Hi. Thanks again 
We have found out that we maybe made an mistake by defining our engines in our “OwnAicrfat-FlightGear-Model”. So if we just simulate the same model with only one engine, it is flying with JSBSim. As soon as we add a second engine to our model, the vehicle isn`t flying anymore.
(sim_vehicle.py -f jsbsim:OwnModel)
Now we had an team-meeting and our group-master decided, that we first should try the easier way with SIM_Plane.cpp and so on. (sim_vehicle.py -j4 -f quadplane)
But when we will have time we will try the JSBSim- variant with five engines. And we will update this forum if we have success and how.