# Robotized Mobile Platform for Non-Destructive Inspection of Aircraft Structures
## 3 Testing and Experimental Validation
### Inspection Results and Discussion  
Initial tests using the EC technique were mainly aimed at verifying the possibility of cooperation between the devices. The probe used is dedicated to detecting corrosion and cracks in multi-layer structures. From the point of view of the conducted research, its advantage is the ability to observe the internal elements of the tested part. The tests were performed at a signal frequency of 4 kHz. This is a relatively low frequency that provides sufficient penetration depth. The preliminary test results from the two elements tested are presented below. The first scan (Figure 12) comes from the rudder of the MiG-29 aircraft.  
The scan shows single vertical dashed lines indicating that the maximum speed allowed by the measurement system has been exceeded. Apart from that, the result can be considered correct. The scanned element has a variable thickness. A lighter color corresponds to an area of greater thickness. There were no defects in the tested element.  
The second result from the wing of the PZL-130 aircraft presented in Figure 13 was collected correctly. This means that the MP speed and the pressure of the measuring probe were appropriate. The obtained scan shows rivets and the longitudinal member, which is visible in Figure 13, as a light diagonal strip and color equidistant spots representing the rivets. The A-scan in the location of a rivet is presented on the left-hand side in the monitor of the Omniscan defectoscope. There was no damage in the recorded area. Based on the results obtained, the possibility of cooperation of MP with the ECA system can be confirmed. The ECA system is able to collect measurement data, which means that the pressure of the measuring probe is even and the vehicle is able to move at a sufficiently low speed and maintain its trajectory.  
Figure 12: The result obtained during the tests on MiG-29 rudder. Thickness changes are visible. Black dashed lines indicate places where the MP speed was too high.  
The data presented in Figures 12 and 13, including the positioning data, are coming from the eddy current sensor. In order to reduce the cost of the presented prototype, information from the encoder attached to the ECA was used. In this case, we used all features provided by the commercial ECA solutions, and there is no need to use an additional system for positional data from the platform.  
The performance of the presented MP is highly dependent on the maximum payload that the robot can carry. To estimate the capability of the equipped robot to perform a specific NDT task, additional information should be taken into account. To evaluate the capability of the MP, among others, the range of the operation of the robot (additional mass of the cables), the friction coefficient of the investigated surface, and the maximum inclinations should be known. Then, based on these parameters, the required thrust force can be estimated and compared with the maximum thrust that the platform can generate including the required safety margin.  
Table 2 shows a comparison of different parameters of the considered MP with other similar solutions published in the following articles: [22, 25, 27, 28, 29, 31, 43, 44]. In all of the compared solutions, only platforms with the negative pressure generation mechanism were selected. Some of the MPs presented were only laboratory tested and did not have NDT accessories, or this information was not reported. In such cases, only the information about the payload is relevant regarding the capability of the other MP to perform NDT with the selected equipment. The proposed MP belongs to lightweight constructions (about 2 kg) with comparable compact sizes and similar speed. The maximum power consumption of the proposed MP belongs to the lowest range of values in the presented comparison.  
Figure 13: The result obtained during the tests on PZL-130 wing.