Shapes of Actual Wings

To convey a concept of the various wing shapes that have actually been used in airplanes, the. profile thickness ratio 5=t/c, the aspect ratio A = b2/A, and the sweepback angle of the leading edge ipf of some airplanes are plotted in Fig. 3-4 against the flight Mach number. The plots show a clear trend of profile thickness and aspect ratio in the transition from subsonic to supersonic airplanes.

The profile thickness ratio decreases sharply with increasing Mach number, reaching values of tjc = 0.04 for supersonic airplanes. The aspect ratios are particularly large in the subsonic range for long-distance airplanes but considerably smaller for maneuverable fighter planes. In the supersonic range, the implementation of larger aspect ratios is no longer required for aerodynamic reasons. In this range, therefore, design considerations have led to aspect ratios as small as A — 2. The sweepback angle is close to zero at low Mach numbers but increases to ^45° at high subsonic speeds. In the supersonic range, airplanes with both relatively large sweepback (tp/^60o) and small sweepback (^«30°) are found. Truckenbrodt [86] has shown to what extent the geometric wing data of Fig. 3-4 have been determined by a decisive understanding of the drag of wings.