B: On the Drag Coefficient

Abstract

Aircraft drag can be expressed as 1 2 D V C S D 2 where C D is the aircraft total drag coefficient. A typical set of curves of the drag coefficient is shown in Figure B.1 as a function of the Mach number for selected lift coefficients. It is seen that the drag coefficient remains nearly constant in the subsonic region up to the critical Mach number and starts increasing rapidly in the transonic range after reaching the drag divergence Mach number. In the supersonic range the drag coefficient tends to decrease rapidly. The level of depends on the type of aircraft (glider, fighter, C D0 transport, etc.). For some typical data of see Appendix C. C D0 The drag coefficient C D plays a crucial role in aircraft performance evaluation because it represents most of the aircraft aerodynamics in its variation with the flight parameters. In its accurate and complete representation, the drag coefficient may be given in a graphical (see Figure B.1) or piecewise polynomial form to accommodate both the required lift and Mach number ranges. For practical engineering calculations where analytical results are desirable, the following expression is used for the drag coefficient of an airplane: Aircraft Performance. Maido Saarlas