Hop has to let the boy know that his father did not survive the crash landing. 

Hop and Tank learn about a new airplane called the Chanel Wing which can take off at speeds of fifteen miles an hour or less and at the same time reach supersonic speeds. Hop and Tank learn that in the envelope are plans that are copied from an excavated ancient Mayan Wall that are of this very same airfoil. The ancient Mayans had designed the plane before flying had ever been invented.