The Design of Sailplanes for High Performance: An Analysis of the Basic Requirements for Maximum Performance in Thermal Soaring

A sailplane designer will normally base a new design on his experience of the relative success of various earlier types in competitive flying and will be guided by a few simple performance criteria such as minimum sinking speed, glide ratio and the less precisely defined property of ‘penetration’ (this being, roughly, the ability to achieve a good glide ratio at a high forward speed). This empirical approach has resulted in the evolution of an aerodynamic form of considerable efficiency. It is not easy, however, to see precisely why the present form has proved so effective or what potential development lies ahead. One reason for this is that none of the criteria mentioned is an absolute index of efficiency nor does it represent the range of operations that a sailplane is called upon to cover in practice. A clearer insight demands a deeper analysis of the basic requirements for sailplane performance, to see whether a more effective index of efficiency can be found. Such an index is developed in this paper and the effectiveness of varying the main design parameters is examined with its aid.