Control testing in wind tunnels

Abstract

If ad hoc wind-tunnel work on controls is to be of value it is essential that the same precautions should be taken as are necessary for fundamental research. For the model there must be careful selection of material and accurate finish. Attention must be paid during the experiments to the observation and control of transition in the boundary layer; a suitable technique for doing this is outlined. Control power may be measured on complete models of reasonable size, but usually hinge moments can only be measured satisfactorily on partial models, which provide control surfaces large enough for accurate reproduction of contours and detailed features. The great care and time involved in the construction of models and testing of controls for design purposes are frequently not justified when the only purpose is to determine the effects of balance, gaps, or small changes of shape. On the model scale the main object of tests should be to determine the properties of the basic control shape chosen by the designer, recognising that there will in general be differences of detail in the actual aircraft for which a margin must be allowed.