V.I. Biryuk - Ph.D. (Eng.), Moscow Institute of Physics and Thechnology; Chief Research Fellow; Central Aerohudrodynamic Institute. E-mail: v_biryuk@yahoo.com
Nguyen Hong Phong - Post-Graduate Student, Moscow Institute of Physics and Thechnology. E-mail: loicuagio100884@yahoo.com

In this paper, first, the loads on the rigid wing in the aircraft system were studied using the discrete vortex method. Then the influence of anisotropy on the distribution of the twisting angles of straight wing due to bending was investigated. The optimal distributions of orientation angles of composite material were compared. The bending, twisting moments and shear force along the rigid wing span were calculated. These power factors were compared with calculated results carried out on an isolated wing with the assumption that the load distribution on the wing area is constant. Comparison showed that the simplified approach can be used in the optimization process of the anisotropy in the composite wing panels. The results show that for straight wing of UAV with high aspect ratio, the use of anisotropy properties of composite material in wing skins allows to reduce angles of attack of each wing cross-sections. This is an additional factor for weight reduction. For the considered wing box, when the orientation angles of composite material are from -20 to -30 (in case of unidirectional composite), and from -35 to -40 (in case of quasi-isotropic composite) depending on failure criteria applied, the wing twisted to highest degrees in direction of angle of attack reduction. Here we must bear in mind that for quasi-isotropic composite, we only change the orientation of those layers which were originally 0 degrees, the orientation of the other layers are saved. The application of the three composite failure criteria: Hill, Hoffman, Tsai Wu led to slight differences in optimized weight. But, despite the same trend of twisting the wing towards the reduction of angles of attack, the differences in the distribution of torsion angles and their values give evidence for detailed experimental research on constructive samples in order to study this issue thoroughly.