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JSBSim uses thruster models to convert engine power into aerodynamic forces. The following table shows which engine-thruster combinations work.
'''[[JSBSim]]''' uses '''thruster''' models to convert engine power into aerodynamic forces. The following table shows which engine-thruster combinations work.
{| class="wikitable" style="text-align:center;"
 
|
{| class="wikitable" style="text-align:center;border: none; background: none;"
|-
! colspan="2" rowspan="2" style="border: none; background: none;" |
! colspan=4 | Thrusters
|-
| style="width:60px;" | [[JSBSim Thrusters#FGDirect|Direct]]  
| style="width:60px;" | [[JSBSim Thrusters#FGDirect|Direct]]  
| style="width:60px;" | [[JSBSim Thrusters#FGNozzle|Nozzle]]
| style="width:60px;" | [[JSBSim Thrusters#FGNozzle|Nozzle]]
Line 7: Line 11:
| style="width:60px;" | [[JSBSim Thrusters#FGRotor|Rotor]]  
| style="width:60px;" | [[JSBSim Thrusters#FGRotor|Rotor]]  
|-
|-
! rowspan=5 | Engines
|[[JSBSim Engines#FGElectric|Electric]]
|[[JSBSim Engines#FGElectric|Electric]]
| style="background-color: #FF3333;" |
| style="background-color: #33FF33;" |
| style="background-color: #FF3333;" |
| style="background-color: #FF3333;" |
| style="background-color: #33FF33;" |
| style="background-color: #33FF33;" |
Line 39: Line 44:


== FGDirect ==
== FGDirect ==
Thrust is computed directly by the engine, the direct thruster file is a stub. Currently only the FGTurbine engine uses this thruster.
Thrust is computed directly by the engine, the direct thruster file is a stub. Currently FGTurbine engines use this thruster and it can also be used with FGElectric.
=== Configuration File Format ===
 
=== Configuration file format ===
This is the complete configuration file. Copy and paste into your 'direct.xml' file.
This is the complete configuration file. Copy and paste into your 'direct.xml' file.
<syntaxhighlight lang="xml">
<syntaxhighlight lang="xml">
Line 47: Line 53:
</direct>  
</direct>  
</syntaxhighlight>
</syntaxhighlight>
=== Notes ===
=== Notes ===
* The direct thruster creates a property called propulsion/engine[#]/reverser-angle-rad
* The direct thruster creates a property called propulsion/engine[#]/reverser-angle-rad
Line 53: Line 60:
== FGNozzle ==
== FGNozzle ==
FGNozzle is for the FGRocket engine.
FGNozzle is for the FGRocket engine.
=== Configuration File Format ===
 
=== Configuration file format ===
<syntaxhighlight lang="xml">
<syntaxhighlight lang="xml">
<?xml version="1.0"?>  
<?xml version="1.0"?>  
Line 60: Line 68:
</nozzle>
</nozzle>
</syntaxhighlight>
</syntaxhighlight>
=== Parameter definitions ===
=== Parameter definitions ===
{| class="prettytable"
{| class="prettytable"
Line 66: Line 75:
|Nozzle area at the exit plane.
|Nozzle area at the exit plane.
|}
|}
=== Notes ===
=== Notes ===
* All parameters MUST be specified.
* All parameters MUST be specified.
* The area specified times the sea level pressure (2117 lbf/ft^2) is the amount thrust is reduced at sea level


== FGPropeller ==
== FGPropeller ==
FGPropeller models a propeller given the tabular data for Ct and Cp, indexed by the advance ratio "J".  
FGPropeller models a propeller given the tabular data for Ct and Cp, indexed by the advance ratio "J".
=== Configuration File Format ===
 
=== Configuration file format ===
<syntaxhighlight lang="xml">
<syntaxhighlight lang="xml">
<!-- Sense goes in the parent tag -->
<!-- Sense and P factor go in the parent tag of the propeller, i.e. in the <thruster> element -->
<sense> {1 | -1} </sense>  
<sense> {1 | -1} </sense>  
<p_factor> {number} </p_factor>
<?xml version="1.0"?>  
<?xml version="1.0"?>  
<propeller name="{string}">
<propeller name="{string}">
Line 87: Line 101:
   <constspeed> {number} </constspeed>
   <constspeed> {number} </constspeed>
   <reversepitch> {number} </reversepitch>
   <reversepitch> {number} </reversepitch>
  <p_factor> {number} </p_factor>
   <ct_factor> {number} </ct_factor>
   <ct_factor> {number} </ct_factor>
   <cp_factor> {number} </cp_factor>
   <cp_factor> {number} </cp_factor>
Line 114: Line 127:
     </tableData>
     </tableData>
   </table>
   </table>


</propeller>
</propeller>
</syntaxhighlight>
</syntaxhighlight>
=== Parameter definitions ===
=== Parameter definitions ===
{| class="prettytable"
{| class="prettytable"
|-
|-
|ixx
| valign="top" | ixx
|Propeller rotational inertia. (Note: This appears to be in metric units, kg * meters^2, for a thin rod of mass m (kg) and diameter D (meters) spinning about its center, formula is m*D^2/12. See the [http://en.wikipedia.org/wiki/List_of_moments_of_inertia Moments of inertia reference page] and [http://www.engineeringtoolbox.com/moment-inertia-torque-d_913.html list of conversion factors for different units for moment of inertia].)
|Propeller rotational inertia. This can be english units, slug & feet^2:
 
<ixx unit="SLUG*FT2">      8.95 </ixx>
 
Or in metric units, kg * meters^2:
 
<ixx unit="KG*M2">        12.14 </ixx>
 
For a thin rod of mass m (kg) and diameter D (meters) spinning about its center, the formula is m*D^2/12. See the [http://en.wikipedia.org/wiki/List_of_moments_of_inertia Moments of inertia reference page] and [http://www.engineeringtoolbox.com/moment-inertia-torque-d_913.html list of conversion factors for different units for moment of inertia].)
|-
|-
|diameter
|diameter
Line 152: Line 173:
|-
|-
|sense
|sense
|Direction of rotation (1=clockwise as viewed from cockpit, -1=anti-clockwise as viewed from cockpit). Sense is specified in the parent tag of the propeller.
|Direction of rotation (1= clockwise as viewed from rear, -1=counter-clockwise as viewed from rear). Sense is specified in the parent tag of the propeller. ''See [[JSBSim_Thrusters#Sense_bug_affecting_gyroscopic_moment|important note below]] regarding a JSBSim bug affecting sense and the direction of the resulting gyroscopic moment.''
|-
|-
|p_factor
|p_factor
|P factor.
|P factor. It is specified in the parent tag of the propeller.
|-
|-
|ct_factor
|ct_factor
|A multiplier for the coefficients of thrust.
|A multiplier for the coefficients of thrust (multiplies the dependent variable in the C_THRUST table by this factor).
|-
|-
|cp_factor
|cp_factor
|A multiplier for the coefficients of power.
|A multiplier for the coefficients of power (multiplies the dependent variable in the C_POWER table by this factor).
|}
|}
The parameters <sense> and <p_factor> must be specified at the parent level i.e. in the <thruster> element. This allows to specify different sense and P factor values for each propeller of the model while using the same definition file for all the propellers.
=== C_THRUST and C_POWER tables ===
The C_THRUST and C_POWER tables are required.
The independent variable for both tables is [http://en.wikipedia.org/wiki/Advance_ratio Advance Ratio] (J). The dependent variable is the coefficient of thrust (Ct) for the C_THRUST and the coefficient of power (Cp) for C_POWER.
For variable pitch propellers, it is possible to give a two-dimensional table, showing Ct and Cp for different J and different pitch angles of the propeller.  See example below.
[http://www.mh-aerotools.de/airfoils/pylonprops_1.htm Propellors for F3D Models explains the theory] and has [http://www.mh-aerotools.de/airfoils/pylonprops_2.htm formulas] and [http://www.mh-aerotools.de/airfoils/pylonprops_3.htm many graphs] showing the relationship between J, Ct, and Cp.
Relevant formulas relating the variables in the tables (and metric system units):
* Thrust: T = Ct * rho * n^2 * D^4
* Power: P = Cp * rho * n^3 * D^5)
* Advance Ratio: J = v/(n*D)
* Efficiency: eta = Ct/Cp * v/(n*D) (or equivalently, eta = Ct/Cp * J )
In the formulas
* Ct = coefficient of thrust
* Cp = coefficient of power
* v = true velocity of aircraft (m/s)
* D = diameter of propeller disk (m)
* n = rotations per second (1/s) (note RPS, not RPM)
* rho = density of air (kg/m^3)
* P = power (W)
* T = thrust (N)
For a typical propeller, both Cp and Ct are downward sloping curves that reach 0 when J is somewhere in the range 0-4 (depending on blade angle and other factors). Cp and Ct can be negative; this indicates the drag induced by the prop when the airspeed is relatively fast compared with prop RPM. At higher pitch angles Ct may have a positive slope or be flat in the lower J range.
Ct/Cp gives the efficiency (eta), and propeller shape and general design give each propeller a distinctive [http://www.mh-aerotools.de/airfoils/pylonprops_3.htm efficiency curve]. For fixed-pitch propellers, the propeller is generally designed to reach peak efficiency either at climb velocity & RPM, cruise velocity and RPM, or some compromise between the two.  [http://en.wikipedia.org/wiki/Controllable_pitch_propeller Variable pitch propellers] and [http://en.wikipedia.org/wiki/Constant_speed_propeller constant speed propellers] bring different factors into play.
Note that several of the values mentioned above can be viewed while FG is running, in the property tree under /fdm/jsbsim/propulsion/engine.  This is useful for seeing how the settings and tables play out under various conditions and fine-tuning the settings.
==== Sample C_THRUST and C_POWER tables ====
These example tables are from FlightGear's C172P aircraft:
<syntaxhighlight lang="xml">
  <table name="C_THRUST" type="internal">
      <tableData>
        0.0    0.068
        0.1    0.068
        0.2    0.067
        0.3    0.066
        0.4    0.064
        0.5    0.062
        0.6    0.059
        0.7    0.054
        0.8    0.043
        0.9    0.031
        1.0    0.019
        1.1    0.008
        1.2  -0.001
        1.3  -0.008
        1.4  -0.019
        1.5  -0.029
        1.6  -0.040
        1.7  -0.050
        1.8  -0.057
        1.9  -0.061
        2.0  -0.064
        2.1  -0.066
        2.2  -0.067
        2.3  -0.068
        5.0  -0.068
      </tableData>
    </table>
 
    <table name="C_POWER" type = "internal">
      <tableData>
        0.0  0.0580
        0.1  0.0620
        0.2  0.0600
        0.3  0.0580
        0.4  0.0520
        0.5  0.0457
        0.6  0.0436
        0.7  0.0420
        0.8  0.0372
        0.9  0.0299
        1.0  0.0202
        1.1  0.0111
        1.2  0.0075
        1.3  0.0111
        1.4  0.0202
        1.5  0.0280
        1.6  0.0346
        1.7  0.0389
        1.8  0.0421
        1.9  0.0436
        2.0  0.0445
        2.1  0.0445
        2.2  0.0442
        2.3  0.0431
        2.4  0.0424
        5.0  0.0413
      </tableData>
    </table>
</syntaxhighlight>
Example of table for variable pitch propeller ([http://www.mail-archive.com/flightgear-devel@lists.sourceforge.net/msg32187.html source]):
<syntaxhighlight lang="xml">
<!-- thrust coefficient as a function of advance ratio and blade angle -->
    <table name="C_THRUST" type="internal">
        <tableData>
                  -10        0        15        25        35        45        55        65      90
        -0.2      -0.0734    0.0413    0.1503    0.1842    0.2030    0.2142    0.1974    0.1691  0.0000
        0.0      -0.1090    0.0000    0.1503    0.1842    0.2030    0.2162    0.2021    0.1691  0.0000
        0.2      -0.1222  -0.0376    0.1297    0.1804    0.2001    0.2162    0.2021    0.1691  0.0000
        0.4      -0.1222  -0.0873    0.0977    0.1786    0.1963    0.2142    0.2021    0.1691  0.0000
        0.6      -0.1222  -0.1222    0.0517    0.1607    0.1879    0.2087    0.1992    0.1691  0.0000
        0.8      -0.1222  -0.1222    0.0029    0.1203    0.1824    0.2012    0.1992    0.1691  0.0000
        1.0      -0.1222  -0.1222  -0.0489    0.0734    0.1748    0.1908    0.1974    0.1691  0.0000
        1.2      -0.1222  -0.1222  -0.1006    0.0226    0.1437    0.1842    0.1974    0.1691  0.0000
        1.4      -0.1222  -0.1222  -0.1222  -0.0329    0.1034    0.1813    0.1936    0.1691  0.0000
        1.6      -0.1222  -0.1222  -0.1222  -0.0836    0.0564    0.1748    0.1899    0.1691  0.0000
        1.8      -0.1222  -0.1222  -0.1222  -0.1222    0.0095    0.1503    0.1842    0.1691  0.0000
        2.0      -0.1222  -0.1222  -0.1222  -0.1222  -0.0376    0.1174    0.1834    0.1691  0.0000
        2.2      -0.1222  -0.1222  -0.1222  -0.1222  -0.0846    0.0846    0.1804    0.1691  0.0000
        2.4      -0.1222  -0.1222  -0.1222  -0.1222  -0.1222    0.0451    0.1473    0.1691  0.0000
        2.6      -0.1222  -0.1222  -0.1222  -0.1222  -0.1222    0.0057    0.0932    0.1503  0.0000
        2.8      -0.1222  -0.1222  -0.1222  -0.1222  -0.1222  -0.0338    0.0610    0.1222  0.0000
        3.0      -0.1222  -0.1222  -0.1222  -0.1222  -0.1222  -0.0734    0.0320    0.0940  0.0000
        3.2      -0.1222  -0.1222  -0.1222  -0.1222  -0.1222  -0.1128    0.0029    0.0658  0.0000
        3.4      -0.1222  -0.1222  -0.1222  -0.1222  -0.1222  -0.1222  -0.0263    0.0376  0.0000
        3.6      -0.1222  -0.1222  -0.1222  -0.1222  -0.1222  -0.1222  -0.0555    0.0095  0.0000
        3.8      -0.1222  -0.1222  -0.1222  -0.1222  -0.1222  -0.1222  -0.0846  -0.0188  0.0000
        4.0      -0.1222  -0.1222  -0.1222  -0.1222  -0.1222  -0.1222  -0.1137  -0.0471  0.0000
        6.0      -0.1222  -0.1222  -0.1222  -0.1222  -0.1222  -0.1222  -0.1222  -0.1222  0.0000
        </tableData>
    </table>
 
  <!-- power coefficient as a function of advance ratio and blade angle -->
    <table name="C_POWER" type="internal">
      <tableData>
                -10        0        15        25        35        45        55        65      90
        -0.2      0.0108  0.0215    0.0753    0.1710    0.2949    0.4194    0.4839    0.5355  0.5355
        0.0      0.0430  0.0108    0.0645    0.1594    0.2820    0.4194    0.4859    0.5355  0.5355
        0.2      0.0613  0.0172    0.0624    0.1484    0.2697    0.4194    0.4859    0.5355  0.5355
        0.4      0.0826  0.0376    0.0537    0.1368    0.2562    0.4194    0.4859    0.5355  0.5355
        0.6      0.1013  0.0570    0.0355    0.1271    0.2400    0.4110    0.4839    0.5355  0.5355
        0.8      0.1194  0.0763    0.0108    0.1078    0.2258    0.3923    0.4839    0.5355  0.5355
        1.0      0.1374  0.0948    0.0108    0.0755    0.2129    0.3723    0.4820    0.5355  0.5355
        1.2      0.1561  0.0758  -0.0355    0.0290    0.1884    0.3568    0.4788    0.5355  0.5355
        1.4      0.1742  0.1310  -0.0536  -0.0215    0.1452    0.3516    0.4729    0.5355  0.5355
        1.6      0.1923  0.1497  -0.0626  -0.0645    0.0916    0.3420    0.4626    0.5162  0.5355
        1.8      0.2110  0.1678  -0.0645  -0.1078    0.0269    0.3033    0.4484    0.5052  0.5355
        2.0      0.2291  0.1858  -0.0826  -0.1503  -0.0323    0.2581    0.4271    0.4949  0.5355
        2.2      0.2471  0.2045  -0.1013  -0.1936  -0.0968    0.2097    0.4142    0.4729  0.5355
        2.4      0.2658  0.2226  -0.1194  -0.2368  -0.1613    0.1497    0.4020    0.4626  0.5355
        2.6      0.2839  0.2407  -0.1374  -0.2794  -0.2045    0.0626    0.3923    0.4465  0.5355
        2.8      0.3020  0.2594  -0.1561  -0.3226  -0.2452  -0.0213    0.3839    0.4407  0.5355
        3.0      0.3207  0.2774  -0.1742  -0.3658  -0.2903  -0.0968    0.3710    0.4407  0.5355
        3.2      0.3387  0.2955  -0.1923  -0.4084  -0.3336  -0.1723    0.3471    0.4304  0.5355
        3.4      0.3568  0.3142  -0.2110  -0.4517  -0.3762  -0.2471    0.2691    0.4194  0.5355
        3.6      0.3755  0.3323  -0.2291  -0.4949  -0.4194  -0.3226    0.1890    0.4084  0.5355
        3.8      0.3936  0.3504  -0.2471  -0.5355  -0.4626  -0.3981    0.1052    0.3955  0.5355
        4.0      0.4117  0.3691  -0.2658  -0.5355  -0.5355  -0.4729    0.0213    0.3658  0.5355
        6.0      0.5355  0.5355  -0.5355  -0.5355  -0.5355  -0.5355  -0.5355  -0.3226  0.5355
      </tableData>
    </table>
 
  <!-- thrust effects of helical tip Mach -->
  <table name="CT_MACH" type="internal">
    <tableData>
      0.85  1.0
      1.05  0.8
    </tableData>
  </table>
  <!-- power-required effects of helical tip Mach -->
  <table name="CP_MACH" type="internal">
    <tableData>
      0.85  1.0
      1.05  1.8
      2.00  1.4
    </tableData>
  </table>
<syntaxhighlight lang="xml">
=== CT_MACH and CP_MACH ===
The CT_MACH and CP_MACH tables are optional. They apply a factor to Ct and Cp based on the helical tip Mach. The CP_MACH table models the [http://en.wikipedia.org/wiki/Drag_divergence_Mach_number Drag Divergence Mach Number] for the propeller airfoil. The CT_MACH table models the thrust reduction.
Examples:
<syntaxhighlight lang="xml">
<!-- thrust effects of helical tip Mach -->
  <table name="CT_MACH" type="internal">
    <tableData>
      0.85  1.0
      1.05  0.8
    </tableData>
  </table>
 
  <!-- power-required effects of helical tip Mach -->
  <table name="CP_MACH" type="internal">
    <tableData>
      0.85  1.0
      1.05  1.8
      2.00  1.4
    </tableData>
  </table>
</syntaxhighlight>
=== Sense ===
Sense is the direction of rotation. 1=clockwise (typically as seen from rear of aircraft or the cockpit of a typical front-propeller aircraft, but this may vary depending on how you have set up the coordinate system for your aircraft) and -1 is counter-clockwise.
The sense tag goes in the parent tag of the thruster, ie, in the <propulsion><thruster> section which is typically in the main JSBSim XML file.  Example:
<syntaxhighlight lang="xml">
    <propulsion>
        <engine file="Clerget9B">
            <location unit="IN">
                <x> 12 </x>
                <y> 0 </y>
                <z> 0 </z>
            </location>
            <orient unit="DEG">
                <roll> 0 </roll>
                <pitch> 0 </pitch>
                <yaw> 0 </yaw>
            </orient>
            <feed>0</feed>
            <thruster file="CamelProp">
                '''<sense>1</sense>'''
                <location unit="IN">
                    <x> 0 </x>
                    <y> 0 </y>
                    <z> 0 </z>
                </location>
                <orient unit="DEG">
                    <roll> 0 </roll>
                    <pitch> 0 </pitch>
                    <yaw> 0 </yaw>
                </orient>
            </thruster>
        </engine>
        <tank type="FUEL">
            <location unit="IN">
                <x> 60 </x>
                <y> 0 </y>
                <z> -5.62 </z>
            </location>
            <capacity unit="LBS">133.6</capacity>
            <contents unit="LBS">133.6</contents>
        </tank>
    </propulsion>
</syntaxhighlight>
====Sense bug affecting gyroscopic moment====
Prior to about 2015--and continuing in current JSBSim and FlightGear versions unless you take the corrective steps outlined below--a JSBSim bug cause the gyroscopic moment of the propeller to be reversed.
To fix this bug and get the correct sign for your gyroscopic effect, you must add version="1.1" (or higher--any version greater than 1.0 should work) to your propeller definition, as shown in this example:
<syntaxhighlight>
<propeller name="prop" version="1.1">
  <!-- propeller definition -->
</propeller>
</syntaxhighlight>
The bug with the sign of gyroscopic effect and the fix are outlined under [https://sourceforge.net/p/jsbsim/bugs/110/ JSBSim Bug #110].
For most aircraft and engine/propeller systems the gyroscopic effect is fairly subtle and thus the bug is difficult to detect. But for some aircraft, such as small, light, rotary-engined WWI-era aircraft, the gyroscopic effect is very noticeable, and the reverse in direction of the effect created by the bug is very noticeable as well.
=== Starter speed (for piston engines) ===
There is a somewhat complex relationship among the power coefficient, the maxhp, and idlerpm.  Both maxhp and idlerpm are set in the engine xml file.
The power of the starter motor is equal to 0.4*sqrt(maxhp).  The minimum RPM needed to start the engine is 80% of the idlerpm.  The greater the power coefficient (for J near 0), the more power the propeller will require to spin when starting the engine with the aircraft at rest.
If your propeller will not spin fast enough to start, you can try some combination of:
* Open the throttle. Pulling a partial vacuum in the intake manifold takes some power.
* Increase maxhp (increases the power of the starter motor)
* Decrease idlerpm (decreases the minimum RPM needed to start the engine)
* Decrease the power coefficient in the C_POWER table, for values of J close to (or equal to) 0.  This will reduce the amount of power it takes for the propeller to spin at a given RPM where J is close to 0 (which is the typical situation when starting the engine and the aircraft is at a dead stop).
You can open the property tree and watch the value of J (/fdm/jsbsim/propulsion/engines/advance-ratio) to get an idea of which values you need to change in the C_POWER table.
''' Code is in FG 2.8 to independently control the power of the piston starter motor, to include battery effects. '''
starter-torque (fgfs 2.8) is a value specifying the zero RPM torque in lb*ft the starter motor provides. Current default value is 40% of the maximum horsepower value.
starter-rpm (fgfs 2.8) is a value specifying the maximum RPM the unloaded starter motor can achieve. Loads placed on the engine by the propeller and throttle will further limit RPM achieved in practice. Peak starter power is achieved at 1/2 starter-rpm. At 1/2 starter-rpm torque is 1/2 starter-torque. Peak power can be calculated by the standard formula HP=(Torque*RPM)/5252
=== Development tips ===
* If you open the property tree browser within FG to /fdm/jsbsim/propulsion/engines you can see a number of helpful variables in action, including RPM, horsepower, advance ratio, thrust coefficient, and others.
=== References ===
* Barnes W. McCormick, "Aerodynamics, Aeronautics, and Flight Mechanics", Wiley & Sons, 1979 ISBN 0-471-03032-5
* Edwin Hartman, David Biermann, "The Aerodynamic Characteristics of Full Scale Propellers Having 2, 3, and 4 Blades of Clark Y and R.A.F. 6 Airfoil Sections", NACA Report TN-640, 1938 (?)
* Various NACA Technical Notes and Reports


=== Notes ===
*  Two tables are needed. One for coefficient of thrust (Ct) and one for coefficient of power (Cp).
*  Two tables are optional. They apply a factor to Ct and Cp based on the helical tip Mach. 
*  Several references were helpful, here:
**Barnes W. McCormick, "Aerodynamics, Aeronautics, and Flight Mechanics", Wiley & Sons, 1979 ISBN 0-471-03032-5
**Edwin Hartman, David Biermann, "The Aerodynamic Characteristics of Full Scale Propellers Having 2, 3, and 4 Blades of Clark Y and R.A.F. 6 Airfoil Sections", NACA Report TN-640, 1938 (?)
**Various NACA Technical Notes and Reports
== FGRotor ==
== FGRotor ==
FGRotor moodels a helicopter rotor.
FGRotor models a helicopter rotor.
=== Configuration File Format ===
 
=== Configuration file format ===
<syntaxhighlight lang="xml">
<syntaxhighlight lang="xml">
<!-- Sense goes in the parent tag -->
<!-- Sense goes in the parent tag -->
Line 201: Line 507:
   <groundeffectexp> {number} </groundeffectexp>
   <groundeffectexp> {number} </groundeffectexp>
   <groundeffectshift unit="{LENGTH}"> {number} </groundeffectshift>
   <groundeffectshift unit="{LENGTH}"> {number} </groundeffectshift>
  <freewheelthresh> {number} </freewheelthresh>
</rotor>
</rotor>
</syntaxhighlight>
</syntaxhighlight>
Line 272: Line 576:
|groundeffectshift
|groundeffectshift
|Further adjustment of ground effect, approx. hub height or slightly above.  
|Further adjustment of ground effect, approx. hub height or slightly above.  
|-
|freewheelthresh
|Ratio of thruster power to engine power. The FWU will release when above the threshold. The value shouldn't be too close to 1.0, 1.5 seems ok. 0 disables this feature, which is also the default.
|}
|}


=== Notes ===
=== Notes ===
==== Controls ====
==== Controls ====
* The behavior of the rotor is controlled/influenced by following inputs.
The behavior of the rotor is controlled/influenced by following inputs.
** The power provided by the engine. This is handled by the regular engine controls.
* The power provided by the engine. This is handled by the regular engine controls.
** The collective control input. This is read from the <tt>fdm</tt> property <tt>propulsion/engine[x]/collective-ctrl-rad</tt>. See below for tail rotor
* The collective control input. This is read from the <tt>fdm</tt> property <tt>propulsion/engine[x]/collective-ctrl-rad</tt>. See below for tail rotor
** The lateral cyclic input. Read from <tt>propulsion/engine[x]/lateral-ctrl-rad</tt>.
* The lateral cyclic input. Read from <tt>propulsion/engine[x]/lateral-ctrl-rad</tt>.
** The longitudinal cyclic input. Read from <tt>propulsion/engine[x]/longitudinal-ctrl-rad</tt>.
* The longitudinal cyclic input. Read from <tt>propulsion/engine[x]/longitudinal-ctrl-rad</tt>.
** The tail collective (aka antitorque, aka pedal) control input. Read from <tt>propulsion/engine[x]/antitorque-ctrl-rad</tt> or <tt>propulsion/engine[x]/tail-collective-ctrl-rad</tt>.  
** The tail collective (aka antitorque, aka pedal) control input. Read from <tt>propulsion/engine[x]/antitorque-ctrl-rad</tt> or <tt>propulsion/engine[x]/tail-collective-ctrl-rad</tt>.  


==== Tail/tandem rotor ====
==== Tail/tandem rotor ====
 
Providing '''&lt;ExternalRPM&gt; 0 &lt;/ExternalRPM&gt;''' the tail rotor's RPM is linked to to the main (=first, =0) rotor, and specifying '''&lt;controlmap&gt; TAIL &lt;/controlmap&gt;''' tells this rotor to read the collective input from '''propulsion/engine[1]/antitorque-ctrl-rad''' (The TAIL-map ignores lateral and longitudinal input). The rotor needs to be attached to a dummy engine, e.g. an 1HP electrical engine. A tandem rotor is setup analogous.
    Providing '''&lt;ExternalRPM&gt; 0 &lt;/ExternalRPM&gt;''' the tail rotor's RPM
    is linked to to the main (=first, =0) rotor, and specifying
    '''&lt;controlmap&gt; TAIL &lt;/controlmap&gt;''' tells this rotor to read the
    collective input from '''propulsion/engine[1]/antitorque-ctrl-rad'''
    (The TAIL-map ignores lateral and longitudinal input). The rotor needs to be  
    attached to a dummy engine, e.g. an 1HP electrical engine.
    A tandem rotor is setup analogous.


==== Sense ====
==== Sense ====
The 'sense' parameter from the thruster is interpreted as follows, sense=1 means counter clockwise rotation of the main rotor, as viewed from above. This is as a far as I know more popular than clockwise rotation, which is defined by setting sense to -1. Concerning coaxial designs - by setting 'sense' to zero, a Kamov-style rotor is modeled (i.e. the rotor produces no torque).


    The 'sense' parameter from the thruster is interpreted as follows, sense=1 means
==== Engine issues ====
    counter clockwise rotation of the main rotor, as viewed from above. This is as a far
In order to keep the rotor speed constant, use of a RPM-Governor system is encouraged (see examples).
    as I know more popular than clockwise rotation, which is defined by setting sense to
    -1. Concerning coaxial designs - by setting 'sense' to zero, a Kamov-style rotor is
    modeled (i.e. the rotor produces no torque).


==== Engine issues ====
==== Development hints ====
Setting '''&lt;ExternalRPM&gt; -1 &lt;/ExternalRPM&gt;''' the rotor's RPM is controlled by the '''propulsion/engine[x]/x-rpm-dict''' property. This feature can be useful when developing a FDM.


    In order to keep the rotor speed constant, use of a RPM-Governor system is
==== Properties ====
    encouraged (see examples).
The rotor model creates the following properties:


==== Development hints ====
{| class="prettytable"
|-
|propulsion/engine[#]/rotor-rpm
|RPMs of the rotor
|-
|propulsion/engine[#]/engine-rpm
|RPMs of the Engine, as seen from this rotor.
|-
|propulsion/engine[#]/a0-rad
|Rotor's coning angle in radians
|-
|propulsion/engine[#]/a1-rad
|Longitudinal flapping angle with respect to the rotor shaft in radians
|-
|propulsion/engine[#]/b1-rad
|Lateral flapping angle with respect to the rotor shaft in radians
|-
|propulsion/engine[#]/inflow-ratio
| Lambda or λ
|-
|propulsion/engine[#]/advance-ratio
|the tip-speed (aka advance) ratio Mu or μ
|-
|propulsion/engine[#]/induced-inflow-ratio
| Nu or ν
|-
|propulsion/engine[#]/vi-fps
|Induced Velocity in feet per second
|-
|propulsion/engine[#]/thrust-coefficient
|
|-
|propulsion/engine[#]/torque-lbsft
| Rotor torque in pound * feet
|-
|propulsion/engine[#]/theta-downwash-rad
|Down wash θ angle - positive values point forward (given a horizontal spinning rotor) in radians
|-
|propulsion/engine[#]/phi-downwash-rad
|Down wash Φ angle - positive values point leftward (given a horizontal spinning rotor) in radians
|-
|propulsion/engine[#]/groundeffect-scale-norm
|
|}


    Setting '''&lt;ExternalRPM&gt; -1 &lt;/ExternalRPM&gt;''' the rotor's RPM is controlled  by
(Control Inputs)
    the '''propulsion/engine[x]/x-rpm-dict''' property. This feature can be useful
{| class="prettytable"
    when developing a FDM.
|-
|propulsion/engine[#]/antitorque-ctrl-rad
|
|-
|propulsion/engine[#]/tail-collective-ctrl-rad
|
|-
|propulsion/engine[#]/lateral-ctrl-rad
|
|-
|propulsion/engine[#]/longitudinal-ctrl-rad
|
|-
|propulsion/engine[#]/collective-ctrl-rad
|
|-
|propulsion/engine[#]/lateral-ctrl-rad
|
|-
|propulsion/engine[#]/longitudinal-ctrl-rad
|
|}


=== References:===
=== References ===
{| class="prettytable"
{| class="prettytable"
|-
|-
Dany9a3
49

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