km/h, 2kg car off the shelf. I'm not saying they're a comparable risk, the car wouldn't (normally) fly and hit you on the head, but if all we're looking at is energy on impact then that's significantly higher.

It seems a bit of a moot point anyway though when the mini 3 can go at what is pretty much its freefall terminal velocity when flying in a straight line. It's probably a bigger hazard with the props going full-clip as well.

 

[Cookedinlh]

I teach UAS/RPAS Flight Testing at the International Test Pilots School in London ON Canada and we are constantly doing formal "Risk Assessment" for virtually every flight from L39 Jets to Helicopters and drones up to 1500lb weight class. It's about evaluating the severity of the potential damage, when combined with the likelihood of the occurrence. Here are a couple of graphs I made few years ago to illustrate how really insignificant the 1kg class and especially the under 250g class is in the grander scheme of things. It takes a bit of examination to understand the point of these graphics . . but bottom line, "under 250g" is not worth even talking about. Given how over-regulated commercial drones are already. . . . regardless of where the risk actually comes from or the likelihood of it occurring, the risk does not even warrant being on a chart. Thes

 

[Xitor]

Visiting this thread 2.5 years late, but wondering why no one has dropped a dead one (with props that still spin) out of a helicopter to verify the math here. Even if tumbles and does auto-rotate, seems like props would add additional resistance. Also of course why its falling. Just power off probably more likely to auto-rotate, than a bird strike or something like that.

 

[Meta4]

Visiting this thread 2.5 years late, but wondering why no one has dropped a dead one (with props that still spin) out of a helicopter to verify the math here. Even if tumbles and does auto-rotate, seems like props would add additional resistance. Also of course why its falling. Just power off probably more likely to auto-rotate, than a bird strike or something like that.

No need.
The data from several incidents where a drone has fallen without losing power has demonstrated the calculations were quite close to what actually happens.
The terminal velocity of a falling drone is just a little less.

 

[Cookedinlh]

When the Canadian Part IX rules came out in 2019 I did an analysis of the Canadian sRPAS 922 Safety Standards that looked at what speed a Mavic or similar drone became LETHAL. It resulted in some interesting ideas. Like, unless you are racing around at top speed all the time these flying cameras are not anywhere near lethal. Here's a link to the full analysis.