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using a modern (graphical) user-interface.
Refs.[12] and [31] present some practical examples of integrated FCS design environments.
These papers particularly emphasize the need for multidisciplinary design
in which aerodynamic, structural, propulsive, and control functions are considered
all together. This is important, because modern flight controllers may excite structural
modes of the aircraft and interact with the control-actuator dynamics, and because
of the increasing need to integrate flight controls with engine controls and
load-alleviation functions. Interactions between the aerodynamic, propulsive, and
structural models must be taken into account, especially for modern aircraft that employ
extensive use of composite materials (resulting in greater aero-elastic coupling)
and relaxed static stability.
The Flight Dynamics and Control toolbox that is presented in this report attempts
to bring the required tools and models together in the MATLAB / SIMULINK environment.
It basically provides easy access to the flight dynamics models and other
relevant dynamic models, allowing the FCS designer to use MATLAB (if necessary
including a selection of the available control system design tools) for the initial FCS
development, and use SIMULINK for the subsequent nonlinear off-line simulations.
The toolbox itself provides an analytical software tool to trim aircraft models for
steady-state flight. It applies SIMULINK functions to extract linear state-space de8
Chapter 1. Flight control system development
M
S
F
A
A
M
S
F
Linearized
models
SIMULINK
model-library
with nonlinear
aircraft model
Flightsimulator
model-library
with nonlinear
aircraft model
Linear
FCS design
Nonlinear FCS
validation &
fine-tuning
Evaluation in
real-time
piloted flightsimulation
Implementing
FCS hardware
and software
Evaluation in
real flight
Trimming &
Linearization
Future: automatic
transfer of models?
Update sensor/actuator models
Update aero/engine models
Current
scope of the
FDC environment
Future
enhancements
M
S
F
A
=
=
=
=
MATLAB
SIMULINK
Real-time flightsimulator
Actual aircraft
Figure 1.3: FCS design cycle using MATLAB and SIMULINK
scriptions of aircraft models and perform digital flight simulation. Several other
MATLAB toolboxes, from The Mathworks and others, can be used to perform a multitude
of analytical operations on the linear equations.
1.5 FCS design and the FDC toolbox
The current scope of the FDC toolbox is shown in figure 1.3, above the dashed line on
the right. Starting from the SIMULINK model library, it is possible to obtain linearized
models. Using designated control system design tools from otherMATLAB toolboxes,
controllers can be developed for the resulting linear systems. The resulting control
laws can be evaluated in SIMULINK, by means of nonlinear simulations; the required
models are again obtained from the FDC model library.
However, the FDC toolbox does not (yet) offer any help to simplify the subsequent
design steps, being evaluation in a real-time piloted flight simulator and eval1.5.
FCS design and the FDC toolbox 9
}Off-line
}Real-time
Graphical SIMULINK system Graphical SIMULINK system
Flight Control Computer
Flight Simulator
Control Laws
(block-diagram)
Control Laws
(C-code)
Control Laws
(C-code) Control Laws
(C-code)
C-code
generator
Figure 1.4: ‘Portable’ control laws
uation in real flight. If the designer wants to move his control laws to these next
levels, he or she will still have to convert the control laws and the dynamic models
manually to the flightsimulator and/or the flight control computers of the airplane;
the FDC toolbox does not provide any assistance for that task. This is obviously still
a major obstacle in the FCS development process, because it increases the chance of
encountering conversion errors, as explained earlier.
The figure suggests that automatic transfer of complete simulation models from
the SIMULINK environment to a flightsimulator might be feasible. However, it would
probably not be easy to ensure the integrity of such automatically converted models.
A less ambitious, but perhaps more realistic proposal would be to focus on automatic
conversion of the control laws only, using e.g. automatic code-generation software
to translate SIMULINK models into a high-level programming language like C.
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FDC 1.4 – A SIMULINK Toolbox for Flight Dynamics and Contro(9)
