Hello heinekenbottle,

when I suppose, that your tank is designed with the x-axis pointing forward, then the result is clear. The normal vector is pointing away from the scanned surface, meaning upwards with a slight deviation depending on terrain slope. Vec-to-angle copies this direction to the pan and tilt angles of your tank, so it is pointing upwards, too. Instead you should try to apply the (90-tilt) angle of the normal vector to the tilt and roll angle of your tank depending on direction of the terrain slope which you can find in the pan angle of the normal vector. It should point to downward direction of slope.

Sorry, it is that complex.