📄 apilot.htm
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FDC help: APILOT1/2/3
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<h2>
The autopilot simulation models</i>
</h2>
<p>The systems <i><a href="#APILOT1">APILOT1</a></i>, <i><a href=
"#APILOT2">APILOT2</a></i>, and <i><a href="#APILOT3">APILOT3</a></i>
contain the simulation models of the 'Beaver' autopilot, coupled to
the non-linear model of the 'Beaver' itself. The three versions of the
autopilot simulation systems differ in their complexity and computation
speed. Other closed-loop models are the systems <i><a href="#PAHRAH">PAH</a></i>, <i><a href="#PAHRAH">RAH</a></i>, and <i><a href="#PAHRAH">PAHRAH</a></i>, which contain implementations of the Pitch and/or Roll Attitude Hold modes only (neglecting the influence of signal limiters).</p>
<p>For more information, see the <a href="#References">references</a> below
and the help-texts for the subsystems <i><a href="actuatr.htm">Actuator
& cable dynamics</a></i>, <i><a href="sensors.htm">Sensors / Add
initial inputs</a></i>, <i><a href="ap_symm.htm">Symmetrical autopilot
modes</a></i>, <i><a href="ap_asymm.htm">Asymmetrical autopilot
modes</a></i>, and <i><a href="modectrl.htm">Mode Controller</a></i>.
Details about the autopilot initialization can be found in the help-texts
for the routines <i><a href="apinit.htm">APINIT</a></i> and <i><a href=
"apmode.htm">APMODE</a></i>. See the descriptions of the blocks <i><a href=
"ils.htm">ILS</a></i> and <i><a href="vor.htm">VOR</a></i> for more
information about the radio-navigation blocks.</p>
<p>See also the <a href="colors.htm">color definitions</a> for the FDC
toolbox.</p>
<h3>
<a name="APILOT1"><i>APILOT1</i></a>
</h3>
<p>This system contains the basic autopilot modes: </p>
<ul>
<li>
Pitch Attitude Hold
</li>
<li>
Altitude Hold
</li>
<li>
Altitude Select
</li>
<li>
Roll Attitude Hold
</li>
<li>
Heading Hold / Heading select
</li>
</ul>
<p>For reasons of computing speed, it does <i>not</i> contain: </p>
<ul>
<li>
approach and navigation modes
</li>
<li>
mode-switching loops for approach and navigation modes
</li>
<li>
ILS and VOR blocks
</li>
<li>
any noisy disturbances (sensors, atmospheric turbulence)
</li>
<li>
a Moving Average filter for the Altitude Hold mode
</li>
</ul>
<p><i>APILOT1</i> can be used for fast evaluation of the basic autopilot
results, using the ODE15s integrator, which is quite efficient for
systems with relatively smooth signals (i.e. few discontinuities, or none
at all). In that case, the simulations will be very fast, and the number of
timesteps will be limited.</p>
<h3>
<a name="APILOT2"><i>APILOT2</i></a>
</h3>
<p>This system contains all control laws of the 'Beaver'
autopilot: </p>
<ul>
<li>
Pitch Attitude Hold
</li>
<li>
Altitude Hold
</li>
<li>
Altitude Select
</li>
<li>
Roll Attitude Hold
</li>
<li>
Heading Hold / Heading Select
</li>
<li>
longitudinal and lateral approach modes
</li>
<li>
VOR-navigation mode
</li>
</ul>
<p>Due to the inclusion of the approach and navigation modes, it also
contains: </p>
<ul>
<li>
mode-switching loops for approach and NAV (call M-files with
mode-switching criteria, which slows down simulations)
</li>
<li>
ILS and VOR blocks
</li>
</ul>
However, for reasons of computing speed, <i>APILOT2</i> does <i>not</i>
contain:
<ul>
<li>
any noisy disturbances (sensors, ILS noise, turbulence)
</li>
<li>
a Moving Average filter for the Altitude Hold mode
</li>
</ul>
<p><i>APILOT2</i> simulations are slower than those of <i>APILOT1</i> due to the additional blocks. ODE15s is still a suitable solver for this system, because it doesn't contain any noisy disturbances or sharp discontinuities.</p>
<h3>
<a name="APILOT3"><i>APILOT3</i></a>
</h3>
This system is equal to <i>APILOT2</i>, but it also includes:
<ul>
<li>
ILS noise in the block ILS
</li>
<li>
a Moving Average filter for the Altitude Hold mode
</li>
<li>
atmospheric turbulence
</li>
</ul>
<p>Due to the noisy signals, the time steps are all equal to their minimum
value, which means very slow simulations (unless you have a very fast PC or
workstation). ODE45 is a suitable solver for this system.</p>
<h3>
<a name="PAHRAH"><i>PAH</i>, <i>RAH</i>, and <i>PAHRAH</i></a>
</h3>
<p>These systems contain implementations of the Pitch Attitude Hold mode (excluding the turn-compensation loops and neglecting any signal limiters), the Roll Attitude Hold mode (including the turn-coordination loops, but neglecting the signal limiters), and a combination of both, respectively. </p>
<p>Compared to the <i>APILOT</i> systems, the appearance of these PAH/RAH models is more similar to the representation of typical control systems in textbooks and the figures from the FDC manual. The main advantage of this appearance is that these models are a little bit easier to understand; the main disadvantage is that it is much harder to enhance them with outer-loop controllers. The <i>APILOT</i> systems are more similar to the control law representation in the Flight Control Computer of the aircraft.</p>
<p>In general, simulations of these PAH/RAH models will be quite fast, as these models do not include any noisy disturbances or sharp discontinuities, and they do not contain any outer-loop blocks. ODE15s is a suitable solver for these systems.</p>
<h3>
<a name="References">References</a>
</h3>
<p>For a detailed description of the 'Beaver' autopilot, refer to the FDC user-manual. More information can be found in the following
references:</p>
<ol>
<li>
M.O. Rauw: <i>A Simulink environment for Flight Dynamics and Control
analysis - Application to the DHC-2 'Beaver'</i> (PART II).
MSc-thesis, Delft University of Technology, Faculty of Aerospace
Engineering, Delft, The Netherlands, 1993.
</li>
<li>
P.N.H. Wever: <i>Ontwerp en implementatie van de regelwetten van de De
Havilland DHC-2 'Beaver'</i> (in Dutch). MSc-thesis, Delft
University of Technology, Faculty of Aerospace Engineering, Delft, The
Netherlands, 1993.
</li>
</ol>
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