5

Introduction to Steady Aerodynamics

Aircraft are able to fly because the lift generated by the airflow over the wings and horizontal tail surfaces supports their weight. For a flexible aircraft, these lift forces give rise to deflections in the aerodynamic shape, which in turn change the characteristics of the airflow, hence leading to aeroelastic phenomena and affecting the dynamic loads. An understanding of how aerodynamic flow around a two-dimensional aerofoil (a section of a typical wing profile) or a three-dimensional aerodynamic surface generates the forces and moments that are applied to aircraft during flight is very important in order to be able to develop mathematical models that describe the aeroelastic behaviour. In this book, the majority of the mathematical treatment concerns lifting surfaces that are described as continuous, but in some cases the surfaces are discretized, as discussed earlier in Chapter 4.

In this chapter, some of the fundamentals of fluid mechanics and aerodynamics are reviewed, with particular emphasis on the lift/drag forces and moments that occur when air flows around a two-dimensional aerofoil or three-dimensional aerodynamic surface (i.e. wing, tailplane or fin). Other parts of the chapter examine the atmosphere, as well as the effect of adding camber and control surfaces to the wing. The final sections briefly discuss supersonic and transonic flows. Both continuous and discretized wings are considered. More detail about the material in this ...

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