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Prediction of Lift and Drag on a Flight Vehicle
We treat aerodynamic forces as though they could be separate entities acting on various components, such as wings and bodies. For example, we show that the drag on a wing consists of several parts, including profile drag contributed by the pressure forces over the surfaces; skin-friction drag due to viscous interactions on the surfaces; and induced drag, which largely is due to three-dimensional effects involving vortices produced near the wing tips in the process of lift generation. It is implied that when these effects act in unison, our estimates can be combined in a simple, linearly additive way to determine the characteristics of the complete aerodynamic assembly. However, it is not clear that these models are dependable when the wing is attached to a fuselage or when nacelles containing engines, fuel, or external stores are attached to the wing. Is there some type of mutual influence or interference among the components? What happens if the surfaces are degraded by the presence of rivet heads or lap joints in the skin? What happens if the tail surfaces lie in the wake of the wing? What changes in the flow-field results when a propulsion system is operating? What happens if turbulent eddies from a separated flow in one component enter the otherwise laminar flow on another? There is a seemingly endless list of such questions: Some were adequately addressed in the past in a practical manner; some await satisfactory resolution.
We now must ask questions regarding the application of basic aerodynamic analyses of the type presented in this textbook to a complete aircraft or watercraft (i. e., a boat or submarine) or, perhaps, even ground vehicles. Such questions immediately invoke specialized answers; generalities are difficult to make. However, we attempt to set the stage for the student’s further studies in this important area. A short but useful bibliography is included to aid in the process of reducing the basics to a form that can be applied in solving real problems.
