Spray method by means of the helicopter has many problems，like as the pollution due to the sprayed chemicals. Therefore, this study has a purpose of the drift prevention of sprayed particle.
The drift of sprayed particle was affected by the wind velocity of both down wash through the rotor and natural wind. And the nature of down wash had wind velocity in proportion to the rotor radius, and the maximum wind velocity was at 80% of rotor radius owing to the contraction of air flow, getting through the simple test by the Model Rotor.
Based on this nature, theoretical analyses on the drift under the effects of the down wash and the natural wind, respectively, were carried out.
On the result, the drift was affected by the sprayed altitude, forward velocity of helicopter, radius of rotor, and radius of sprayed particle, etc. And the position of spray apparatus aiming to shortening the drift, and a method of data analysis were proposed.