Theory and Practice of Aircraft Performance

CHAPTER 9Aircraft Drag

9.1 Overview

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 DOC  (direct operating cost), which is drag‐dependent. Just one count of drag (i.e. ) could account for several million US dollars in operating costs over the lifespan of a small fleet of midsized aircraft. This will become increasingly important with increasing 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 the English language on aircraft drag is compiled by NACA/NASA  (National Advisory Committee for Aeronautics/National Aeronautics and Space Administration), RAE, AGARD  (Advisory Group for Aerospace Research and Department), ESDU, DATCOM, RAeS  (Royal Aeronautical Society), AIAA  (American Institute for Aeronautics and Astronautics) and others [1–11]. These publications indicate that the drag phenomena are still not fully understood [10], and that the way to estimate aircraft drag is by using semi‐empirical relations. CFD  (computational fluid dynamics) ...