Aeroelastically Corrected Stability Derivatives

An important by-product of both the early and modern quasi-static aeroelastic methods is a set of aeroelastically corrected stability and control derivatives, such as Cma and Cms, which can be used in the ordinary equations of rigid-body motion. For example, Etkin (1972) derives the quasi-static aeroelastic contributions of symmetrical first-mode wing bending to tail and wing lift, which become ingredients in stability derivatives.

The wind tunnel provides a complete set of rigid-body aerodynamic stability and con­trol data for most new airplane projects. These data are usually corrected for quasi-static aeroelastic effects using the concept of elastic-to-rigid ratios (Collar and Grinsted, 1942). Elastic-to-rigid ratios preserve in the aeroelastically corrected data all of the nonlinearities and other specific detail of the rigid data. Finite-element methods provide a modern source of elastic-to-rigid ratios for this purpose.

Wind-tunnel tests of elastic models have also been used to obtain aeroelastically corrected stability derivatives. Still another approach is the wind-tunnel test of a rigid model that has been distorted to represent a particular set of airloads, such as those caused by a high load factor. A distorted model of the Tornado was tested in a wind tunnel, to determine aeroelastic effect on stability derivatives.