## 5 Stability Analysis and Augmentation Adjustment of UAV
### Influence Analysis of Dynamic Stability
#### 5.3.2 Lateral/Directional Stability Augmentation Design
Figure 16: The damping ratio \(\xi\) and the oscillation frequency \(\omega_{n}\) of the Dutch roll modal of the pre-selected models after the stability augmentation adjustment with \(\Lambda\text{out}\) corresponding to the configurations when \(\text{Ma}=0.4\). (**a**) Damping ratio \(\xi\), (**b**) oscillation frequency \(\omega_{n}\). Figure 15: The damping ratio \(\xi\) and the oscillation frequency \(\omega_{n}\) of the Dutch roll modal of the pre-selected model after the stability augmentation adjustment with \(\Lambda\text{out}\) corresponding to the configurations when \(\text{Ma}=0.3\). (**a**) Damping ratio \(\xi\), (**b**) oscillation frequency \(\omega_{n}\). Tables 8 and 9 present the roll damping of pre-selected models under the stability augmentation adjustment when Ma = 0.3 and Ma = 0.4. Based on the calculation results of the lateral/directional modals of the multi-section variable-sweep wing UAV under the action of stability augmentation adjustment, it can be observed that with the increase in the wingspan proportion of the inner section, the adjustment effect of the stability augmentation system on the lateral/directional Dutch roll modal of the UAV is gradually weakened. With the increase in flight speed, the adjustment of the lateral/directional stability augmentation system is gradually enhanced. The following conclusions are drawn:  
1. When the \(\Lambda_{\text{out}}\), corresponding to the configurations, varies in the range of 0-15\({}^{\circ}\), and the flight speed is low, Model4 has a larger value of Dutch roll \(\xi\) and \(\omega_{n}\). The multi-section variable-sweep wing UAV system exhibits better lateral/directional stability. At this time, the wingspan ratio of the inner and outer sections is approximately 1.78. At higher flight speeds, Model2 has better lateral/directional stability, followed by Model3, and the corresponding wingspan ratios of the inner and outer sections are 1.13 and 1.41, respectively. 2. When \(\Lambda_{\text{out}}\), corresponding to the configurations, varies in the range of 15-30\({}^{\circ}\), the Dutch roll \(\xi\) decreases with an increase in the wingspan proportion of the inner section. When the flight speed is low, Model2 has better lateral/directional stability, followed by Model3, and the corresponding wingspan ratios of the inner and outer wing sections equal 1.13 and 1.41, respectively. At higher flight speeds, the oscillation period of Molde5 is shorter, followed by Model4, and the corresponding wingspan ratios of the inner and outer sections equal 2.28 and 1.78, respectively. 3. In addition, the change in configuration, and the wingspan ratio of the inner and outer wing sections of the pre-selected models have little effect on the rolling damping \(\xi\) under the adjustment of the stability augmentation system. With the increase in flight speed, the absolute value of the roll damping \(\xi\) increases gradually. variable-sweep wing technology in the high-aspect-ratio heavy-duty UAV. Simulation analysis verifies the effectiveness of the dynamic stability augmentation system. These results are all extremely encouraging and motivate further investigation of multi-section wing morphing technology. The following aspects should be covered in future research. First, five pre-selected models are constructed, based on the distribution characteristics of wing structure in this research. The weight gain of the actuator and deformation structure adopts the assumption of uniform distribution, which is acceptable in the initial design stage of morphing UAVs. In fact, the weight gain distribution of the actuator and deformation structure is not a negligible quantity, and the effect on aircraft performance may be decisive in certain flight environments. This research takes the pre-selected models with different mass ratios of wing sections as the research object, and shows the influence of actuator and structural weight distribution on aircraft performance in a broader scope.