## 6 Conclusions  
This paper focuses on the mitigation of the airflow disturbance effects on the \(TRMS\), with particular attention to reducing the impact of a fan ventilator. Due to the inherent time delay in the \(TRMS\) dynamics, a control scheme based on the Smith predictor has been employed. Furthermore, a novel modification of the Smith predictor has been developed to enhance the control performance on the \(TRMS\). This research makes several key contributions, outlined as follows: (1) a multi-variable control method based on the Smith predictor controller capable of compensating for time delays and mitigating the effects of external disturbances while exhibiting good robustness features; (2) a novel methodology that adapts the \(SP-H\) structure-originally developed in [31] for a second order plus time-delay system--to control higher-order time delay systems, specifically applied to the \(TRMS\); (3) a comparative simulation analysis demonstrates that the proposed scheme achieves the same set-point tracking performance as the widely known \(SP\) (for the nominal process) while greatly improving the attenuation of air disturbances caused by the fan; and (4) an experimental evaluation of this control scheme on a \(TRMS\) prototype, confirming its superior performance compared to the standard \(SP\). All comparisons were conducted fairly, using the same controller \(C(s)\) in each case. The \(SP\) structure is highly sensitive to inaccuracies in the nominal time delay. This paper has not addressed the issue of varying time delays. However, this limitation can be mitigated by rapidly estimating the time delay in real time using algebraic identification techniques, which enables retuning of the internal model used in the \(SP\). We refer to our recent work [36], where an adaptive \(SP\) was designed and implemented on a teleoperated flexible-link robot with time-varying delay, based on real-time delay estimation using such an algebraic identification technique. If the hardware-induced delay were known, it could be incorporated into the nominal model's time delay and, consequently, into the \(SP\) structure. If not, an identification method--such as the aforementioned algebraic identification technique--could be employed to estimate the delay in real time and retune the Smith predictor accordingly. Our \(SP-H\) eliminates steady-state errors caused by impulse or step-like disturbances. Since we are using linearized models, this property is validated independently of the disturbance amplitude. Such amplitude may introduce a steady-state error and/or alter the response shape only if it is large enough to drive the system dynamics outside the valid region of the linearization, or if it causes actuator saturation. It is worth noting, however, that ramp or parabolic-like disturbances would still result in steady-state errors. Even in these cases, our \(SP-H\) enhances the disturbance rejection capabilities compared to the original \(SP\). The main contribution of this work is the enhancement of flight control for unmanned aerial vehicles (\(UAV\)s) of the helicopter type in the presence of strong air currents, thereby improving the system's overall stability and performance. This advancement enables more precise and reliable operation, even under challenging environmental conditions. \begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline \multirow{2}{*}{**Controller**} & \multicolumn{4}{c}{**Vertical Plane**} & \multicolumn{4}{c}{**Horizontal Plane**} \\ \cline{2-9}  & \(IAE\) & \(ISE\) & \(TV\) & \(ME\) & \(IAE\) & \(ISE\) & \(TV\) & \(ME\) \\ \hline SP & 0.2825 & 0.0121 & 14.4361 & 0.1111 & 0.9497 & 0.1414 & 9.9422 & 0.2895 \\ SP-H & 0.1355 & 0.0024 & 13.9009 & 0.0618 & 0.3132 & 0.0220 & 15.2019 & 0.1547 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Performance comparison of controllers for horizontal and vertical planes in an experimental environment. **Author Contributions:** Conceptualization, A.M. and V.F.-B. ; methodology, A.M. and V.F.-B. ; software, A.M.; validation, A.M.; formal analysis, V.F.-B.