INSECTICIDES AND REPELLENTS 



53 



estimate of the amount of spray deposit can thus be obtained. The 

 approximate quantity can also be estimated by comparing the cards 

 with calibrated standard cards. 



It is usually desirable, especially at low wind speeds, to apply the 

 sprays at right angles to the wind direction, to give a wider and more 

 even distribution. However, it is not always feasible to fly cross 

 wind, or the wind direction may vary during the operation. For 

 this reason the minimum effective swath width should be determined 

 for flying into as well as cross wind. 



After the swath width, dosage, and concentration of spray have 

 been decided upon, the required flow rate (F) per gallon per minute 

 for a known plane speed may be determined by the formula 



F=SD W 14,95 



in which S indicates the speed of the plane in miles per hour, D, the 

 dosage in gallons per acre, and W, the swath width in feet. 



This formula may be rearranged to give any one of the factors 

 when the others are known. For example, the dosage for a known 

 flow rate may be determined by Z)=495 F/SW. It is often more 

 convenient to adjust the concentration of the spray to give the desired 

 amount of DDT per acre rather than to change the flow rate. 



Flight pattern. — The area to be treated should be studied both from 

 detailed maps and from the air, and then the flight pattern and 

 boundary markers should be selected and arrangements made for 

 marking the swaths. The flight pattern should be planned to begin 

 the runs on the downwind side to avoid flying into the drifting spray 

 on subsequent runs. For short areas the pilot may make all the 

 runs from one direction, circling completely around on the turns. 



DROPLETS PER 

 SQUARE INCH 



550 450 350 250 150 50 50 150 250 350 450 550 600 



DISTANCE FROM LINE OF FLIGHT(FEET) 



Figure 22. — Distribution of a spray deposit on the ground at different distances 

 from the line of flight in tests with a C-47 plane equipped with underwing 

 spray booms. 



