# Estimation of Stability Parameters for Wide Body Aircraft Using Computational Techniques
## 3 Xflr
### XFLR Analysis Technique  
The preliminary task to perform for analysis in XFLR is the modeling of a wing, aircraft, or any lifting surface. The 3D panel method, the vortex lattice method (VLM), and lifting line theory (LLT) are employed to analyze wing/airfoil design and perform various other analyses. Each method has its own salient features for different applications; i.e., lift curve slope accounting for the viscous effects can be precisely estimated using the LLT approach. However, there are some limitations of these methods as well; i.e., the panel method does not improve the accuracy of the results notably. It has been observed that the obtained values of aerodynamic forces/moments using this software approach are very close to the experimental results. XFLR comprises of XFoil program for foil analysis and three-dimensional analysis methods for the planes that include: (i) stability analysis of the planes, (ii) a two vortex-lattice method and a 3D panel method for the analysis of the aerodynamic performance of wings/plane operating at low Reynolds numbers, and (iii) a non-linear lifting line method for a standalone wing. Radio-controlled (RC) aircraft can also be designed by using XFLR software [54]. Another application of XFLR software is to analyze the two-dimensional viscous results obtained from the XFoil subsonic airfoil development system and the time-independent incompressible flow solution obtained from the Laplace equation. Even for aircraft design, the foremost step is to analyze the associated airfoils before exclusively proceeding with the aircraft design [45]. In order to analyze the wing/tail airfoil, coordinates are imported in XFLR, and geometry is generated. Figure 8 shows the airfoil geometry developed and analyzed in XFLR. Figure 8: BAC474 airfoil developed in XFLR; it is used for the Boeing 747-200 wing tip. The variations of moment, lift, and drag coefficients are obtained during aerodynamic analysis. Moreover, airfoil analysis, as well as pressure distribution, can also be obtained to study the performance characteristics. The pressure distribution depicted by the graphical result also provides an insight into the separation region. In XFLR, the entire aircraft can be modeled with the liberty of creating different auxiliary lifting surfaces. This software is widely used in aircraft design and the computed data agrees with the XFoil software. Experiments have shown that XFLR produces reliable results based on the vortex lattice method, as these results were verified by wind tunnel tests. The correlation between XFLR and ANSYS software can be established to obtain more realistic data and to verify the setup used. Aircraft dynamics can also be simulated using control/stability derivatives with the help of XFLR modeling; i.e., elevator deflection at specific trim conditions can be simulated by modeling aircraft with known dimensions. The stability augmentation system of the flying wing can be used to determine the feedback control obtained from proportional derivatives to reduce pitch instability [44]. Another application is to simulate the sideslip and angle of attack with the help of XFLR modules. In XFLR, the order of sideslip and angle of attack applications has its significance. (i) The model analysis is carried out by conventional panel or vortex lattice technique, (ii) sideslip is designed by model rotation about the \(z\)-axis, and (iii) this method is preferred, as the implementation of this technique is comparatively simple. By convention, sideslip rotation is applied after the angle of attack and the final position may be slightly different as compared to the experimental results at high sideslip or angle of attack values. The rolling/yawing moments and coefficients of lateral forces can also be determined from the non-viscous portion of the panel or vortex lattice method. Theoretically, the results are closed at all speeds; however, a difference may be observed during experimentation that leads to the effect of viscosity on the distribution of pressure forces.