IEEE - Aerospace and Electronic Systems - July 2023 - 24

Flight Control Method Using Neural Network in Prediction for Suppressing Ship Airwake Impact in Carrier Landing
FLIGHT CONTROL SYSTEM DESIGN
SYSTEM DESIGN
Figure 4.
BP neural network structure diagram of the longitudinal airwake
component model.
Back propagation (BP) neural network is a multilayer
feedforward neural network trained according to the error
BP algorithm. BP neural network is a highly nonlinear
mapping mainly composed of input layer, hidden layer,
and output layer. Each node represents a neuron and contains
a specific activation function. In order to balance
the fitting effect and the time required for calculation, the
network contains one hidden layer with 10 nodes. The
activation function is hyperbolic tangent function, and
the learning rate is set to 0.001. Levenberg-Marquardt
optimization algorithm is applied as the neural network
training function. The set of training error target is set to
105 m/s. Figure 4 is the BP neural network structure
diagram of the longitudinal-airwake-component prediction
model.
Merely predicting the size of the ship airwake at the
next moment cannot meet the need for MPC. Therefore,
the predicted values of the airwake at each time are used
as the input for the next time to perform repeated predicting
calculations. Then the predicted values of the airwake
at the next n moment can be obtained.
Simulation is conducted to verify the prediction algorithm
using BP neural network. Table 1 shows the statistical
results of the prediction error of ship airwake. It can be
seen that the prediction error gradually increases with the
increase in the length of prediction time. Figure 5 shows
the prediction error of the airwake at the next 5th moment.
When predicting the vertical component at the next sixth
moment, the prediction error can reach 1.0 m/s, which is
no longer suitable for use. Considering the balance
between accuracy and forecast duration, it is recommended
that the forecast duration does not exceed 5 sampling
times.
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To suppress the effects of the airwake, two key points are the
prediction ofthe airwake encountered by the aircraft and putting
the airwake prediction value into the flight control model.
The flight control system are designed based on the MPC
algorithm and prediction model of the ship airwake. Figure 6
shows the schematic diagram of the flight control system for
suppressing ship airwake impact in carrier landing. The carrier
landing guidance system gets the flight data including
ship motion, aircraft air speed, and so on. Then the preset trajectory
deviation caused by ship motion, position, speed, and
attitude relative to the carrier runway is used to calculate the
trajectory needed by the control system. On the other hand,
the ground speed, air speed, AOA, sideslip angle, the aircraft
position in FS are provided to the prediction module of ship
airwake based on the neural network algorithm. The predicted
values of the airwake and trajectory deviation are inputted
into the control system based on MPC algorithm to calculate
the control command. Finally, the aircraft rudder surface
takes actions to control the aircraft motion coping with the
effects ofthe ship airwake.
In the flight control system based on MPC, the predicted
values of the airwake in the future period of
time is used to establish the disturbed state of the carrier-based
aircraft in the next n moments. And the
objective function related to the future deviation of the
reference gliding trajectory is designed to solve the
optimal control commands at the current time. Therefore,
the influence caused by the airwake is compensated
in advance to improve the tracking accuracy of
the aircraft to the reference trajectory and the speed of
response to the influence of the airwake.
At the same time, in order to reduce the error caused by
the prediction model, the actual state ofthe carrier-based aircraft
obtained by the sensor is used for feedback correction.
MODEL FOR PREDICTIVE CONTROL
When the aircraft is disturbed by the ship airwake, the surrounding
incoming flow speed and direction are changed,
resulting the changes in the aerodynamic force and torque
received by the aircraft. The force balance state of the aircraft
will be broken, causing the trajectory offset of the
aircraft. The airspeed, AOA, and sideslip angle of the aircraft
can be used to describe the changes in aerodynamic
forces received by the aircraft, so as to establish the relationship
between the airwake affect and the control model
of the aircraft.
In this article, the disturbance term of the ship airwake
is introduced in the small-disturbance motion
equation of the carrier-based aircraft. The longitudinal
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JULY 2023

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