I used Bob Tait and only just passed Aerodynamics, 75% I passed all my cpl exams 1st time round using BT. If I didn't understand something I just emailed him and he would graciously return my email with an explanation, he's very helpful. Aero is a hard one to understand espeacilly when you are trying to understand it from a text book and from home study. There are many dvds out there that may be of use particularly Oxford aviation products are really good, Sportys is also really good. I bought a Jeppesen dvd on aerodynamics and that was quite helpful but not quite in depth enough.