UBRARV 
 
 March 1951 ^^ pLANT BOARU ET-294 
 
 United States Department of Agriculture 
 
 Agricultural Research Administration 
 
 Bureau of Entomology and Plant Quarantine 
 
 DUAL SPRAY EQUIPMENT FOR AIRPLANE SPRAYING TESTS 
 
 By J. M. Miller, Division of Forest Insect Investigations, Bureau of 
 Entomology and Plant Quarantine, and D. A. Isler, Division of Farm 
 Machinery, Bureau of Plant Industry, Soils and Agricultural Engineering 
 
 For several years the Bureau of Entomology and Plant Quarantine, in 
 cooperation with the Bureau of Plant Industry, Soils and Agricultural 
 Engineering, has been developing and testing aerial spray equipment for 
 use in controlling forest-insect pests. The principal objective of this 
 work has been to develop a system that will distribute a uniform deposit 
 of properly atomized spray over a swath of maximum width. In addition 
 to the problems involved in the design and construction of this equipment, 
 it has been difficult to devise a method of evaluating its performance, or 
 of comparing the effectiveness of various arrangements of its parts, of 
 different pump pressures, or of different insecticide formulations. 
 
 The performance of an aerial spray system is governed by many 
 factors, not all of which are controllable. The controllable factors 
 include type of nozzle or discharge orifice, position of the orifice, 
 pressure exerted on the spray, and insecticide formulation. The un- 
 controllable factors include direction and velocity of the wind, temperature 
 and humidity, and convection, inversion, and turbulence of the air. To 
 determine the most satisfactory nozzle to use, its correct position, or 
 the proper pressure, it is necessary to hold the renaaining factors con- 
 stant. For wind direction and velocity this is practically impossible. 
 
 The method used in the past to evaluate performance has been to fly 
 the plane directly into the wind while liberating spray over the center of 
 lines laid out at right angles to the line of flight, collect samples of spray 
 deposit at regular intervals along these lines, and determine the quantity 
 by laboratory methods. Despite efforts to fly the plane directly into the 
 wind, slight shifts in wind direction while the plane was passing over the 
 sample lines frequently caused drifting of the spray. It was not unusual 
 for the wind to affect the deposit pattern to a greater extent than changes 
 in type or arrangement of equipment. 
 
 This paper describes the construction and installation of an aerial 
 spray apparatus with which various types and arrangements of spray 
 nozzles, pressures, and insecticide formulations can be tested under 
 
identical meteorological conditions. Its use permits a direct comparison 
 of the effect of any of these factors on spray dispersal. While it does not 
 eliminate the need for replicating test flights, it does provide a simulta- 
 neous check flight for each test. This apparatus consists of two complete 
 spray systems, each consisting of a tank, pump, boom, and control acces- 
 sories mounted on a single plane. 
 
 Equipment 
 
 The equipment used in constructing this dual spray system is a 
 modification of previously described equipment (U. S. Bur. Plant Indus., 
 Soils, and Agr. Engin., Inform. Ser. 87), and it has been installed in a 
 Stearman N2S5 airplane. The layout of the two systems is shown in 
 figure 1. 
 
 1. Tank 
 
 2. Pressure gage 
 
 3. Pressure regulator 
 
 4. Shut-off valve 
 
 5. Centrifugal pump, 
 
 wind-driven 
 
 6. Gear pump, engine-driven 
 
 7. Boom and nozzle 
 
 Figure 1. --Schematic diagram of dual spray units. 
 
-3- 
 
 Two spray tanks (1) are located in the front cockpit, one in the space 
 normally occupied by the front seat and the other immediately behind the 
 firewall. A wind-driven 1 l/4rby 1-inch centrifugal pump (5) is used in 
 one system and an engine-driven gear pump(6) of the same size in the other. 
 The gear pump is used to produce higher pressures in tests of the effect 
 of pump pressure on spray dispersal. The centrifugal pump is mounted 
 between the landing- gear struts and the gear pump on the generator pad 
 of the aircraft engine. 
 
 Both systems are equipped with adjustable pressure regulators (3) in 
 order that desired spray pressures can be maintained uniformly. Each 
 system is equipped with an emergency dump valve located in the tank 
 outlet line (not shown in fig. 1), and in both the spray-control valves (4) 
 are of the quick-opening gate type. Controls for pressure regulators, 
 spray control valves, and dump valves are located in the cockpit, within 
 easy reach of the pilot. 
 
 Each spray system has its own boom. They are mounted one imme- 
 diately behind the other, approximately 9 inches below the lower surface 
 of the lower wing, and they extend from wing tip to wing tip (fig. 2 and 3). 
 The inboard half of each boom consists of 1 l/8-inch tubing, the outboard 
 half of 1-inch tubing. It will be noted in figure 2 that the boom outlets 
 are directed downward and to the rear at an angle of 45°. Short nipples 
 and 45*^ elbows are used for attachment of the nozzles. This arrangement 
 prevents the spray from wetting the booms when tangential -type hollow- 
 cone spray nozzles are used with the orifices directed either forward or 
 backward. Variations in orifice direction are obtained by rotating the 
 booms on their long axes or by changing the fittings. 
 
 Performance 
 
 Results of tests with this dual spray system indicate that it is a distinct im - 
 provement over earlier systems. No longer is it necessary, for instance, 
 to attempt the well-nigh impossible task of duplicating meteorological 
 conditions in successive test flights to compare performances of various 
 nozzles, nozzle positions, and pump pressures. 
 
 Comparisons of performances between the two systems can be made 
 by using different dyes in the liquids of the two systems. For accurate 
 comparisons there must be little or no combining of the drops from one 
 system with those from the other while the spray is falling through the 
 air. Tests have shown that there is very little such combining of drops. 
 The quantity of spray delivered by each system at any point in the swath 
 is determined by the use of a sensitive spectrophotometer. To record 
 the quantity of the two dyes on the sample, it is only necessary to expose 
 the sample to two different specific wave lengths. The quantity of spray 
 deposited by each system at any station can be calculated from the quantity 
 of dye recorded by this means. 
 
Digitized by the Internet Archive 
 in 2013 
 
 http://archive.org/details/dualsprayequipmeOOunit 
 
Figure 2. --Details of attachment of dual spray booms and nozzles. 
 
 Figure 3. --Stearman airplane with dual spray equipment. 
 
UNIVERSITY OF FLORIDA 
 
 3 1262 09242 9447