Assessing transferred energy in drone impacts using rigid impactor tests

The rapid development of unmanned aerial systems (UAS) has led to their widespread use and affordability. A major safety issue is understanding the health consequences of drone-human collisions, which largely depends on rigorous testing methods. The aim of this paper is to determine the response of the anthropomorphic test device (ATD) using a rigid impactor with gradually increasing impact kinetic energy (KE) and to obtain a validated dataset for subsequent comparisons in case of vertical impact to the top of the head. A total of 30 tests were performed with kinetic energy at impact ranging from 5 to 180 J. It was assumed that the majority of the kinetic energy during impacts was absorbed by the ATD head. This enables the derivation of scalable results across various impact energies and orientations. These results were subsequently compared with actual UAS impact tests. The findings suggest that with increasing kinetic energy of the UAS impact, the percentage of transferred energy decreases. For this reason, it is not possible to confirm a linear trend similar to that observed in tests with rigid impactors. This phenomenon is particularly evident in the design of the DJI Phantom, whose plastic frame underwent significant deformation, thereby reducing energy transmission to the head. The comparison with impactor tests showed that, although the UAS was potentially able to reach a KE of up to 280 J at a limit speed of 20 m/s, the transmitted energy was only about 20%. This observed trend was confirmed by biomechanical criteria, including Peak Head Acceleration, Head Injury Criterion, 15 ms (HIC15), and Neck Injury Criterion (Nij). In cases where testing facility capabilities are limited and tests cannot be performed at the critical speed or terminal velocity, the HIC15 relationship to KE seems to be more accurate than peak head acceleration. It should be noted that the proposed approach is validated only for vertical, top-of-head impacts. For these reasons, the safety criteria currently used for UAS, which are primarily based on a linear energy transfer assumption, may lead to overly restrictive injury predictions when applied to the more pliable and deformable UAS structures.