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a corresponding timeline for the simulation. Demux, Inport, and Outport blocks provide
access points for external SIMULINK systems and MATLAB functions. The actual aircraft
model has been implemented in a single subsystem, called ‘DeHavilland DHC-2 Beaver
dynamics and output equations’, or shortly: Beaver Level 2.
Inputs
The motions of the aircraft are affected by six control inputs (elevator, ailerons, rudder,
flaps, engine RPM, and engine manifold pressure), and six inputs representing atmospheric
disturbances (three wind velocity components, and their time-derivatives). These
signals have all been represented by scalar Inport blocks, and sorted by means of Mux
blocks, to obtain the three external input vectors uaero, uprop, and uwind:
8.2. The aircraft model block libraries 139
uaero = [ de da dr df ]T aerodynamic control inputs, uaero
uprop = [ n pz ]T external propulsion inputs, uprop
uwind = [ uw vw ww u˙w v˙w w˙ w ]T wind velocity components along body-axes
and their time-derivatives, uwind
Outputs
The time-trajectories of the above mentioned input signals are collected in the workspace
variable In, while the time-trajectories of all output signals from the subsystem Beaver
Level 2 are collected in the workspace variable Out. A clock signal is collected in the
workspace variable time, to provide a corresponding time-axis. In and Out are matrices
whose columns represent time-trajectories of the individual input or output signals, and
whose rows represent data-points; the number of data-points corresponds to the length
of the vector time. See appendix D for the exact definitions of these variables.
A subset of the output signals is sent to the Outport blocks in this top-level, which
allow the model to be connected to external systems, or to be accessed by MATLAB functions.
The subset of outputs includes the twelve state variables, the rate of climb/descent,
and the dimensionless pitch rate, roll rate, and yaw rate; these outputs are extracted from
the following output vectors from Beaver Level 2:
x = [ V a b p q r y q j xe ye H ]T state vector, x
˙x = [ ˙V
˙a
˙b
˙ p ˙ q ˙ r ˙y
˙q
˙j
˙ xe ˙ ye ˙H ]T time-derivative of state vector, xdot
ydl = [ pb
2V
qc
V
rb
2V ]T dimensionless angular velocities, ydl
Note: the stand-alone model Beaver and one of the subsystem equivalents use scalar
Outport blocks to send these output signals to the outside world. The second subsystem
equivalent combines the state variables and the rate of climb/descent in a single output
vector, which is connected to the first Outport block, and sends the dimensionless angular
velocities to the second Outport block.
Parameters
Beaver level 1 (or rather: Beaver Level 2) requires the variables AM, EM, GM1, GM2, and
xinco to be defined in the MATLAB workspace. The definitions of these variables can be
found in appendix C; they can be loaded from the file AIRCRAFT.DAT, using the utility
DATLOAD (see section 12.4.2). If this datafile has somehow inadvertently been deleted, it
can be re-created by running the program MODBUILD (see section 12.6.1).
The vector xinco contains the initial value of the state vector. A steady-state initial
value can be computed using the aircraft trim routine ACTRIM (see section 11.1), or it can
be loaded into the MATLAB workspace from file, using TRILOAD (see section 12.4.2). Of
course, it is also possible to manually enter xinco, if required.
Furthermore, an optional vector xfix may be defined in the MATLAB workspace, to
artificially fix certain states to their initial values; see the description of the block xfix for
an explanation. If xfix is not present in the workspace when the aircraft model equations
are evaluated, it will automatically be set to its default value ones(1,12) by the block xfix.
If it is desired to artificially fix certain states, xfix should be entered manually (it must be
a vector of length 12, with all elements being either one or zero), or by running the utility
FIXSTATE (see section 12.6.2).
Connections
Beaver Level 1 is the interface level of the aircraft model, where all input and output
vectors are collected and sent to the MATLAB workspace. The Inport and Outport blocks
provide connections to external models and MATLAB functions.
Type browse level1 at the command-line for on-line help about this level of the aircraft
model. Type browse inputs or browse outputs for help about the input/output definitions.
140 Chapter 8. Aircraft model block reference
Beaver level 2 Beaver level 1 / Beaver level 2
Main FDC library / Complete system Beaver / Beaver level 2
Type
Second level of the Beaver dynamics model. This masked subsystem contains the nonlinear
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FDC 1.4 – A SIMULINK Toolbox for Flight Dynamics and Contro(69)
