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FDC help: ILS example
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<h2>
The radio-navigation subsystem <i>ILS example</i>, and the <i>ILS</i> blocks from the systems <i>APILOT2</i> and <i>APILOT3</i>.
</h2>
<p>The subsystem <i>ILS example</i> from the library <i><a href=
"navlib.htm">NAVLIB</a></i> demonstrates how to combine the different ILS
blocks in one subsystem. First, the nominal signals are computed in the
block <i><a href="ils.htm">ILS (Nominal ILS values)</a></i>. Then, the
steady-state errors are added (blocks <i><a href="gserr.htm">GSerr</a></i>
and <i><a href="locerr.htm">LOCerr</a></i>), and finally glideslope noise
and localizer noise are added (blocks <i><a href=
"gsnoise.htm">GSnoise</a></i> and <i><a href=
"locnoise.htm">LOCnoise</a></i>). Double-clicking the block <i>ILS
example</i> will reveal this internal structure. <i><a href=
"navlib.htm">NAVLIB</a></i> also includes a variant of this subsystem without
the ILS noise.</p>
<p><b>Note:</b> the block <i>ILS</i> and the error blocks need to be
double-clicked too in order to specify their parameters. See the <a
href="#References">references</a> below for more information about the
block-parameters.</p>
<p>A slightly different version of the noiseless variant is used in the
system <i><a href="apilot.htm#APILOT2">APILOT2</a></i>,
while a slightly different version that includes noise is used in the system
<i><a href="apilot.htm#APILOT3">APILOT3</a></i> (the difference being altered
I/O definitions, and the addition of differentiating filters to compute the
time-derivatives of the glideslope and localizer signals). </p>
<h3>
Inputvector: <i>x</i>
</h3>
<pre>
x = [V alpha beta p q r psi theta phi xe ye H]' (aircraft states)
{V : airspeed [m/s] }
{alpha: angle of attack [rad] }
{beta : sideslip angle [rad] }
{p : roll rate [rad/s] }
{q : pitch rate [rad/s] }
{r : yaw rate [rad/s] }
{psi : yaw angle [rad] }
{theta: pitch angle [rad] }
{phi : roll angle [rad] }
xe : x-coordinate in Earth-fixed reference frame [m]
ye : y-coordinate [m]
H : altitude above sea-level [m]
</pre>
<p><b>Note:</b> these inputvariables are usually extracted from a
nonlinear 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>
system is a good example of this type of nonlinear aircraft model.</p>
<h3>
Output signals: <i>epsilon_gs_true</i> and <i>Gamma_loc_true</i>
</h3>
<pre>
epsilon_gs_true : true value of the glideslope deviation = nominal value +
+ steady-state error + glideslope noise, [rad]
Gamma_loc_true: true value of the localizer deviation = nominal value +
+ steady-state error + localizer noise, [rad]
'glideslope deviation' = the angle between the line from the aircraft's
center of gravity to the glideslope antenna, and the line of the nominal
glide path
'localizer deviation' = the angle between the ground-projection of the
line from the aircraft's center of gravity to the localizer antenna,
and the extended runway centerline, [rad]
</pre>
<p>The noise and error models are according to the
<a href="#References">references</a> given at the end of this page.</p>
<p>During simulations, the time-trajectories of the nominal ILS signals and
several interim results from the block ILS are sent to the matrix
<i>yils</i> in the Matlab workspace. Each row from this matrix corresponds
with the vector <i>yils_workspace</i> at a certain time <i>t</i>, according
the following definition (notice the difference between the workspace
variable <i>yils</i> and the Simulink vector <i>yils</i> within <i>ILS
example</i>): </p>
<pre>
yils_workspace = [yils1; yils2; yils3; yils4]'
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 from the aircraft's c.g. to the
glideslope antenna and nominal glide path, [rad]
Gamma_loc : angle between ground-projection of line from the
aircraft's c.g. to the localizer antenna, and the
extended 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 FDC user-manual. </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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