![]() ![]() Instead, at the instant of starting the streamlines over the rear part of the wing section are as shown in Fig. When a wing is accelerated from rest the circulation round it, and therefore the lift, is not produced instantaneously. ![]() Each of these may be treated separately but it should be remembered that they are all component parts of one whole. The vortex system can be divided into three main parts: the starting vortex the trailing vortex system and the bound vortex system. Lanchester's contribution was essentially the replacement of the lifting wing by a theoretical model consisting of a system of vortices that imparted to the surrounding air a motion similar to the actual flow, and that sustained a force equivalent to the lift known to be created. Provided the aspect ratio is fairly large and the assumptions of thin-aerofoil theory are met (see Section 4.3 above), the theory can be applied to wing planforms and sections of any shape. The aerofoil data can either be obtained empirically from wind-tunnel tests or by means of the theory described in Chapter 4. It is this derivation of the aerodynamic characteristics of wings that is the concern of this chapter. The basis on which historical solutions to the finite wing problem were arrived at are explained in detail and the work refined and extended to take advantage of more modern computing techniques.Ī great step forward in aeronautics came with the vortex theory of a lifting aerofoil due to Lanchester* and the subsequent development of this work by Prandtl.t Previously, all aerofoil data had to be obtained from experimental work and fitted to other aspect ratios, planforms, etc., by empirical formulae based on past experience with other aerofoils.Īmong other uses the Lanchester-Prandtl theory showed how knowledge of two-dimensional aerofoil data could be used to predict the aerodynamic characteristics of (three-dimensional) wings. Theoretical fluid mechanics of vortex systems are employed, to model the loading properties of lifting wings in terms of their geometric and attitudinal characteristics and of the behaviour of the associated flow processes. In this chapter such a classic theory is developed to the stage of initiating the preliminary low-speed aerodynamic design of straight, swept and delta wings. Some theories have survived to provide successful working processes for wing design that are capable of further exploitation by computational methods. The fact that low-speed flight was the classic flight regime has meant that over the years a vast array of empirical data has been accumulated from flight and other tests, and a range of theories and hypotheses set up to explain and extend these observations. Whatever the operating requirements of an aeroplane may be in terms of speed endurance, pay-load and so on, a critical stage in its eventual operation is in the low-speed flight regime, and this must be accommodated in the overall design process. ![]()
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