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 lvl.4
Flight distance : 666483 ft
Netherlands
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achim1989 Posted at 2018-2-25 08:47
That is pure theoretical b*******t The spark has a takeoff weight of about 300g which is barely 50g above the threshold. And when I switch it to sports mode it can do 50 kph. So if I fly someone into the face at full speed he or she will be injured severely! The 50g will make no difference there.
You are right that in the wrong hands it could definately raise havoc, and it has been raised in the risk assessments.
The focus has been on blunt trauma from impact to the head. Flying someone in the face has been mentioned as 'not being likely' due to the fact that people tend to shift or cover themselves with their hands if a drone comes spearing at them.
The <900 classes are considered to have little risk of creating blunt trauma and therefore are considered to be safe to fly over uninvolved people occasionally. 900 grams is considered the threshold between blunt trauma or not.
The reason that <250 grams doesn't need to be registrerd is because they are not big enough to carry a payload in the case of terrorism.
Here is the blunt trauma risk assessment out of NPA 2017-05 B.
Rationale behind MTOM/energy thresholds for UAS Class C0 and C1
MTOM/energy thresholds are one of the criteria for the subcategorisation of UAS in the open category. These criteria are used together with others in order to define subcategories of operations and UAS classes. This paper intends to provide the rationale behind the masses and energy thresholds defined with regard to the risk posed by blunt-trauma injury (non-penetrating injury) inflicted on people by a UAS. It focuses on Subcategory A1, Classes C0 and C1:
Penetrating injuries should be prevented by a UAS design that does not expose uninvolved persons to the risk of injury inflicted by acuminated parts or cutting edges, for example, blade protection. But this aspect is not addressed by this paper.
Subcategory A1, Class C0
This UAS Subcategory and Class can be operated by minors, without any training required. Occasionally, UAS might fly over assemblies of people. In view of the above, a UAS of this Subcategory and Class must be intrinsically unable to harm people in case it collides with people due to remotepilot error or UA failure. The 250-g MTOM threshold is proposed as a conservative mass to prevent significant blunt trauma. This threshold is justified by the following:
— It has been adopted for the smallest proposed category by the FAA Micro ARC of the March 2016, aimed at making a recommendation for a future FAA rule for UA allowed to fly over people.
— It is the MTOM threshold identified by the FAA registration task force: UA with an MTOM of less than 250 g are not registered. To identify this MTOM, the risk equation was applied.
— Considering RCC studies-based estimates, it has been shown that a kinetic energy of 44 J impacting a human body, averaged on the body of a person standing, would result in a probability of fatality (PoF) of 1%. From a linearisation of the relationship between MTOM and terminal kinetic energy, valid for small rotorcraft, this equates to about 250 g. There is some evidence that RCC studies are overly conservative if applied to UAS collisions with people, however, given the scope of this Subcategory and Class, it is preferred to retain a very conservative value.
Subcategory A1, Class C1
In this case, a minimum age and a minimum level of knowledge would be required for operating the UA, and flying over crowds, even occasionally, would be prohibited; it would be allowed to fly the UA only over isolated people and at a safe distance. A kinetic-energy value was calculated based on experiments that better resemble the possible UAS impact on a person.
The impact scenario considered is that of a multi-rotor UA95 falling from the maximum allowed altitude and reaching a person’s head at a 45 ° angle with respect to the vertical. Among available data from literature, it is proposed to consider the Gurdjian experiments96 with real embalmed human heads being dropped from a certain height on a solid, not moving plate. 17 specimens were impacted on the anterior parietal zone, 10 on the posterior parietal zone. The frontal zone is not considered as people would normally spot a UAS approaching, with their frontal zone facing the UAS, and would either shift or cover themselves with their hands. Temporal data are not available.
From the reported terminal speeds, when the initial fracture was recorded, as well as from the weight of the specimens, it is possible to derive the kinetic energy at impact and take the overall average. The result is about 80 J.
A Monash University paper97 refers to computer simulation of head impacts on a flat rigid structure, yielding energy values between 80 and 95 J, to start seeing skull fractures. This information seems to conservatively confirm the 80 J identified through the Gurdjian experiments.
Other fracture experiments are also available in literature, where pressure was applied to various parts of the skull:
In some cases, recorded data include peak forces and accelerations, but the skulls seem to have been compressed on relatively smaller areas. It is believed that between the two kinds of experiments, those involving collision with a flat surface have a better resemblance with the blunt trauma resulting from a possible UAS impact.
In the Gurdjian experiments, the energy is fully transferred to the head as there is no deformation or movement of the surface impacted. In conclusion, the value of 80 J is retained as the threshold kinetic energy that the head of the average person would be able to absorb without the skull being fractured.
It is difficult to associate a PoF with this threshold, but there are reasons to consider the above estimate as conservative:
— the experiments with the skull specimens included several impacts before fracture; as a consequence, it may be assumed that the skulls could have been weakened before reaching the rupture threshold;
— a living person’s head should be more resistant than the embalmed heads used in the experiments; and
— the rupture of the skull does not necessarily lead to a fatality (although it would certainly be a major trauma).
This substantiates the 80-J threshold value of absorbed kinetic energy as an acceptable one for Class C1. In a collision with a UA, only a fraction of the UA kinetic energy would be transferred to the head. As described further in the text, the kinetic energy absorbed in average by a human head hit by a UA in free fall is estimated to be 46.5 % of the terminal kinetic energy of the UA, expressed as half of the aircraft MTOM multiplied by the square of its terminal velocity (reaching ground). This fractional value may have been conservatively calculated, and, given the uncertainties of collision dynamics, other assumptions may be possible.
A terminal kinetic energy under 80/0.465 = 172 J for the UA would be therefore allowed. Using a linear approximate relationship between terminal kinetic energy and MTOM (about 48 J for every 250 g of MTOM of relatively small multicopter currently available on the market), the 172-J threshold equates to an MTOM of approximately 900 g.
In conclusion, an MTOM of 900 g can be considered as a good threshold to allow a Class C1 UA to be flown over isolated people. UAS with a greater MTOM could also qualify if the manufacturer demonstrates that the kinetic energy transmitted to the head would be less than 80 J.
Note: on 28 April 2017, the final report of the FAA UAS Center of Excellence Task A4 ‘UAS Ground Collision Severity Evaluation’ was published98. This very detailed and rich in information report will be analysed by EASA during the public-consultation period of this NPA, to assess potential implications for the thresholds established above.
Considerations on the kinetic energy transferred to a human head during a collision with a vertically falling multicopter.
The most common mass-produced multicopter UA on the market, with an MTOM between 250 g and 2 kg, is the Phantom DJI. Its dimensions are approximately the ones provided in the following picture:
In general, it is assumed that if the UA hits a person’s head with one of its arms, the UA would rotate away and a relatively small fraction (F1) of the impacting kinetic energy would be transferred during the impact. The fraction would be much higher (F2) if the collision would occur at the center of or within the square area of the 145-mm side in the example above. The following is an evaluation of those values (F1 and F2):
For value F1 and based on information presented during expert meetings on the subject of small UA and energy balances that could be considered during a collision, as well as on engineering judgment, it is considered that by hitting exactly in the centre, the UA would partially bend or be destroyed, absorbing in the process about 7 % of the impacting kinetic energy:
Kinetic energy transferred = 0.93 x impacting kinetic energy
As for value F2, if the UA would hit the head with its terminal part of the arm (tip), the transferred kinetic energy would tend to zero as the UA would most likely rotate away.
In order to simplify those two scenarios, a linear behaviour of the kinetic energy transferred to the person’s head between the following two extremes is assumed:
— impact at the centre: 0.93 x impacting kinetic energy; and
— impact at the tip: 0.
The average would therefore be (0.93 x impacting kinetic energy + 0)/2 = 0.465 x impacting kinetic energy.
The impacting kinetic energy of a UAS in free fall can be conservatively considered to be its terminal kinetic energy.
In conclusion, according to the above estimates, it is considered that the kinetic energy of a UA in free fall transmitted to a person’s head would be in average 46.5 % of the UA terminal kinetic energy.
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First Officer
Captain
lvl.2
Same here in the Netherlands, we are waiting on new rulings to be efectuated, but I'd rather they wait on these European Rules.
