Flights in Earth’s

Flights in Earth’s atmosphere existed long before the presence of mankind. 300 million years ago it was performed by insects with wings, 60 million years ago by birds and 50 million years ago by bats as flying mammals (Hitching 1982). Man, on the other hand, being the most recently emerged species among the living things first realized the concept of flight by depicting the flying animals in his creative works related to mythology or real life (Gibbs-Smith 1954). Needles to say, as a discipline, the science of Aerodynamics provides the most systematic and fundamental approach to the concept of flight.

The Aerodynamics discipline which determines the basic conditions of flying made great progress during the past hundred years, which is slightly longer than the average life span of a modern man (Anderson 2001). The reason of this progress is mainly the existence of wide range of aerospace applications in mili­tary and civilian industries. In the civilian aerospace industries, the demand for development of fast, quiet and more economical passenger planes with long ran­ges, and in the military the need for fast and agile fighter planes made this progress possible. The space race, on the other hand, had an accelerating effect on the progress during the last 50 years.

Naturally, the faster the planes get the more complicated the related aerody­namics become. As a result of this fast cruising, the lifting surfaces like wings and the tail planes start to oscillate with higher frequencies to cause in turn a phase lag between the motion and the aerodynamic response. In order to predict this phase lag, the concept of unsteady aerodynamics and its underlying principles were introduced. In addition, at higher speeds the compressibility of the air plays an important role, which in turn caused the emergence of a new branch of aerody­namics called compressible aerodynamics. At cruising speeds higher than the speed of sound, completely different aerodynamic behavior of lifting surfaces is observed. All these aerodynamical phenomena were first analyzed with mathe­matical models, and then observed experimentally in wind tunnels before they were tested on prototypes undergoing real flight conditions. Nature, needless to say, inspired many aerodynamicists as well. In recent years, the leading edge

U. Gulfat, Fundamentals of Modern Unsteady Aerodynamics, 1

DOI: 10.1007/978-3-642-14761-6_1, © Springer-Verlag Berlin Heidelberg 2010

vortex formation which gives extra lift for highly swept wings at high angles of attack has been studied extensively. During the last decade, the man made flight has no longer been based on a fixed wing. The flapping wing aerodynamics which utilizes the unsteady aerodynamic concepts is used in designing and building micro air vehicles to serve mankind in various fields.

First, let us introduce various pertinent definitions in order to establish a firm convention in studying the topics of unsteady aerodynamics in general.