Book excerpt: Knowledge is not merely everything we have come to know, but also ideas we have pondered long enough to know in which way they are related, and 1 how these ideas can be put to practical use. Modern aviation has been made possible as a result of much scienti c - search. However, the very rst useful results of this research became ava- able a considerable length of time after the aviation pioneers had made their rst ights. Apparently, researchers were not able to nd an adequate exp- nation for the occurrence of lift until the beginning of the 21st century. Also, for the fundamentals of stability and control, there was no theory available that the pioneers could rely on. Only after the rst motorized ights had been successfully made did researchers become more interested in the science of aviation, which from then on began to take shape. In modern day life, many millions of passengers are transported every year by air. People in the western societies take to the skies, on average, several times a year. Especially in areas surrounding busy airports, travel by plane has been on the rise since the end of the Second World War. Despite becoming familiar with the sight of a jumbo jet commencing its ight once or twice a day, many nd it astonishing that such a colossus with a mass of several hundred thousands of kilograms can actually lift off from the ground.