I didn't know much about
Andrew Loomis until I took an Advanced Figure Drawing class taught by the legendary
Mark Tennant (more on this later). In his class Tennant used many examples from Loomis's books to help illustrate the basics of human proportions, perspective, composition, etc. Many of these diagrams and studies are listed in 'Creative Illustration' but unfortunately it's out of print and will set you back a couple of hundred should you want to buy a copy. So, listed below is a .pdf of the book! Enjoy
Creative Illustration