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Parameters
The block Engmod reads the engine model parameter matrix EM from the MATLAB workspace;
the block FMdims requires the parameter vector GM1. 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; uprop is an external input vector containing the
engine control inputs; yatm comes from Atmosph; yad1 comes from Airdata1.
out: ypow from Power is connected to the block Engmod; Cprop from Engmod is connected
to FMdims; FMprop from FMdims is connected to FMsort.
Type browse enggrp at the command-line for on-line help.
144 Chapter 8. Aircraft model block reference
Engmod (Beaver) Beaver level 1 / Beaver level 2 / Engine Group / Engmod (Beaver)
Main FDC library / Engine forces and moments
Type
Aircraft-dependent masked subsystem block, essential for solving the equations of motion.
Description
The block Engmod (Beaver) determines the propulsive forces and moments for the Beaver
aircraft, using a model from ref.[34]. It computes the force and moment coefficients which
are caused by the operation of the powerplant (this includes the engine thrust, gyroscopical
effects caused by the rotating propeller, and the influence of the propeller slipstream
upon the aerodynamic forces and moments), as a function of the dimensionless increase
in air pressure across the working plane of the propeller. The latter signal is determined
by the separate block Power (Beaver).
Engmod (Beaver) needs to be updated if one wishes to implement a model of a different
aircraft within the FDC framework. Thanks to its black-box structure, it is relatively
easy to change the structure of the equations if necessary, e.g. to incorporate look-up table
functions, to implement functions which are typical for a jet engine, or to increase the
number of engines.
Equations
The propulsive force and moment coefficients of the Beaver are expressed in terms of
nonlinear polynomial functions of the state variables and the dimensionless increase in
pressure across the working plane of the propeller. The equations are based on ref.[34];
see section 3.3.2 for more details.
• Propulsive force and moment coefficients measured in the body-fixed reference frame:
CXp = CXdptdpt + CXa dpt2 a dpt2
CYp = 0
CZp = CZdptdpt
Clp = Cla2dpt
a2dpt
Cmp = Cmdptdpt
Cnp = Cndpt3 dpt3
The coefficients of the polynomials represent engine stability and control derivatives of
the Beaver; they have been listed in table B.4 of appendix B. A closer look at the internals
of the block Engmod (Beaver) reveils that the polynomial evaluation has been implemented
in practice by means of a multiplication of the vector:
h
dpt dpt3 a · dpt2 dpt · a2
iT
with the constant parameter matrix EM in which the engine stability and control derivatives
of the Beaver are contained.
Inputs
x = [ V a b p q r y q j xe ye H ]T state vector, x
ypow = [ dpt P ]T engine power related variables, ypow
Outputs
Cprop = [ CXp CYp Czp Clp Cmp Cnp ]T propulsive force and moment coefficients, Cprop
8.2. The aircraft model block libraries 145
Parameters
Engmod needs the parameter matrix EM to be present in the MATLAB workspace, in order
to read out the stability and control coefficients of the engine forces and moments model.
The definition of this matrix can be found in appendix C. EM 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; ypow comes from Power.
out: Cprop is connected to FMdims.
Type browse engmod at the command-line for on-line help.
146 Chapter 8. Aircraft model block reference
Eulerdot Beaver level 1 / Beaver level 2 / Aircraft Equations of Motion / 12 ODEs / Eulerdot
Main FDC library / Equations of motion
Type
Aircraft-independent masked subsystem block, contains three (out of twelve) state equations.
Description
The block Eulerdot is used to compute the time-derivatives of the Euler angles, i.e. the
yaw angle y, pitch angle q, and roll angle j. These three variables form a subset of the
twelve state variables of the nonlinear aircraft model.
Equations
The equations used by the block Eulerdot have been discussed in some more detail in
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FDC 1.4 – A SIMULINK Toolbox for Flight Dynamics and Contro(72)
