It is based on a kinetic impact study. In Europe in its RE 2019947, https://eur-lex.europa.eu/legal-content/ES/TXT/PDF/?uri=CELEX:02019R0947-20200606&from=EN (and I believe that the FAA, in its regulation, too)... the threshold of 80J of kinetic impact is established for said classification. Here I leave the old study about it...
250g Question - Why?
- Thread starter PacificSkyDreamn
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The 80 joule number was taken from a really ancient military study trying to predict injury potential from explosion shrapnel. It has been widely used ever since to imply that an 80 joule impact has a 30% probability of causing fatality. That sounds really ominous. But it sounds much less dire if you say it the other way around, i.e. the same impact is 70% probable to not cause fatality.
Your link is DJI's Dec 2016 response to the original Registration Task Force (RTF) report of Nov 2015, which I linked in post#11 above.
Both the original RTF report, and DJI's response a year later, should be required reading for everyone.
Walter Stockwell and Brendan Schulman very eloquently laid out all the reasons why the RTF report is deeply flawed. They outline many compelling reasons why 250grams is an overly restrictive number to have been chosen for the threshold now used almost universally around the world as the "Lowest-Risk UAS Category".
The DJI analysis suggests that 2.2 kg would have been a more reasonable conclusion for the same accepted risk level. It should be noted that, at the time, DJI's popular Phantom series weighed ~1.2kg.
Bottom line, there is no data anywhere to suggest sub-250 gram drones present any risk of fatality, nor even severe injury. Any proposed tightening of regulations for this class of UAV would need to be based on grounds other than risk of physical injury.
Our European agencies (EASA) and the national one, AESA have kinetic impact assignment tables, according to a specific model (when you register your aircraft to operate in a specific category). Generalizing, only aircraft with a MTOW greater than 800 gr. exceed those 80 Joules of kinetic impact, which implies that you must use mitigations such as a parachute. Although parachutes are required by law with aircraft with MTOW greater than 250 gr when flying in an urban setting (specific cat.)
That makes far more sense than using only mass as the determining factor. Velocity is an important contributing factor.
Kinetic Energy K.E. = 1/2 Mass x Velocity squared.
kilograms-meters squared per second squared (Joules) = 1/2m (kg) x V(m/sec)^2
But it significantly complicates the regulations. It's so much easier to just pick weight as the determining factor, even if it makes no sense.
If you need to take velocity into account, as described in DJI's response, then you need to know either the maximum vertical velocity of the drone falling at terrminal velocity out of the sky, or it will be the horizontal velocity at the drone's maximum speed capability, or a combination of the two. That's starting to get complicated...
But here again we have the grossly over simplified 80 Joules number. Kinetic energy alone isn't enough to determine what sort of injury may result. Given a known mass and a known velocity, you can calculate the Kinetic Energy. But surely the shape of an object will significantly affect what sorts of damage will be delivered by that energy.
A sharply pointed dart or arrowhead will produce a totally different type of injury, compared to a golf ball, compared to a basketball, compared to a piece of sharp metal shrapnel, compared to a styrofoam model plane, compared to a plastic multirotor drone, even if each of them were equally carrying 80 Joules of kinetic energy.
It's ridiculous to claim you have the exact same 30% chance of fatality if struck in the head in each of the above cases.
And yet those parachutes are required only for unmanned aircraft weighing more than 250 grams, not for all aircraft (i,e, manned aircraft). Curious, isn't it? A lot of effort has gone into imposing regulations to address problems that don't seem to exist.
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