Some wind-tunnel developments of the spoiler as a form of lateral control

Abstract

The following investigation formed part of a more general research on problems associated with high-lift flaps. To obtain the maximum advantage from such devices, a satisfactory alternative to the conventional aileron is required, permitting the flap to extend over the full wing span. Spoilers meet this condition, but further development to improve their hinge moment and response characteristics was clearly necessary at the time. The present work was undertaken for this reason. The static rolling, yawing and hinge moments were examined on (1) a series of hinged-plate spoilers, (2) a series of circular-arc spoilers, particular attention being given to the development of satisfactory hinge moment characteristics. Subsequently, the latter, which proved to be of considerably greater promise with respect to the above consideration, were investigated for response. For a spoiler of the type illustrated in Fig. 2b, the hinge moment is sensitive to the degree of bevel y. By hinging the surface concerned, so that y can vary with displacement of the spoiler, it is shown, by means of an example, that promising hinge-moment characteristics are obtainable with a quite simple link system for controlling the bevel angle in the necessary manner. The present experiments, however, are mainly of interest in emphasizing the value of this device as a very effective way in which the required hinge-moment characteristics can be approached, and are by no means an exhaustive survey of what may be achieved in this direction. From the dynamic experiments, it is concluded that a spoiler-aileron fitted to a wing with full-span flap of the dimensions considered in the present investigation will have a satisfactory response under high speed or cruising and climb conditions in flight, but may become deficient in this respect as the stall is approached. An intersurface slot behind the spoiler, when the latter has to be located so far from the trailing edge (at approximately 80 per cent. of the wing chord), proves to be essential both in promoting a satisfactory initial development of static rolling moment, and in preventing an inadequate response. The slot, however, if unsealed when the control is not in operation, introduces a drag increment which would be excessive for high performance.