I was messing around with a physics thruster and attached it to a simple lander craft. Why is it though when I add thrust stregnth to get it moving upward that it starts leaning in one direction when it is directly pointing down?
Because it is physics simulation. Center of mass of mesh you pushing is not exactly aligned with thruster. To test physics use cube with some rounded dimensions like 10x10x10.
Even if mesh looks symmetrical, silly difference of alignment on single side may result if asymmetrical behavior. I know that 3dmax loves to shift stuff just a tiny bit, like (0.000002727 cm to the side). And i am unsure how unreal handles calculating center of mass, if it can see symmetry or just follows collision hull. There are probably cases that different mass is calculated on same mesh depending on vertices indexing. So if one side was copied and mirrored different mass is calculated for that side just because indexing is flipped. But i am guessing now.
I even went as far as making all physics objects in my game invisible cubes with collision, then i attached to them purely visual objects that have no collision. This way is easier to control how they behave.