# The Effect of Inflatable Pressure on the Strain Deformation of Flexible Wing Skin Film
## 4 Results and Discussion
### Analysis of the Strain Deformation of Flexible Wing Film
flexible wing surface pressure load needs to focus on the strain deformation characteristics of the middle part of the upper surface to prevent excessive deformation failure and damage in this area. Moreover, as the internal inflation pressure load increases, the internal and external pressure difference loads of the upper surface skin film increase synchronously, the strain value of the upper wing surface increases rapidly along the chord-wise line, and the maximum strain increment value is located in the middle area of the chord-wise direction (up to 2.035 \(\times\) 10\({}^{-4}\)), which indicates that the internal inflation pressure directly affects the strain deformation of the upper wing surface in the chord-wise direction. The larger the internal inflation pressure, the larger the chord-wise strain deformation, but the increase in internal inflation pressure has a very small influence on the strain change in the chord forward and trailing edges. So, the increase in the internal inflation pressure needs to focus on the strain deformation characteristics of the upper chord surface on the wing, and among the allowable strain range, the chord strain deformation change could be ignored along the forward and trailing edges of the upper wing. According to the strain deformation shown in Table 10 and Figure 9, it can be seen that under the same inflation pressure load, the strain value of the lower surface of the flexible wing increases slightly along the spanning characteristic line near the wing root. Then, the strain deformation value gradually decreases linearly along the wing root towards the wing tip direction, and the maximum strain value is located near the wing root position. Comparing with the Formulas (7)-(8), when designing the lower wing stiffness of the flexible wing, it is quite necessary to focus on the excessive strain deformation of the lower surface near the wing root to prevent failure due to excessive local deformation. And with the increase in the internal inflation pressure, the strain deformation of the lower surfaces gradually increases, but due to the large deformation value of the lower surface, the strain value increment exhibits a wave-like change due to the comprehensive influence of the chord-wise deformation. However, the strain deformation value near the wing root decreases with the increase in inflation pressure, which indicates that the increase in inflation pressure is beneficial to alleviate the strain deformation near the root of the lower wing surfaces. However, the strain deformation in the middle part of the lower surface shows a wave-like change, and the strain deformation value in the vicinity of the wing tip continues to increase with the  
Figure 9: Strain deformation curves of the lower wing surfaces along the spanning-wise characteristic line under different inflation pressure loads. increase in the inflation pressure. So, the result shows that the internal inflation pressure load directly leads to an increase in the strain deformation value of the middle part of the lower wing surface and the wing tip position, which affects the distribution of strain change. However, it is quite beneficial to improve the strain deformation near the wing root position of the wing. That is, the increase in inflation pressure could improve the warping deformation near the wing root of the inflatable wing. Moreover, it could also improve the bearing stiffness of the whole flexible inflatable wing, but the maximum strain value near the wing root continues to increase with the increase in the internal inflation pressure. Therefore, the overall stiffness design of the flexible inflatable wing needs to consider the distribution law of the maximum strain deformation near the wing root, which could help ensure that the stiffness of the lower surfaces of the flexible wing is fully deformed to meet the allowable strain requirements.