Differences in aircraft reaction between space-fixed and time-fixed simulations of wake encounters

Abstract

A simulation study was performed for quantification of the differences in aircraft reaction between space-fixed and time-fixed wake encounter simulations. In DLR’s terminology, “space-fixed” encounter simulation means that the aircraft encounters the wake on a free flight path, whereas for “time-fixed” encounter simulations the vortex induced forces and moments for a specific, predefined flight path through the vortex’ flow field are evaluated and recorded prior the actual encounter simulation. These pre-recorded force and moment histories are then played back during the encounter simulation time-based and independent on the actual position of the aircraft. The results show a good accordance in aircraft reaction between both encounter simulation methods in most cases. Only very long lasting encounters (e.g. due to very small encounter angles) showed considerable differences, although the maxima were of comparable magnitude. Assuming, that space-fixed encounter simulations show realistic encounter characteristics, the results show that time-fixed encounters are indeed less realistic but can be regarded as reasonable approach for encounter simulation.