Many aspects of flight can be used for design inspiration and resources. Airport signs and symbols, plane wings, jet engines, plane schematics, airbrush illustrations, baggage dispensation, flight cards... etc. Pictured here is the Rockwell OV-10A Bronco - airbrush illustration from the Encyclopedia Of World Air Power. This book, which I picked up for NZ$12.00 in a second hand bookshop has over 600 diagrams and colour illustrations.