Test techniques used by nasa for investigating dynamic stability characteristics of vstol models

Abstract

The three techniques covered in the paper are 1) the free-flight technique for studies of the motions of remotely controlled models with complete freedom, 2) the control-line technique for studies of the longitudinal motions of laterally restrained models, and 3) the forced-oscillation method for quantitative determination of the dynamic stability derivatives. The test techniques and hardware used in the tests are described, but the emphasis is placed on the use of the various techniques, with illustrations of the types of results that have been obtained. The two flight techniques are particularly valuable in providing an over-all view of the basic characteristics of a configuration. The test results are usually qualitative, but very often they outline quickly the areas of satisfactory behavior as well as areas in which further research is needed to produce acceptable flight behavior. In cases where some improvement in flight behavior is required, the changes can be made very quickly and cheaply at model scale, and the effects of the changes can then be evaluated rapidly by subsequent flight tests. Correlation between model tests and experience with full-scale aircraft has proven to be very good, as long as proper consideration is given to Reynolds number effects. The forced-oscillation tests are made to provide dynamic stability derivatives for theoretical analyses and simulator studies.