Lift and Drag at Low Speeds

In the previous chapter the flow around basic bodies such as cylinders, spheres and wings was treated. Special attention was paid to drag. Although the discussed aerodynamic principles are valid for other parts of an aircraft as well, it is particularly important for any knowledge of aeronautics to understand how lift is generated and which consequences the lifting force has for the drag of an aeroplane. This chapter will focus on the properties of

aerofoils

and

aerofoil sections

. An aerofoil is a streamline body designed in such a way that, when set at a suitable angle to the airflow, it produces much more lift than drag. Aircraft wings and tailplane surfaces are examples of aerofoils, though tail surfaces are functionally different from wings and will be discussed separately in Chapter 7. This chapter is restricted to lift and drag at subsonic speeds at which the compressibility of air can be presumed irrelevant. Aerodynamic properties of high-speed aerofoils will be discussed in Chapter 9.