Aerodynamics of Flight

3K 3K No Wind Vortex Movement Near Ground - No Wind 3K Wind 6K 0 (3K - 3K) (3K + 3K) Vortex Movement Near Ground - with Cross Winds Figure 5-15. When the vortices of larger aircraft sink close to the ground (within 100 to 200 feet), they tend to move laterally over the ground at a speed of 2 or 3 knots (top). A crosswind will decrease the lateral movement of the upwind vortex and increase the movement of the downwind vortex. Thus a light wind with a cross runway component of 1 to 5 knots could result in the upwind vortex remaining in the touchdown zone for a period of time and hasten the drift of the downwind vortex toward another runway (bottom). 5-10 52 Wake ends Wake begins Rotation Touchdown Figure 5-14. Avoid turbulence from another aircraft.