Trajectories and stability of trailing vortices very near the ground

Trajectories and stability of trailing vortices very near the ground

Drummond, A.M.
Onno, R.
Panneton, B.

National Research Council Canada, Institute for Aerospace Research

1991-12-31

The behaviour of the trailing vortices of a Harvard aircraft used as the spraying vehicle during a set of experiments in aerial spraying over flat terrain for agricultural applications is discussed. The aircraft flew at a nominal attitude of 3 m (10 ft.) above ground at a speed of 56.7 m/s (110 knots). The stability and trajectory of a chosen element of the trailing vortices were measured by analyzing movie films taken by a ground-based camera and by a camera in a helicopter have ring at about 244 m (800 ft.) above the aircraft. The vortices decayed by core bursting in every case and the time to burst was usually in agreement with other published data for a light aircraft out of ground effect. The downwind vortex almost always burst betore the upwind vortex and in most cases, both upwind and downwind vortices exhibited about the same amount of rebound even though the downwind vortex generally had a shorter lifetime. The classical inviscid theory for vortex descent was not a good model for the current experiments but it was able to predict with some success the lateral separation between the vortices when the aircraft wing tip height was arbitrarily reduced by a factor of 0.85. It was concluded that vortex core bursting and rebound must be included in any procedure for calculating aerial spray deposit on the ground.

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National Research Council Canada

Campus only

Institute for Aerospace Research Aeronautical Note IAR-AN 74; NRC No. 32151

Aerospace Engineering Reports

report

(c) 1991 National Research Council Canada