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CIRCULAR 9 7 7, U. S. DEPARTMENT OF AGRICULTURE 



For large areas the consecutive flights are made in opposite directions 

 with a tight bank and turn at each end, but if the area is both wide 

 and long a double-strip pattern may be used to advantage. In this 

 pattern the turn at the end of each run is more gradual, and the 

 return run is made several swaths away from the first one or through 

 the center of the plot. For an area requiring eight swaths, for 

 example, the order of flying would be swaths 1, 5, 2, 6, 3, 7, 4, and 8, 

 swaths 1 to 4 being flown in one direction and 5 to 8 in the opposite 

 direction. 



An experienced pilot can cover the small areas thoroughly without 

 the use of swath markers, but for most flight operations marking of 

 the swaths at some point is necessary to insure even coverage. Various 

 types of markers have been used, such as cloth flags or cones on poles, 

 weather balloons held by strings, and smoke grenades. Fluorescent 

 cloth for flags is more visible under some conditions than ordinary 

 white cloth. Weather balloons are satisfactory if a source of hydrogen 

 or helium for inflating them is readily available. Smoke grenades 





Figure 23. — Smoke grenade on a pole as marker for an airplane spray run. 



(fig. 23) are probably the best, especially for large operations, except 

 when the wind is so strong that the smoke is rapidly dispersed. 

 Ordinarily the smoke is visible for several miles, and when used in 

 woods the grenades can be raised on poles to get the smoke above the 

 treetops. Another advantage is that they keep the pilot and ground 

 crew T s informed of changes in the wind direction. Since the emission 

 of smoke from a grenade is of short duration, careful timing must be 

 used in starting them to insure a good cloud when the pilot is lining 

 up his run. In covering large areas the plane is flown on a compass 

 course lined up to fly over the marker, which is moved the proper 

 interval bv the ground crew after each run. 



