In the design of keels and rudders well established principles from aircraft aerodynamics may be employed. Although most aircraft today fly at speeds at which the compressibility of the air is important (more than 100 m/s), much information may be gleaned also for the incompressible water flow, partly due to the early aerodynamic research carried out more than 50 years ago. In this chapter we will first give a short introduction to the basic principles of the flow around a wing (keel or rudder) at an angle of attack, and the corresponding force generation. The remaining part of the chapter deals with the two main aspects of wing design: the planform and the wing section. As in the previous chapter we also provide statistics, enabling the designer to select a suitable size for the keel and rudder.
Flow around a wing When a wing works properly the flow 011 both sides is attached. No separation occurs, and the streamlines around a section of the wing resemble those in Fig 6.1. If we assume for a moment that the wing is infinitely long with a constant cross-section and that the flow is at right angles to the span, there is a stagnation point close to the leading edge (nose), where the flow is divided into two parts, following the upper and lower surfaces of the section, respectively. At the stagnation point itself there is 110 flow in either direction along the surface, and since the fluid does not penetrate the wing there is no velocity at right angles to the surface either. A similar point with zero velocity is found at the trailing edge (tail) of the section. This is the so called two-dimensional case, where the properties at all cross-sections are the same. In practice this is accomplished by putting the wing between two walls at right angles to the span, for instance in a wind tunnel. The properties of the section (profile) may then be investigated.
Fig 6.1 Flow around a wing section
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Lets start by identifying what exactly certain boats are. Sometimes the terminology can get lost on beginners, so well look at some of the most common boats and what theyre called. These boats are exactly what the name implies. They are meant to be used for fishing. Most fishing boats are powered by outboard motors, and many also have a trolling motor mounted on the bow. Bass boats can be made of aluminium or fibreglass.