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On problems of flight over an extended angle-of-attack range

To ensure successful operation of aircraft at high angles of attack (or high lift) conditions, attention must be paid to two basic design aims. These are the ability to achieve an adequate high lift performance and the need to ascertain that inadvertent penetration of the post-stall regime (or more generally any critical condition, which may for a particular aircraft be considered as replacing the conventional stall) does not lead to uncontrollable and thus potentially dangerous flight conditions. The first aim is concerned primarily with the maintenance of the flow pattern associated with the normal flight regime and the augmentation of the lifting capability of the wings to sufficiently high lift coefficients. It, therefore, relates to the design of the wings, leading-edge devices and the flap system, if any, in respect of the onset of the flow breakdown.