Fig. 1. Structure of touch-down navigation system

Fig. 2. Block diagram of improved UAV flight control system

Fig. 3. Flowchart of improved UAV flight control system

Fig. 4. Main hardware parts of UVA flight control experimental system

Fig. 5. Static errors

Fig. 6. Histogram of landing positions

Fig. 7. Result of the third experiment

Fig. 8. Flying curves of UAV in different strategies

Fig. 9. Comparison of landing time