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recognisable in the SIMULINK model.
Apart from the aerodynamic and propulsive forces, all elements from figure 3.2
are independent of the airplane under consideration. This is also true for the SIMULINK
model from figure 8.1, with the exception of a single aircraft-dependent
correction block xdotcorr (Beaver) that is contained in the subsystem ‘Aircraft Equations
of Motion (Beaver)’. Notice how all aircraft-dependent elements (which have
currently been elaborated for the Beaver aircraft) have been distinguished by their
suffix ‘(Beaver)’.
From left to right and from top to bottom we can distinguish the following blocks
and subsystems in the SIMULINK model from figure 8.1:
• Airdata Group. This subsystem evaluates airdata equations and computes important
atmospheric properties such as temperature and pressure, which are
118 Chapter 8. Aircraft model block reference
required to determine the external forces and moments (and hence, to solve
the equations of motion).
• Aerodynamics Group (Beaver), Engine Group (Beaver), Gravity, and Fwind. These
subsystems determine the individual contributions to the external forces and
moments upon the airplane. Not surprisingly, the aerodynamic and propulsive
forces and moments are currently valid for the Beaver aircraft only.
• FMsort. This block computes the body-axes components of the resulting forces
and moments, and it stores the results in a separate force vector and moment
vector.
• Aircraft Equations of Motion (Beaver). The core element of the nonlinear aircraft
model. This subsystem first determines the time-derivative of the state vector
by evaluating the differential equations from section 2.5. Next, this vector is
sent through an Integrator block, to find the state vector itself. The subsystem is
aircraft-dependent in that it contains a block which corrects the time-derivative
of the state vector for a term that was omitted from the aerodynamic model
(this is related to the implicit nature of the state equations; see section 3.4 and
the description of the block xdotcorr (Beaver) for more information).
• Additional Outputs. This subsystem computes some additional observation signals
that are not needed to solve the equations of motion, yet may be useful for
post-simulation analysis of the airplane responses.
• Hlpfcn. This block computes some frequently used sines and cosines of angular
values from the state vector. It has been located in the internal feedback-loop
of the aircraft model, because of the trivial nature of the results. The feedbackloop
itself is necessary, because the external forces and moments that determine
the movements of the airplane are themselves dependent upon the airplane
motions.
On the left-hand side of figure 8.1, we see the external inputvectors uaero and uprop,
which contain the control inputs to the aerodynamic and engine models (control surface
deflections, engine RPM, and engine manifold pressure). The third inputvector
is uwind, which is used to account for unsteady atmosphere; it contains the wind velocity
components along the aircraft’s body-axes and the time-derivatives of these
velocities. This vector can include both deterministic stochastic terms (i.e. wind and
atmospheric turbulence). See table D.3 in appendix D for the exact definitions of the
input vectors.
The output vectors from the blocks in figure 8.1 are all gathered on the left-hand
side of this model. In total there are 18 output vectors, which have been defined in
table D.2 of appendix D.
In order to handle the input/output functions for this flight simulation model, an additional
system level was introduced. This system level makes sure that the relevant
input and output signals are logged into the MATLAB workspace, and it provides
connections for external models and access points for MATLAB functions.
In the system hierarchy, this ‘interface level’ forms an additional layer on top of
the actual aircraft model from figure 8.1, which is why this level will be designated
‘Beaver Level 1’ in the remainder of this report. The actual aircraft model is consid8.1.
The aircraft model and its subsystem equivalents 119
yhlp
x
xdot
18
yad3
17
yad2
16
yad1
15
yatm
14
Fwind
13
Fgrav
12
FMprop
11
FMaero
10
Cprop
9
Caero
8
yacc
7
ypow
6
yfp
5
ydl
4
yuvw
3
ybvel
2
xdot
1
x
Fwind
Wind forces
Gravity
Gravity forces
x
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FDC 1.4 – A SIMULINK Toolbox for Flight Dynamics and Contro(59)
