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 ...