JSBSim Thrusters: Difference between revisions

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Revision as of 01:05, 3 November 2011

5,900 bytes added ,  3 November 2011
→‎C_THRUST and C_POWER tables
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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.  
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.
[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.
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* T = thrust (N)
* T = thrust (N)


For a typical propeller, both Cp and Ct are downward sloping curves that reach 0 near J=1. Typically Ct is slightly greater than than Cp for small J, crosses (is equal to) Cp at some point (typically, when J is between 0.6 and 0.8), and then remains smaller than Cp for larger J.  Cp and Ct can be negative (typically for J > 1, approximately); this indicates the drag induced by the prop when the airspeed is relatively fast compared with prop RPM.
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). Typically Ct is slightly greater than than Cp for small J, crosses (is equal to) Cp at some point (typically, 60-80% of the way from J=0 to the point where Ct=0)), and then remains smaller than Cp for larger J.  Cp and Ct can be negative; this indicates the drag induced by the prop when the airspeed is relatively fast compared with prop RPM.


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.
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.
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     </table>
     </table>
</nowiki>
</nowiki>
Example of table for variable pitch propeller ([http://www.mail-archive.com/flightgear-devel@lists.sourceforge.net/msg32187.html source]):
<nowiki>
<!-- 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>
</nowiki>


=== CT_MACH and CP_MACH ===
=== CT_MACH and CP_MACH ===
Flug
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