This study investigates the effect of a polyurethane (PUR) foam layer on impact force, impact duration, and deformation with regard to radiosondes during drop tests. Numerical (Finite Element Method) and experimental approaches were used to model collisions with and without protective PUR layers. The numerical results demonstrated that adding a soft PUR foam layer reduced peak impact force by 10% while it increased impact duration up to 71%. Experimental drop tests confirmed the numerical outcomes as peak impact force difference was 7% between simulations and experiments, while impact duration differed only by 11%. Besides force and duration, impact deformation was also investigated by an FEM model and high-speed camera footage on radiosondes with a PUR foam layer. The FEM model was able to approximate well the deformation magnitude since the numerical deformation was only 2% lower compared to the experimental data. In summary, a reliable and validated FEM model was created. On the one hand, this model allows the analysis of different protective layers around a radiosonde. On the other hand, it can adequately predict the impact behavior of radiosondes by incorporating multiple important factors. In addition, it has been confirmed that incorporating a soft PUR foam layer significantly improves safety by reducing impact force and extending impact duration.

Payloads for light unmanned free balloons must meet several safety requirements such as being able to protect the inner electronics in order to extract scientific data and to reduce the chance of inflicting personal injury in case of an accidental fall. This article proposes a novel payload structure, which exhibits the form of a dodecahedron. The actual form was determined by carrying out theoretical drop tests on different polyhedrons using the finite element method (FEM). From the simulations, it could be deduced that the dodecahedron was the optimal choice, since the duration of the impact was longer, while the impact force was slightly lower. The payload was produced by additive technologies; therefore, after performing tensile tests on probable materials, PLA was selected as the optimal candidate. The theoretical results about the dodecahedron’s ability were validated by laboratory and real-life drop tests, where the new payload was subjected to 56% less impact force under a 78% longer collision time compared to a classic, rectangular cuboid design. Based on these tests, it was demonstrated that the new structure is safer and it is applicable.

This paper deals with safety requirements for radiosondes and their possible finite element method (FEM) simulations. This article proposes a soft outer layer, which exhibits the use of a Polyurethane foam (PUR foam) layer on radiosondes. Analysis and tests of normal and PUR foam layer coated radiosonde's collisions with test targets were done. FEM models were created to model the collisions of radiosondes with virtual targets at drop tests in different scenarios. To compare and verify the virtual results, specified real-life drop test measurements were carried out. The measured data was analyzed and showed an average accuracy of 8% in force measurements, and 2.22% accuracy in duration of the tests. Based on these virtual and real-life tests it was demonstrated, that an FEM model can simulate the end result of using PUR foam layers on radiosondes. It also demonstrated that the applicable PUR foam layer increases a safer collision also increasing the chance of maintaining functionality of the radiosondes.