# Assessment of a Mid-Fidelity Numerical Approach for the Investigation of Tiltrotor Aerodynamics
## 3 Numerical Models
### Full Vehicle Numerical Model  
The full vehicle numerical model of the XV-15 tiltrotor was built while considering the full scale dimensions and components of the aircraft. The model included the fuselage with a length of 14.1 m, the horizontal and vertical tailplanes, the wing equipped with control surfaces (i.e., flap and flaperon), and the two proprotors with nacelles. Table 3 reports the main characteristics of the full vehicle geometry, including the airfoil series used to build the numerical model. It must be remarked that the CFD works, selected as a reference for comparison with the DUST results, present some geometry inaccuracies with respect to the real aircraft. Indeed, during flight tests [48] the wing presented a Gurney flap, as reported in the last work by [PERSON] and [PERSON] [16]. This feature was not modelled in the work by [PERSON] et al. [17] that was used hereafter for the comparison with DUST in hover and cruise conditions, while it was included in the latest simulations by the same authors [16] that were considered to be more accurate for the comparison in conversion mode. For DUST simulations of the full vehicle, the authors decided to model the aircraft wing without a Gurney flap. Indeed, a possible attempt to model this feature with panel methods would provide a higher complexity and add potential inaccuracies to the numerical results that were not justified by the main scope of the work. Consequently, due to the difference in modelling between the numerical models built for the two CFD works used for reference, the overall lift of the aircraft will not be presented in the results discussion. On the other hand, the rotation of the vehicle wing control surfaces was correctly reproduced in the DUST simulations. Indeed, the last portion of the wing airfoil was tilted for the spanwise region of the flaps and flaperos, as indicated by the real aircraft geometry parameters that are presented in Table 3. The proprotor blades for the full vehicle simulations were modelled using lifting line elements using the spatial discretisation that is described in Section 3.1. All of the remaining components of the vehicle were modelled using surface panels. In particular, a total of 13758 elements were used to model the fuselage and tailplanes, 873 elements were used for each of the two nacelles, and each semi-span wing was modelled using 5400 elements. A picture of the mesh that was built for the full XV-15 tiltrotor is shown in Figure 4. No dependence studies were performed for the spatial discretisation of the full vehicle. Nevertheless, the meshing of the aircraft components surfaces was performed following best practices provided by a previous work performed with DUST on full aircraft configurations [30]. Moreover, the choice of the selected spatial and time discretisations for the full vehicle was dictated by the need to limit \begin{table}
\begin{tabular}{c c c c} \hline  & **Wing** & **Horizontal Tail** & **Vertical Tail** \\ \hline Airfoil & NACA 64A223 & NACA 64015 & NACA 0009 \\ Span & 9.8 m & 3.91 m & 2.34 m \\ Mean aerodynamic & 1.60 m & 1.20 m & 1.13 m \\ chord & \(-6.5^{\circ}\) & \(0^{\circ}\) & \(31.6^{\circ}\) \\ Shepardal & \(2.0^{\circ}\) & \(0^{\circ}\) & - \\ Incidence & \(3.0^{\circ}\) & \(0^{\circ}\) & \(0^{\circ}\) \\ \hline  & **Flap** & **Flaperon** & \\ \hline Span along hinge line & 1.30 m & 2.40 m & \\ Chord/Wing chord & 0.25 & 0.25 & \\ Maximum deflection & \(75^{\circ}\) & \(47^{\circ}\) & \\ \hline \end{tabular}
\end{table} 
Table 3: Geometrical characteristics of the XV-15 full vehicle numerical model. the computational effort of the simulations. Indeed, the main aim of this work is to show the possible engineering application of a mid-fidelity numerical approach for aerodynamics for use in the preliminary design of novel tiltrotor configurations requiring a huge number of simulations.