Aerodynamic Considerations

3.1 Overview

This chapter is concerned with the aerodynamic information required at the concep­tual design stage of a new aircraft design project. It provides details that influence shaping and other design considerations and defines the various parameters integral to configuring aircraft mould lines. Any object moving through air interacts with the medium at each point of the wetted (i. e., exposed) surface, creating a pressure field around the aircraft body. An important part of aircraft design is to exploit this pressure field by shaping its geometry to arrive at the desired performance of the vehicle, including shaping to generate lifting surfaces, to accommodate payload, to house a suitable engine in the nacelle, and to tailor control surfaces. Making an air­craft streamlined also makes it looks elegant.

Aeronautical engineering schools offer a series of aerodynamic courses, starting with the fundamentals and progressing toward the cutting edge. It is assumed that readers of this book have been exposed to aerodynamic fundamentals; if so, then readers may browse through this chapter for review and then move on to the next chapter. Presented herein is a brief compilation of applied aerodynamics without detailed theory beyond what is necessary. Many excellent textbooks are available in the public domain for reference. Because the subject is so mature, some nearly half­century-old introductory aerodynamics books still serve the purpose of this course; however, more recent books relate better to current examples.

3.1.1 What Is to Be Learned?

This chapter covers the following topics:

Introduction to aerodynamics Atmosphere through which aircraft flies Useful equations

Airflow behavior past a body; viscosity and boundary layer con­cepts introduced to explain drag Aircraft motion and the forces acting on it Aerofoil definition and classification

Definition of relevant aerodynamic coefficients (e. g., CL, CD)

Lift generation, aerodynamic center, and center of pressure Types of stall

Comparison of aerofoils and selection of appropriate choice Introduction to high-lift devices Transonic effects (area rule)

Wing aerodynamics (3D geometry)

Aspect ratio correction (2D to 3D)

Wing planform reference area definition, dihedral angle Mean aerodynamic chord Compressibility effect Wing stall and twist

Influence of wing area and span on aerodynamics Finalizing wing design parameters Empennage, tail volume definition, canard Fuselage

Undercarriage (see Chapter 7)

Nacelle and intake Speed and dive brakes

3.1.2 Coursework Content

The information in this chapter is essential for designers. Coursework is postponed until Chapter 6 (except for the mock market survey in Chapter 2). Readers should return to Chapters 2 through 5 to extract information necessary to configure the aircraft in Chapter 6.