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Submodels are objects which can be dropped or launched from the user
aircraft. The trigger is a boolean property, which you define, which when
"true" causes the submodel to be released/launched.

A submodel will create an AIBallistic object which will follow a ballistic
path. By default one submodel will be released when the corresponding
trigger is "true".

Notes:
   1.  This utility is intended for ballistic objects which align to the
   trajectory. Drag is applied based on this assumption: no allowance is
   for changes in drag for objects which do not conform to this asumption.
   made

  2.  While Inertia is calculated properly, Moment of Inertia and rotational
  aerodynamic damping are simulated. It is assumed that the object is a cylinder
  of uniform density - if your object does not conform to this, there will be
  inaccuracies.

  3.  The program does not calculate windage for ballistic objects well. While
  adequate for smoke effects, etc., for bullets, bombs, droptanks this is probably
  best left at "False". Since the effects of wind on various ballistic objects is
  uncertain, there is no plan to change this situation.

  4. Submodels can be ensted to any depth, thus a submodel on expiry or impact etc,
  can launch a child submodel, which in turn can launch a submodel. and so on. This
  is the basis for Persistent Contrails, but any use is possible.

The initial conditions (IC) define the object's starting point (relative
to the user aircraft's "reported position"), and its initial speed and
direction (relative to the user aircraft).  If you want to release many
similar objects with similar IC, then you may use the <repeat>, <delay>
and <count> properties to define this.  The allowed properties are:

<name>         The name of the submodel.
<model>        The path to the visual model.
<trigger>      The property which will act as the trigger. If this tag is not
               included, the submodels will be released continuously, provided
               <count> is set to -1.
<speed>        Initial speed, in feet/sec, relative to user aircraft.
<speed-prop>   The property containing the Initial speed, in feet/sec, relative to
               user aircraft. If this path is found, <speed> will be overwritten.
<repeat>       Set "true" if you want multiple releases of this submodel.
<delay>        Time, in seconds, between repeated releases.
<count>        Number of submodels available for multiple release.
               -1 defines an unlimited number.
<slaved>       If true, the submodel is slaved to the parent model.
<x-offset>     Submodel's initial fore/aft position (in feet), relative to user
               aircraft.  Fore is positive.
<y-offset>     Submodel's initial left/right position (in feet), relative to user
               aircraft.  Right is positive.
<z-offset>     Submodel's initial up/down position (in feet), relative to user
               aircraft.  Up is positive.
<yaw-offset>   Submodel's initial azimuth, in degrees, relative to user
               aircraft'snose. Right is positive.
<pitch-offset> Submodel's initial elevation, in degrees, relative to user aircraft's
               pitch. Up is positive.
<life>         Life span in seconds.
               Default is 900.0.
<buoyancy>     In ft/sec/sec.  Works opposite acceleration of gravity.
               For example, if set to 32 the submodel will feel no
               gravity. If greater than 32 the object will rise.
               Default is 0.
<wind>         Set to true if you want the submodel to react to the wind. Default
               is "false".
<cd>           The Coeffient of Drag. Varies with submodel shape - 0.295 for a
               bullet, 0.045 for an airfoil. Enter an appropriate value. Defaults to
               0.295.
<random>       When this is true the Cd is varied by +- 5%. Useful for smoke or
               contrails.
<eda>          Effective drag area (sq ft). Usually the cross-sectional area of the
               submodel normal to the airflow.
<weight>       The weight of the submodel (lbs). NOT set to 0 on submodel release.
               You may wish to set this value to 0 by means of key bindings or Nasal
               script. Defaults to 0.25.
<contents>     The path to the contents of a submodel. The contents must be in lbs.
               Intended for use with drop tanks. The property value will be set to
               0 on release of the submodel: do not also set to 0 elsewhere e.g. in
               key bindings. Defaults to 0.
<random>       Varies CD by +- 10%, initial azimuth by +- 10 degs, and life by
               <randomness>
<randomness>   If <random> is true, <randomness> is applied to <life>. 0 > Value < 1
               are valid. Defaults to 0.5.
<no-roll>      If true the submodel does not roll.
<impact>       If true, the impact location (lat/lon) on the terrain is calculated.
               The Material (e.g Grass)of the terrain, load resistance, and impact
               velocity. Altitude agl is calculated.
<collision>    If true, collisions with other objects is tested. If a collision is
               detected then the position data are written to the "Report Node".
<fuze-range>   Used in detecting collisions. The distance in feet between an object
               and a submodel at which a collision is deemed to have occurred.
<expiry>       If true, the current position of the submodel is written to the
               "Report Node" when the submodel life expires.
<impact-reports> Defines a "Report Node". When an impact happens, then the path of
               the submodel will be written to this node. An attached listener
               function can evaluate the impact properties. If unset, reports go to
               /ai/models/model-impact.

***** experimental ****

<external-force> If true the submodel is subjected to an external force
<force-path> A string describing the property where the magnitude, azimuth and
             elevation of the external force are to be found. The following child
              properties are instantiated:
               ~/force-lb
              ~/force-azimuth-deg
              ~/force-elevation-deg

You will have to set these values by some means (Nasal script etc.) to make use of this
utility.

<PropertyList>

  <submodel>
    <name>left gun</name>
    <model>Models/Geometry/tracer.ac</model>
    <trigger>ai/submodels/submodel[0]/trigger</trigger>
    <speed>2750.0</speed>
    <repeat>true</repeat>
    <delay>0.25</delay>
    <count>100</count>
    <x-offset>1.0</x-offset>
    <y-offset>-7.0</y-offset>
    <z-offset>-2.0</z-offset>
    <yaw-offset>0.4</yaw-offset>
    <pitch-offset>1.8</pitch-offset>
    <life>2.0</life>
  </submodel>

  <submodel>
    <name>right gun</name>
    <model>Models/Geometry/tracer.ac</model>
    <trigger>ai/submodels/submodel[0]/trigger</trigger>
    <speed>2750.0</speed>
    <repeat>true</repeat>
    <delay>0.25</delay>
    <count>100</count>
    <x-offset>1.0</x-offset>
    <y-offset>7.0</y-offset>
    <z-offset>-2.0</z-offset>
    <yaw-offset>-0.4</yaw-offset>
    <pitch-offset>1.8</pitch-offset>
    <life>2.0</life>
  </submodel>

  <submodel>
    <name>droptank-l</name>
    <model>Aircraft/Hunter/Models/droptank-100gal.ac</model>
    <trigger>controls/armament/station[0]/jettison-all</trigger>
    <speed>0</speed>
    <repeat>false</repeat>
    <count>1</count>
    <x-offset>0.820</x-offset>
    <y-offset>-9.61</y-offset>
    <z-offset>-2.39</z-offset>
    <yaw-offset>0</yaw-offset>
    <pitch-offset>0</pitch-offset>
    <wind>false</wind>
    <eda>2.11348887</eda>
    <weight>170</weight>
    <cd>0.045</cd>
    <contents>consumables/fuel/tank[2]/level-lbs</contents>
  </submodel>

  <submodel>
    <name>droptank-r</name>
    <model>Aircraft/Hunter/Models/droptank-100gal.ac</model>
    <trigger>controls/armament/station[1]/jettison-all</trigger>
    <speed>0</speed>
    <repeat>false</repeat>
    <count>1</count>
    <x-offset>0.820</x-offset>
    <y-offset>9.61</y-offset>
    <z-offset>-2.39</z-offset>
    <yaw-offset>0</yaw-offset>
    <pitch-offset>0</pitch-offset>
    <wind>false</wind>
    <eda>2.11348887</eda>
    <weight>170</weight>
    <cd>0.045</cd>
    <contents>consumables/fuel/tank[3]/level-lbs</contents>
  </submodel>

  <submodel>
    <name>engine exhaust r</name>
    <model>Aircraft/seahawk/Models/exhaust_s.xml</model>
    <trigger>sim/ai/aircraft/exhaust</trigger>
    <speed-node>engines/engine/n1</speed-node>
    <speed>10</speed>
    <repeat>true</repeat>
    <delay>0.1</delay>
    <count>-1</count>
    <x-offset>-3.5</x-offset>
    <y-offset>2.6768</y-offset>
    <z-offset>-0.3937</z-offset>
    <yaw-offset>170</yaw-offset>
    <life>10</life>
    <buoyancy>128</buoyancy>
    <aero-stabilised>0</aero-stabilised>
    <wind>true</wind>
    <eda>1</eda>
    <cd>0.95</cd>
    <weight>1</weight>
    <random>1</random>
  </submodel>

</PropertyList>

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