## 3 Results and Discussion
The following dynamic frequency analysis evaluated the system's periodic response to cyclical loads of frequency-dependent amplitude. The load input corresponded to the measurements performed with the accelerometer and took the form of a driving frequency with the corresponding amplitudes. In our case, the dynamic frequency analysis was performed to calculate the amplitude of accelerations as the response to a load oscillating at different frequencies. From Figure 11, it is obvious that the simulation results correspond to the previously performed simulations and also to the measurement results. This means that it was confirmed that with the increasing ambient temperature, the natural frequency of the aircraft construction decreases. This is caused by the temperature dependence of the various material characteristics, which results in the change in the stresses due to the thermal expansion of the materials. Since the simulation results confirmed the correctness of the calculation model, this model can be used for further calculations. Thanks to the model, it is possible to simula  
Figure 3:1 FFT analysis results (**a**) for the temperature of 5 \({}^{\circ}\)C; (**b**) for the temperature of 30 \({}^{\circ}\)C.  
Figure 3:2 Simulation model of the aircraft with the results of the modal analysis. characteristics for any measurement point of the construction. Furthermore, the obtained model will serve as a basis for further sensor development, including the calibration of the sensor output. For this purpose, the calibration results can be compared to the results of the CAE analysis. This article presents the latest results of the long-term ongoing research in the area of contactless tensile stress measurement based on the microwire sensors embedded into the composite materials. For the first time, we performed the measurements outside the laboratory facility. For this purpose, we had to re-build the laboratory prototype [47] into the battery-powered [48] defectoscopy prototype. As our goal was to perform flight tests, this prototype was modified. We tried to achieve this goal after the ground tests performed in the hangar during the same day. However, during the flight test, the prototype electronics was affected by the vibrations generated by the aircraft engine and the propeller. During these in-flight measurements, blackouts of the system occurred. Our further research will be therefore focused on the solution to this problem. One of the main advantages of the developed solution is that the microwire-based tensile stress sensors can be used not only for the pre-flight and post-flight diagnostics, but they can be used also for the in-flight monitoring and diagnostics of the system. As we have the CAD model of the aircraft, it is possible to determine the most convenient positions that are characterized by the highest values of the stresses for the microwire placement. The sensing element can be embedded directly into the composite structure of the aircraft during the production process, but it can be added also additionally. Thanks to the dimensions of the microwire and to the manufacturing costs and speed (from 1 kg of alloy, it is possible to manufacture 40,000 km of microwire, with the production speed of 400 m/min), it is possible to choose many points for the measurement. Those points which will not be used for the continuous in-flight monitoring can be used during the aircraft inspection. Moreover, information from the microwires with no response will be useful because it can point to the overloading of the construction. The proposed sensor solution of the aircraft construction monitoring can improve the diagnostic procedures because, in addition to the in-flight monitoring, it also allows the quick check of the aircraft construction, which can lead to the reduction of the maintenance costs, because the intervals for the aircraft maintenance can be extended. In this way, it is possible to extend also the lifetime of the aircraft.