What is the last thing you learned on purpose?
For me it was about Kline Fogleman Airfoil. The KF airfoil is a revolutionary airfoil first developed some time in the 70's. It was used on a world record holding paper airplane but it was laughed at by aviation experts because they did not understand how it work. It involves putting a step about midway on either the top or the bottom of a wing. The step creates some turbulence which then generates a surprising amount of lift. Right now it is getting a lot of attention by remote control model airplane enthusiasts. (That is where I picked up the idea.) YouTube, Google, a couple of podcasts, and many discussion forums were my partners in my research.
A challenge: What was the last thing you really learned on purpose? I don't mean something that you learned in passing. I mean something you went out of your way to find out about. Not because you had to but because you wanted to. I am passing the challenge on to a few of you (and anyone else is welcome to join in).