Fig.1

Schematic diagram of towed aerial recovery structure［7］

Fig.2

Model of cable-drogue-UAV assembly

Fig.3

Position tracking control scheme

Fig.4

Schematic of force on drogue-UAV assembly

Fig.5

Optimization framework of UAV recovery trajectory based on trajectory mapping network

Fig.6

Error analysis of trajectory optimization

Fig.7

Cable recovery speed profile

Fig.8

Structure diagram of trajectory mapping network based on BiLSTM

Fig.9

Data generation and training methods for trajectory mapping network

Table 1

Comparison between parameters and test results of BiLSTM and LSTM

Fig.10

Trajectory mapping results of test set （Scenario 1）

Fig.11

Trajectory mapping results of test set （Scenario 2）

Fig.12

Trajectory mapping results of test set （Scenario 3）

Fig.13

Average error distribution of trajectory mapping network

Fig.14

Comparison of running time of each mapping model

Fig.15

Comparison of wing folding and cable retrieval profiles

Fig.16

Comparison between commands and actual recovery trajectories

Fig.17

Shape change curves of cable during recovery

Fig.18

Change curves of cable of comparison method

Fig.19

Comparison of combination state curves in recovery process

Fig.20

Comparison of drogue-UAV-assembly control inputs in recovery process

Fig.21

Wind on UAV during recovery process using proposed method

Table 2

Comparison of UAV recovery trajectory indicators through 50 Monte Carlo simulations

Fig.22

Trajectory optimization results at different initial positions

Fig.23

Recovery trajectories under the same optimization command at different initial positions