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<h1>Helicopter parameters in xml, helicopter model version 1</h1>
<h2>0 About this document</h2>
<p>
This document should not provide examples. Please take a look at the files
you got when downloading/installing CRRCSim.
<tt>heli.xml</tt> should provide an example for every parameter which
can be defined.
</p>
<p>
You need to know basics about xml files: they are structured text. Whitespace and line breaks do not
matter in most places. Just take a look at the examples and you will understand.
</p>
<p>
The files can be edited using a text editor. There are lots of them. Use something like notepad, vi,
emacs, joe...
</p>
<h3>0.1 Changes</h3>
<table border="1">
<tr><td>16.09.2008</td><td>J. W. Wulf</td>
<td>
First version.
</td>
</tr>
<tr><td>02.10.2008</td><td>J. W. Wulf</td>
<td>
Explained new parameters.
</td>
</tr>
</table>
<h2>1 General information</h2>
<p>
The file format and its structure is very similar to the one used for
fixed wing airplanes, see <a href="index.html">its description</a>.
Because of this, not every part of the file will be explained in this
document. To understand it, you need to read 'General information' and
'Units' of the former document at least.
</p>
<h3>1.1 Axis mapping</h3>
throttle controls climb<br>
rudder controls yaw<br>
aileron controls roll<br>
elevator controls pitch<br>
<h2>2 Ground effect: section <tt>GroundEffect</tt></h2>
<p>
<tt>GroundEffect.dist.mul</tt> is a value bigger than zero which tells
how much stronger disturbances are near ground.
</p>
<h2>3 Center of gravity: section <tt>CG</tt></h2>
<p>
Position of center of gravity in body axes with regard to coordinates used by
<tt>wheels</tt> and the 3D graphics file.<br>
Unit is feet (<tt>units="0"</tt>) or meters (<tt>units="1"</tt>).
x positive forward, y positive right, z positive down. Example:
<div class="fragment"><pre class="fragment">
<CG units="0" x="-0.2234252" y="0" z="-0.043131893" />
</pre></div>
</p>
<p>
This section and values do not have to exist, it is optional.
However, it gives you the following advantage:
There is no need to create the 3D model (and the points in the <tt>wheels</tt> section)
around the center of gravity. You can use any reference
point and give the position of the CG using your coordinates in this section.
</p>
<p>
This also makes it possible to change the location of the CG without changing the 3D model and
<tt>wheels</tt>.
</p>
<p>
You can visually check the position of the CG using test mode, as the airplane rotates
around the center of gravity (given that throttle=0).
</p>
<h2>4 Configuration: section <tt>config</tt></h2>
There can be more than one configuration for an helicopter, so there may be several
<tt>config</tt> sections. Because of this, each <tt>config</tt> needs a description.
See <a href="index.html">airplane file format</a>.
<h3>4.1 Subsection <tt>mass_inertia</tt></h3>
<p>
This is the same as described <a href="index.html">here</a>.
</p>
<h3>4.2 Subsection <tt>aero</tt></h3>
<p>
Set <tt>aero.coaxial="1"</tt> if the helicopter is of coaxial type.
In this case some parameters are automatically set to
zero and the main rotor does not create a yaw moment.
</p>
<p>
There are subsections <tt>yaw</tt>, <tt>roll</tt> and <tt>pitch</tt>,
which are similar.<br>
Every one of those subsections has an attribute <tt>ctrl</tt>,
which states rotational velocity around that axis at full stick
input in radians/s (so 2*3.1416 means one revolution per second).<br>
There is an attribute called <tt>damp</tt> which dampens rotation around
that axis -- generally higher values make the heli easier to fly.
Damping of <tt>roll</tt> and <tt>pitch</tt> axis is fixed, but
<tt>yaw</tt> axis is different: damping is <tt>yaw.damp</tt> with
zero stick input and decreases to
<tt>yaw.damp * yaw.damp_min_rel</tt> at full stick input.<br>
The attribute <tt>dist</tt> describes disturbances around that axis;
bigger values meaning more disturbance.
</p>
<p>
If you describe a helicopter with a 'heading hold' or 'heading lock'
gyro, add an attribute <tt>yaw.HeadingHold</tt> with a value greater
than zero, which describes the gain of the heading hold controller.
</p>
<p>
The whole <tt>pitch</tt> subsection can be omitted; values will be
taken from the <tt>roll</tt> subsection in this case.
</p>
<p>
<tt>yaw.off</tt>: yaw offset for non-coaxial helicopters without
heading hold.<br>
<tt>yaw.cp_to_yaw</tt>: mixes collective pitch/throttle to yaw<br>
<tt>yaw.moment_mul</tt>: set it to zero to not simulate main rotor
torque, set it to one to simulate it realistically, or set it to
anything in between.
</p>
<p>
<tt>roll.ForwardToRoll</tt>: when flying forward/sidewards/any
direction, there is a
90°-coupling caused by the difference in lift of the rotor. It is
automatically set to zero for coaxial type.
</p>
<p>
<tt>cp.ctrl</tt>: control throw for collective pitch type.<br>
<tt>cp.off</tt>: pitch offset for collective pitch type, throttle
offset for fixed pitch type.<br>
<tt>cp.auto_off</tt>: Is assumed to be <tt>1</tt> if not defined. If
it is equal to one, cp.off will automatically be set so that the
heli will lift from ground as your command more pitch or throttle
than neutral stick. So you only need to set <tt>cp.off</tt> in case
you don't like this automatic setting.<br>
</p>
<p>
<tt>power.automagic.F</tt> (in case of fixed type) is similar to
pitch control throw in case of collective pitch type.
</p>
<p>
<tt>speed.damp</tt>: higher values make the model easier to fly
</p>
<p>
<tt>yaw.vane</tt> and <tt>pitch.vane</tt> are set to bigger than
zero to simulate the weather vane effect caused by horizontal and
vertical stabilizers at the tail.
</p>
<h3>4.3 Power system: section <tt>power</tt></h3>
<p>
Only the main rotor is modelled.
This section only differs from the airplane-style power section by the
optional attribute <tt>fixed_pitch</tt> which is defined to "1" if
this helicopter is a fixed pitch (in contrast to collective pitch) type.
</p>
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