Before reading this book, I didn't know that at cruising speed a Boeing 747 burns ten tons of fuel per hour, and that as airliners burn fuel, they have to climb in order to maintain their speed; that hummingbirds hover at maximum power, which requires them to eat their own weight in nectar every 18 hours; that, as one of the most calorie-dense foods at 180 calories per ounce, it would cost approximately $.32 per passenger-mile to run an amtrak train on peanut butter; or that Lance Armstrong can sustain a power of 7 watts/kg. of body weight, making him a true freak of nature. This book is primarily about things that fly, from bees to sparrows to human-powered flying machines to jets with undersized wings like the 737 to jets like the A380 that can't have a wingspan greater than 80 meters because of airport constraints. Tennekes uses enough math to make the concepts enjoyable and comprehensible without becoming tedious or overwhelming. I thoroughly enjoyed this book.