Which direction is vertical velocity to a flying object

This answer completely depends on the trajectory of the flying object. If it is increasing in altitude (such as a plant at take off) then it will have a positive vertical velocity directly upward (perpendicular to the ground). If the object is cruising (like a plane) at a fixed altitude, the vertical speed and velocity will be zero, so there will be no angle. If the object is descending in altitude, then there will be a vertical velocity with direction toward the ground.