+
+ Additionally, various turbulence models are available. They are specified
+ via the property <tt>atmosphere/turb-type</tt>. The following models are
+ available:
+ - 0: ttNone (turbulence disabled)
+ - 1: ttStandard
+ - 2: ttBerndt
+ - 3: ttCulp
+ - 4: ttMilspec (Dryden spectrum)
+ - 5: ttTustin (Dryden spectrum)
+
+ The Milspec and Tustin models are described in the Yeager report cited below.
+ They both use a Dryden spectrum model whose parameters (scale lengths and intensities)
+ are modelled according to MIL-F-8785C. Parameters are modelled differently
+ for altitudes below 1000ft and above 2000ft, for altitudes in between they
+ are interpolated linearly.
+
+ The two models differ in the implementation of the transfer functions
+ described in the milspec.
+
+ To use one of these two models, set <tt>atmosphere/turb-type</tt> to 4 resp. 5,
+ and specify values for <tt>atmosphere/turbulence/milspec/windspeed_at_20ft_AGL-fps<tt>
+ and <tt>atmosphere/turbulence/milspec/severity<tt> (the latter corresponds to
+ the probability of exceedence curves from Fig. 7 of the milspec, allowable
+ range is 0 (disabled) to 7). <tt>atmosphere/psiw-rad</tt> is respected as well;
+ note that you have to specify a positive wind magnitude to prevent psiw from
+ being reset to zero.
+
+ Reference values (cf. figures 7 and 9 from the milspec):
+ <table>
+ <tr><td><b>Intensity</b></td>
+ <td><b><tt>windspeed_at_20ft_AGL-fps</tt></b></td>
+ <td><b><tt>severity</tt></b></td></tr>
+ <tr><td>light</td>
+ <td>25 (15 knots)</td>
+ <td>3</td></tr>
+ <tr><td>moderate</td>
+ <td>50 (30 knots)</td>
+ <td>4</td></tr>
+ <tr><td>severe</td>
+ <td>75 (45 knots)</td>
+ <td>6</td></tr>
+ </table>
+
+ @see Yeager, Jessie C.: "Implementation and Testing of Turbulence Models for
+ the F18-HARV" (<a
+ href="http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19980028448_1998081596.pdf">
+ pdf</a>), NASA CR-1998-206937, 1998
+
+ @see MIL-F-8785C: Military Specification: Flying Qualities of Piloted Aircraft
+