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created. This can cause simulations to slow down considerably, and such an algebraic loop may be too
complicated for SIMULINK to solve altogether. For this reason, feeding back ‘additional outputs’ into
the aircraft model should be prevented.
126 Chapter 8. Aircraft model block reference
Connections
in: x comes from the block Integrator; x˙ comes from xfix; yhlp comes from Hlpfcn; Ftot
comes from FMsort; Fgrav comes from Gravity.
out: yfp from Flightpath, yuvw from uvwdot, and yacc from Accel are not connected to any
other block in the aircraft model.
Type browse moreouts at the command-line for on-line help.
8.2. The aircraft model block libraries 127
Aerodynamics Group (Beaver) Beaver level 1 / Level 2 / Aerodynamics Group (Beaver)
Main FDC library / Aerodynamics
Type
Aircraft-dependent subsystem, essential for solving the equations of motion. The subsystem
is not masked.
Description
The subsystem Aerodynamics Group (Beaver) contains blocks for computing the aerodynamic
forces and moments that act on the aircraft under consideration. In this case
the aerodynamic model is valid for the DHC-2 Beaver aircraft. It uses model data from
ref.[34] (see also section 3.3.1). Notice that the subsystem Aerodynamics Group does not
compute propeller slipstream related contributions to the aerodynamic forces and moments;
that task is performed by the subsystem Engine Group instead.
Subsystems and/or blocks
The subsystem Aerodynamics Group (Beaver) contains three blocks:
Aeromod computes dimensionless aerodynamic force and moment coefficients for the
aircraft under consideration (currently Aeromod contains the aerodynamic model
of the Beaver from ref.[34], which has been described in section 3.3.1),
Dimless computes dimensionless angular velocities,
FMdims converts the dimensionless force and moment coefficients to dimensional forces
and moments.
Since the block Aeromod (Beaver) is aircraft-dependent, it needs to be replaced if the user
wants to implement a model of a different aircraft in the FDC framework. However, if
the new aircraft model also uses different definitions of the non-dimensional angular velocities,
it may be more convenient to replace the complete subsystem Aerodynamic Group
instead. Either way, this modular construction allows the user to build a comprehensive
SIMULINK library of aerodynamic models.
Inputs
x = [ V a b p q r y q j xe ye H ]T state vector, x
uaero = [ de da dr df ]T aerodynamic control inputs, uaero
yad1 = [ a M qdyn ]T basic airdata variables, yad1
Outputs
ydl = [ pb
2V
qc
V
rb
2V ]T dimensionless angular velocities, ydl
Caero = [ CXa CYa CZa Cla Cma Cna ]T aerodynamic force and moment coefficients, Caero
FMaero = [ Xa Ya Za La Ma Na ]T dimensional aerodynamic forces and moments, FMaero
Parameters
The block Dimless and the block FMdims read the parameter-vector GM1 from the MATLAB
workspace; the block Aeromod (Beaver) needs the parameter-matrix AM. The definitions
of these variables can be found in appendix C. The variables 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).
Connections
in: x comes from the block Integrator; uaero is an external input vector containing aerodynamic
control inputs; yad1 comes from the block Airdata1.
out: ydl from Dimless is used by the block Aeromod; Caero from Aeromod is used by
FMdims; FMaero from FMdims is used by the block FMsort.
Type browse aerogrp at the command-line for on-line help.
128 Chapter 8. Aircraft model block reference
Aeromod (Beaver) Beaver level 1 / Beaver level 2 / Aerodynamics Group / Aeromod (Beaver)
Main FDC library / Aerodynamics
Type
Aircraft-dependent masked subsystem block, essential for solving the equations of motion.
Description
The block Aeromod (Beaver) contains the aerodynamic model of the DHC-2 Beaver aircraft.
The model is based on ref.[34], which expresses the aerodynamic forces and moments
in terms of nonlinear polynomial functions of state variables and external aerodynamic
control inputs. This block needs to be updated if one wishes to implement a model
of a different aircraft within the FDC framework. Thanks to the black-box structure of
Aeromod, it is relatively easy to change the structure of the equations if necessary, e.g. to
incorporate look-up table functions, which often define the aerodynamic equations for
different airplane models.
Note: Aeromod (Beaver) does not take into account contributions to the forces and moments
　
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