Chapter 10
Radio-navigation block reference
This chapter provides a detailed description of the SIMULINK implementation of the
VOR and ILS models from chapter 5. If you want to manipulate these blocks, or gain
a better insight in the block structure, it is recommended to compare the internal
block equations with the descriptions from this chapter. The internal block equations
have been hidden behind a mask interface; refer to section 7.8 for more information
about the mask interface of the FDC systems.
10.1 The radio-navigation blocklibrary
All radio-navigation blocks have been collected in the SIMULINK library NAVLIB,
which is shown in figure 10.1. It can be accessed from the main FDC library (shown
in figure 7.7 of chapter 7) by double-clicking the ‘ILS/VOR radio-nav library’ button,
or by typing navlib in the MATLAB command-window. NAVLIB itself consists of two
sublibraries: NAVLIB1, which contains the ILS models, and NAVLIB2, which contains
the VOR models. These sublibraries have been shown in figures 10.2 and 10.3.
Figure 10.1: Radio-navigation library NAVLIB
180 Chapter 10. Radio-navigation block reference
Figure 10.2: Sublibrary with ILS models
Figure 10.3: Sublibrary with VOR models
The remainder of this chapter (pages 181 to 192) provides detailed descriptions
of the individual blocks from the radio-navigation library. The blocks have been
listed in alphabetical order; their locations have been referenced in relation to
the main FDC library and the radio-navigation library.
10.1. The radio-navigation blocklibrary 181
GSerr Main FDC library / ILS/VOR radio-nav / ILS signals / GSerr
Radio-navigation library / ILS signals / GSerr
Type
Masked subsystem block.
Description
The block GSerr computes steady-state errors in the glideslope signal. The errors are
expressed in terms of electrical currents, used to drive the glideslope deviation indicator
in the cockpit.
Equations
For a detailed discussion of the equations from the block GSerr, refer to section 5.1.2.
• Glideslope signal with steady-state errors, [μA]:
igs,actual = KSgs
igs,nominal + Digs
The multiplication factor KSgs takes into account the offset in glideslope sensitivity Sgs,
while the error Digs is caused by an offset in the nominal glideslope elevation angle ggs, i.e.
by a glideslope misalignment. The signals are expressed in terms of cockpit instrument
currents.
Inputs
igs,nominal nomimal glideslope current, igs (nominal)
Outputs
igs,actual actual glideslope current, including steady-state errors, igs (actual)
Parameters
The user must specify the ILS performance category (1, 2, or 3; see figure 5.6 from chapter
5), the offset in glideslope sensitivity, and the glideslope misalignment. The offsetvalues
are both expressed as a percentage of the maximum allowable error shown in
table 5.2. The parameters can be entered in the mask dialog, which can be opened by
double-clicking GSerr.
Connections
in: igs,nominal is retrieved from the block ILS, which determines the nominal ILS signals.
out: igs,actual is in general added to a glideslope noise signal, obtained by GSnoise. This
signal can e.g. be used as an input signal for an automatic approach controller.
Type browse gserr at the command-line for on-line help.
182 Chapter 10. Radio-navigation block reference
GSnoise1 (2) Main FDC library / ILS/VOR radio-nav / ILS signals / GSnoise1 (2)
Radio-navigation library / ILS signals / GSnoise1 (2)
Type
Masked subsystem blocks.
Description
The blocks GSnoise1 and GSnoise2 determine glideslope noise signals. GSnoise1 is based
on a noise model from AGARD report R-632 [1], while GSnoise2 uses an alternative model
from NASA report CR-2022 [22]. These reports have also been referenced in the block
icons. The noise signals are expressed in terms of the electrical currents, used to drive the
glideslope deviation indicator in the cockpit.
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