Chapter 4 helps the reader develop a basic understanding of boundary layers and their impact on aerodynamic flows, and be able to obtain solutions for basic laminar flows and use the results to estimate properties, such as boundary layer thickness, shear stress, and skin friction. Descriptions are included for the characteristics of turbulent boundary layers, and how they compare to laminar boundary layers. Readers will be presented with information on how drag is impacted by laminar and turbulent boundary layers, including friction and separation. Analysis approaches will be presented to estimate turbulent boundary layer properties, such as boundary layer thickness, shear stress, and skin friction, including how to complete a control volume analysis of a boundary layer flow. Information is also presented for how to calculate the heat transfer and heat-transfer rate for a constant-property flow.

Basic concepts are developed for supersonic airfoils, including why supersonic airfoils have low lift-to-drag ratios compared to subsonic airfoils. Supersonic airfoil flows are discussed, leading to a basic understanding of the flow around supersonic airfoils and the shock/expansion wave patterns that develop. Three supersonic airfoil theories are then developed, including linear theory, second-order theory, and shock-expansion theory.

Learn about the primary ways to determine the aerodynamics of a vehicle, including semi-empirical methods, as well as various fidelity levels for computational approaches to predicting aerodynamics. Readers should be able to determine which levels of computational aerodynamic tools are appropriate for determining various aerodynamic characteristics (e.g., stall, cruise drag, cruise lift). Know the advantages of ground-based experimental testing, as well as the limitations and inaccuracies, as well as flight testing. Understand why the integrated triad of ground test, flight test, and computational simulation are important.

The chapter begins with the basic thermodynamic concepts that form the basis of high-speed flow theory, including a basic physical understanding of the second law of thermodynamics. This results in the ability to use the isentropic flow relationships in analyzing the properties of a compressible flow field, which results in the ability to analyze flow in a stream tube, and understand how a converging–diverging nozzle works. The basic relations for determining the change in flow properties across shock waves and expansion fans are developed, which make it possible to analyze flow fields using shock and expansion calculation methods. The basic relations for viscous flow are developed, leading to the relations for calculating the local skin-friction coefficient for a compressible boundary layer. The reader will then be able to understand the cause and effect of shock–boundary layer and shock–shock interactions. Finally, concepts for how flight vehicles are tested in wind tunnels are developed, which explains why it is difficult to fully model full-scale flight characteristics.

Readers will learn why aerodynamics is important in determining the performance characteristics of airplanes. This will begin with a development of a basic understanding of fluid properties such as density, temperature, pressure, and viscosity and how to calculate these properties for a perfect gas. Basic details about the atmosphere are presented and why we use a “standard atmosphere” model to perform aerodynamic calculations; learn how to perform calculations of fluid properties in the atmosphere. Basic components of an airplane are presented and descriptions are included to describe what the components are used for.

Readers will understand the physical laws that form the basis of the fluid equations of motion, and will learn how to obtain the equations of fluid motion in both derivative and integral form. Presentations are included to show how to apply the equations of motion to calculate properties of fluid flows. Readers will understand dynamic similarity and how to calculate Mach number and Reynolds number, including descriptions of the various Mach and Reynolds number regimes and their distinguishing characteristics.

The concept of circulation is presented, including the physical and mathematical concepts of circulation and lift. A description of how potential flow theory is used to model flow for airfoils, including the predictions of lift. Readers are presented with the concept of the Kutta condition, including how it impacts the development of airfoil theory. Thin-airfoil theory is developed for symmetric and cambered airfoils and methods for prediction lift and pitching moment are presented. The accuracy and limitations of thin-airfoil theory is also presented. Descriptions are presented for why laminar flow airfoils have different geometries than airfoils used at higher Reynolds numbers. Finally, high-lift systems are discussed, including why they are important for aircraft design.

The chapter will begin with the five characteristics that distinguish hypersonic flow from supersonic flow and then discuss each of the characteristics. Analysis methods will then be discussed, including Newtonian and Modified Newtonian methods, as well as tangent wedge and tangent cone methods. Analysis techniques are developed to determine the flow characteristics in the region of the stagnation point of a hypersonic vehicle, as well as the lift, drag, and pitch moment for simple geometries at hypersonic speeds. Information on the importance of heating at hypersonic speeds will be presented, followed by analysis approaches for estimating heating rates on blunt bodies. Finally, the complexities of hypersonic boundary-layer transition are introduced, including details about why transition is so challenging to predict.

Basic concepts are presented to show the difference between airfoils and wings, as well as the physical processes that cause those differences, such as wing-tip vortices. A physical description is presented for the impact of wing-tip vortices on the flow around the airfoil sections that make up a wing, and lift-line theory is developed to predict the effects of wing-tip vortices. A general description and calculation methods are presented for the basic approach and usefulness of panel methods and vortex lattice methods. A physical description for how delta wings produce lift and drag is also presented, including the importance of strakes and leading-edge extensions. High angle of attack aerodynamics is discussed, including the physical mechanisms that cause vortex asymmetry. Unmanned aerial vehicles and aerodynamic design issues are discussed. Finally, basic propeller theory and analysis approaches are introduced, including the use of propeller data to design low-speed propellers.

Readers will understand what is meant by inviscid flow, and why it is useful in aerodynamics, including how to use Bernoulli’s equation and how static and dynamic pressure relate to each other for incompressible flow. Concepts are presented to describe the basic process in measuring (and correcting) air speed in an airplane. A physical understanding of circulation is presented and how it relates to predicting lift and drag. Readers will be presented with potential flow concepts and be able to use potential flow functions to analyze the velocities and pressures for various flow fields, including how potential flow theory can be applied to an airplane.