📄 ils.htm
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FDC help: ILS
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<h2>
The radio-navigation subsystem <i>ILS (Nominal ILS signals)</i>
</h2>
<p>The masked subsystem block <i>ILS</i>, which is contained in the library
<i><a href="navlib.htm">NAVLIB</a></i>, is used to compute nominal values
of the glideslope and localizer signals, for a given position of the
aircraft. It also checks the validity of the signals, using the separate
subsystem block <i><a href="ilstest.htm">ILStest</a></i>. See the <a href=
"#References">references</a> below for more details about the variables and
parameters from the block <i>ILS</i>.</p>
<h3>
Inputvector
</h3>
<pre>
uils = [xe ye H]'
xe: X-coordinate of aircraft in Earth-axes, [m]
ye: Y-coordinate of aircraft in Earth-axes, [m]
H : altitude of aircraft above sea level, [m]
</pre>
<p><b>Note:</b> these inputvariables are usually <i>extracted</i> from a
<i>non-linear</i> aircraft model. The block <i>ILS</i> computes the nominal
values of the ILS signals, using the actual aircraft position. Therefore it
does <i>not</i> give correct results whenever a small-deviations model is
used for the aircraft dynamics! The <i><a href="beaver.htm">Beaver</a></i> model is a good example of this type of nonlinear aircraft model.</p>
<h3>
Outputvectors
</h3>
<pre>
yils1 = [igs iloc]'
yils2 = [epsilon_gs Gamma_loc]'
yils3 = [xf yf Hf dgs Rgs Rloc]'
yils4 = [LOC_flag GS_flag]'
igs : nominal localizer current, [micro-Ampere]
iloc : nominal glideslope current, [micro-Ampere]
epsilon_gs: angle between line through aircraft's c.g. and
glideslope antenna and nominal glide path, [rad]
Gamma_loc : angle between ground-projection of line through
aircraft's c.g. and localizer antenna, and runway
centerline, [rad]
xf : X-coordinate of aircraft in runway-fixed reference
frame XF-YF-ZF, [m]
yf : Y-coordinate of aircraft in runway-fixed reference
frame XF-YF-ZF, [m]
Hf : altitude of aircraft in runway-fixed reference
frame XF-YF-ZF, [m]; Hf = -zf
dgs : distance from aircraft's c.g. to nominal glide path,
measured perpendicularly to nominal glide path, [m]
Rgs : 2D-distance from c.g. of aircraft to glideslope an-
tenna (as seen from above), [m]
Rloc : 2D-distance from c.g. of aircraft to localizer an-
tenna (as seen from above), [m]
LOC_flag : flag which is set to one if localizer signal cannot
be received with appropriate accuracy, else,
LOC_flag = 0
GS_flag : flag which is set to one if glideslope signal can-
not be received with appropriate accuracy, else,
GS_flag = 0
</pre>
<p><b>Note:</b> <i>i<sub>gs</sub></i> is proportional to <i>epsilon_gs</i>,
<i>i<sub>loc</sub></i> is proportional to <i>Gamma_loc</i>. Both
<i>i<sub>gs</sub></i> and <i>i<sub>loc</sub></i> are limited to +/- 150
[micro-Ampere]. For more information about the definitions of the
variables, consult the <a href="#References">references</a> below.</p>
<h3>
Parameters that need to be specified in dialog-boxes of the masked
subsystem <i>ILS</i>
</h3>
<ul>
<li>
position of the origin of the runway-fixed reference frame
<i>X<sub>F</sub>Y<sub>F</sub>Z<sub>F</sub></i> (given by the
coordinates <i>x<sub>RW</sub></i>, <i>y<sub>RW</sub></i>, and the
altitude above sea level <i>H<sub>RW</sub></i>, measured relatively to
Earth-fixed reference frame)
</li>
<li>
heading of the runway, <i>psi_RW</i>
</li>
<li>
nominal glideslope angle, <i>gamma_gs</i>
</li>
<li>
<i>X</i>-distance from runway threshold to localizer antenna,
<i>x<sub>loc</sub></i>
</li>
<li>
<i>X</i>-distance from runway threshold to glideslope antenna,
<i>x<sub>gs</sub></i>
</li>
<li>
<i>Y</i>-distance from runway centerline to glideslope antenna,
<i>y<sub>gs</sub></i>
</li>
</ul>
<p>Double-click the block <i>ILS</i> if you want to specify these variables
(the units of measurements are given in the dialog-boxes).</p>
<h3>
More information
</h3>
<p>The block <i>ILS</i> can be used in combination with other blocks that
implement steady-state errors or noise signals in the glideslope and
localizer currents. The blocks <i><a href="gserr.htm">GSerr</a></i> and
<i><a href="locerr.htm">LOCerr</a></i> determine steady-state errors in the
glideslope and localizer currents, respectively, while <i><a href=
"gsnoise.htm">GSnoise</a></i> and <i><a href=
"locnoise.htm">LOCnoise</a></i> determine glideslope and localizer noise.
The combination of all these blocks has been illustrated in the system
<i><a href="ilsxmpl.htm">ILS example</a></i>. All ILS-related blocks have
been gathered in the ILS sublibrary of the block-library <i><a href=
"navlib.htm">NAVLIB</a></i>.</p>
<p><b>Note:</b> the autopilot simulation models <i><a href=
"apilot.htm#APILOT2">APILOT2</a></i> or <i><a href=
"apilot.htm#APILOT3">APILOT3</a></i> provide a good demonstration of the
practical use of the radio-navigation models from <i>NAVLIB</i>. </p>
<h3>
<a name="References">References</a>
</h3>
<p>Apart from the FDC user-manual, the following reference contains more information about the ILS signals:</p>
<ol>
<li>
M.O. Rauw: <i>A Simulink environment for Flight Dynamics and Control
analysis - Application to the DHC-2 'Beaver'</i>, part I:
<i>Implementation of a model library in Simulink</i>. Delft University
of Technology, September 1993
</li>
</ol>
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