[Flightgear-flightmodel] Wind calculation

[<gi...@mu...>]

Dear flightmodel community,

i have to use flightgear for my master thesis. Currently I am trying  
to understand how flightgear calculates the wind. I think in the line

vTotalWindNED = vWindNED + vGustNED + vCosineGust + vTurbulenceNED;

in FGWinds.cpp of the FDM JSBSim the total wind is determined, isn't  
it? I've interpreted vWindNED (Calculation with the method  
SetWindspeed) as the mean wind and I think vCosineGust (Calculation  
with the method CosineGust) describes the 1-cosine gust shape and  
vTurbulenceNED (Calculation with the method Turbulence) the  
atmospheric turbulence?! But I don't understand the meaning of  
vGustNED and where it is calculated?

Further information about the background:

I am using JSBSim only in combination with flightgear. According to my  
knowledge the situation is as follows:
The decision which flight dynamic model (FDM) flightgear will use is  
determined by the aircraft which you are flying (You find in the  
internet the follwing sentence: ''Every aircraft simulated by  
FlightGear must use one of these models.'' And after this sentence you  
get a list of possible FDM used by flight gear, amongst other things  
JSBSim).  In the file aicraftname-set.xml (e.g. c172p-set.xml for the  
cessna) you find an specific entry for the using FDM:

<author>David Megginson</author>
   <status>early production</status>
   <rating>
     <FDM type="int">3</FDM>
     <systems type="int">4</systems>
     <model type="int">5</model>
     <cockpit type="int">4</cockpit>
   </rating>


   <flight-model archive="y">jsb</flight-model>
   <aero archive="y">c172p</aero>    . . .

In the future I will only use aircrafts which can be connected to the  
FDM JSBSim because it is better documented in the internet than for  
example the YASim model. The aim of my master thesis is to implement a  
3D turbulent wind velocity field simulated by the LES model PALM for a  
specific region so that the airplane fly through a ''real'' wind  
field. After I will implement the 3D windfield I will determine the  
differences referring to the flight attitude. Therefore I am very  
interested in how flighgear calculates the atmospheric parameters  
especially the wind(mean wind, turbulence, gusts?). I've found out  
that flightgear provides its own atmophere model by default but can  
also uses the atmosphere model from JSBSim (look at:  
http://wiki.flightgear.org/JSBSim_Atmosphere) . I dont know which one  
is better or which one can handle better with the detailed weather  
settings you can set at the beginning and during flight, but let us  
assume that the we use the default variant (FlightGear provides the  
atmosphere model). Now I'm not really sure where the total wind is  
calculated and where the wind influences the forces on the airplane  
and therefore the flight attitude. I think this must happen all in the  
FDM JSBSim. As a consequence, I found the file FGWinds.cpp in the code  
and the informations in the internet confirm me that, at least, the  
turbulence is calculated in JSBSim and not in the atmosphere model of  
flightgear (http://wiki.flightgear.org/JSBSim_Atmosphere). So maybe  
Flightgear uses only the turbulence calculation of JSBSim  
(vTurbulenceNED) and not vTotalWindNED but how? If so, only the lines  
in FGWind.cpp where the turbulence is calculated where relevant. I  
hope you can undestand my English and my problem of understanding :-(.  
I hope some of you can help. That would be great!

Best regards,
Sebastian

PS.: vGustNED is set in the FGWinds.h file, isnt't it  
(vGustNED(eNorth)=gn; ...? Where are the values gN, gE, gD come from?