Mark, I think a better analogy is the rudder on a boat. On a crankbait, the airstream is hitting the flat side of the lip, not the edges of the fletching like on an arrow. And the lip is applying asymetrical force on the crankbait, not like the fletching distributed around the shaft of an arrow. The more the rudder is turned, or the steeper the lip angle on a crankbait, the more deflection force (aka tumbling force) is applied. Deep divers with large lips and very small lip angles (often zero angle) tend to cast best. Weight balance over the whole bait is also critical. If the lure is front heavy, it may fly OK on a perfect cast but the least little aerodynamic change will cause it to tumble. I built some chest weighted deep divers and found this out the hard way! Fortunately, my casting has developed to such perfection now that it really isn't a problem