Conceptual Aircraft Design

11Aircraft Drag

11.1 Overview

After the completion of the concept definition that concluded in Chapter 10, the next phase is to end the Phase I stage of the new aircraft project with concept finalisation through the formal method of aircraft sizing and engine matching exercise in Chapter 14 that will require aircraft performance analyses. This will require aircraft drag polar to be dealt with in this chapter and engine performance data to be dealt with in the next two chapters, Chapters 12 and 13.

An important task for aircraft performance engineers is to make the best possible estimation of all the different types of drag associated with aircraft aerodynamics. Commercial aircraft design is sensitive to the Direct Operating Cost (DOC), which is aircraft drag dependent. Just one count of drag (i.e. C_D = 0.0001) could account for several million US dollars in operating cost over the lifespan of a small fleet of midsized aircraft. This becomes increasingly important with the trend in rising fuel costs. Accurate estimation of the different types of drag remains a central theme. (Equally important are other ways to reduce DOC; one of them is reducing manufacturing cost.)

For a century, a massive effort has been made to understand and estimate drag and the work is still continuing. Possibly some of the best work in English language on aircraft drag is compiled by National Advisory Committee for Aeronautics (NACA)/National Aeronautics and Space Administration (NASA), RAE (the Royal Aircraft ...