# 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
Consequently, the strain deformation data on the spanning characteristic line of the upper surfaces of the flexible wing under different inflation pressures is listed in Table 11, and the corresponding strain value changing curves are shown in Figure 6. The strain deformation data of the chord characteristic line of the upper wing surfaces of the flexible wing is listed in Table 12, and the corresponding strain changing curves are shown in Figure 7. And the strain deformation data of the lower surfaces of the flexible wing along the spanning characteristic line is listed in Table 13, and the corresponding strain value changing curves are shown in Figure 8.  
Figure 6: Characteristic line positions of the upper and lower surfaces of the flexible wing film along the spanning and chord direction [6]. Figure 7: Strain deformation curves of the upper wing surfaces along the spanning characteristic line under different inflation pressure loads. According to the strain deformation data and the variation curves of the upper surfaces of the flexible inflatable wing in Table A1 and Figure 7, it can be seen that under the same inflation pressure load conditions, the strain deformation of the surface of the flexible wing gradually decreases along the spanning-wise direction, but the jump with a sudden increase occurs near the vicinity of the wing root, which indicates there is a large concentrated load or bending deformation near the wing tip. And as the internal inflation pressure increases, the strain value near the spanning direction of the wing root becomes larger, but the strain deformation in the middle position becomes slightly smaller, and the vicinity of the wing tip continues to become larger. So, the result shows that the strain deformation near the wing root and the wing tip are positively correlated with the internal inflation pressure, and the increase in the internal inflation pressure causes a more severe local deformation of the wing root to induce an excessive fracture failure problem. The strain deformation in the middle of the surface on the upper wing increases with the increase in the internal inflation pressure, which makes the wing's warpage deformation decrease, and the overall stiffness becomes larger, and the strain deformation of the wing skin surface is also reduced. Meanwhile, due to the deformation along the chord direction of the flexible wing, the tensile strain deformation of the middle part of the wing exhibits a wave-like change at different positions with the increase in the internal inflation pressure. So, it is verified that the higher inflation pressure is quite beneficial to improve the strain deformation characteristics of the upper surface of the wing skin film, and the upper surface has a larger curvature due to biaxial tensile deformation. Therefore, considering the deformation safety of the flexible wing, it is necessary to consider the biaxial deformation of the surfaces of flexible wings along the spanning and the chord-wise direction together with the internal inflation pressure synchronously. From the strain deformation data and curves along the chord-wise characteristic line of the upper surfaces of the flexible wing in Table A2 and Figure 8, it can be seen that under the same inflation pressure load, the strain deformation of the upper wing surfaces of the flexible wing changes with the wave-like law. The strain near the leading edge is quite small and then increases toward the middle of the chord-wise direction, and the strain decreases near the trailing edge, which shows that the chord-wise direction of the upper wing surface is mainly subjected to a large pressure load from the middle of the wing surfaces; furthermore, due to the large radius of the curvature of the local structure, the strain deformation is quite small around the leading and the rear edges. Therefore, the  
Figure 8: Strain deformation curves of the upper wing surfaces along the chord-wise characteristic line under different inflation pressure loads.