[Flightgear-flightmodel] Wind calculation

[g***@muk.uni-hannover.de]

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?