Xwang

Thanks you for your help. What i don't understand is how doing calculation in the inertial frame would resolve the problem. in such a way I still have all the acceleration given in absolute terms and not only the "relative to the air" ones (considering the air still, of course). Moreover computing all the equation in ECi, I will have to recompute the inertial tensor every step. Do you agree? Xwang

Hi to all! I'm developing a six degree of freedom which uses the oblate rotating Earth and which wil be used to simulate the motion and the trajectory of airplane and spacecrafts around the world (so no simplification is actuable). My work is based on Steven's "Aircraft Control and Simulation" and is pretty similar to this one: http://www.mathworks.com/access/helpdesk/help/toolbox/aeroblks/6dofecefquaternion.html One of the requirements is that it is possible to use the same model also for calculate the trim condition. To do that I need the variation of velocity vector expressed in body axis and the relative angular acceleration ([math]\dot{\vec{V_{b}}}[/math] and [math]\dot{\vec{\omega_{rel}}}[/math]). The first one is already calculated, but the angular relative acceleration is unknown since only the absolute angular acceleration is given (it contains the effects given by the motion of NED system above an oblate Earth). How can I calculate it? Thank you, Xwang