I didn't realize this is a free download - this is an AWESOME reference: the "Pilot's Handbook of Aeronautical Knowledge" - if you are interested in aviation, this is an incredible reference for learning the basics about flight, navigation, airplanes, etc. I asked for this book for my birthday last year, and really enjoy having it as a coffee table book.

http://www.faa.gov/library/manuals/a...ilot_handbook/