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



of the spray were drilled in the boom, and a breaker bar with a slightly 

 beveled face was mounted behind the boom to increase the breakup 

 of the spray droplets as they emerged from the drilled openings. 

 Spray nozzles were also used on the spray booms instead of the drilled 

 openings and breaker-bar device. 



After the war large numbers of surplus training planes, principally 

 PT-17's, became available, and most of the civilian mosquito-control 

 work has been done with planes of this type. A tank of 75 to 90 

 gallons' capacity was installed in the front cockpit, and the insecticide 

 solution fed to the spray booms under pressure furnished by a wind- 

 driven pump mounted on a landing-gear strut or suspended beneath 

 the fuselage back of the landing-gear assembly. Either a gear pump 

 with pressures up to 100 p. s. i. or a centrifugal pump with pressures 

 of 25 to 30 p. s. i. is used. The centrifugal pump permits the use of 

 suspensions as well as solutions. Tanks of 80-gallon capacity have 

 been approved for planes with 225-hp. engines and tanks of 200-gallon 

 capacity for planes with 450-hp. engines equipped with motor-driven 

 pumps. 



This type of equipment, which can be installed without structural 

 alteration to the plane, has been used on military planes of various 

 models. Equipment installed in a C-47 plane for use in Alaska con- 

 sisted of two wing booms each 18 feet long and a center boom 8% feet 

 long, two 375-gallon tanks mounted in the front of the cargo compart- 

 ment, five 24-volt fuel-transfer pumps each with a capacity of 850 

 gallons per hour at a pressure of 14 p. s. i., and a switch box with a 

 control for each boom mounted on the rear wall of the pilot compart- 

 ment for operation by the copilot. 



Spray -outlet holes of 0.064-inch diameter were spaced 2}{ inches 

 apart on the rear face of each boom, a total of about 80 on each 

 18-foot section. With two pumps in operation, the delivery rate of 

 20-percent DDT airplane spray was 28.3 gallons per minute, thus 

 giving a coverage of 226 acres per minute at an air speed of 140 m. p. h. 

 and allowing for a swath width of 800 feet. This gave a dosage of 

 about 1 pint of solution containing 0.2 pound of DDT per acre. For 

 this output the center section boom was not needed. The droplets, 

 as estimated in the calibration tests, had a mass median diameter of 

 136 microns, with 77 percent having a diameter of less than 100 

 microns. The equipment later adopted for the C-47 by the Special 

 Aerial Spray Flight of the Tactical Air Command consisted of full- 

 length wing booms equipped with nozzles and a centrifugal pump 

 operated by a 1/2-hp. gasoline motor and developing pressures of 

 about 25 p. s. i. 



A C-47 plane with two underwing booms about 17 feet long with 

 12 nozzles (Spraying Systems No. 1/8 B-10) on each was employed 

 in tests at Belts ville, Md., by members of the Division of Forest 

 Insect Investigations of the former Bureau of Entomology and Plant 

 Quarantine. With the 20-percent airplane spray solution and a 

 pump pressure of 20-21 p. s. i. the discharge rate was 37 gallons per 

 minute. The flights were made into the wind at an elevation of 

 about 90 feet and with ground wind speeds varying from less than 1 to 

 6.2 m. p. h. As estimated from the droplets recovered on dyed cards 

 in six tests, the average swath width over which the deposit was at 

 least 0.05 gallon per acre was only 475 feet and the maximum about 



