Physical Parameters Affecting Aircraft Spray Application - American

9 Physical Parameters Affecting Aircraft Spray Application

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 21, 2017 | http://pubs.acs.org Publication Date: January 16, 1984 | doi: 10.1021/bk-1984-0238.ch009

NORMAN B. AKESSON and WESLEY E. YATES

Department of Agricultural Engineering, University of California, Davis, CA 956

The several physical parameters affecting aircraft spray applications for (1) deposit in flagged swath, (2) deposit in extended downwind swath and (3) airborne portions of the released spray are discussed. The drop size spectrum (usually expressed as a volume median diameter) is the most significant factor affecting the spray movement. Drop size is most easily attained by using different type atomizers, or various sizes of a given type such as the hollow cone and fan series. The formulations used are custsomarily either a water base or an oil base. Considerable interest is being generated in vegetable o i l sprays which are less phytotoxic to crop plants and trees than petroleum oils. Aircraft swath data and total recovery of deposited sprays as a percent of the released material are presented for a few selected systems and formulations. Physical parameters which c o n t r o l the d i s p e r s i o n , d e p o s i t , coverage ( o f t a r g e t p l a n t s ) as w e l l as d r i f t l o s s e s of l i q u i d p e s t i c i d e s released from a i r c r a f t i n mountainous f o r e s t land are (1) spray drop s i z e and spray f o r m u l a t i o n , (2) l o c a l meteorology, (3) l o c a l t e r r a i n a t spray s i t e and (4) type of a p p l i c a t i o n aircraft* 1* The t r a n s p o r t phenomenon f o r any spray m a t e r i a l released i n the a i r i s foremost a f u n c t i o n of the p a r t i c l e s i z e and s i z e d i s t r i b u t i o n of the released spray* The p a r t i c l e d e n s i t y plays a minor r o l e , the s e t t l i n g rate from Stokes law f o r example v a r i e s as the square root of the d e n s i t y * F u r t h e r , the d e n s i t y d i f f e r ences between l i q u i d s commonly used f o r p e s t i c i d e s i s very l i t t l e , v a r y i n g only s l i g h t l y from water a t d e n s i t y of 1 gm/ml* Other f o r m u l a t i o n p h y s i c a l f a c t o r s of surface t e n s i o n , v i s c o s i t y and v i s c o e l a s t i c i t y play s i g n i f i c a n t r o l e s i n the atomization process* These are a l t e r e d by the a d d i t i o n of petroleum and vegetable o i l as solvents and c a r r i e r s as w e l l as a host of adjuvants i n v a r y i n g 0097-6156/84/0238-0095506.50/0 © 1984 American Chemical Society

Garner and Harvey; Chemical and Biological Controls in Forestry ACS Symposium Series; American Chemical Society: Washington, DC, 1984.


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amounts of the t o t a l spray to 100% use of vegetable o i l s as carriers for certain specific spray f o r m u l a t i o n s . The vapor pressure, or p a r t i a l pressure of the various multi-phase formulations can a f f e c t the rate of v a p o r i z a t i o n l o s s of the f i n i s h e d spray. The atomizers may vary i n design from h y d r a u l i c , and t w o - f l u i d to spinning screen and d i s c types* The d i r e c t i o n of the released spray relative to the a i r s t r e a m and the a i r s t r e a m v e l o c i t y ( a i r c r a f t v e l o c i t y ) r e l a t i v e to the l i q u i d emission v e l o c i t y a l s o p l a y a fundamental r o l e i n the atomization process* 2* The l o c a l meteorology, p r i n c i p a l l y the temperature and wind v e l o c i t y gradients from ground l e v e l , through the f o r e s t canopy to the spray r e l e a s e height, and to 300 m (1000 f t ) or more above the r e l e a s e height, can have a dramatic e f f e c t on the spray d i s p e r s i o n and deposit i n the target area and can i n f l u e n c e the d r i f t losses downwind f o r s e v e r a l miles* For i n s t a n c e , a temperature i n v e r s i o n c e i l i n g w i l l prevent small drop s i z e spray released below the c e i l i n g height from d i s p e r s i n g upward, thus having the charact e r i s t i c of c o n f i n i n g t h i s spray and p e r m i t t i n g i t to concentrate below the c e i l i n g and be transported f o r c o n s i d e r a b l e d i s t a n c e s on ambient winds* On the other hand, l a r g e r drops over 75 to 100 microns diameter are l e s s a f f e c t e d by a i r motion and have suff i c i e n t f a l l v e l o c i t y to deposit nearby, u s u a l l y w i t h i n 60 to 152 m (200 to 500 f t ) of the r e l e a s e * For convenience we have designated drops l e s s than 100 microns diameter as being capable of a i r t r a n s p o r t f o r 1 to s e v e r a l miles while those above 100 microns can be expected to f a l l out i n an extended swath p a t t e r n downwind* Obviously the l a t t e r w i l l be i n f l u e n c e d by the height of r e l e a s e and the wind v e l o c i t y while the airborne drops w i l l a c t u a l l y have decreased c o n c e n t r a t i o n with higher wind and more t u r b u l e n t mixing type a i r c o n d i t i o n s * The temperature i n v e r s i o n c o n d i t i o n acts p r i n c i p a l l y on the small d r i f t prone drops producing undesirable concentrations downwind* However, i t should be noted that c e r t a i n a e r o s o l i n g a p p l i c a t i o n s such as a d u l t i c i d i n g for mosquitoes r e q u i r e s the i n v e r s i o n i n order to maintain a l e t h a l downwind c o n c e n t r a t i o n * R e l a t i v e humidity a l t e r s spray drop s i z e by i t s e f f e c t on spray evaporation* 3* The type of t e r r a i n , mountains, h i l l s and v a l l e y s which c o n s t i t u t e a i r drainage systems exerts a s i g n i f i c a n t i n f l u e n c e on the c o n c e n t r a t i o n i n the downwind area from a spray r e l e a s e * The t e r r a i n along with l o c a l weather problems can act to concentrate a i r b o r n e p a r t i c l e s such as i n a v a l l e y , e s p e c i a l l l y when combined with an i n v e r s i o n c e i l i n g l e s s than the height of the v a l l e y walls* Such a phenomenon i s q u i t e common i n mountainous f o r e s t land areas and may c o n t r i b u t e to high concentrations of p e s t i c i d e s appearing i n the a i r and c o l l e c t e d by water, s o i l and p l a n t s downwind i n a v a l l e y * 4* The type, s i z e and c o n f i g u r a t i o n of the a i r c r a f t equipment can of i t s e l f have a s i g n i f i c a n t e f f e c t on swath patterns and downwind



9.

AKESSON AND YATES

Physical Parameters of Spray Application

transport of spray drops. Larger a i r c r a f t create greater vort i c i t y i n wing t i p and p r o p e l l e r areas and also because of safety requirements the l a r g e r a i r c r a f t must u s u a l l y be flown higher than small a i r c r a f t ^ at 1600 to 3200 m (500 to 1000 f t ) elevations i n s t e a d of the more d e s i r a b l e 165 to 328 m (50 to 100 f t ) above the canopy. H e l i c o p t e r equipment g e n e r a l l y i s flown at slower speed, 80 to 125 km/hr (50 to 75 mi/hr) i n comparison with f i x e d wing a i r c r a f t at 165 to 200 km/hr (100 to 120 mi/hr) f o r smaller a i r c r a f t and 250 to 500 km/hr (150 to 300 mi/hr) f o r l a r g e r m u l t i engine types. The a i r wake created by e i t h e r f i x e d or r o t a r y wing a i r c r a f t i s b a s i c a l l y a f u n c t i o n of the a i r c r a f t weight, wing or r o t o r disk loading (higher loading u s u a l l y means higher speed and g r e a t e r v o r t i c i t y ) and a i r c r a f t speed. The e f f e c t of increased v o r t i c i t y and a i r wake i s to move the spray release to a greater a l t i t u d e which i n turn produces a wider swath displacement f o r the b a l l i s t i c s i z e drops and greater d i s p e r s i o n f o r airborne s i z e drops. Studies on swath deposit and airborne drift l o s s e s have followed a basic pattern or p r o t o c o l as accepted by State and F e d e r a l regulatory agencies. For example, sprays are c o l l e c t e d on (a) a r t i f i c i a l c o l l e c t i o n sheets, such as Mylar, T e f l o n , g l a s s , metal or other m a t e r i a l s from which residues are r e a d i l y removed; and (b) plant samples are taken e i t h e r of the trees or crop plants i n the area or from plants i n f l a t s or pots which are used e i t h e r f o r s p e c i f i c plant response ( h e r b i c i d e s ) or plant spray deposit (6). A i r samples f o r airborne portions may be taken with high volume a i r samples 0.67-0.85 m (20-30 f t / m i n . ) through a glass f i b e r f i l t e r backed up with a r e s i n type (Rohm and Haas XAD) absorbing column or l i q u i d bubbler f o r gas phase trapping where desired. Any type a p p l i c a t i o n may be monitored downwind with these type of c o l l e c t o r s at ground l e v e l , or v e r t i c a l tower c o l l e c t i o n can be provided f o r impacted drops or f o r those drawn i n t o a i r samplers. The manner of site s e l e c t i o n and weather monitoring i s g e n e r a l l y r e l a t e d to the s p e c i f i c m a t e r i a l to be used or f o r e s t crop i n which i t w i l l be a p p l i e d . Progressive passes may be made across the target area or where a study i s designed f o r maximum r e t u r n of information i t i s f r e q u e n t l y d e s i r a b l e to apply a l l of the m a t e r i a l with the t e s t a i r c r a f t to a s i n g l e l i n e or pass, making 5 to 10 passes to b u i l d up a s u f f i c i e n t concentration f o r increased downwind sampling s e n s i t i v i t y . A t y p i c a l layout (Figure 1) could thus be with a sampling l i n e on a l o g r i t h m i c pattern such as 12, 25, 50, 100, 200, 300, 800, 1600 and 3200 m (40 f t to 2 mi. downwind) with the f a l l o u t , plants and a i r c o l l e c t o r s located at each of these s t a t i o n s . The a p p l i c a t i o n l i n e would be at 90 degrees to the sampling l i n e and should be of a length equal to the sampling l i n e i n order to insure deposits on the furthermost s t a t i o n when small wind v a r i a t i o n s occur. I f a v e r t i c a l tower c o l l e c t o r i s used, i t should be located w i t h i n 45 to 75 m (150 to 250 f t ) of the a p p l i c a t i o n l i n e and be of s u f f i c i e n t height to 3

3


97


ft


805

2640

4 Mylar I5X 46cm(6X I8in) sheets, all stations 2 Air filters,all except 12 5(4lft)and 25m(82ft) 4 Flats of plants at all stations Weather Station Approx. Location

North

I

402

1320

200

660

100

330

50

164

25

82

Prevailing wind direction from South

FIELD LAYOUT

8 0 5 m (2640ft)

1

2

5

-I2.5-L

41

Application Path

-40

I Mylar 15 X 46cm(6XI8in )sheet each 2ft from -12.5 to 25m (-40to-r80ft)

Figure 1 .

Field layout for aircraft spray tests.



9.

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99

extend above the released c l o u d . A 15 to 30 m (50 to 100 f t ) tower at t h i s distance w i l l handle most a p p l i c a t i o n s a p p l i e d w i t h i n 2.5 to 7.5 m (10 to 25 f t ) of the ground, higher towers would be needed f o r greater a p p l i c a t i o n heights such as above a f o r e s t canopy. The deposit of a c t i v e chemical, the d r i f t l o s s e s and drop s i z e range can be found and would be f u n c t i o n s of the spray formulat i o n s and a p p l i c a t i o n equipment which are under t e s t i n a given weather and a p p l i c a t i o n t e r r a i n . I n order to compare d i f f e r e n t t e s t run data, the r e s u l t s may be p l o t t e d as a s e r i e s of 2nd degree polynomial r e g r e s s i o n curves ( 6 ) . A c t u a l chemical a n a l y s i s of the released spray caught on the samplers provides the most accurate measure of deposit and airborne l o s s e s , but c a l c u l a t i o n of these f u n c t i o n s from the drop s i z e s found can a l s o be done. A t o t a l deposit recovery as a % of the amount released can be determined. By r e p l i c a t i n g these t e s t s under a s e r i e s of d i f f e r i n g weather c o n d i t i o n s and d i f f e r i n g t e r r a i n , we are able to observe the e f f e c t s these and other parameters have on the amount of deposit i n the target area, burden i n the a i r and residues on the f a l l o u t c o l l e c t o r s l o c a t e d at the downwind s t a t i o n s ( 2 ) . There are many s t u d i e s published on both f i e l d c o l l e c t i o n data as obtained i n a c t u a l f i e l d measurements of d r i f t - l o s s (1,2) as w e l l as from p r e d i c t i v e models of varying s o p h i s t i c a t i o n . The l a t t e r are derived b a s i c a l l y from s i n g l e drop s i z e behavior coupled with the b a s i c atmospheric d i f f u s i o n parameters ( 3 , 4 ) . The references l i s t e d are not a l l i n c l u s i v e but w i l l a s s i s t the reader i n o b t a i n i n g a broader view of a e r i a l a p p l i c a t i o n s t u d i e s . Spray Drop Size E v a l u a t i o n Because so much of the a e r i a l spray operation i s r e l a t e d to and dependent on drop s i z e c h a r a c t e r i s t i c s i t f o l l o w s that more accurate knowledge of drop s i z e and s i z e range of the released sprays would be d e s i r a b l e . A l s o s p e c i f i c e f f e c t s on drop s i z e from atomizer type, formulations and i n s t a l l a t i o n on the a i r c r a f t would not only enable more accurate e v a l u a t i o n of s p e c i f i c systems and spray r e l e a s e s , but could a l s o be used to a i d i n p r e d i c t i o n of the swath and downwind t r a n s p o r t regime f o r these r e l e a s e s . One of the newest instruments a v a i l a b l e f o r drop s i z e s t u d i e s i s the P a r t i c l e Measuring Systems ruby l a s e r . This instrument has a wide range of probe u n i t s f o r d i f f e r e n t s i z e ranges. The imaging probes w i l l measure from a minimum of around 20 microns to s e v e r a l m i l l i m e t e r s diameter while the forward l i g h t s c a t t e r u n i t s w i l l measure downward from 100 to about 0.1 microns. We are pres e n t l y using t h i s instrument f o r e v a l u a t i o n of a i r c r a f t sprays e i t h e r by mounting the probe on the a i r c r a f t for i n - f l i g h t s t u d i e s of i n d i v i d u a l atomizers or by use of a wind tunnel where a wide v a r i e t y of atomizers and formulations can be r e a d i l y handled.



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C H E M I C A L AND BIOLOGICAL CONTROLS IN FORESTRY

The use of v a r i o u s f o r m u l a t i o n a d d i t i v e s and s t r a i g h t veget a b l e o i l base sprays has been considered many times i n the p a s t . With the present favorable cost r e l a t i o n s h i p of vegetable to petroleum o i l s , a renewed i n t e r e s t has prompted us to examine the p o t e n t i a l b e n e f i t s as w e l l as p o s s i b l e problems that vegetable o i l c a r r i e r s might produce. The advantages that may occur from use of vegetable o i l base sprays are p r i m a r i l y (1) the p o t e n t i a l f o r reduction i n t o t a l volume a p p l i e d (low or u l t r a - l o w volume) and (2) the p o t e n t i a l f o r b e t t e r adherence, longer r e s i d u a l and p o s s i b l e increase i n b i o l o gical activity. The o i l s may be more compatible with c e r t a i n types of a c t i v e p e s t i c i d e formulations where s o l u b i l i t y or m i s c i b i l i t y may be increased and fiowable p a r t i c u l a t e type formulations may be b e t t e r adaptable to the o i l s than the customary water-base. But, i n order to o b t a i n a r e d u c t i o n i n t o t a l volume of a p p l i c a t i o n the drop s i z e of the released spray must be reduced i n order that coverage and contact of the spray w i t h the target i n s e c t be maint a i n e d . P h y s i c a l l y t h i s i s not d i f f i c u l t to do. For example, i f the water-base spray has an average drop s i z e of 300 microns and we reduce t h i s by one-half to 150 microns the t o t a l number of drops i s increased by a f a c t o r of 8 (2 cubed). I f the a p p l i e d volume i s then reduced from 19 A (2 g a l / a c r e ) to 2.3 i/ha (1 q t / a c r e ) the volume decrease i s a l s o by a f a c t o r of 8 which means that 2.3 Z/ha (1 q t / a c r e ) can be a p p l i e d w i t h drop numbers or equal coverage to the 19 A/ha (2 g a l / a c r e ) water-base spray. But t h i s i s not a l l of the s t o r y . F i g u r e 2 shows the graphic drop s i z e d i s t r i b u t i o n of a spray from a D6-45 (.24 cm or 6/64 i n . o r i f i c e , #45 w h i r l p l a t e ) cone type nozzle d i r e c t e d with a 165 km/hr (100 mi/hr) a i r s t r e a m . The vmd (volume median d i a . - h a l f the drop volume i s i n drops above the vmd, and h a l f below t h i s s i z e ) i s 327 microns, there are 2% of drop volume i s i n drops l e s s than 122 microns d i a . (the d r i f t - p r o n e drops) and the R.S. or width of the spray drop s i z e d i s t r i b u t i o n i s 0.71 where: Ki>

=

90% s i z e = 10% s i z e 50% s i z e

F i g u r e 3 shows data f o r a spinner atomizer i n a 110 mi/hr airstream. The vmd i s 140 microns, the % volume i n drops l e s s than 122 microns i s now 24% w h i l e the r e l a t i v e span has increased to 1.23. I t i s t h i s tremendous increase of drops ( l e s s than 122 microns d i a . ) from 2.0% f o r the 300 microns spray to 24% f o r the 150 microns spray that i s a p o t e n t i a l source of trouble from a i r borne transport of these small drops. These are c a r r i e d away from the treatment area and a p o t e n t i a l e x i s t s f o r contact with humans and animals as w e l l as unwanted deposit on non-target c r o p s . These small drops have been found at d i s t a n c e s of s e v e r a l m i l e s from the a c t u a l a p p l i c a t i o n s ( 5 ) . I f the m a t e r i a l being released i s of low t o x i c i t y , or i n a remote area, the problem i s not serious. But f o r high t o x i c i t y m a t e r i a l s the 24% l o s s which i s not c o n t r o l l e d , poses a s e r i o u s problem.



AKESSON AND YATES

30r-

D 6 - 4 6 BACK 4 0 l b / i n , 100 mi/hr 2

276 k P a , I65km/hr


20 CE

II %

ω ω

< 122 jam

nmd 263

3

100 200

400

>im

600

SPRAY DROP

800

DIA.

(MICRONS)

20r-

D 6 - 4 6 BACK

1.6 % < 122 jum 10

vmd 435

'

/im

RS.96

D I T-rrrru-^. 100 2 0 0

400

600

800

1000

1200

SPRAY DROP DIA. ( M I C R O N S )

Figure 2.

Drop size from hollow cone, D6-U6 nozzle.




70 " m 6 0 - // ^ 50-

MINI MICR0NAIR, FLOW RATE 276 kPo (40 lb/in*) NMDim 93%im

1

l5//min.(4 gol/min.)

or

ω 40 •

3

2

3020100•

L

MzLI

200

50

r

400 P A R T I C L E SIZE

ι

600 800 MICROMETERS

1000

600 800 MICROMETERS

1000

J

ι

1

VMD = I22 μπ\ R.S. « 0.99 50 %< 122 μπ\

40L

3 —I

30

Ο

> 20h

10

m

ÂÏLa-

-m L 200 400 P A R T I C L E SIZE

Figure 3 .

Drop s i z e from M i c r o n a i r spinner atomizer.



9.

AKESSON AND YATES


103

I t i s to be noted that an increased p e s t i c i d e e f f i c a c y can f r e q u e n t l y be obtained with the small drop s i z e sprays over the l a r g e r ; t h i s i n s p i t e of the 24% l o s s p o t e n t i a l that smaller drop s i z e sprays may have. Thus the i n f e r e n c e has been drawn that s m a l l drop s i z e sprays, where they can be used s a f e l y , are poten t i a l l y more b i o l o g i c a l l y a c t i v e than l a r g e drop s i z e sprays. J u s t how f a r t h i s theory can be c a r r i e d remains a f u n c t i o n not only of the basic t o x i c i t y of the a p p l i e d spray to the target organism, but a l s o i s h i g h l y dependent on a p p l i c a t i o n parameters. In g e n e r a l , f i n e sprays and a e r o s o l s are more d i f f i c u l t to c o n t r o l than l a r g e r drop s i z e sprays. Another f a c t o r d i f f i c u l t to r a t i o n a l i z e occurs when a spray cloud moves downwind. The l e a d i n g edge c l o s e to the crop canopy i s turned under w h i l e the upper por t i o n s move forward thus producing a r o l l i n g motion at the boundary of the cloud and the crop. D i f f e r e n t crop canopies would induce d i f f e r e n t degrees of r o l l i n g and contact w i t h the c l o u d . Larger drops may be shattered upon contact w i t h the canopy and t h i s t u r bulent mixing motion undoubtedly a i d s i n o b t a i n i n g b e t t e r t a r g e t coverage as w e l l as f i l t r a t i o n of spray drops from the c l o u d . The t o t a l deposit recovery of a e r i a l l y a p p l i e d sprays can be p l o t t e d as i n F i g u r e 4. Here Mylar p l a s t i c f a l l o u t sheets were l o c a t e d at 0.6 m (2 f t ) i n t e r v a l s from 12 m (40 f t ) upwind to 25 m (82 f t ) downwind and at greater i n t e r v a l s out to 800 m (1/2 mi.) (see F i g . 1 ) . These were analyzed f o r d e p o s i t of chemical and c u m u l a t i v e l y p l o t t e d by computer to o b t a i n the curves of F i g u r e 4* The two curves, one f o r a water-base ec and the other i s o i l - b a s e spray, had drop diameters of approximately 300 microns vmd f o r the water and 150 microns vmd f o r the o i l . As can be seen, the reco v e r y out to 106 m (350 f t ) i s low a t around 66% f o r the o i l and 80% f o r the water and i s r e l a t e d b a s i c a l l y to the drop s i z e being produced. F i g u r e 5 shows a s e r i e s of recovery curves f o r sprays of d i f f e r e n t drop s i z e s commencing at the top f o r Curves A, B, C of very large drop s i z e of 500 t o 1,000 microns vmd used f o r her bicides. These are produced with simple o r i f i c e - j e t and l a r g e hollow cone nozzles such as D6-46 and D6-56 (Spraying Systems Co.). The a d d i t i o n of a polymer t h i c k e n e r to a water-base spray w i l l a l s o produce very l a r g e drop s i z e . Curve D f o r a 200 microns spray and Curve Ε f o r a spinner at 150 microns vmd show r e c o v e r i e s out to 660 f t of 90% and 59% r e s p e c t i v e l y . These l a t t e r curves are f o r the drop s i z e s commonly used f o r i n s e c t c o n t r o l sprays. F i g u r e 6 shows the r e s u l t i n g downwind d r i f t - l o s s p a t t e r n when an o i l and a water-base spray of the same drop s i z e i s used. Here the evaporation of the water reduces the deposit at points c l o s e r to the a p p l i c a t i o n while the non-evaporative o i l shows a higher deposit out to about one m i l e , where the two curves c r o s s . The c h a r a c t e r i s t i c of non-evaporative o i l sprays i s to deposit i n g r e a t e r amounts out to about one mile d i s t a n c e when compared with water base sprays, a l s o the o i l appears to have l e s s m a t e r i a l l e f t to deposit beyond the one m i l e . Thus a low evaporative base spray produces a wider extended swath and r e q u i r e s wider b u f f e r s than a water-base a p p l i c a t i o n .



104

C H E M I C A L AND BIOLOGICAL CONTROLS IN FORESTRY

Figure k.

Deposit recovery, o i l and water base sprays.



Figure 5.

Deposit recovery from five different drop sizes.


C H E M I C A L A N D BIOLOGICAL CONTROLS IN FORESTRY


At.9kg/ho(llb/oc)

J_J 100

I 200

.

I

II

1

I

1000

2000

I I I

500 DISTANCE

•

I

Iι ι

5000

ι ι

(ft)

DOWNWIND

Figure 6. Spray deposit from o i l and water base sprays.



9.

AKESSON AND YATES


107

F i g u r e 7 i l l u s t r a t e s the r e l a t i o n s h i p of the (A) flagged swath width (B) a c t u a l t o t a l downwind or extended swath and (C) the a i r borne or what we i d e n t i f y as the d r i f t - l o s s p o r t i o n . Allowance must be made (such as b u f f e r zones) f o r the swath displacement which a c t u a l l y i s d e s i r a b l e i n smoothing out the f r e q u e n t l y rough d i s t r i b u t i o n patterns i n an a i r c r a f t swath (Figure 8)· The port i o n of Figure 7 w i t h which we should always be concerned i s the a i r b o r n e d r i f t - l o s s from drops of 100 microns d i a . and s m a l l e r . F i g u r e 8 i l l u s t r a t e s the swath p a t t e r n r e s u l t i n g from the use of a polymer v i s c o e l a s t i c m a t e r i a l added to the water-base spray. As can be seen the swath width i s reduced from 15 to 13 m (60 to 42 f t ) and deposit i n the flagged swath increased from 29% to 70%. But the drop s i z e has increased from around 400 microns vmd to 800 microns. This i s q u i t e s a t i s f a c t o r y as long as the m a t e r i a l being used remains b i o l o g i c a l l y e f f e c t i v e i n such l a r g e drops. But the use of polymer a d d i t i v e s i s b a s i c a l l y l i m i t e d to h e r b i c i d e s and i s not normally s u i t e d to f u n g i c i d e s and i n s e c t i c i d e s where smaller drops are needed f o r b i o l o g i c a l e f f e c t i v e n e s s . A f u r t h e r complic a t i o n i n polymer use i s i l l u s t r a t e d i n Table 1. Here a D6-46 n o z z l e i s operated at 275 kPa (40 l b / i n ) i n a 165 km/hr (100 mi/hr) a i r s t r e a m . The vmd f o r water when d i r e c t e d w i t h the a i r s t r e a m (0 degrees) i s 451 microns. When d i r e c t e d at 90 degrees to the a i r i t i s 286 microns. When the polymer i s added, the drop s i z e a t 0 degrees i n c r e a s e s to 850 and at 90 degrees to 538 microns. But note what happens to the % volume i n drops under 122 microns. With water t h i s was 1.2 and 3% f o r 0 and 90 degrees, but when polymer was added i t Was 1% f o r 0 and 4% f o r 90 degrees. Thus there would be no r e d u c t i o n i n the airborne losses w i t h the polymer added even though the swath width was narrowed and deposit i n t h i s measured or flagged swath was up from the water spray. This point must c a r e f u l l y be considered before adding a polymer to any spray. Also shown i n Table 1 i s drop s i z e data on sprays w i t h B i v e r t a spray adjuvant and chlordimeform, an i n s e c t i c i d e . These showed a small increase i n vmd when B i v e r t was added and reduced vmd w i t h chlordimeform. The % volume i n drops l e s s than 122 ym i s increased above that of water. Table 2 shows the r e s u l t s of drop s i z e s t u d i e s on an 8001 f a n n o z z l e spraying o i l and water at 0 and 90 degrees to the a i r s t r e a m of 100 mi/hr. L i q u i d pressure was maintained at 275 kPa (40 l b / i n ) . As can be seen the o i l (cottonseed) caused the vmd to be reduced somewhat, and increased the % volume i n drops l e s s than 122 microns d i a . The c h l o r d i m e f o r m - P y d r i n - o i l mixture increased the vmd s l i g h t l y . Table 3 shows a s e r r a t e d cup spinner operated a t d i f f e r e n t a i r speeds w i t h water and w i t h o i l . Again the drop s i z e decreases w i t h the o i l , but even more i m p r e s s i v e l y the drops below 122 microns have gone up s i g n i f i c a n t l y due to the charact e r i s t i c of t h i s spinner to produce small drops. The changes i n r o t a t i o n a l speed and l i q u i d flow rate a l t e r the drop s i z e s i g n i f i cantly. Table 4 presents data on the M i c r o n a i r AU 5000 operated 2

2



·.;·/ / (Large)

5-8km/hr (3-5mi/hr)

(Medium drops)

(Small drops)

F i g u r e 7.

A i r c r a f t spray p a t t e r n s .

(C) Airborne drift-loss (B) Swath displacement Indefinate distance Swath 12-I8m(40-60ft) 46-6lm(l50-200ft) Less than 100 microns 100-200 microns Drop size 200 microns and larguer AIRCRAFT DOWNWIND SPRAY P A T T E R N R E L E A S E D SPRAY DROP SIZE 3 0 0 - 4 0 0 MICRONS

+(A) Flagged

Wind


Ο

π ο π

> r

η

r Ο Ο

δ

> α

>

π

ο X m

00

ο


AKESSON AND YATES


AIRCRAFT T - T H R U S H 13.5m ( 4 4 f t ) WING , 9.2 m ( 3 0 f t) BOOM SWATH WIOTH 12.8m ,18.3 ( 4 2 , 6 0 f t ) % DEPOSITION ( S W A T H ) 2 9 % , 7 0 %

48

36

24

12

0

12

24

36

48

(ft)

Figure 8 . Aircraft swath pattern, water and water plus polymer.



88 78

90 90

237 m* (.5 p t ) Ch/19 I (5 g a l ) H 0

13.3 mi (.5 oz) Polymer/237 mi (.5 p t ) Ch/19 i (5 g a l ) H 0

2

Η Ο

2!

ο ο

> r

η

ο

r Ο

δ

H ?o -

η >

η χ m

π

70

538

268

60 69

299

61

4

1.1

3

1.2

% < 122 ]im

Ch - Chlordimeform

2

13.3 mi (.5 p t ) Bv 13.3 mi (.5 p t ) Ch/19 i (5 g a l ) H 0

2

2

64

94

90

Bv .47* (1 p t ) 19 i (5 g a l ) H 0

90

850

62

86

0

13.3 mi (.5 oz) Polymer/19 i (5 g a l ) H 0 2

286

56

100

90

2

H0

451

49

125

0

2

vmd

H0

% < 122 ym

nmd

Formulation

Direction degrees to airstream

2

TABLE I . D6-46 Cone Nozzle 275 kPa (40 l b / i n ) 165 km/hr (100 ml/hr)



15 19 18 11 14

179 174 175 200 187

78 83 84 73 81

Physical Parameters Affecting Aircraft Spray Application - American

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