**4. Discussion**

The present study focuses on two major chapters. First, is a test of the aerodynamic characteristics of the canopy in its activation phase to obtain the opening shock load during its activation. The second part is the application of this specific load to the harness and finding the redistribution of the total applied load to the different structural nodes of the harness. The force application is extended to loads in different configurations.

In the canopy testing phase, it was important to maintain the design parameters, which were determined based on the terminal speeds at which a parachutist falls in free fall. For the purpose of the test, the speed was set at 200 km/h. The progress of the test confirmed the normal canopy function, and the results from the first test were used for the postprocessing. The logging of the individual parameters proved to be sufficient to provide the data for the following harness analysis, which is the main goal of the research. The G-force data were used to calculate the opening shock load. As a supplement, measuring carabiners on each side of the canopy hinge were also used. The existing measuring carabiners showed non-standard behavior during the test, and therefore, the results were not included in the evaluation. However, they are the subject of additional internal development, and further practical use is planned for future tests. The maximum value of the measured opening shock overload was G = 6.3. With a weight mass of m = 130 kg, this overload was converted to an opening shock load of Fshock\_load = 8035 N. For subsequent analysis, it was stated that the testing force could be rounded up to the value of Fshock\_load = 8000 N. The provided methodology proved to be adaptable and can be used for a variety of activation speeds and ballast masses or types of parachutes. This brings the possibility of filling the certification requirements defined by the Technical Standard 135 in the section "Structural Overload Tests" [4].

The second section of this paper focuses on a comprehensive loading study of the fully articulated parachute harness structure. The decomposition and incorporation of each element's strength limits, as well as the determination of the applied force's redistribution into separate parts, shed light on the sizing of individual elements. Load cells based on the minimum dimension parameters were developed to measure forces in separate webbings. With this benefit, serial production parts were used for the strain gauge installation. This procedure ensured minimum costs and, due to the load cell's small dimensions, minimal

structural influence once it was sewn into the final harness. During calibration, it was verified that laterally uneven loading of the measuring feature has no effect on the measurement precision. It was one of the biggest concerns when considering the location of the separate features. It was expected that, because of the required number of load cells, there would not be enough space to locate them all in ideal positions. The element on the webbing heading to the back of the dummy was, despite all efforts, loaded partly by bending. The aim of future work will be to develop an element that will not be sensitive to the bending component. A very important observation was identified. Once the harness settles on the dummy body, the redistribution of the forces related to the applied force does not change significantly. This opened the possibility of generalizing the research. It can be expected that by increasing the applied force above the presented value of 8000 N, the same trend of redistribution will follow. This means that the use of a different canopy or changes in activation speed resulting in a different opening shock load can be applied for recalculation.

In all cases, the buckle located on the chest webbing was identified as the weakest element. Based on the results, the fixed spatial position that loads this element the most is an asymmetrically loaded case. This is because the chest strap took some of the force from the opposite side through the cross-connection. However, the amount of load transferred by this carabiner is strongly dependent on how tight the strap is. It was identified that the difference in critical force can vary by up to 107%. This result is also expected because the loosening of the chest webbing causes the main load to pass from the pilot's buttocks directly to the upper hinge points. When tightened, the webbing tends to create two triangles that tend to expand under the load. When using the harness, it is therefore a good idea to tighten the harness, but in the case of the chest strap, tighten it only to the point that the harness cannot come loose on the pilot. Any overtightening will not bring any benefit. It will only cause overloading of the structural node.

It can be expected that the maximum allowed load declared by the manufacturer uses some safety factors. This means that even though elements would reach their maximum limit, no visible damage would be observable. Compared to the test of a complete assembly according to TS-135 [4], exceeding the recommended limit of single structural nodes is not controlled. After the test, the harness structure must only be inspected for visible damage. Hence, the testing procedure proposed in this study is considered safer as it allows for the direct monitoring of each component.

For further extension of this study, the strength test of individual components up to visible damage is suggested. Incorporating the maximum strength limits of the parts assumes a significant increase in the maximum load limit of the entire harness.
