Nordstern.xml

<?xml version="1.0" encoding="utf-8"?>
<!--

  Zeppelin LZ 121 "Nordstern" airship flight model for JSBSim.

    Copyright (C) 2010 - 2023  Anders Gidenstam  (anders(at)gidenstam.org)

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.
  
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
  
    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  
-->
<?xml-stylesheet type="text/xsl" href="http://jsbsim.sourceforge.net/JSBSim.xsl"?>
<fdm_config name="LZ 121" version="2.0" release="BETA"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:noNamespaceSchemaLocation="http://jsbsim.sourceforge.net/JSBSim.xsd">

 <fileheader>

  <author>Anders Gidenstam</author>
  <email>anders at gidenstam dot org</email>

  <filecreationdate>2010-04-20</filecreationdate>
  <version>2023-12-06</version>

  <description>JSBSim model of the Zeppelin LZ 121 "Nordstern".</description>

  <license>
   <licenseName>GPL v2+</licenseName>
   <licenseURL>http://www.gnu.org/licenses/old-licenses/gpl-2.0.html</licenseURL>
  </license>
  <note>
   This model was created using publicly available data, publicly available
   technical reports, textbooks, and guesses. It contains no proprietary or
   restricted data. It has been validated only to the extent that it may seem
   to "fly right", and possibly to comply to published, publicly known, 
   performance data (maximum speed, endurance, etc.).

   This model is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
  </note>

  <reference
   refID="PK:1994:LZ120"
   author="Peter Kleinheins"
   title="LZ 120 „Bodensee“ und LZ 121 „Nordstern“  Luftschiffe im Schatten des Versailler Vertrages"
   date="1994"/>

  <reference
   refID="Vissering:1922:ZS"
   author="Harry Vissering"
   title="Zeppelin  The Story of a Great Achievement"
   date="1922"/>

  <reference
   refID="Flight:1918:MB"
   author="Flight"
   title="THE 300 H.P. MAYBACH ENGINE."
   date="29 Aug. 1918"/>

  <reference
   refID="DR:1979:Bodensee"
   author="Douglas H. Robinson"
   title="The Commercial Zeppelins Bodensee and Nordstern"
   date="1979"/>

  <reference
   refID="LD:1924:25YOAC"
   author="Dr. Ludwig Dürr"
   title="25 Years Of Airship Construction"
   date="1924/"/>

  <reference
   refID="HE:1919:BIPZ"
   author="Dr. Hugo Eckener"
   title="Brief Instructions and Practical Hints for Piloting Zeppelin Airships for the Flight Personnel of the ''DELAG''"
   date="1919"/>

 </fileheader>

 <!--
 ==== Metrics ===============================================================
 -->

 <metrics>

  <documentation>
   NOTE: The center of the mooring coupler at bow of the hull is the
         origo of the body coordinate system.
         x/y/z = back/right/up
  </documentation>

  <documentation>
   Summary of technical data in [PK:1994:LZ120] and
   [http://de.wikipedia.org/wiki/LZ_120]:

   Hull
     Length:       130.8 m
     Max diameter:  18.71 m
     #gas cells:    13
     Gas volume:    22500 m^3 hydrogen
     Material: "... Baumwolle und war mit Zellonlack getränkt."
               "... verlieh dem Schiff ein silbergraues Äußeres."

   Engines
     Type:   Maybach-Reihen-Sechszylinder-Motoren Mb IVa
     Number: 4
     Power:  240 HP (below 1800 m)
     
   Propellers
     Side cars (2):
       Engines:  1 (each)
       Diameter: 3.2 m
       #blades:  2
       Reversible.
     Aft car:
       Engines:  2
       Diameter: 5.2 m
       #blades:  2
       Gearing:  2:1

   Empty weight: 14700 kg
   Useful load:  11500 kg

   Range: 1700 km

   Crew:
     "Standardbesatzung: 12 Mann:
      Kommandant, „Steuermann“ bzw. Wachhabender (entspr. 1. Offizier),
      1 Höhensteuermann, 1 Seitensteuermann, 1 Funker, 1 Steward,
      6 Maschinisten"
  </documentation>

  <!-- Reference quantities. -->
  <wingarea unit="M2">  797.0 </wingarea>  <!-- V^(2/3).-->
  <wingspan unit="M">    28.2 </wingspan>  <!-- V^(1/3). -->
  <chord unit="M">       28.2 </chord>     <!-- V^(1/3). -->
  <htailarea unit="M2"> 119.0 </htailarea> <!-- FIX these... -->
  <htailarm unit="M">    54.4 </htailarm>  <!-- From CG? -->
  <vtailarea unit="M2">  58.4 </vtailarea>
  <vtailarm unit="M">    54.4 </vtailarm>  <!-- From CG? -->
  <!-- Total gas volume vol = 22500 m^3 -->

  <!-- Aerodynamic Reference Point.
       Must be on the axis of symmetry of the hull. -->
  <location name="AERORP" unit="M">
   <x> 56.4 </x>
   <y>  0.0 </y>
   <z>  0.0 </z>
  </location>

  <location name="EYEPOINT" unit="M">
   <x> 21.0 </x>
   <y>  0.0 </y>
   <z> -9.0 </z>
  </location>

  <!-- Visual Reference Point -->
  <location name="VRP" unit="M">
   <x>  0.0  </x>
   <y>  0.0  </y>
   <z>  0.0  </z>
  </location>

 </metrics>

 <!--
 ==== Mass balance =========================================================
 -->

 <mass_balance>

  <emptywt unit="KG"> 9750 </emptywt>

  <documentation>
   The empty weight is estimated to consist of:
    - The hull structure           7000 (guesstimate from LZ-129 ratio)
    - The hull cover               1125 (guesstimate from LZ-129 ratio)
    - The empty gas cells          1625 (guesstimate from LZ-129 ratio)

    The car and engines etc will be added as point masses.
  </documentation>

  <documentation>
   % Very rough estimation model of the empty weight CG and inertia tensor.
   % Assume the empty weight of is to 60% a cylindrical shell and
   % to 40% a thin rod (i.e. the keel).
   % The keel is located r meters below the centrum line.

   m = 9750.0   % KG
   r = 7.05     % meter
   l = 130.8    % meter

   % Very rough estimate of center of gravity (based on the inertial estimate):
   CGx = l / 2
   CGy = 0
   CGz = - 1/6 * pi * r

   % Steiners theorem:
   % Ixx = \bar{Ixx} + m sqrt(\bar{y}^2 + \bar{z}^2)
   % Ixy = \bar{Ixy} + m \bar{x} \bar{y}

   % Very rough estimation model of Ixx, Iyy and Izz relative the CG.
   Ixx = (0.6*m) * r^2 + (0.6*m) * 1/6 * pi * r + \
         (0.4*m) * r * (1 - 1/6*pi)

   Iyy = 1/2*(0.6*m) * r^2 + 1/12*(0.6*m)*l^2 + (0.6*m) * 1/6 * pi * r + \
         1/12*(0.4*m)*l^2 + (0.4*m) * r * (1 - 1/6*pi)

   Izz = 1/2*(0.6*m) * r^2 + 1/12*(0.6*m)*l^2 + \
         1/12*(0.4*m) * l^2

   Ixy = 0
   Ixz = 0
   Iyz = 0

  </documentation>

  <ixx unit="KG*M2">   325450.0 </ixx>
  <iyy unit="KG*M2"> 14081000.0 </iyy>
  <izz unit="KG*M2"> 14046000.0 </izz>
  <ixy unit="KG*M2">      0.0 </ixy>
  <ixz unit="KG*M2">      0.0 </ixz>
  <iyz unit="KG*M2">      0.0 </iyz>

  <location name="CG" unit="M">
   <x> 65.400 </x>
   <y>  0.000 </y>
   <z> -3.690 </z>
  </location>

  <!--
  === Ballast ================================================
  -->
  <documentation>
   Ballast according to [Vissering:1922:ZS]:
     Frame 10
       4x 100 l "Ballasthose" (Emergency ballast)
     Frame 20
       2x 500 l "Ballastsack" (Trim ballast)
     Frame 50
       2x 500 l "Ballastsack" (Trim ballast)
     Frame 70
       2x 500 l "Ballastsack" (Trim ballast)
     Frame 105
       2x 500 l "Ballastsack" (Trim ballast)
     Frame 110
       6x 100 l "Ballasthose" (Emergency ballast)
  </documentation>

  <!-- Real ballast setup. -->
  <pointmass name="Ballasthose 1L Frame 10"> <!-- n=0 -->
   <location unit="M">
    <x> 109.8 </x>
    <y>  -2.5 </y>
    <z>  -4.5 </z>
   </location>
   <weight unit="KG"> 100 </weight>
  </pointmass>
  <pointmass name="Ballasthose 2L Frame 10"> <!-- n=1 -->
   <location unit="M">
    <x> 109.8 </x>
    <y>  -1.5 </y>
    <z>  -4.5 </z>
   </location>
   <weight unit="KG"> 100 </weight>
  </pointmass>
  <pointmass name="Ballasthose 1R Frame 10"> <!-- n=2 -->
   <location unit="M">
    <x> 109.8 </x>
    <y>   1.5 </y>
    <z>  -4.5 </z>
   </location>
   <weight unit="KG"> 100 </weight>
  </pointmass>
  <pointmass name="Ballasthose 2R Frame 10"> <!-- n=3 -->
   <location unit="M">
    <x> 109.8 </x>
    <y>   2.5 </y>
    <z>  -4.5 </z>
   </location>
   <weight unit="KG"> 100 </weight>
  </pointmass>

  <pointmass name="Ballastsack L Frame 20"> <!-- n=4 -->
   <location unit="M">
    <x> 100.0 </x>
    <y>  -0.6 </y>
    <z>  -6.3 </z>
   </location>
   <weight unit="KG"> 500 </weight>
  </pointmass>
  <pointmass name="Ballastsack R Frame 20"> <!-- n=5 -->
   <location unit="M">
    <x> 100.0 </x>
    <y>   0.6 </y>
    <z>  -6.3 </z>
   </location>
   <weight unit="KG"> 500 </weight>
  </pointmass>

  <pointmass name="Ballastsack L Frame 50"> <!-- n=6 -->
   <location unit="M">
    <x>  70.0 </x>
    <y>  -0.6 </y>
    <z>  -8.2 </z>
   </location>
   <weight unit="KG"> 500 </weight>
  </pointmass>
  <pointmass name="Ballastsack R Frame 50"> <!-- n=7 -->
   <location unit="M">
    <x>  70.0 </x>
    <y>   0.6 </y>
    <z>  -8.2 </z>
   </location>
   <weight unit="KG"> 500 </weight>
  </pointmass>

  <pointmass name="Ballastsack L Frame 70"> <!-- n=8 -->
   <location unit="M">
    <x>  50.0 </x>
    <y>  -0.6 </y>
    <z>  -8.2 </z>
   </location>
   <weight unit="KG"> 500 </weight>
  </pointmass>
  <pointmass name="Ballastsack R Frame 70"> <!-- n=9 -->
   <location unit="M">
    <x>  50.0 </x>
    <y>   0.6 </y>
    <z>  -8.2 </z>
   </location>
   <weight unit="KG"> 500 </weight>
  </pointmass>

  <pointmass name="Ballastsack L Frame 105"> <!-- n=10 -->
   <location unit="M">
    <x>  17.5 </x>
    <y>  -0.6 </y>
    <z>  -6.7 </z>
   </location>
   <weight unit="KG"> 500 </weight>
  </pointmass>
  <pointmass name="Ballastsack R Frame 105"> <!-- n=11 -->
   <location unit="M">
    <x>  17.5 </x>
    <y>   0.6 </y>
    <z>  -6.7 </z>
   </location>
   <weight unit="KG"> 500 </weight>
  </pointmass>

  <pointmass name="Ballasthose 1L Frame 110"> <!-- n=12 -->
   <location unit="M">
    <x>  10.8 </x>
    <y>  -1.0 </y>
    <z>  -5.5 </z>
   </location>
   <weight unit="KG"> 100 </weight>
  </pointmass>
  <pointmass name="Ballasthose 2L Frame 110"> <!-- n=13 -->
   <location unit="M">
    <x>  10.8 </x>
    <y>  -0.75 </y>
    <z>  -5.5 </z>
   </location>
   <weight unit="KG"> 100 </weight>
  </pointmass>
  <pointmass name="Ballasthose 3L Frame 110"> <!-- n=14 -->
   <location unit="M">
    <x>  10.8 </x>
    <y>  -0.5 </y>
    <z>  -5.5 </z>
   </location>
   <weight unit="KG"> 100 </weight>
  </pointmass>
  <pointmass name="Ballasthose 1R Frame 110"> <!-- n=15 -->
   <location unit="M">
    <x>  10.8 </x>
    <y>   0.5 </y>
    <z>  -5.5 </z>
   </location>
   <weight unit="KG"> 100 </weight>
  </pointmass>
  <pointmass name="Ballasthose 2R Frame 110"> <!-- n=16 -->
   <location unit="M">
    <x>  10.8 </x>
    <y>   0.75 </y>
    <z>  -5.5 </z>
   </location>
   <weight unit="KG"> 100 </weight>
  </pointmass>
  <pointmass name="Ballasthose 3R Frame 110"> <!-- n=17 -->
   <location unit="M">
    <x>  10.8 </x>
    <y>   1.0 </y>
    <z>  -5.5 </z>
   </location>
   <weight unit="KG"> 100 </weight>
  </pointmass>

  <!-- 
  === Crew and payload =======================================
  -->
  <documentation>
   Payload storage along the keel according to [Vissering:1922:ZS]:
     Frame 40-45 (between the frames)
       4x Gepäcknetz für 200 kg
     Frame 75 (2 fore and 1 aft right of the frame)
       3x Gepäcknetz für 200 kg
  </documentation>

  <pointmass name="Control car payload"> <!-- n=18 -->
   <weight unit="KG"> 1500.0 </weight>
   <location name="POINTMASS" unit="M">
    <x> 21.0 </x>
    <y>  0.0 </y>
    <z> -8.5 </z>
   </location>
  </pointmass>

  <pointmass name="Frame 40L Cargo"> <!-- n=19 -->
   <weight unit="KG"> 80.0 </weight>
   <location name="POINTMASS" unit="M">
    <x> 78.5 </x>
    <y> -1.0 </y>
    <z> -8.0 </z>
   </location>
  </pointmass>
  <pointmass name="Frame 40R Cargo"> <!-- n=20 -->
   <weight unit="KG"> 80.0 </weight>
   <location name="POINTMASS" unit="M">
    <x> 78.5 </x>
    <y>  1.0 </y>
    <z> -8.0 </z>
   </location>
  </pointmass>
  <pointmass name="Frame 45L Cargo"> <!-- n=21 -->
   <weight unit="KG"> 100.0 </weight>
   <location name="POINTMASS" unit="M">
    <x> 76.5 </x>
    <y> -1.0 </y>
    <z> -8.2 </z>
   </location>
  </pointmass>
  <pointmass name="Frame 45R Cargo"> <!-- n=22 -->
   <weight unit="KG"> 100.0 </weight>
   <location name="POINTMASS" unit="M">
    <x> 76.5 </x>
    <y>  1.0 </y>
    <z> -8.2 </z>
   </location>
  </pointmass>

  <pointmass name="Frame 75R Aft Cargo"> <!-- n=23 -->
   <weight unit="KG"> 100.0 </weight>
   <location name="POINTMASS" unit="M">
    <x> 46.5 </x>
    <y>  1.0 </y>
    <z> -8.7 </z>
   </location>
  </pointmass>
  <pointmass name="Frame 75L Fore Cargo"> <!-- n=24 -->
   <weight unit="KG"> 100.0 </weight>
   <location name="POINTMASS" unit="M">
    <x> 43.5 </x>
    <y> -1.0 </y>
    <z> -8.7 </z>
   </location>
  </pointmass>
  <pointmass name="Frame 75R Fore Cargo"> <!-- n=25 -->
   <weight unit="KG"> 100.0 </weight>
   <location name="POINTMASS" unit="M">
    <x> 43.5 </x>
    <y>  1.0 </y>
    <z> -8.7 </z>
   </location>
  </pointmass>

  <!-- 
  === Crew ===================================================
  -->
  <pointmass name="Watch Officer"> <!-- n=26 -->
   <weight unit="KG"> 85 </weight>
   <location unit="M">
    <x> 22.0 </x>
    <y>  0.5 </y>
    <z> -9.9 </z>
   </location>
  </pointmass>
  <pointmass name="Rudder Man"> <!-- n=27 -->
   <weight unit="KG"> 85 </weight>
   <location unit="M">
    <x> 20.5 </x>
    <y>  0.0 </y>
    <z> -9.9 </z>
   </location>
  </pointmass>
  <pointmass name="Elevator Man"> <!-- n=28 -->
   <weight unit="KG"> 85 </weight>
   <location unit="M">
    <x> 22.2 </x>
    <y> -0.5 </y>
    <z> -9.9 </z>
   </location>
  </pointmass>
  <pointmass name="Steward">  <!-- n=29 -->
   <weight unit="KG"> 85 </weight>
   <location unit="M">
    <x> 33.0 </x>
    <y>  0.5 </y>
    <z> -9.9 </z>
   </location>
  </pointmass>
  <pointmass name="Rigger"> <!-- n=30 -->
   <weight unit="KG"> 85 </weight>
   <location unit="M">
    <x> 51.0 </x>
    <y>  0.0 </y>
    <z> -8.4 </z>
   </location>
  </pointmass>

  <!-- 
  === Engines ================================================
  -->
  <pointmass name="Left Engine Car">
   <weight unit="KG"> 550.0 </weight>
   <location name="POINTMASS" unit="M">
    <x>  60.0 </x>
    <y>  -6.5 </y>
    <z> -10.0 </z>
   </location>
  </pointmass>
  <pointmass name="Right Engine Car">
   <weight unit="KG"> 550.0 </weight>
   <location name="POINTMASS" unit="M">
    <x>  60.0 </x>
    <y>   6.5 </y>
    <z> -10.0 </z>
   </location>
  </pointmass>
  <pointmass name="Aft Engine Car">
   <weight unit="KG"> 800.0 </weight>
   <location name="POINTMASS" unit="M">
    <x>  90.0 </x>
    <y>   0.0 </y>
    <z> -11.0 </z>
   </location>
  </pointmass>

  <!-- 
  === Structure ==============================================
  -->

  <pointmass name="Mooring cone">
   <!-- Pure guess. -->
   <weight unit="KG"> 200.0 </weight>
   <location name="POINTMASS" unit="M">
    <x>  0.0 </x>
    <y>  0.0 </y>
    <z>  0.0 </z>
   </location>
  </pointmass>
  <pointmass name="Control car">
   <!-- Pure guess. -->
   <weight unit="KG"> 3000.0 </weight>
   <location name="POINTMASS" unit="M">
    <x> 30.0 </x>
    <y>  0.0 </y>
    <z> -9.0 </z>
   </location>
  </pointmass>

 </mass_balance>

 <!--
 ==== Ground reactions ======================================================
 -->

 <ground_reactions>

  <!--
  === Landing gears ===================================================
  -->
  <contact type="BOGEY" name="CAR_BUMPER_BAG">
   <location unit="M">
    <x>  21.33 </x>
    <y>   0.00 </y>
    <z> -11.80 </z>
   </location>
   <static_friction>  0.8 </static_friction>
   <dynamic_friction> 0.5 </dynamic_friction>
   <rolling_friction> 0.5 </rolling_friction>
   <spring_coeff unit="N/M"> 50000 </spring_coeff>
   <damping_coeff unit="N/M/SEC"> 10000 </damping_coeff>
   <max_steer unit="DEG"> 0.0 </max_steer>
   <brake_group> NONE </brake_group>
   <retractable>0</retractable>
  </contact>

  <contact type="BOGEY" name="AFT_ENGINE_CAR_BUMPER_BAG">
   <location unit="M">
    <x>  90.00 </x>
    <y>   0.00 </y>
    <z> -12.70 </z>
   </location>
   <static_friction>  0.8 </static_friction>
   <dynamic_friction> 0.5 </dynamic_friction>
   <rolling_friction> 0.5 </rolling_friction>
   <spring_coeff unit="N/M"> 50000 </spring_coeff>
   <damping_coeff unit="N/M/SEC"> 10000 </damping_coeff>
   <max_steer unit="DEG"> 0.0 </max_steer>
   <brake_group> NONE </brake_group>
   <retractable>0</retractable>
  </contact>

  <!--
  === Other contact points ============================================
  -->
  <!-- These should induce structural failure. -->
  <contact type="STRUCTURE" name="NOSE">
   <location unit="M">
    <x> 0.0 </x>
    <y> 0.0 </y>
    <z> 0.0 </z>
   </location>
   <static_friction>  0.2 </static_friction>
   <dynamic_friction> 0.2 </dynamic_friction>
   <spring_coeff unit="N/M">      100000 </spring_coeff>
   <damping_coeff unit="N/M/SEC">  20000 </damping_coeff>
  </contact>

  <contact type="STRUCTURE" name="LEFT_ENGINE_CAR">
   <location unit="M">
    <x>  60.0 </x>
    <y>  -7.0 </y>
    <z> -11.0 </z>
   </location>
   <static_friction>  0.2 </static_friction>
   <dynamic_friction> 0.2 </dynamic_friction>
   <spring_coeff unit="N/M">      100000 </spring_coeff>
   <damping_coeff unit="N/M/SEC">  20000 </damping_coeff>
  </contact>

  <contact type="STRUCTURE" name="RIGHT_ENGINE_CAR">
   <location unit="M">
    <x>  60.0 </x>
    <y>   7.0 </y>
    <z> -11.0 </z>
   </location>
   <static_friction>  0.2 </static_friction>
   <dynamic_friction> 0.2 </dynamic_friction>
   <spring_coeff unit="N/M">      100000 </spring_coeff>
   <damping_coeff unit="N/M/SEC">  20000 </damping_coeff>
  </contact>

  <contact type="STRUCTURE" name="LOWER_FIN">
   <location unit="M">
    <x> 120.0 </x>
    <y>   0.0 </y>
    <z>  -8.0 </z>
   </location>
   <static_friction>  0.2 </static_friction>
   <dynamic_friction> 0.2 </dynamic_friction>
   <spring_coeff unit="N/M">      100000 </spring_coeff>
   <damping_coeff unit="N/M/SEC">  20000 </damping_coeff>
  </contact>

  <contact type="STRUCTURE" name="TAIL">
   <location unit="M">
    <x> 130.8 </x>
    <y>   0.0 </y>
    <z>   0.0 </z>
   </location>
   <static_friction>  0.2 </static_friction>
   <dynamic_friction> 0.2 </dynamic_friction>
   <spring_coeff unit="N/M">      100000 </spring_coeff>
   <damping_coeff unit="N/M/SEC">  20000 </damping_coeff>
  </contact>

 </ground_reactions>

 <!--
 ==== Propulsion ============================================================
 -->

 <propulsion>
 
  <documentation>
   4 Maybach Mb IVa high altitude engine.

   [Vissering:1922:ZS]:
     260 HP above 10000ft
     From engine performance table, assuming that Maybach 1918 is MbIVa:
     260 HP, 1400 RPM, 390 kg, 0.200 kg/(hp hr)

   [PK:1994:LZ120] for Bodensee:
     Side engines had a propeller diameter of 3.2 m
     The aft engine had a propeller diameter of 5.2 m geared down about 2:1.
     4 Maybach Mb IVa-Höhenleistungsmotoren (6 cylinder inline)
       190 kW max above 1800 m
       180 kW max below 1800 m
       2.2 kg/kW (implying an engine weight of 418kg)
       Specific fuel consumption: 270 g/kWh @ 1400 RPM
       Cruise consumption: about 45 kg/h (per engine)
     Power settings (page 46 on the Bodensee test flights):
       AK (all out):    1460 rpm (130.5 km/h @ 4 engines)
       Marsch (cruise): 1360 rpm (119.6 km/h @ 4 engines)

   [Flight:1918:MB, pp. 960 - 965, 995 - 1000]
     Technical description of captured Maybach 300 HP aircraft engine.
     Seems very similar to the Mb IVa.

     Bore:              165 mm
     Stroke:            180 mm (Computed from bore, compression ratio
                                and clearance volume)
     Compression ratio: 5.94:1
     Clearance volume:  778.9 cm^3

   [DR:1979:Bodensee]
     The side engines had reversing gear and no reduction gear.
     The rear engines had a 26:49 ratio reduction gear.

   [LD:1924:25YOAC, pages 78 - 79]
     Bore:              165 mm
     Stroke:            180 mm
     Compression ratio: 6.08:1
     "The performance of the engine on the ground was limited to 245 hp as at
      this level the carburettor was not yet fully open; full flow was not
      achieved until an altitude of 1800 m had been reached. Performance up to
      this height was consequently maintained at 245 hp. Fuel consumption was
      200 gm/hp hour. When dry the engine weighed 400 kg (1916), later 390 kg."
  </documentation>

  <!--
  === Engine ================================================
  -->
  <!-- Left engine -->
  <engine file="eng_Maybach_Mb_IVa">
   <feed>4</feed>
   <feed>6</feed>
   <feed>8</feed>
   <feed>10</feed>
   <thruster file="prop_Zeppelin3m">
    <location unit="M">
     <x>  62.5 </x>
     <y>  -6.5 </y>
     <z> -10.0 </z>
    </location>
    <orient unit="DEG">
     <roll>  0.0 </roll>
     <pitch> 0.0 </pitch>
     <yaw>   0.0 </yaw>
    </orient>
   </thruster>
  </engine>
  <!-- Right engine -->
  <engine file="eng_Maybach_Mb_IVa">
   <feed>5</feed>
   <feed>7</feed>
   <feed>9</feed>
   <feed>11</feed>
   <thruster file="prop_Zeppelin3m">
    <location unit="M">
     <x>  62.5 </x>
     <y>   6.5 </y>
     <z> -10.0 </z>
    </location>
    <orient unit="DEG">
     <roll>  0.0 </roll>
     <pitch> 0.0 </pitch>
     <yaw>   0.0 </yaw>
    </orient>
   </thruster>
  </engine>
  <!-- Aft engines -->
  <engine file="eng_Maybach_Mb_IVa">
   <feed>0</feed>
   <feed>1</feed>
   <feed>2</feed>
   <feed>3</feed>
   <thruster file="prop_Zeppelin3m">
    <location unit="M">
     <x>  92.50 </x>
     <y>   0.00 </y>
     <z> -11.20 </z>
    </location>
    <orient unit="DEG">
     <roll>  0.0 </roll>
     <pitch> 0.0 </pitch>
     <yaw>   0.0 </yaw>
    </orient>
   </thruster>
  </engine>
  <engine file="eng_Maybach_Mb_IVa">
   <feed>0</feed>
   <feed>1</feed>
   <feed>2</feed>
   <feed>3</feed>
   <thruster file="prop_Zeppelin3m">
    <location unit="M">
     <x>  92.50 </x>
     <y>   0.00 </y>
     <z> -11.20 </z>
    </location>
    <orient unit="DEG">
     <roll>  0.0 </roll>
     <pitch> 0.0 </pitch>
     <yaw>   0.0 </yaw>
    </orient>
   </thruster>
  </engine>

  <!--
  === Fuel tanks ============================================
  -->
  <documentation>
   Fuel tanks according to [Vissering:1922:ZS]:
   Along the keel walkway.
     Frame 40 (aft of)
       4x "Benzinfass" the two on the right jettisonable.
     Frame 50 (fore and aft of)
       4x "Benzinfass"
     Frame 70 (fore and aft of)
       4x "Benzinfass" all jettisonable.

   According to [PK:1994:LZ120] for Bodensee:
     12 "Benzinfass" of 260 l / 185 kg each.
     4  "Ölfass" of 60 kg each. One close each engine.
  </documentation>

  <!-- Tanks at frame 40. n = 0 - 3 -->
  <tank type="FUEL">
   <location unit="M">
    <x> 81.9 </x>
    <y> -0.8</y>
    <z> -7.8 </z>
   </location>
   <type>AVGAS</type>
   <capacity unit="KG"> 185.0 </capacity>
   <contents unit="KG"> 150.0 </contents>
  </tank>
  <tank type="FUEL">
   <location unit="M">
    <x> 81.9 </x>
    <y>  0.8</y>
    <z> -7.8 </z>
   </location>
   <type>AVGAS</type>
   <capacity unit="KG"> 185.0 </capacity>
   <contents unit="KG"> 150.0 </contents>
  </tank>
  <tank type="FUEL">
   <location unit="M">
    <x> 80.9 </x>
    <y> -0.8</y>
    <z> -7.8 </z>
   </location>
   <type>AVGAS</type>
   <capacity unit="KG"> 185.0 </capacity>
   <contents unit="KG"> 150.0 </contents>
  </tank>
  <tank type="FUEL">
   <location unit="M">
    <x> 80.9 </x>
    <y>  0.8</y>
    <z> -7.8 </z>
   </location>
   <type>AVGAS</type>
   <capacity unit="KG"> 185.0 </capacity>
   <contents unit="KG"> 150.0 </contents>
  </tank>

  <!-- Tanks at frame 50. n = 4 - 7 -->
  <tank type="FUEL">
   <location unit="M">
    <x> 71.5 </x>
    <y> -0.8</y>
    <z> -8.0 </z>
   </location>
   <type>AVGAS</type>
   <capacity unit="KG"> 185.0 </capacity>
   <contents unit="KG"> 150.0 </contents>
  </tank>
  <tank type="FUEL">
   <location unit="M">
    <x> 71.5 </x>
    <y>  0.8</y>
    <z> -8.0 </z>
   </location>
   <type>AVGAS</type>
   <capacity unit="KG"> 185.0 </capacity>
   <contents unit="KG"> 150.0 </contents>
  </tank>
  <tank type="FUEL">
   <location unit="M">
    <x> 68.5 </x>
    <y> -0.8</y>
    <z> -8.0 </z>
   </location>
   <type>AVGAS</type>
   <capacity unit="KG"> 185.0 </capacity>
   <contents unit="KG"> 150.0 </contents>
  </tank>
  <tank type="FUEL">
   <location unit="M">
    <x> 68.5 </x>
    <y>  0.8</y>
    <z> -8.0 </z>
   </location>
   <type>AVGAS</type>
   <capacity unit="KG"> 185.0 </capacity>
   <contents unit="KG"> 150.0 </contents>
  </tank>

  <!-- Tanks at frame 70. n = 8 - 11 -->
  <tank type="FUEL">
   <location unit="M">
    <x> 51.5 </x>
    <y> -0.8</y>
    <z> -8.0 </z>
   </location>
   <type>AVGAS</type>
   <capacity unit="KG"> 185.0 </capacity>
   <contents unit="KG"> 150.0 </contents>
  </tank>
  <tank type="FUEL">
   <location unit="M">
    <x> 51.5 </x>
    <y>  0.8</y>
    <z> -8.0 </z>
   </location>
   <type>AVGAS</type>
   <capacity unit="KG"> 185.0 </capacity>
   <contents unit="KG"> 150.0 </contents>
  </tank>
  <tank type="FUEL">
   <location unit="M">
    <x> 48.5 </x>
    <y> -0.8</y>
    <z> -8.0 </z>
   </location>
   <type>AVGAS</type>
   <capacity unit="KG"> 185.0 </capacity>
   <contents unit="KG"> 150.0 </contents>
  </tank>
  <tank type="FUEL">
   <location unit="M">
    <x> 48.5 </x>
    <y>  0.8</y>
    <z> -8.0 </z>
   </location>
   <type>AVGAS</type>
   <capacity unit="KG"> 185.0 </capacity>
   <contents unit="KG"> 150.0 </contents>
  </tank>

 </propulsion>

 <!--
 === Gas cell ==============================================================
 -->
 <system name="Gas heat exchange - external factors">
  <!-- External environment properties -->
  <!-- Not yet used. -->
  <property>environment/sun-angle-rad</property>
  <property>environment/sun-radiation-norm</property>

  <!-- Gas cell constants -->

  <!-- Base conductivity [lb / (K ft sec)] (Guess) -->
  <property value="0.05">buoyant_forces/heat-coeffs/base-conductivity</property>
  <!-- Emissivity [0,1] (Guess) -->
  <property value="0.1">buoyant_forces/heat-coeffs/emissivity</property>

  <channel name="Conductivity">

   <!-- The heat transfer to/from the cell should increase with the
        airflow over the cell (or over the hull surrounding the cell).
        Exactly how is still a mystery to me, so I'll just assume it is
        proportional to qbar for now.
   -->
   <fcs_function name="buoyant_forces/heat-coeffs/conductivity">
    <function>
     <sum>
      <property>buoyant_forces/heat-coeffs/base-conductivity</property>
      <product>
       <value>1.0</value>
       <property>aero/qbar-psf</property>
       <property>buoyant_forces/heat-coeffs/base-conductivity</property>
      </product>
     </sum>
    </function>
   </fcs_function>

  </channel>
 </system>
 <buoyant_forces>
  <documentation>
   According to [PK:1994:LZ120]:
     Total gas volume 22500m^3 in 13 cells.
     Each cell had a relief valve in the lower part (Bodensee).
     4 cells had maneuvering valves (Bodensee, before the lengthening).
  </documentation>

  <documentation>
   % Estimation of gas cell sizes and volumes.
   % 13 cells numbered 1 to 13 in aft to fore order.
   % Layout:
   %   fcf (frame cell frame) 
   %   r r (radius at frame)
   %    h  (width of cell)
   % Radius of cell ends from drawing in [Vissering:1922:ZS].
   %r = [1.2 2.9 5.3 6.9 8.0 8.6 9.0 9.2 9.2 9.1 8.7 7.9 6.2 2];
   %h = [6.4 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 9.0];
   % The first two cells are connected and have a single relief valve.
   r = [1.2 5.3 6.9 8.0 8.6 9.0 9.2 9.2 9.1 8.7 7.9 6.2 2];
   h = [16.4 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 9.0];

   % Assumption: Each cell is shaped like a frustum of right cone.
   %   s        = sqrt((r1 + r2)^2 + h^2)
   %   S_tot    = pi*(r1^2 + r2^2 + (r1 +r2)*s)
   %   S_mantel = pi*(r1 +r2)*s
   %   V        = pi*h/3 * (r1^2 + r1*r2 + r2^2)

   for i = 1:length(h)
     V(i) = pi*h(i)/3 * (r(i)^2 + r(i)*r(i+1) + r(i+1)^2);
     S_mantel(i) = pi*(r(i) +r(i+1))*sqrt((r(i) + r(i+1))^2 + h(i)^2);
   endfor
   
   % Radius of cylinder with same width and volume
   r_eq = sqrt(V./(pi.*h));

  </documentation>
  <limitations>
  </limitations>

  <!-- Gas cell constants -->
  <property value="3877.6">buoyant_forces/gas-cell[0]/external-area-ft2</property>
  <property value="6507.9">buoyant_forces/gas-cell[1]/external-area-ft2</property>
  <property value="9041.5">buoyant_forces/gas-cell[2]/external-area-ft2</property>
  <property value="10878.0">buoyant_forces/gas-cell[3]/external-area-ft2</property>
  <property value="12048.0">buoyant_forces/gas-cell[4]/external-area-ft2</property>
  <property value="12781.0">buoyant_forces/gas-cell[5]/external-area-ft2</property>
  <property value="13030.0">buoyant_forces/gas-cell[6]/external-area-ft2</property>
  <property value="12905.0">buoyant_forces/gas-cell[7]/external-area-ft2</property>
  <property value="12289.0">buoyant_forces/gas-cell[8]/external-area-ft2</property>
  <property value="10878.0">buoyant_forces/gas-cell[9]/external-area-ft2</property>
  <property value="8242.1">buoyant_forces/gas-cell[10]/external-area-ft2</property>
  <property value="3376.1">buoyant_forces/gas-cell[11]/external-area-ft2</property>

  <!-- Cell 1 and 2 -->
  <gas_cell type="HYDROGEN">
   <location unit="M">
    <x> 115.0 </x>
    <y> 0.0 </y>
    <z> 2.0 </z>
   </location>
   <x_width  unit="M"> 16.4 </x_width>
   <y_radius unit="M"> 3.46 </y_radius>
   <z_radius unit="M"> 3.46 </z_radius>
   <max_overpressure unit="PA"> 0.0 </max_overpressure> 
   <valve_coefficient unit="M4*SEC/KG"> 0.02 </valve_coefficient>
   <fullness> 0.95 </fullness>
   <!-- heat exchange with the environment. [lb ft / sec] -->
   <heat>
    <!-- Heat transfer due to temperature difference. -->
    <function name="buoyant_forces/gas-cell[0]/dU_conduction">
     <product>
      <property> buoyant_forces/heat-coeffs/conductivity </property>
      <property> buoyant_forces/gas-cell[0]/external-area-ft2 </property>
      <difference>
       <property> atmosphere/T-R </property>
       <property> buoyant_forces/gas-cell[0]/temp-R </property>
      </difference>
     </product>
    </function>
    <function name="buoyant_forces/gas-cell[0]/dU_radiation">
     <product>
      <value> 0.1714e-8 </value> <!-- Stefan-Boltzmann's constant
                                      [Btu / (h ft^2 R^4)] -->
      <property> buoyant_forces/heat-coeffs/emissivity </property>
      <property> buoyant_forces/gas-cell[0]/external-area-ft2 </property>
      <difference>
       <pow>
        <property> atmosphere/T-R </property>
        <value> 4.0 </value>
       </pow>
       <pow>
        <property> buoyant_forces/gas-cell[0]/temp-R </property>
        <value> 4.0 </value>
       </pow>
      </difference>
     </product>
    </function>
   </heat>
  </gas_cell>

  <!-- Cell 3 -->
  <gas_cell type="HYDROGEN">
   <location unit="M">
    <x> 105.0 </x>
    <y> 0.0 </y>
    <z> 3.0 </z>
   </location>
   <x_width  unit="M"> 10.0 </x_width>
   <y_radius unit="M"> 6.12 </y_radius>
   <z_radius unit="M"> 6.12 </z_radius>
   <max_overpressure unit="PA"> 0.0 </max_overpressure> 
   <valve_coefficient unit="M4*SEC/KG"> 0.02 </valve_coefficient>
   <fullness> 0.95 </fullness>
   <!-- heat exchange with the environment. [lb ft / sec] -->
   <heat>
    <!-- Heat transfer due to temperature difference. -->
    <function name="buoyant_forces/gas-cell[1]/dU_conduction">
     <product>
      <property> buoyant_forces/heat-coeffs/conductivity </property>
      <property> buoyant_forces/gas-cell[1]/external-area-ft2 </property>
      <difference>
       <property> atmosphere/T-R </property>
       <property> buoyant_forces/gas-cell[1]/temp-R </property>
      </difference>
     </product>
    </function>
    <function name="buoyant_forces/gas-cell[1]/dU_radiation">
     <product>
      <value> 0.1714e-8 </value> <!-- Stefan-Boltzmann's constant
                                      [Btu / (h ft^2 R^4)] -->
      <property> buoyant_forces/heat-coeffs/emissivity </property>
      <property> buoyant_forces/gas-cell[1]/external-area-ft2 </property>
      <difference>
       <pow>
        <property> atmosphere/T-R </property>
        <value> 4.0 </value>
       </pow>
       <pow>
        <property> buoyant_forces/gas-cell[1]/temp-R </property>
        <value> 4.0 </value>
       </pow>
      </difference>
     </product>
    </function>
   </heat>
  </gas_cell>

  <!-- Cell 4 -->
  <gas_cell type="HYDROGEN">
   <location unit="M">
    <x> 95.0 </x>
    <y> 0.0 </y>
    <z> 3.0 </z>
   </location>
   <x_width  unit="M"> 10.0 </x_width>
   <y_radius unit="M"> 7.46 </y_radius>
   <z_radius unit="M"> 7.46 </z_radius>
   <max_overpressure unit="PA"> 0.0 </max_overpressure> 
   <valve_coefficient unit="M4*SEC/KG"> 0.02 </valve_coefficient>
   <fullness> 0.95 </fullness>
   <!-- heat exchange with the environment. [lb ft / sec] -->
   <heat>
    <!-- Heat transfer due to temperature difference. -->
    <function name="buoyant_forces/gas-cell[2]/dU_conduction">
     <product>
      <property> buoyant_forces/heat-coeffs/conductivity </property>
      <property> buoyant_forces/gas-cell[2]/external-area-ft2 </property>
      <difference>
       <property> atmosphere/T-R </property>
       <property> buoyant_forces/gas-cell[2]/temp-R </property>
      </difference>
     </product>
    </function>
    <function name="buoyant_forces/gas-cell[2]/dU_radiation">
     <product>
      <value> 0.1714e-8 </value> <!-- Stefan-Boltzmann's constant
                                      [Btu / (h ft^2 R^4)] -->
      <property> buoyant_forces/heat-coeffs/emissivity </property>
      <property> buoyant_forces/gas-cell[2]/external-area-ft2 </property>
      <difference>
       <pow>
        <property> atmosphere/T-R </property>
        <value> 4.0 </value>
       </pow>
       <pow>
        <property> buoyant_forces/gas-cell[2]/temp-R </property>
        <value> 4.0 </value>
       </pow>
      </difference>
     </product>
    </function>
   </heat>
  </gas_cell>

  <!-- Cell 5 -->
  <gas_cell type="HYDROGEN">
   <location unit="M">
    <x> 85.0 </x>
    <y> 0.0 </y>
    <z> 3.0 </z>
   </location>
   <x_width  unit="M"> 10.0 </x_width>
   <y_radius unit="M"> 8.30 </y_radius>
   <z_radius unit="M"> 8.30 </z_radius>
   <max_overpressure unit="PA"> 0.0 </max_overpressure> 
   <valve_coefficient unit="M4*SEC/KG"> 0.02 </valve_coefficient>
   <fullness> 0.95 </fullness>
   <!-- heat exchange with the environment. [lb ft / sec] -->
   <heat>
    <!-- Heat transfer due to temperature difference. -->
    <function name="buoyant_forces/gas-cell[3]/dU_conduction">
     <product>
      <property> buoyant_forces/heat-coeffs/conductivity </property>
      <property> buoyant_forces/gas-cell[3]/external-area-ft2 </property>
      <difference>
       <property> atmosphere/T-R </property>
       <property> buoyant_forces/gas-cell[3]/temp-R </property>
      </difference>
     </product>
    </function>
    <function name="buoyant_forces/gas-cell[3]/dU_radiation">
     <product>
      <value> 0.1714e-8 </value> <!-- Stefan-Boltzmann's constant
                                      [Btu / (h ft^2 R^4)] -->
      <property> buoyant_forces/heat-coeffs/emissivity </property>
      <property> buoyant_forces/gas-cell[3]/external-area-ft2 </property>
      <difference>
       <pow>
        <property> atmosphere/T-R </property>
        <value> 4.0 </value>
       </pow>
       <pow>
        <property> buoyant_forces/gas-cell[3]/temp-R </property>
        <value> 4.0 </value>
       </pow>
      </difference>
     </product>
    </function>
   </heat>
  </gas_cell>

  <!-- Cell 6 -->
  <gas_cell type="HYDROGEN">
   <location unit="M">
    <x> 75.0 </x>
    <y> 0.0 </y>
    <z> 3.0 </z>
   </location>
   <x_width  unit="M"> 10.0 </x_width>
   <y_radius unit="M"> 8.80 </y_radius>
   <z_radius unit="M"> 8.80 </z_radius>
   <max_overpressure unit="PA"> 0.0 </max_overpressure> 
   <valve_coefficient unit="M4*SEC/KG"> 0.02 </valve_coefficient>
   <fullness> 0.95 </fullness>
   <!-- heat exchange with the environment. [lb ft / sec] -->
   <heat>
    <!-- Heat transfer due to temperature difference. -->
    <function name="buoyant_forces/gas-cell[4]/dU_conduction">
     <product>
      <property> buoyant_forces/heat-coeffs/conductivity </property>
      <property> buoyant_forces/gas-cell[4]/external-area-ft2 </property>
      <difference>
       <property> atmosphere/T-R </property>
       <property> buoyant_forces/gas-cell[4]/temp-R </property>
      </difference>
     </product>
    </function>
    <function name="buoyant_forces/gas-cell[4]/dU_radiation">
     <product>
      <value> 0.1714e-8 </value> <!-- Stefan-Boltzmann's constant
                                      [Btu / (h ft^2 R^4)] -->
      <property> buoyant_forces/heat-coeffs/emissivity </property>
      <property> buoyant_forces/gas-cell[4]/external-area-ft2 </property>
      <difference>
       <pow>
        <property> atmosphere/T-R </property>
        <value> 4.0 </value>
       </pow>
       <pow>
        <property> buoyant_forces/gas-cell[4]/temp-R </property>
        <value> 4.0 </value>
       </pow>
      </difference>
     </product>
    </function>
   </heat>
  </gas_cell>

  <!-- Cell 7 -->
  <gas_cell type="HYDROGEN">
   <location unit="M">
    <x> 65.0 </x>
    <y> 0.0 </y>
    <z> 3.0 </z>
   </location>
   <x_width  unit="M"> 10.0 </x_width>
   <y_radius unit="M"> 9.10 </y_radius>
   <z_radius unit="M"> 9.10 </z_radius>
   <max_overpressure unit="PA"> 0.0 </max_overpressure> 
   <valve_coefficient unit="M4*SEC/KG"> 0.02 </valve_coefficient>
   <fullness> 0.95 </fullness>
   <!-- heat exchange with the environment. [lb ft / sec] -->
   <heat>
    <!-- Heat transfer due to temperature difference. -->
    <function name="buoyant_forces/gas-cell[5]/dU_conduction">
     <product>
      <property> buoyant_forces/heat-coeffs/conductivity </property>
      <property> buoyant_forces/gas-cell[5]/external-area-ft2 </property>
      <difference>
       <property> atmosphere/T-R </property>
       <property> buoyant_forces/gas-cell[5]/temp-R </property>
      </difference>
     </product>
    </function>
    <function name="buoyant_forces/gas-cell[5]/dU_radiation">
     <product>
      <value> 0.1714e-8 </value> <!-- Stefan-Boltzmann's constant
                                      [Btu / (h ft^2 R^4)] -->
      <property> buoyant_forces/heat-coeffs/emissivity </property>
      <property> buoyant_forces/gas-cell[5]/external-area-ft2 </property>
      <difference>
       <pow>
        <property> atmosphere/T-R </property>
        <value> 4.0 </value>
       </pow>
       <pow>
        <property> buoyant_forces/gas-cell[5]/temp-R </property>
        <value> 4.0 </value>
       </pow>
      </difference>
     </product>
    </function>
   </heat>
  </gas_cell>

  <!-- Cell 8 -->
  <gas_cell type="HYDROGEN">
   <location unit="M">
    <x> 55.0 </x>
    <y> 0.0 </y>
    <z> 3.0 </z>
   </location>
   <x_width  unit="M"> 10.0 </x_width>
   <y_radius unit="M"> 9.20 </y_radius>
   <z_radius unit="M"> 9.20 </z_radius>
   <max_overpressure unit="PA"> 0.0 </max_overpressure> 
   <valve_coefficient unit="M4*SEC/KG"> 0.02 </valve_coefficient>
   <fullness> 0.95 </fullness>
   <!-- heat exchange with the environment. [lb ft / sec] -->
   <heat>
    <!-- Heat transfer due to temperature difference. -->
    <function name="buoyant_forces/gas-cell[6]/dU_conduction">
     <product>
      <property> buoyant_forces/heat-coeffs/conductivity </property>
      <property> buoyant_forces/gas-cell[6]/external-area-ft2 </property>
      <difference>
       <property> atmosphere/T-R </property>
       <property> buoyant_forces/gas-cell[6]/temp-R </property>
      </difference>
     </product>
    </function>
    <function name="buoyant_forces/gas-cell[6]/dU_radiation">
     <product>
      <value> 0.1714e-8 </value> <!-- Stefan-Boltzmann's constant
                                      [Btu / (h ft^2 R^4)] -->
      <property> buoyant_forces/heat-coeffs/emissivity </property>
      <property> buoyant_forces/gas-cell[6]/external-area-ft2 </property>
      <difference>
       <pow>
        <property> atmosphere/T-R </property>
        <value> 4.0 </value>
       </pow>
       <pow>
        <property> buoyant_forces/gas-cell[6]/temp-R </property>
        <value> 4.0 </value>
       </pow>
      </difference>
     </product>
    </function>
   </heat>
  </gas_cell>

  <!-- Cell 9 -->
  <gas_cell type="HYDROGEN">
   <location unit="M">
    <x> 45.0 </x>
    <y> 0.0 </y>
    <z> 3.0 </z>
   </location>
   <x_width  unit="M"> 10.0 </x_width>
   <y_radius unit="M"> 9.15 </y_radius>
   <z_radius unit="M"> 9.15 </z_radius>
   <max_overpressure unit="PA"> 0.0 </max_overpressure> 
   <valve_coefficient unit="M4*SEC/KG"> 0.02 </valve_coefficient>
   <fullness> 0.95 </fullness>
   <!-- heat exchange with the environment. [lb ft / sec] -->
   <heat>
    <!-- Heat transfer due to temperature difference. -->
    <function name="buoyant_forces/gas-cell[7]/dU_conduction">
     <product>
      <property> buoyant_forces/heat-coeffs/conductivity </property>
      <property> buoyant_forces/gas-cell[7]/external-area-ft2 </property>
      <difference>
       <property> atmosphere/T-R </property>
       <property> buoyant_forces/gas-cell[7]/temp-R </property>
      </difference>
     </product>
    </function>
    <function name="buoyant_forces/gas-cell[7]/dU_radiation">
     <product>
      <value> 0.1714e-8 </value> <!-- Stefan-Boltzmann's constant
                                      [Btu / (h ft^2 R^4)] -->
      <property> buoyant_forces/heat-coeffs/emissivity </property>
      <property> buoyant_forces/gas-cell[7]/external-area-ft2 </property>
      <difference>
       <pow>
        <property> atmosphere/T-R </property>
        <value> 4.0 </value>
       </pow>
       <pow>
        <property> buoyant_forces/gas-cell[7]/temp-R </property>
        <value> 4.0 </value>
       </pow>
      </difference>
     </product>
    </function>
   </heat>
  </gas_cell>

  <!-- Cell 10 -->
  <gas_cell type="HYDROGEN">
   <location unit="M">
    <x> 35.0 </x>
    <y> 0.0 </y>
    <z> 3.0 </z>
   </location>
   <x_width  unit="M"> 10.0 </x_width>
   <y_radius unit="M"> 8.90 </y_radius>
   <z_radius unit="M"> 8.90 </z_radius>
   <max_overpressure unit="PA"> 0.0 </max_overpressure> 
   <valve_coefficient unit="M4*SEC/KG"> 0.02 </valve_coefficient>
   <fullness> 0.95 </fullness>
   <!-- heat exchange with the environment. [lb ft / sec] -->
   <heat>
    <!-- Heat transfer due to temperature difference. -->
    <function name="buoyant_forces/gas-cell[8]/dU_conduction">
     <product>
      <property> buoyant_forces/heat-coeffs/conductivity </property>
      <property> buoyant_forces/gas-cell[8]/external-area-ft2 </property>
      <difference>
       <property> atmosphere/T-R </property>
       <property> buoyant_forces/gas-cell[8]/temp-R </property>
      </difference>
     </product>
    </function>
    <function name="buoyant_forces/gas-cell[8]/dU_radiation">
     <product>
      <value> 0.1714e-8 </value> <!-- Stefan-Boltzmann's constant
                                      [Btu / (h ft^2 R^4)] -->
      <property> buoyant_forces/heat-coeffs/emissivity </property>
      <property> buoyant_forces/gas-cell[8]/external-area-ft2 </property>
      <difference>
       <pow>
        <property> atmosphere/T-R </property>
        <value> 4.0 </value>
       </pow>
       <pow>
        <property> buoyant_forces/gas-cell[8]/temp-R </property>
        <value> 4.0 </value>
       </pow>
      </difference>
     </product>
    </function>
   </heat>
  </gas_cell>

  <!-- Cell 11 -->
  <gas_cell type="HYDROGEN">
   <location unit="M">
    <x> 25.0 </x>
    <y> 0.0 </y>
    <z> 3.0 </z>
   </location>
   <x_width  unit="M"> 10.0 </x_width>
   <y_radius unit="M"> 8.30 </y_radius>
   <z_radius unit="M"> 8.30 </z_radius>
   <max_overpressure unit="PA"> 0.0 </max_overpressure> 
   <valve_coefficient unit="M4*SEC/KG"> 0.02 </valve_coefficient>
   <fullness> 0.95 </fullness>
   <!-- heat exchange with the environment. [lb ft / sec] -->
   <heat>
    <!-- Heat transfer due to temperature difference. -->
    <function name="buoyant_forces/gas-cell[9]/dU_conduction">
     <product>
      <property> buoyant_forces/heat-coeffs/conductivity </property>
      <property> buoyant_forces/gas-cell[9]/external-area-ft2 </property>
      <difference>
       <property> atmosphere/T-R </property>
       <property> buoyant_forces/gas-cell[9]/temp-R </property>
      </difference>
     </product>
    </function>
    <function name="buoyant_forces/gas-cell[9]/dU_radiation">
     <product>
      <value> 0.1714e-8 </value> <!-- Stefan-Boltzmann's constant
                                      [Btu / (h ft^2 R^4)] -->
      <property> buoyant_forces/heat-coeffs/emissivity </property>
      <property> buoyant_forces/gas-cell[9]/external-area-ft2 </property>
      <difference>
       <pow>
        <property> atmosphere/T-R </property>
        <value> 4.0 </value>
       </pow>
       <pow>
        <property> buoyant_forces/gas-cell[9]/temp-R </property>
        <value> 4.0 </value>
       </pow>
      </difference>
     </product>
    </function>
   </heat>
  </gas_cell>

  <!-- Cell 12 -->
  <gas_cell type="HYDROGEN">
   <location unit="M">
    <x> 15.0 </x>
    <y> 0.0 </y>
    <z> 3.0 </z>
   </location>
   <x_width  unit="M"> 10.0 </x_width>
   <y_radius unit="M"> 7.07 </y_radius>
   <z_radius unit="M"> 7.07 </z_radius>
   <max_overpressure unit="PA"> 0.0 </max_overpressure> 
   <valve_coefficient unit="M4*SEC/KG"> 0.02 </valve_coefficient>
   <fullness> 0.95 </fullness>
   <!-- heat exchange with the environment. [lb ft / sec] -->
   <heat>
    <!-- Heat transfer due to temperature difference. -->
    <function name="buoyant_forces/gas-cell[10]/dU_conduction">
     <product>
      <property> buoyant_forces/heat-coeffs/conductivity </property>
      <property> buoyant_forces/gas-cell[10]/external-area-ft2 </property>
      <difference>
       <property> atmosphere/T-R </property>
       <property> buoyant_forces/gas-cell[10]/temp-R </property>
      </difference>
     </product>
    </function>
    <function name="buoyant_forces/gas-cell[10]/dU_radiation">
     <product>
      <value> 0.1714e-8 </value> <!-- Stefan-Boltzmann's constant
                                      [Btu / (h ft^2 R^4)] -->
      <property> buoyant_forces/heat-coeffs/emissivity </property>
      <property> buoyant_forces/gas-cell[10]/external-area-ft2 </property>
      <difference>
       <pow>
        <property> atmosphere/T-R </property>
        <value> 4.0 </value>
       </pow>
       <pow>
        <property> buoyant_forces/gas-cell[10]/temp-R </property>
        <value> 4.0 </value>
       </pow>
      </difference>
     </product>
    </function>
   </heat>
  </gas_cell>

  <!-- Cell 13 -->
  <gas_cell type="HYDROGEN">
   <location unit="M">
    <x> 5.0 </x>
    <y> 0.0 </y>
    <z> 2.0 </z>
   </location>
   <x_width  unit="M"> 9.0 </x_width>
   <y_radius unit="M"> 7.07 </y_radius>
   <z_radius unit="M"> 7.07 </z_radius>
   <max_overpressure unit="PA"> 0.0 </max_overpressure> 
   <valve_coefficient unit="M4*SEC/KG"> 0.02 </valve_coefficient>
   <fullness> 0.95 </fullness>
   <!-- heat exchange with the environment. [lb ft / sec] -->
   <heat>
    <!-- Heat transfer due to temperature difference. -->
    <function name="buoyant_forces/gas-cell[11]/dU_conduction">
     <product>
      <property> buoyant_forces/heat-coeffs/conductivity </property>
      <property> buoyant_forces/gas-cell[11]/external-area-ft2 </property>
      <difference>
       <property> atmosphere/T-R </property>
       <property> buoyant_forces/gas-cell[11]/temp-R </property>
      </difference>
     </product>
    </function>
    <function name="buoyant_forces/gas-cell[11]/dU_radiation">
     <product>
      <value> 0.1714e-8 </value> <!-- Stefan-Boltzmann's constant
                                      [Btu / (h ft^2 R^4)] -->
      <property> buoyant_forces/heat-coeffs/emissivity </property>
      <property> buoyant_forces/gas-cell[11]/external-area-ft2 </property>
      <difference>
       <pow>
        <property> atmosphere/T-R </property>
        <value> 4.0 </value>
       </pow>
       <pow>
        <property> buoyant_forces/gas-cell[11]/temp-R </property>
        <value> 4.0 </value>
       </pow>
      </difference>
     </product>
    </function>
   </heat>
  </gas_cell>

 </buoyant_forces>

 <!--
 ==== Ballast controls ======================================================
 -->
 <!-- system file="ballast-jsbsim"/ -->

 <!--
 ==== Initial static condition weigh-off ====================================
 -->
 <system name="Weight, lift and balance">
  <channel name="static-condition">
   <!-- This system ensures that the ship starts slightly heavy. -->
   <!-- The weight of inertia/pointmass-weight-lbs[0] is set from Nasal. -->

   <summer name="static-condition/net-lift-lbs">
    <input>buoyant_forces/gas-cell[0]/buoyancy-lbs</input>
    <input>buoyant_forces/gas-cell[1]/buoyancy-lbs</input>
    <input>buoyant_forces/gas-cell[2]/buoyancy-lbs</input>
    <input>buoyant_forces/gas-cell[3]/buoyancy-lbs</input>
    <input>buoyant_forces/gas-cell[4]/buoyancy-lbs</input>
    <input>buoyant_forces/gas-cell[5]/buoyancy-lbs</input>
    <input>buoyant_forces/gas-cell[6]/buoyancy-lbs</input>
    <input>buoyant_forces/gas-cell[7]/buoyancy-lbs</input>
    <input>buoyant_forces/gas-cell[8]/buoyancy-lbs</input>
    <input>buoyant_forces/gas-cell[9]/buoyancy-lbs</input>
    <input>buoyant_forces/gas-cell[10]/buoyancy-lbs</input>
    <input>buoyant_forces/gas-cell[11]/buoyancy-lbs</input>
    <input>-inertia/weight-lbs</input>
   </summer>

   <fcs_function name="static-condition/static-pitch-moment-lbsft">
    <function>
     <sum>
      <product>
       <property>buoyant_forces/gas-cell[0]/buoyancy-lbs</property>
       <sum>
        <value>-377.29659</value>
        <product>
         <value>0.083333333</value>
         <property>inertia/cg-x-in</property>
        </product>
       </sum>
      </product>
      <product>
       <property>buoyant_forces/gas-cell[1]/buoyancy-lbs</property>
       <sum>
        <value>-344.48819</value>
        <product>
         <value>0.083333333</value>
         <property>inertia/cg-x-in</property>
        </product>
       </sum>
      </product>
      <product>
       <property>buoyant_forces/gas-cell[2]/buoyancy-lbs</property>
       <sum>
        <value>-311.67979</value>
        <product>
         <value>0.083333333</value>
         <property>inertia/cg-x-in</property>
        </product>
       </sum>
      </product>
      <product>
       <property>buoyant_forces/gas-cell[3]/buoyancy-lbs</property>
       <sum>
        <value>-278.87139</value>
        <product>
         <value>0.083333333</value>
         <property>inertia/cg-x-in</property>
        </product>
       </sum>
      </product>
      <product>
       <property>buoyant_forces/gas-cell[4]/buoyancy-lbs</property>
       <sum>
        <value>-246.06299</value>
        <product>
         <value>0.083333333</value>
         <property>inertia/cg-x-in</property>
        </product>
       </sum>
      </product>
      <product>
       <property>buoyant_forces/gas-cell[5]/buoyancy-lbs</property>
       <sum>
        <value>-213.25459</value>
        <product>
         <value>0.083333333</value>
         <property>inertia/cg-x-in</property>
        </product>
       </sum>
      </product>
      <product>
       <property>buoyant_forces/gas-cell[6]/buoyancy-lbs</property>
       <sum>
        <value>-180.44619</value>
        <product>
         <value>0.083333333</value>
         <property>inertia/cg-x-in</property>
        </product>
       </sum>
      </product>
      <product>
       <property>buoyant_forces/gas-cell[7]/buoyancy-lbs</property>
       <sum>
        <value>-147.6378</value>
        <product>
         <value>0.083333333</value>
         <property>inertia/cg-x-in</property>
        </product>
       </sum>
      </product>
      <product>
       <property>buoyant_forces/gas-cell[8]/buoyancy-lbs</property>
       <sum>
        <value>-114.8294</value>
        <product>
         <value>0.083333333</value>
         <property>inertia/cg-x-in</property>
        </product>
       </sum>
      </product>
      <product>
       <property>buoyant_forces/gas-cell[9]/buoyancy-lbs</property>
       <sum>
        <value>-82.020997</value>
        <product>
         <value>0.083333333</value>
         <property>inertia/cg-x-in</property>
        </product>
       </sum>
      </product>
      <product>
       <property>buoyant_forces/gas-cell[10]/buoyancy-lbs</property>
       <sum>
        <value>-49.212598</value>
        <product>
         <value>0.083333333</value>
         <property>inertia/cg-x-in</property>
        </product>
       </sum>
      </product>
      <product>
       <property>buoyant_forces/gas-cell[11]/buoyancy-lbs</property>
       <sum>
        <value>-16.404199</value>
        <product>
         <value>0.083333333</value>
         <property>inertia/cg-x-in</property>
        </product>
       </sum>
      </product>
     </sum>
    </function>
   </fcs_function>

  </channel>
 </system>

 <!--
 ==== Flight control system =================================================
 -->

 <flight_control name="FCS">

  <documentation>
   According to [DR:1979:Bodensee] the rudder deflections were +/- 20 deg.
  </documentation>

  <!--
  === Pitch ==================================================
  -->
  <channel name="Pitch">

   <!-- pid name="fcs/elevator-pos-cmd-norm">
    <input>fcs/elevator-cmd-norm</input>
    <kp> 0.0 </kp>
    <ki> 0.4 </ki>
   </pid -->

   <summer name="fcs/elevator/pos-cmd-norm">
    <input>fcs/elevator-cmd-norm</input>
    <input>fcs/pitch-trim-cmd-norm</input>
    <input>crew/elevatorman/elevator-cmd-norm</input>
    <clipto>
     <min>-1</min>
     <max>1</max>
    </clipto>
   </summer>

   <aerosurface_scale name="fcs/elevator/pos-rad">
    <input>fcs/elevator/pos-cmd-norm</input>
    <domain>
     <min>-1</min>
     <max>1</max>
    </domain>
    <range>
     <min>-0.3491</min>
     <max>0.3491</max>
    </range>
    <output>fcs/elevator-pos-rad</output>
   </aerosurface_scale>

   <aerosurface_scale name="fcs/elevator/pos-norm">
    <input>fcs/elevator-pos-rad</input>
    <domain>
     <min>-0.3491</min>
     <max>0.3491</max>
    </domain>
    <range>
     <min>-1</min>
     <max>1</max>
    </range>
    <output>fcs/elevator-pos-norm</output>
   </aerosurface_scale>
  </channel>

  <!--
  === Yaw ====================================================
  -->
  <channel name="Yaw">

   <!-- pid name="fcs/rudder/pos-cmd-norm">
    <input>-fcs/aileron-cmd-norm</input>
    <kp> 0.0 </kp>
    <ki> 0.2 </ki>
   </pid -->

   <summer name="fcs/rudder/pos-cmd-norm">
    <input>-fcs/aileron-cmd-norm</input>
    <input>fcs/rudder-cmd-norm</input>
    <input>fcs/yaw-trim-cmd-norm</input>
    <input>crew/helmsman/rudder-cmd-norm</input>
    <clipto>
     <min>-1</min>
     <max>1</max>
    </clipto>
   </summer>

   <aerosurface_scale name="fcs/rudder/pos-rad">
    <input>fcs/rudder/pos-cmd-norm</input>
    <domain>
     <min>-1</min>
     <max>1</max>
    </domain>
    <range>
     <min>-0.3491</min>
     <max>0.3491</max>
    </range>
    <output>fcs/rudder-pos-rad</output>
   </aerosurface_scale>

   <aerosurface_scale name="fcs/rudder/pos-norm">
    <input>fcs/rudder-pos-rad</input>
    <domain>
     <min>-0.3491</min>
     <max>0.3491</max>
    </domain>
    <range>
     <min>-1</min>
     <max>1</max>
    </range>
    <output>fcs/rudder-pos-norm</output>
   </aerosurface_scale>

  </channel>

 </flight_control>

 <!--
 ==== External reactions ====================================================
 -->

 <external_reactions>

  <force name="mooring-coupling-north" frame="LOCAL">
   <location unit="M">
    <x> 0.0 </x>
    <y> 0.0 </y>
    <z> 0.0 </z>
   </location>
   <direction>
    <x> 1.0 </x>
    <y> 0.0 </y>
    <z> 0.0 </z>
   </direction>
  </force>
  <force name="mooring-coupling-east" frame="LOCAL">
   <location unit="M">
    <x> 0.0 </x>
    <y> 0.0 </y>
    <z> 0.0 </z>
   </location>
   <direction>
    <x> 0.0 </x>
    <y> 1.0 </y>
    <z> 0.0 </z>
   </direction>
  </force>
  <force name="mooring-coupling-down" frame="LOCAL">
   <location unit="M">
    <x> 0.0 </x>
    <y> 0.0 </y>
    <z> 0.0 </z>
   </location>
   <direction>
    <x> 0.0 </x>
    <y> 0.0 </y>
    <z> 1.0 </z>
   </direction>
  </force>

  <force name="added-mass-bx" frame="BODY">
   <location unit="M">
    <x> 56.4 </x>
    <y>  0.0 </y>
    <z> -5.7 </z>
   </location>
   <direction>
    <x> 1.0 </x>
    <y> 0.0 </y>
    <z> 0.0 </z>
   </direction>
  </force>
  <force name="added-mass-by" frame="BODY">
   <location unit="M">
    <x> 56.4 </x>
    <y>  0.0 </y>
    <z> -5.7 </z>
   </location>
   <direction>
    <x> 0.0 </x>
    <y> 1.0 </y>
    <z> 0.0 </z>
   </direction>
  </force>
  <force name="added-mass-bz" frame="BODY">
   <location unit="M">
    <x> 56.4 </x>
    <y>  0.0 </y>
    <z> -5.7 </z>
   </location>
   <direction>
    <x> 0.0 </x>
    <y> 0.0 </y>
    <z> 1.0 </z>
   </direction>
  </force>

  <moment name="added-mass-pitch" frame="BODY" unit="LBSFT">
   <direction>
    <x> 0.0 </x>
    <y> 1.0 </y>
    <z> 0.0 </z>
   </direction>
  </moment>
  <moment name="added-mass-roll" frame="BODY" unit="LBSFT">
   <direction>
    <x> 1.0 </x>
    <y> 0.0 </y>
    <z> 0.0 </z>
   </direction>
  </moment>
  <moment name="added-mass-yaw" frame="BODY" unit="LBSFT">
   <direction>
    <x> 0.0 </x>
    <y> 0.0 </y>
    <z> 1.0 </z>
   </direction>
  </moment>

 </external_reactions>

 <system file="visual-reference-point-extensions"/>
 <system file="airship-mooring">

  <!-- Configuration -->
  <!--  Mooring -->
  <property value="10000.0"> mooring/mooring-spring-coeff-lbs_ft </property>
  <property value="-3000.0"> mooring/mooring-damping-coeff-lbs_fps </property>
  <property value="100000.0"> mooring/max-mooring-force-lbs </property>
  <!--  Wire -->
  <property value="250.0"> mooring/wire-spring-coeff-lbs_ft </property>
  <property value="10000.0"> mooring/max-wire-force-lbs </property>
  <property value="5.0"> mooring/max-winch-speed-fps </property>

 </system>
 
 <!--
 ==== Aerodynamics ==========================================================
 -->
 <system name="constants">

  <!-- Aerodynamic constants. -->
  <property value="429.1"> aero/constants/length-ft </property>
  <property value="61.4"> aero/constants/diameter-ft </property>
  <property value="188201.6"> aero/constants/length-diameter-ft2 </property>
  <property value="796345.7"> aero/constants/volume-ft3 </property>
  <property value="8591.5"> aero/constants/volume-ft3_2_3 </property>

  <!-- Added mass constants. -->
  <!-- k-axial 0.02; k-transverse 0.94; k-rotational 0.81 -->
  <property value="0.02"> aero/constants/added-mass/k-axial </property>
  <property value="0.94"> aero/constants/added-mass/k-transverse </property>
  <property value="0.81"> aero/constants/added-mass/k-rotational </property>

  <channel name="Temporary hack to prevent oscillations.">
   <fcs_function name="aero/constants/added-mass/tweak-factor">
    <function>
     <difference>
      <value> 1.0 </value>
      <property> mooring/moored </property>
     </difference>
    </function>
    <clipto>
     <min> 0.0 </min>
     <max> 1.0 </max>
    </clipto>
   </fcs_function>
  </channel>

 </system>

 <system file="airship_added_mass"/>

 <system file="crew-jsbsim"/>
 <system file="shadow-jsbsim"/>

 <!-- aerodynamics file="Systems/gerris_aero"/ -->
 <aerodynamics file="Systems/datcom_aero"/>

</fdm_config>