# Impact of Aerodynamic Interactions on Aeroelastic Stability of Wing-Propeller Systems +
## 5 Conclusions  
This paper presents original findings on the impact of aerodynamic interaction on aeroelastic stability within a wing-propeller system when considering selected operative  
Figure 13: Damping and frequency trends for unstable mode for all three simulation approaches. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**SDBox**} & \multicolumn{2}{c}{**Hybrid**} & \multicolumn{2}{c}{**Fully Coupled**} \\
**Vel, m s\({}^{-1}\)** & **Freq, Hz** & **Damp,\%** & **Freq, Hz** & **Damp,\%** & **Freq, Hz** & **Damp,\%** \\ \hline
125 & 10.12 & 2.06 & 10.07 & 1.61 & 10.10 & 0.35 \\
130 & 10.00 & 1.01 & 9.94 & 0.48 & 9.95 & \(-0.19\) \\
133 & 9.93 & 0.31 & 9.87 & \(-0.29\) & 9.89 & \(-0.44\) \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Frequencies and damping ratios of the flutter mode in thrusting condition. conditions and proposes an efficient methodology based on coupled multibody-mid-fidelity aerodynamic simulations. The focus is primarily on a flutter mechanism originating from the wing. A baseline model was established featuring a flexible wing and a mid-semispan mounted propeller with a flexible pylon and rigid blades. Flutter for this model was initially predicted using a frequency-domain method that neglected the aerodynamic interactions. To assess the impact of aerodynamic interference, coupled fluid-structure time-domain simulations were performed. Structural modeling was conducted using a multibody dynamics code (MBDyn). For the aerodynamic modeling, two different simulation approaches were defined. With the first approach (hybrid), the propeller aerodynamics were modeled separately from the wing aerodynamics, neglecting interference. Specifically, propeller aerodynamics were modeled using a blade element model together with a 3-state dynamic inflow model within MBDyn, whereas wing aerodynamics were modeled using a 3D panel method with a free wake particle description (DUST). With the second approach (fully coupled), both elements, i.e., the propeller and the wing, were aerodynamically modeled in DUST, with the propeller modeled using lifting line elements. The particle wake description in DUST allows us to consider aerodynamic interactions between the propeller and the wing. A time-marching scheme was applied to find the flutter point for both the hybrid and fully coupled approaches. Two trim points were selected: (1) windmilling and (2) thrusting. The former is known to be most critical for whirl flutter, and the latter represents a typical trim condition in steady-level flight. Trim conditions were ensured by varying the collective pitch of the propeller while holding the rotational speed constant. Time histories were obtained, and eigenfrequencies and damping ratios for the critical mode were extracted using the MPE method. The main findings of these studies are summarized as follows:  
* The inclusion of aerodynamic wing-propeller interaction effects in aeroelastic stability analysis leads to reduced flutter speeds for both windmilling and thrusting cases. This is due to the propeller slipstream effect impacting the wing aerodynamics. * Neglecting aerodynamic interference, the windmilling condition returns the smallest flutter boundaries. This behavior is also seen in the majority of the cases discussed in the literature for the standalone propeller. * Including aerodynamic interference, the thrusting condition returns the smallest stability boundaries due to the increment of dynamic pressure and local lift on the wing induced by the propeller. * The difference in the flutter speed for the analyzed configuration is less than 5% between the frequency-domain approach without aerodynamic interaction and the fully coupled approach. Therefore, the frequency-domain approach is preferable for preliminary analyses. It is faster than time-marching analyses and delivers accurate results, though the outcomes are not conservative regarding flutter speed.