This video shows you how to get the skull that is hidden in Bad Piggies Flight in the Night Level 4-27. The skull is above and a slightly to the left of the starting location. Make your contraption using the balloons but point the second set of soda bottles to the right. You want to quickly propel your contraption to the right with the black soda bottles, wait for it to be lifted by the balloons through the opening. Finally, once you gained enough altitude, boost your contraption leftward and pop the ballons upon reaching the skull.
If you have a different strategy for completing this level feel free to leave a comment below.