Fix from Melchior: It replaces the ridiculous 5 seconds by

the 30 seconds that Maik had originally intended, according to the comment.
This is important for the pending sound and rotor disc changes (and of course
for realism).

src/FDM/YASim/Rotor.cpp

@@ -92,7 +92,7 @@ void Rotor::inititeration(float dt)
 {
    if ((_engineon)&&(_omegarel>=1)) return;
    if ((!_engineon)&&(_omegarel<=0)) return;
-   _omegarel+=dt*1/5.*(_engineon?1:-1); //hier 30
+   _omegarel+=dt*1/30.*(_engineon?1:-1);
    _omegarel=Math::clamp(_omegarel,0,1);
    _omega=_omegan*_omegarel;
    int i;