Aircraft response to atmospheric turbulence is a basic problem in aeronautical design. Several uncertainties still exist about the most adequate mathematical model for it. A recent investigation conducted by AGARD revealed that different users follow very different criteria.
The reasons for this diversity in analysis methods is only partially due to the randomness of the phenomenon. Three elements are the ingredients: structure, aerodynamics and turbulence distribution. No special problems arise from the first element, since structural dynamics and programs relevant to it are well established. For the aerodynamic model, the only choice is between quasi-steady and unsteady formulation, the latter being by far heavier than the former. For turbulence distribution, as is well known(2-4), two different approaches are used, time history and power spectral density (PSD); both are used in the regulations of national certifying agencies. For the latter the turbulence power spectrum must be given, and the aircraft response is evaluated through the classical theory of random vibrations.