Lighter aircraft save fuel and are environment friendly, but they also need to be safe and offer comfort for passengers. Gusts of wind are a particular challenge for lightweight aircraft, because they can cause the wings and horizontal stabilisers to oscillate, subjecting the passengers to a shaking motion. This has prompted the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) to study a model of a lightweight aircraft's wing and tail unit in a wind tunnel at its Göttingen facility. This image shows a computer simulation of the turbulence around models of a wing and horizontal stabiliser, as would occur during a gust of wind. The red areas show strong vortices, the blue shows areas with opposite rotation.