What are the units used within JSBSim? For wind speed, is it in feet
per second or knot? For example, in Atmosphere->SetWindNED(10, 10,
10), what units are the NED speeds in?
On 8/16/05, Jon Berndt <jsb@...> wrote:
> > Thanks, Jon.
> > I can see that in FGAtmosphere.cpp, wind speed vWindNED is used to
> > calculate psiw:
> > if (vWindNED(1) !=3D 0.0) psiw =3D atan2( vWindNED(2), vWindNED(1) );
> > and then psiw is tied to property "atmosphere/psiw-rad":
> > PropertyManager->Tie("atmosphere/psiw-rad", this,
> > &FGAtmosphere::GetWindPsi);
> > But I could not find where either psiw or property
> > "atmosphere/psiw-rad" is used in anywhere else in JSBSim.
> > How can I ascertain that vWindNED really has an effect on the JSBSim
> > simulation, in other words vWindNED is really used in the FDM?
> > Thanks!
> Hi, Aaron:
> It's a bit convoluted. In FGAuxiliary.cpp you'll see this:
> vAeroPQR =3D vPQR + Atmosphere->GetTurbPQR();
> There is a reason for this. Say that your body axis rates are zero, but y=
ou fly through a
> "wind gradient" - that is, the wind vector is different across the aircra=
ft. Maybe you are
> flying into an updraft or something, so the wind at nose consist of an up=
> Say the tail has not yet "seen" the worst of the updraft, yet. So, what t=
> "thinks" is that is has a negative pitch rate - nose down. The aerodynami=
c PQR vector is
> equal to the body PQR rate vector if there is no wind. We have to add the=
current wind PQR
> to that. That's what the GetTurbPQR() call does. It returns the turbulenc=
e vector that
> Turbulence() calculates.
> OK, so that's the rotational effect. There's also a translational effect.=
> vAeroUVW =3D vUVW + Propagate->GetTl2b()*Atmosphere->GetWindNED();
> This adds to the body axis UVW vector the wind vector. Wind is defined in=
the local NED
> coordinate frame. It has to be transformed into the body axis.
> I hope this helps. Ask if you need more help, but again note that my resp=
onse time is
> really slow right now due to some other constraints on my time. Thanks!
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