when you select a object, hit 'n' for a box that shows transform properties. Once there, there is scale. If you centered your object when creating it, this should help. for a wing, if the wing crosses the 'x' line on the ship, duplicate the wing by typing "Shift+D". after this just click right click to cancel movement of the object. Then, go to the transform properties box and make the scale of the wing '=1' or whatever scale it is and make it negative. You dont even need to mess with mirroring the texture or creating a entire new one just to flip the texture.