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In cooperation with the
Air Service, United States Department of War
DEPARTMENT BULLETIN No. 1204
Washington, D. C. Le January, 1924
DUSTING COTTON FROM AIRPLANES.
By B. R. Coan, Entomologist, Bureau of Entomology, E. JoHNSon, Agricultural
Engineer, Bureau of Public Roads, and G. L. McNen, First Lieutenant,
Twenty-Second Observation Squadron, U. S. Air Service.*
CONTENTS.
Page. Field dusting studies—Continued. Page.
lirst use of airplanes in applying Tests of various insecticides___ AIL
TLV ie nts G(s es = 1 Different calcium arsenates_ 3
Dust hopper construction__________ 2 head Sacsenate = 2 = ene 32
The hand-crank hopner _______ 3 PATS, Sree se. 5 eee ae
The air-suction hopper________ 5 pbscryatieys on boll weevil con-
Phe -payion. hopper. ’-> -—- iadleg Mee CP Ole S22 ee eel 33
Field dusting studies _____._______ 9 Gael: aie iene of airplane
Focaviom and plan >. 6 2+ 2 -s= 9 Sips 0a See eee ee a a ee et Se ae Se
Leafworm conditions _________ 12 Acreage dusted per lion oe ee 34
Behavior of the dust in the air_ 12 Advantage of airplanes after
Influence of various air condi- Terni) f= sae == Pee 3
js Til Gs = Se Sere 5 eas ee eee 18 Suitability of terrain —-—2_-—_— 35
Adhesion of poison to plants__ 21 Control of dust spread______~_ 36
Manipulation of planes_______ S PAL Suggestions for future investi-
Flying methods used__________ 22 Tallon Ss wey Piste ee 3
Rate of dust -delivery_________ 26€ Characteristics of airplanes used___ 3
Directing plane operation _____ an b-@ostiot operations =: 552 Sees 39
Leafworm control operations __ (eConelusiena: 22.3 t1e a a 40
FIRST USE OF AIRPLANES IN APPLYING INSECTICIDES.
The possibility of applying insecticides by means of airplanes was
first brought to public attention by the work conducted in August,
1921, by the State Experiment Station of Ohio, in cooperation with
the United States Air Service, near Dayton, Ohio.? This particular
test consisted of distributing lead arsenate from an airplane over a
grove of catalpa trees in an ‘effort to poison the larve of the catalpa
sphinx (Ceratomia catalpae Bdv.), which were defoliating the grove.
The experiment proved quite successful and im mediately suggested
the possibility of using the airplane for the control of other insect
pests. Especial interest was aroused in the possibility of using the
airplane to combat the cotton boll weevil (Anthonomus grandis
Boh.), and plans were made for such experiments to be conducted
+Im conducting the experiments described in this bulletin the writers were assisted by
a number of men from the Delta Laboratory force at Tallulah, La. They are particu-
larly indebted to the following: A. J. Chapman, RU. Make S. B. Hendricks, *R.-E-
Hodges, I. T. Jones, H. Kirkpatrick, P. D. Sanders, C.. M. Smith, and M. T. Young.
2 Fighting Insects with Airplanes. Neillie, C. R., and Houser, J. L. In Nat. Geog.
Mag., vol. 41, no. 3, pp. 232-238, March, 1922.
61979°—24 1
~
2 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE.
during the season of 1922. It was evident, however, that in the pre-
liminary tests, since boll-weevil control is not as immediately obvious
and easy to measure as that of the leaf-feeding insects, difficulty
might be anticipated in determining the thoroughness of poison dis-
tribution. Consequently, it seemed likely that the principal measure
of success in distribution over the plants which might be obtained
from purely preliminary experiments, would be plant analyses to
determine the amount of arsenic present, which is a very unsatis- |
factory expedient at best.
An opportunity to place the tests on an entirely different basis,
however, was afforded by the outbreak of the cotton leafworm (A/a-
bama argillacea Hiibn.) which appeared over several of the Southern
States. The first generation of this worm became active during
the latter part of July, in rather unusual numbers, indicating a heavy
infestation in the next generation, which might be expected about
three weeks later. This provided an excellent opportunity for testing
airplanes as a means of distributing poison over the cotton fields by
making an effort to control the leafworms rather than the weevils.
Arrangements were accordingly immediately made with the Air
Service of the United States Army for detailing planes for these
tests. Tallulah, La., was selected as a suitable location for the ex-
periments, since the conditions found there, as regards flying, are
fairly representative of the more favorable conditions encountered
in the Cotton Belt. Furthermore, the location of the Delta Labora-
tory of the United States Bureau of Entomology at that point pro-
vided exceptional facilities for the construction and other work in- |
volved in the tests. Two planes were detailed to the tests, arriving
about the Ist of August. These were piloted by Lieuts. G. L. Me- |
Neil and Charles T. Skow. Lieutenant McNeil remained throughout
the period of the tests, while Lieutenant Skow was replaced after
about 10 days by Lieut. L. C. Simon. AI] of these men and the equip-
ment were provided by the Montgomery Aerial Intermediate Depot
(now Maxwell Field) of Montgomery, Ala. In addition to the pilots,
three enlisted men were provided, and the experimental work was
further assisted for a few days by the presence of a photographic
plane from the same field, piloted by Lieut. L. P. Arnold, the photo-
graphic work being done by Lieut. J. M. McDonnell.
DUST HOPPER CONSTRUCTION.
The first flights in these tests were made with limited quantities of
poison, carried in bags in the plane and either dropped over the
side by hand or emptied out through an opening in the bottom of
the fuselage. After a few such preliminary flights, it was found ad-—
visable to construct “ hoppers” which would carry the poison dust
and deliver it into the air at a controlled rate. The hopper which
was used at Dayton was constructed to hang outside of the fuselage, -
but it seemed decidedly preferable to fit the new hoppers inside so as
to discharge through the fuselage. The cowling was removed from
the observer’s cockpit of the plane,’ and the hopper was designed to
utilize as much of the available space as possible and still leave room —
for a man to ride behind the hopper to operate it.
* The planes provided for this work were of the type commonly called the ‘ Curtis H,”
équipped for training observers, and thus had a rear cockpit, but without dual controls. —
7? ie,
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DUSTING COTTON FROM AIRPLANES. S.
THE HAND-CRANK HOPPER.
The type of hopper first constructed is illustrated in Figures 1
and 2, Figure 1 showing the manner of installation in the plane
and Figure 2 the hopper as it appeared after removal from the plane.
For convenience the discharge was arranged through the bottom
of the fuselage, although later developments indicated that possibly
this is not the most desirable place. This hopper was constructed of
galvanized sheet metal and occupied practically half of the space
in the observer’s cockpit, leaving barely room enough for the opera-
tor to stand and turn the feeder crank. Furthermore, the presence
of the walking beam for the controls in the front end of the cock-
pit made it necessary to undercut the bottom of the hopper consider-
ably.
Fic. 1.—Curtis plane equipped with hand-crank hopper. Lid of hopper open for filling.
Outlet for discharging dust shown projecting below fuselage.
The apparatus consisted of the dust chamber, the outlet or dis-
charge tube, and the feeding mechanism. A hinged lid was provided |
for filing from the top, and the capacity of the hopper was about
12,500 cubic inches. The poison used in a majority of the tests was
the ordinary calcium arsenate sold on the market for boll-weevil
control, and all references to dusts in the following pages refer to this
material, unless otherwise stated. As the standard specifications for
calcium arsenate for boll-weevil control require a volume between 80
and 100 cubic inches to the pound, and the dust used in these ex-
periments tested practically 100 cubic inches to the pound, the hopper
capacity was approximately 125 pounds.
The outlet or discharge tube at the bottom of the hopper was
intended merely to carry the dust through the bottom of the fuselage
and drop it into the air. It was not possible in the preliminary work
4 ‘BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE.
to stream-line the exposed portion of this tube and thus avoid air
eddies. The air had a tendency to turn up into the outlet tube,
and thus interfered with the proper delivery of the dust. The eddies
created behind the tube tended also to draw the dust upward around
the fuselage instead of permitting it to blow downward. To reduce
this trouble a slot was cut through the forward side of the outlet
tube, just below the bottom of the “fuselage, and a funnel was placed
over this opening with the neck inclined downward at an angle of
about 30°. The de-
livery tube was then
cut away somewhat
toward the rear, and
the air blast created
by the movement of
the plane blowing
through this funnel
helped to break up
the dust, and blew
it downward away
from the fuselage.
The construction of
this funnel is shown
in Figure 2. While
it was not perfect,
the idea can be de-
veloped and probably
used to a very good
advantage in direct-
ing and breaking up
the dust cloud.
The dust - feeding
mechanism consisted
of a cut-off valve in
the bottom of the
hopper and a four-
bladed, rotating pad-
dle wheel. The valve
was constructed to
slide in and out un-
der the paddle wheel
; and was operated by
eg cae ein Pee ener means of 9 ae
rangement for controlling the sliding cut-off valve. and connecting link.
The paddle wheel
was revolved by the operator through a pair of sprocket gears
and a chain leading from the crank gear near the top of the hop-
per. When the valve was opened and the paddle wheel revolved,
the dust was carried from the hopper and dropped into the air
through the outlet tube.
Because of the limitations presented by the plane, it seemed im-
possible to overcome certain difficulties encountered with this type
of feeder. These will be discussed in detail under a later heading.
DUSTING COTTON FROM AIRPLANES. 5.
THE AIR-SUCTION HOPPER.
To meet the difficulties encountered with the first hopper, another
was constructed as shown in Figures 3 to 5, inclusive. This hopper
was intended to be entirely automatic in operation except the open-
ing and closing of the feeder valve. The general shape was much
the same as in the first design, and its size and location in the
plane were practically identical. In this case, however, the paddle
wheel was eliminated and a feeder inserted which consisted of a
funnel extending slightly above the upper wing and connected to
a 4-inch sheet-metal pipe which extended down through the inside
of the hopper and to within 5 inches of the bottom. At the lower
end a box-like section, 7 inches square and 5 inches deep, was con-
structed with its lower side flush with the upper end of the dis-
Fic. 3.—Air-suction hopper installed in Curtis plane. Lid of hopper open for filling.
Outlet for dust discharge is shown projecting belew fuselage, together with a portion of
lever arrangement for controlling the feed valve.
charge pipe. This section acted as a guide for a valve or sleeve
which fitted closely around it, but which was free to slide up and
down. When at its lowest position this sleeve seated on the upper
end of the outlet tube and thus prevented the dust from feeding
out, while the rate of dust flow could be controlled by varying the
height to which this sleeve was raised. The sleeve movement was
controlled through a link joining it to a lever hinged to the bottom
of the fuselage, with a sliding rod and handle attached to the other
end to bring it within reach of the operator.
The details of this internal construction are shown in Figure 5,
and the lever controlling the operation of the valve is shown best
in Figure 4.
The operation of this feeder was as follows: The funnel pointing
_ forward over the wing of the plane was, of course, subjected to a
violent blast of air while in flight, and this high-velocity current
6 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE.
of air blowing down through the tube had a tendency to create a_
vacuum around its lower end, producing a suction effect which
would pull the dust out of the hopper into the air stream whenever
the valve was lifted and would thus carry this dust out through the
discharge tube. In other words, it provided an air current running
down through the hopper and an adjustable opening in the bottom
of the hopper so that varying quantities of dust could be drawn
out with the air. When first tested some trouble was caused by the
dust packing on the sloping
bottom and in the corners
and not feeding out regu-
larly. This difficulty was
overcome by fastening a
small funnel pointing for-
ward on each side of the
top of the hopper and
connecting to each funnel
three small air tubes run-
ning down the inside of the
hopper, discharging along
the sides where the dust
had the greatest tendency
to lodge and in a direction
tending to force it under
the feeder valve. Figures
3 to 5 show the construc-
tion of these auxiliary air
lines. This device kept the
dust loose and gave satis-
factory operation, except
for the fact that no method
of closing these auxiliary
funnels was provided, and
when flying with the feeder
closed, and with only a
small amount of dust in
the hopper, the air blow-
ing down these would agi-
tate the dust and _ force
some of it out through the
cracks of the cover.
To overcome these diffi-
Fic. 4.—Air-suction hopper removed from plane, culties and also to Ee
showing details of exterior construction. the general efficiency of
operation, a modified de-
sign has been prepared as shown in Figure 6. In this case the aux-
iliary funnels have been discarded and the same effect obtained by
connecting these side air lines to the main air duct inside the hopper.
Back pressure in the hopper is prevented by a butterfly valve in the
main air duct just below the intake funnel which closes whenever dust
discharge is cut off, and thus air is passing through the hopper only
when the feeder is open. In addition, the starting and stopping of the
feed has been separated from the control of the amount of feed. A
P|
DUSTING COTTON FROM AIRPLANES. ae
special crank controls the elevation at which the feed regulator is set in
the hopper, and this regulator remains at this point as long as the
same feed rate is desired. The control of delivery is accomplished by
a separate sliding valve operating across the bottom, of the hopper.
For convenience, the first hopper is termed the “ hand-crank ” type
and the other is called the “ air-suction ” type. These two were left
in the two planes throughout the experiments, and all field applica-
- tions were made with one or the other. The manner of operating
- them is shown in Figure 7. The operator stood upright in the rear
_ Fic. 5.—Interior construction of air-suction hopper. Shows main air tube extending
= down through hopper, with box valve at its lower end fully raised. Also shows
arrangement of auxiliary air tubes along the side to keep dust from clogging.
cockpit behind the hopper and controlled the delivery of the dust.
_ This was not a particularly pleasant position but sufficed for the
_ preliminary experimental tests.
‘THE DAYTON HOPPER.
_ _ The hopper which had been used in the experiments at Dayton,
Ohio, was shipped to Tallulah as soon as the tests were arranged. It
arrived about the time the hoppers described above were completed,
_ and was used in a few flights. As shown in Figure 8, this hopper
- was constructed to hang over the side of the plane to the right of
and just in front of the observer’s cockpit. The rate of feed was
> Pe aye
8 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE.
controlled by a sliding valve at the bottom and rear side of the
hopper, while the dust was discharged by a small paddle wheel op-
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Fic. 6.—Diagrammatic sketch showing details of coustruction of improved type of air-
suction hopper. See text for details.
erated by a hand crank through two sprockets and a chain. Clamps
were provided on the inner side for attachment to the upper and
lower longerons of the plane.
: DUSTING COTTON FROM AIRPLANES. 9
FIELD DUSTING STUDIES.
Following the completion of the two very crude hoppers described,
no further efforts were made to perfect the mechanical delivery of
the material, and the tests were devoted to a study of whether cotton
plants can be effectively covered with poison by means of airplanes.
At the outset two problems were paramount: First. Can the planes
be operated over a cotton field in such a manner that the field will
be thoroughly subjected to the cloud of dust? Second. Can the
dust be forced down from the plane into the cotton plants and be
made to adhere to them in a quantity sufficient to control insects?
LOCATION AND PLAN.
Two farms situated from 14 te 5 miles from Tallulah were selected
for the study. Mosaic maps of these made from an elevation of 10,000
Fic. 7.—Dusting plane as used in 1922 ready to take off. The experimental hoppers used
required operation by an extra man who stood upright as shown. Future equipment
on utilize this additional space for poison and the dust delivery will be controlled by
the pilot.
feet are shown in Figures 9 and 10. A large lespedeza meadow
from which the hay had just been cut proved to be an ideal landing
field.. A tent was provided for the storage of poison and other
equipment. Acetylene lights were used for illuminating the field
before daybreak when early morning poisoning was planned, although
no actual flying was done at night. A tower was erected for the
support of wind instruments, to provide definite information on the
conditions of air movement under which the experiments were con-
ducted. This tower was so arranged that the anemometer and wind
vane were mounted about 15 feet from the ground. Records were
_ taken at five-minute intervals on both wind velocity and wind direc-
_ tion throughout the day for the period of the experiment.
_ The landing field was near the center of what is called Shirley
_ plantation. This property was selected because it is a fairly typical
cotton farm, and also affords a wide range of environmental condi-
61979° —23 2
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10 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE.
tions under which to operate. There are approximately 2,000 acres
in the entire property, 675 being in timber and 1,325 in cleared land.
The cleared acreage was distributed as follows: Cotton 400 acres,
corn 250 acres, meadow 250 acres, soy beans 100 acres, pasture 75
acres, weeds 250 acres.
A sketch map was prepared to show the location of the different
fields on the Shirley property, and each cut was numbered, for con-
Fic. 8.—The ‘ Dayton hopper”? removed from plane. This hopper was attached outside
the body of the plane.
venience in keeping records as well as for directing the operation of
the planes. The mosaic map taken photographically from a plane,
shown in Figure 9, was not available until practically the end of the
experiment, but the need for it was very apparent throughout the
work. In arranging the program of work for a day, it frequently
proved difficult to provide a description based on ground conditions
which would exactly locate the area in mind. Such a mosaic map
would also have been of great value in planning in advance the
methods of flight for each field.
Ty (eee
Like all the country in the so-called “ Mississippi Delta” district,
the Shirley plantation is absolutely flat and consists of a large clear-
‘ing irregularly surrounded by timber, with some fields out in the
fg.
Air
Fourth Photo Section,
DUSTING COTTON FROM AIRPLANES. 11
of cotton fields included in experimental dusting
Arnold and McDonnell,
Lieutenants
, Showing cut numbers
La
(Photo made by
a ei
Army.)
Portion of Shirley Plantation, Tallulah,
Vaiss
9.
Landing field indicated by cross mark.
Service,
Iria.
_ open and others tucked back into the timber line. The treatment of
these different fields gave valuable information on the problems
which will be presented by different conditions when attempts are
made to dust from the air.
ue. rire a
12 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE.
Hermione plantation, adjoiming the Shirley property, was selected
as representing a very different type. (See fig. 10.) “This property
is a comparatively narrow strip slightly more : than a mile fia , @X-
tending east and west, bordered on one side by a bayou and on the
other by small clumps of timber. This property presented much
more favorable conditions for low flying than were found on most
of Shirley, because only a few cabins were present in the fields,
except a row along the edge of the bayou. It was especially favor-
able for airplane w vork in the opportunity offered for straight flights
a mile long.
Hermione plantation consists of approximately 1,000 acres, 850
being cleared and the remainder in timber. The cleared land was
distributed as follows: Cotton 270 acres, corn 175 acres, peas 10 acres,
alfalfa 80 acres, pasture 20 acres, open ‘but not cultivated 300 acres.
LEAFWORM CONDITIONS.
The Shirley and Hermione properties were both fairly heavily
infested with the cotton leafworm during the first generation. A
very large number of these pupated successfully in the fields, which
had been practically stripped of foliage by that generation. These
pupe matured and the eggs which’ were laid by the emerging adults
began to hatch about August 20. The number of adults became so
exceedingly great that the infestation of worms which developed
proved to be one of the heaviest ever noted by the writers. Prac-
tically every plant had numerous eggs, and as these hatched some
fields were found to have apparently an average of about 50 worms
per plant. As the infestation varied somewhat from field to field,
and eggs were laid in some fields earlier than in others, it was
necessary to poison the fields at different times. Careful records
were kept on the worm infestation of each field and the individual
fields were poisoned as became necessary for the control of the worms.
Many variations were introduced in the experiments. In some in-
stanc es the worm infestation was allowed to develop more heavily
than in others. The operation of the planes was varied to include
flights at different elevations, at different times of the day, and under
different air conditions. In addition, some poisons were tested
merely to study their suitability for distribution from the plane as
compared with ordinary calcium arsenate.
BEHAVIOR OF THE DUST IN THE AIR.
The behavior of the dust in the air was the subject of the first
studies conducted. In ordinary poisoning of cotton, what has been
termed the “dust cloud” method has been developed. The dusting
machine passing between or over the cotton rows blows out the cal-
cium arsenate in a fog which penetrates between all portions of
the cotton plant, and consequently covers every exposed particle of
plant tissue. Successful dusting of this type can be done only when
the air is calm, and its success is greatly enhanced by the presence
of moisture on the cotton leaves. For these reasons or dinary cotton
dusting has become almost entirely a nocturnal operation, beginning
usut ally during the period from 6 to 8 o’clock in the evening and
continuing in the morning until the dew dries from the leaves, and
the breeze springs up, W hich is usually some time between 6 and 8
, CAULIY “S °*Q ‘aTATag ATyY ‘MOI}~eg OJON YMNo’ ‘JJauuoqoyw pue plourly sj}uruodyNoryT
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14 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE.
Fic. 11.—Dusting plane in operation, showing behavior of dust as discharged under the
body.
Fic, 12,—Dusting plane in operation showing spiral travel of dust caused by rotational
flow of air from the propeller.
DUSTING COTTON FROM AIRPLANES. 15.
a.m. The most favorable conditions for dusting are those existing
from daybreak until very nearly the end of the dusting period, as
the air is especially humid and hazy at that time, and the dust hangs
among the plants well. As a general rule, in the daytime, the dust
is whipped away from the nozzles of the dusting machine and blows
off in the air without reaching the plant.
The first series of flights were made during the day over Shirley
cut No. 2, which immediately adjoined the landing field and offered
a convenient opportunity for studying the behavior of the-dust in
a fairly typical field.
These first flights furnished an absolute surprise. It was found
that when the calcium arsenate was dropped from the plane it was
immediately broken up into a circular cloud which was quickly
Fic. 13.—Dusting plane directly approaching camera, showing trend of dust cloud. Note
how this is blown both downward and to the left of the line of flight of the plane.
blown down among the plants. This was obviously due to the tre-
mendous rush of air past the plane and the additional blast created
by the propeller, or, as it is commonly termed, the “slip stream.”
This combined air blast was so terrific that the powder encountering
it became entirely subjected to its force and the effect of ordinary
air conditions was very largely overcome. Throughout the experi-
mental period flights were made at varying elevations, ranging from
5 feet above the cotton plants to 50 feet above them, and it was almost
always possible to distribute the poison from 25 feet or lower, regard-
less of air conditions. It was sometimes possible to distribute the
dust down among the cotton plants from even as high as 50 feet or
more. Apparently the explanation of this fact lies in the air cur-
rents set up by the plane and its propeller.
Owing to the combined influence of the forward movement of the
plane and the rotation of the propeller, the plane in flight is sur-
16 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE.
rounded by a body of air moving backward considerably faster than
the plane moves forward, and this air flow follows a spiral course,
tending to one side and decidedly downward. Dust dropped from
the plane into this air current immediately becomes subjected to its
influence, this air current being so exceedingly powerful that it com-
pletely counteracts, for some “distance behind the plane, all light
breezes, or other slight air movements existing on the ground. Con-
sequently, for some “distance to the rear of the plane, the dust is still
entirely under the control of this air movement set up by the plane
itself.
I'1G. 14.—Dusting plane just starting across cotton field, illustrating the manner in which
the hopper outlet is opened just after passing the edge of the field. The air current
from the propeller carries the dust backward to the margin of the cotton.
The dust cloud from the planes used in these tests followed a
hollow spiral course, with a decided turn to the left and downward.
The three illustrations shown in Figures 11, 12, and 13 bring out
fairly well these characteristics of dust behavior.
Owing to the extreme crudity of the hoppers and the feed mecha-
nism used, it was necessary, in order to release the quantity of dust
required by the speed of the ‘plane, to drop the poison in large masses,
and to depend upon the air current to break these up. “This was
accomplished fairly well, but there was always a certain percentage
of the material which adhered together in the form of pellets and
dropped immediately to the eround, thus becoming so much waste.
This is an undesirable feature which can be corrected by experimental
development, but which it was not possible to eliminate during these
preliminary experiments.
DUSTING COTTON FROM AIRPLANES. 17
In Figure 11 the behavior of the dust immediately after flowing
from the hopper is noted, and in Figure 12 is seen particularly the
decidedly spiral nature of the cloud following the plane. In Figure
13 is shown, as well as possible, the tendency of the dust to blow to
the left of the line of flight and downward. A1] of these effects were
exceedingly important in the dusting operation. In fact, the down-
ward tendency of the air current is probably one of the greatest con-
tributing factors toward success in forcing the poison dust down
among the plants, regardless of existing air currents.
The effect of the backward blast of the slip stream was quite im-
portant. The dust being delivered under the plane, instead of going
directly to the ground, was blown backward from the point of deliv-
Fie. 15.—Dusting plane in operation in “straight-away” flight. This view shows the
- beginning of the trail of dust behind the plane. The plane is operating about 25 feet
above the plants near midday. The dust does not come in actual contact with the plant
= about the point indicated by a. See Figure 16 for remainder of dust cloud on this
ight.) :
ery by this blast, and in some instances it was found that the dust
was shot 100 feet or more to the rear of the point where it was
dropped from the plane. The practical application of this point is
illustrated in Figure 14, which shows the manner of starting the
flow of dust in crossing a field of cotton. Instead of opening the
hopper at the edge of the field, it is opened a short distance after the
plane has passed into the field, and this backward blast shoots the
dust back to the margin of the cotton. This is also of importance in
connection with maneuvering for dusting difficult situations, as will
be shown later.
Figures 15, 16, and 17 probably illustrate as well as possible the
behavior of the dust after it passes beyond the direct influence of the
61979°—24——_3
18 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE.
air currents created by the plane. In Figure 15, in which the plane is
flying about 15 feet above the cotton plants, it will be noted that to
the point marked @ the dust cloud has followed a regular form, and
has not yet touched the cotton plants. During this time it is still
being carried around the spiral and is rolling over and over. At a,
however, the poison is beginning to catch in the cotton plants, and at
the edge of this picture nearly all the poison is feeling the influence
of the ‘plants. Figure 16 is a continuation of the same cloud, merely
looking farther to ‘the rear. In this view the dust is spread in a fairly
uniform layer over a swath gradually increasing in width as distance
from the plane is incre: ised, and distributed among the plants, with
only a small amount of material going off in the air above. These
Fic. 16.—After taking the view shown in Figure 15, the photographer immediately
snapped this picture leoking over the tail of the photographic plane. Thus this view
shows a continuation of the same dust cloud being released in Figure 15, but consider-
ably to the rear of the dusting plane. Note how the cloud is spread out among the
plants over an area about 200 feet wide. At the time this picture was taken the
dusting plane had just laid down such a cloud nearly 38 miles long.
photographs were taken about 11 a. m., with an 8-mile breeze blowing,
which would render absolutely impossible any effort to dust cotton
with ordinary ground dusting machines. Figure 17 further illus-
trates the behavior of the dust leaving the plane. In this it will be
noted especially that the dust cloud has maintained its spiral shape
to the point marked a, but is then quickly flattened out among the
cotton plants.
INFLUENCE OF VARIOUS AIR CONDITIONS.
In the studies on operating at different times of the day and under
different air conditions, wind records were kept throughout the ex-
perimental period which showed that, as a general rule, there was a
DUSTING COTTON FROM AIRPLANES. 19
period of absolute calm between daybreak and about 7.30 or 8 a. m.
In a few instances daybreak was accompanied by a light breeze, but
this did not last long and there were still about two hours of abso-
lutely calm air. As is generally the case in the Delta country, the
dews were very heavy in the ear rly morning and usually did not dry
off until about 6.30 or 7 o’clock, with sometimes a little dampness
peeing until 8 o’clock. There was also nearly always a heavy fog
“ oround haze” among the cotton plants for the first hour or so
after daybreak.
A short time before daybreak on the day when these particular
tests were undertaken, this haze extended from 50 to 100 feet in the
Fic. 17.—Typical dust cloud being laid down in cotton field by plane. Note particularly
that from the plane to the point marked a the dust cloud is rotating spirally above the
plants and without touching them. At this point, however, the diameter of the cloud
becomes large enough to reach into the plants and the cloud very quickly loses its
spiral shape and flattens out among them. This plane was flying about 35 feet above
the plants.
air in a very irregular form. Just about daybreak it settled into a
very heavy fog, blanketing the earth in a layer from 20 to 30 feet
thick. This condition was ideal for the operation of ground dust-
ing machines, but gave very peculiar results in airplane dusting.
The planes had been prepared late the preceding evening, and the
motors were warmed before the first break of day. Just as soon as
it was light enough to see to fly the planes took off, giving a very
weird effect in the ground haze. This haze was so heavy that vision
did not extend far enough down the field to see them when they left
the ground, and they seemed to simply disappear in the fog. Thirty
feet above the ground. the pilots found that they were out of this fog,
with perfectly good air and vision for flying, but from the ground it
20 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE.
was difficult to see the planes operate. The planes then crossed back
and forth over the cotton fields, flying at about the same level as
during the daytime earlier in the work (about 15 feet above the
eround), and a most curious effect was noted. Instead of a white
dust cloud being swept out behind the plane, almost none was visible,
although the feed valve was wide open and putting out dust at the
usual rate. At this elevation the planes were flying inside of the fog
of ground haze, and they seemed to churn out a channel just slightly
larger than the propeller. The dust delivered was entirely confined
by the wall of fog surrounding this channel and did not spread out
at all, merely coming down in a strip which did not cover more than
three rows of cotton.
In the next flights, made just as soon as the hoppers could be re-
loaded, the planes were operated a few feet above the top of the fog,
and the behavior of the dust changed entirely. It was blown down-
ward until it encountered the fog, but instead of immediately
penetrating through it, it spread out on the top of the fog in a
layer from 50 to 100 feet wide. It seemed to remain at this point
without motion, and the observers standing about in the cotton field
under this fog were puzzled to know what ‘would become of the dust.
It could be observed on the fog for a few moments and then it
seemed gradually to disappear. About the same instant, however,
everyone in the cotton field noted that the air was filled with fine,
almost invisible, particles of dust falling to the plants. After about
two minutes the plants, which had been perfectly green before,
presented the whitened appearance of a very heavy dusting.
Unfortunately various difficulties prevented more careful studying
of this development, so the writers really do not yet know whether
such conditions are exceedingly favorable or exceedingly unfavorable
for airplane dusting. Certainly it seems useless to fly the plane
within the ground haze, but when the dust is distributed on top of
this fog it apparently is spread very thoroughly and settles on the
plants in an effective manner. Further studies must be conducted on
this point, however, before any definite conclusions can be reached
regarding oper ation under these conditions. A few analyses were
made of ‘plants treated during the fog, which indicated satisfactory
arsenical distribution and adhesion, though these can not be taken
too seriously. The fields treated in this manner showed satisfactory:
worm control, but again no final conclusions are possible because
these fields were not as heavily infested with worms as many others
in the experimental area,
Following these tests, flights were made over a period of several
days at intervals during the day, from early morning until late even-
ing, to study the behavior of the dust under the different air condi-
tions. Immediately after the period of calm in the morning there
was usually a light breeze of from 2 to 4 miles an hour, which “eradu-
ally increased to from 4 to 10 miles an hour by midday. This per-
sisted until about 3.30 or 4 in the afternoon, when the morning proc-
ess was reversed and the air again became calm slightly before dark.
In these flights it was found that the dust could be blown down
among the cotton plants at practically any time of day under the
conditions prevailing through the period of these experiments.
Considerations of safety indicate, however, that flying for dusting
should be confined to about seven or eight hours—about four hours
DUSTING COTTON FROM AIRPLANES. 2
in the early morning and three in the late afternoon. Any attempt
at low flying during the middle of the day is dangerous on account
of rough air, and the air temperature is such that the motors over-
heat very badly in a short time.
ADHESION OF POISON TO PLANTS.
To determin2 the amount of arsenic which adhered to the cotton
plants, a series of plants were collected in a line parallel to and
_ directly under the path of the plane, and in parallel lines at varying
_ distances on both sides of the path of the plane. Chemical analyses
_ of these plants showed not only the amount of poison present on the
_ plants directly under the plane, but also the uniformity of distribu-
_ tion and the width of spread.
_ The first series of records of this sort were used in checking up
a flight made at 4 o’clock in the afternoon between 15 and 20 feet
above the cotton plants, with a breeze blowing approximately $
miles an hour at right angles to the path of the plane. The heaviest
distribution of poison was of course. found immediately under the
plane, but there was a strip 45 feet wide on the down-wind side of
the path of the plane which showed a fairly uniform dosage of poi-
_ son. Practically this entire strip showed an arsenic recovery as high
as is normally obtained from a hand gun feeding about 10 pounds
to the acre operated directly over a row of cotton plants i in the early
morning when the plants are moist. This result was all the more
_ surprising because it was almost impossible to see any poison on these
_ plants, which still showed a higher content when analyzed than ‘is
considered necessary for weevil control. Further analyses only
confirmed these, although the series made was by no means complete,
and the results are somewhat sketchy.
; From the results of the analyses, together with the observations
__ made on worm control, however, it seems quite obvious that an aston-
ishing amount of the poison adhered to the plants over a very wide
path under atmospheric conditions such that it would be considered
absolutely impossible to make the dust stick to the plants with the
best of | present. ground dusting machines. The exact cause of this
adhesion is a complicated matter which is now under investigation.
TAD ehh ba
‘ae
ae
MANIPULATION _OF PLANES.
On the two properties on which these tests were made was found
almost every conceivable type of field as regards the difficulties
presented for airplane dusting. In the center of each property
were some cotton fields absolutely open, without obstructions of any
sort surrounding them. Around the margins were the fields ex-
tending along the timber line, which was sometimes very irregular.
Other fields consisted of small clearings of only a few acres tucked
back into the timber and in some cases surrounded on three sides
by trees 50 to 60 feet or more in height. In still other fields which -
_ had been cleared within comparatively recent years a few deadened
tree trunks were still standing, forming snags which were difficult
to see while flying and which had to be very carefully avoided.
Typical fields along an irregular timber line and containing ocea-
sional high snags are shown in Figure 18, which illustrates also the
- interspersed planting of cotton and other crops, since Fields 2i and
eee Nee Po ee ee ee
al
22 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE.
23 are cotton, while Fields 20 and 22 are corn. Cabins and adjoin-
ing outbuildings were present in many fields, and the bayou which
adjoined Hermione on one side and the canal which ran through
the center of Shirley were both lined with trees.
Each type of field was studied as an individual flying problem,
and efforts were made to decide upon the most efficient and safest
manner in which to fly that particular field. Especial attention
was devoted to those fields that presented unusual difficulty for fly-
ing. Throughout the work the individual cut of cotton was treated
as the unit, rather than lining up a series of cuts in a row which
could be treated by straightaw ay flights. In any commercial use
of the planes, every effort should of course be made to arrange the
I'ic. 18.—An oblique view from about 500 feet elevation of Shirley Plantation, Cuts 20 to
23, inclusive. This illustrates the type of flying problem presented by such fields,
extending irregularly along timber and containing occasional isolated tall snags.
cotton and the flying so that straightaway flights as lone as possible
may be used.
Wind direction occasionally proved important in deciding the
manner in which a field should be flown. It is safer to fly low
against the wind than with the wind, and the same degree of sta-
bility can be maintained with a slower ground speed ‘against the
wind than with it. This factor, however, was important ‘only near
the middle of the day, as in arly morning and late evening the
wind velocity was not sufficient to cause difficulty.
FLYING METHODS USED.
The usual manner of treating a field consisted of flying back and
forth on paths which permitted the dust clouds to overlap slightly.
DUSTING COTTON FROM AIRPLANES. a3
The plane would start in along one edge of the field and gradually
work over to the other. Whether the plane was flying with the
rows or at right angles to them seemed to make no important differ-
ence in the behavior of the dust cloud. Usually the plane maneu-
vered at an altitude of from 50 to 100 feet or more until the right
point was reached for entering the field. It then dived down, and
if possible reached the desired altitude of from 10 to 25 feet above
the plants just before coming over the edge of the field. The plane
was then leveled out and shot across the field at this elevation. At
first the manner of leaving the field at the end of each trip was
based somewhat on the surrounding conditions, but it was soon
found that the efficiency of the treatment could be considerably in-
creased by “ zooming” or turning upward sharply just as the plane
reached the edge of the field. This is because the dust is carried
back for some distance by the slip stream, and if the plane is zoomed
as the feeder is closed the last dust.delivered is blown back into the
edge of the cotton field, giving a heavy treatment for the row ends.
In many instances, owing to the crude feeder attachments, the de-
livery of dust did not begin quite quickly enough, and an area of
50 feet or more at the edge of the field where the plane entered was
thus left untreated. To correct this condition, after flying back
and forth over a field in one direction until the field had been covered,
the plane usually made one trip across each edge of the field at
right angles to the previous course, thus making sure of getting an
application on the row ends. This necessity could of course be
eliminated with better feed-valve construction and more accurate
contro] than was possible in this work. |
In treating a field extending along timber it was often possible
to operate without difficulty by simply flying parallel to the timber
line. In some instances, where a field was adjoined on two or more
sides by timber, right-angle corners were presented. After a little
experiment it was found possible to treat these in either of two ways.
If the timber was not too high, the plane would fly directly at the
timber line and zoom upward sharply so that the tail pointed down-
ward and the dust was thus blown down in the corner of the field.
Where this was not possible the plane was flown parallel to one
side of the timber directly toward the right-angle corner and banked
sharply into a climb so that the tail of the plane was again turned
toward the corner. The backward blast of the propeller then blew
the dust into this corner. It was thus found possible to treat any
such situation which was encountered, even though the plane could
not actually be flown over all of the cotton.
Another problem which presented itself was the dusting of cotton
immediately adjoining the cabins. In the district where these ex-
periments were conducted, cotton is raised almost entirely on a tenant
basis, each family having its quota of from 10 to 50 acres which
is cultivated on some share basis. The average per family is
somewhere between 20 and 30 acres. The home is usually either
within, or closely adjacent to this area, and with its outbuildings and
garden occupies a block of perhaps 100 by 200 feet. A considerable
percentage of the cotton fields are dotted with these houses, or
“cabins,” which present obstructions to entering the field. On the
other hand, the cabins are nearly always only one story high, and
are usually the.tallest portion of the obstruction, unless trees are
24 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE.
present mm the yard. By maneuvering the plane through sharp
climbs, rapid dives, or quick turns, the cabins can be avoided with-
out difficulty, and dust can be delivered to situations which at first
seemed utterly out of reach.
Cuts 62 to 64, inclusive, on Shirley plantation presented special
problems. (See fig. 19.) A few years ago these fields were the bed
of a swamp lake, but they were drained and made subject to cul-
tivation by the canal which now extends through Shirley plantation.
At that time the undergrowth was all cleared from the fields, but
many of the cypress trees which were scattered through the lake
were left standing. At present these cuts contain 49 such trees from
60 to 70 feet tall and growing at very irregular intervals. Cotton is
Pic. 19.—Oblique view of Shirley Plantation, Cuts 62 to 64, inclusive, taken from 500 feet
elevation, showing the difficult flying problem presented by cotton growing among
cypress trees.
grown throughout this area right up to the trunks of the trees. These
fields were considered the most difficult in the community for air-
plane dusting. In fact it appeared to everyone except the pilots
that the treatment of these fields was absolutely out of the question,
but they volunteered to dust them. The leafworms developed a fair
infestation only, but still sufficient to require treatment for control
on two different occasions.
Upon examining the fields carefully the pilots found lanes be-
tween the trees navigable for airplane operation, and twice dusted
them in a manner which permitted perfect worm control with the
use of only about 3 pounds of calcium arsenate per acre at each treat-
ment. It was found that most of this cotton could be treated by
direct blast, and that comparatively little of it must be dusted by
drift of poison. After watching this performance the writers were
5
=
DUSTING COTTON FROM AIRPLANES. 25.
convinced that it was possible to deliver dust into almost any field
which would be encountered, as certainly this group presents the
most difficult flying problem in the entire community.
The remaining type of woodland field is well illustrated in
Figure 18. These cuts all extend back into the timber line, and Cut
21 contained several single trees and old snags which stood at some
distance from the timber line, thus increasing the difficulty of getting
poison back to the cotton adjoining the timber. Nevertheless, all of
these fields were poisoned very effectively so far as worm control was
concerned.
There were many fields on Shirley out in the center of the plan-
tation, where they are absolutely free from obstructions of any sort
(see fig. 9), and thus permit maneuvering the plane at any desired
elevation without worry.
Figure 10, showing the general view of Hermione plantation,
illustrates fairly ideal conditions for flying. The three tiers of cuts
extended between the bayou and the timber line paralleling both. One
cabin is present in the corner of Cut 16 and another in Cut 17. Aside
from these, all cabins are in a row along the side of the bayou. Since
these fields extend slightly over a mile along the bayou, it would
be possible to make straightaway flights of a mile back and
forth until overlapping strips had been laid down from: the woods
to the bayou, with only a few cabins to avoid. Cotton extends to
the bayou between these cabins and presents a more difficult problem
of poisoning, but it was found possible to maneuver the planes in
and out between these cabins to treat all of this cotton.
The ends of the fields immediately adjoining the timber presented
a slightly different problem. The timber edge is not a straight line
(see fig. 10), but curves in and out, and cotton is planted in these
small indentations. These were rarely more than 20 or 30 feet
deep, however, and they were poisoned very easily in the following
manner :
The pilot flew the plane on a line paralleling the timber and
whenever he passed one of these short indentations he maintained
his straight line until practically at the end. At this point he would
bank the plane sharply away from the timber; that is, the plane
would be turned somewhat on its side with the wing tip away from
the timber lower than the other, and thus presenting the bottom of
the fuselage somewhat toward the timber line. In addition the turn
of the plane in this maneuver would aim the tail slightly into the
indentation. The whole operation took very careful judgment, but
no pilot remains healthy very long without this qualification, and if
properly done, the slight swing of the plane twisted the dust cloud
over and swept it down through the area in the indentation. The
plane was then immediately righted and placed on a straight course,
to repeat the operation at the next indentation.
The methods which have been described for using straightaway
flights of course present the most efficient manner of treating a planta-
tion laid out like Hermione, and furthermore give the largest acre-
age capacity for the plane. This method, however, was followed
only long enough to obtain a few comparative figures, and in all
other cases the various cuts were treated individually, the plane
_ turning back and forth until one cut had been completed before
moving to another one.
26 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE.
RATE OF DUST DELIVERY.
A number of straightaway flights were made to obtain data on
the rate of delivery of dust from the planes. One plane was loaded
with a known quantity of dust and flown on a straight line across the
fields, paralleling a straight road several miles long. The feeder
valve was opened at a certain starting point marked on the ground,
and dust delivery was continued until the hopper was empty. A
second plane followed this one, flying perhaps 100 feet higher and
carrying an observer who watched the behavior of the dust de-
livered from the first plane, noting carefully with a stop watch the
time from first delivery until the end of the dusting. In addition,
the point at which the dust supply was exhausted was marked by
the second plane, and the distance back. to the point of starting was
measured. In this way the time of delivery of a hopper charge, as
well as the distance it would last, was determined.
The first tests of this nature were conducted with the hand-crank
hopper with the feed mechanism as at first designed. One hundred
and twenty pounds of 100 cubic inch calcium arsenate were loaded
into the hopper, and the dusting plane was flown straight away at
full speed above the cotton plants. The type of dust cloud being put
out can be judged from Figures 15 and 16, which were taken during
one of these test flights.
The average of these flights showed that it required 2 minutes and
15 seconds to empty the hopper each time, and during this time the
plane flew 3.3 miles. In other words, it was operating at an average
rate of ground speed of 88 miles per hour, and the 120 pounds con-
tained in the hopper lasted over a strip 17,424 feet long.
The poundage per acre being delivered depends, of course, on the
width of strip which can be considered as effectively treated. On the
basis of the figures obtained on this flight, it would be necessary to
take a strip only 50 feet wide with the plane to utilize the dust at an
average rate of 6 pounds per acre, the rate at which calcium arsenate
is usually applied in ordinary commercial dusting for boll-weevil
control. Examinations made during these flights showed very plainly
that an effective treatment was being obtained on a strip over 200
feet wide, but reducing this to 150 feet as the average width of the
strip would mean that only 2 pounds of poison was being used per
acre.
This rate of dust delivery was not considered sufficient for the
maximum dust cloud desired, as, of course, every foot which could be
added to the width of the strip at each trip by correspondingly in-
creasing the dust delivery, would reduce the number of trips neces-
sary to poison a field of cotton, and, consequently, add much to the
acreage capacity of a plane.
The feeder opening of the same hopper was therefore enlarged to
the maximum size which could be secured between the cross brace
wires of the fuselage. This allowed an outlet about 9 inches square,
and the paddle wheel was correspondingly enlarged to cover this en-
tire opening. At the same time the gear ratio of the sprockets used
for driving the paddle wheel was changed from 1 to 1 to 2 to 1, so
that the paddle wheel was operated twice as fast as by a simple hand
crank.
Throughout this work an effort was made to maintain about the
same speed of cranking, and the majority of the tests were conducted
-~
DUSTING COTTON FROM AIRPLANES. OF .
at a rate of about 30 revolutions of the crank per minute. A few
special studies were made to determine the effect of variations in
the speed of cranking. Beyond a certain point the rate of dust de-
livery was not increased in proportion to an increase in the rate of
paddle revolution, owing to the fact that after being speeded up
beyond this point the paddle revolved so fast that the spaces between ~
the blades did not have time to pick up a full load of dust, and when
the paddle was operated at a very high speed the dust delivery was
somewhat reduced by the fact that the blades tended to cut out a
channel and the dust did not have time to drop between them.
As finally settled upon for use in the field applications, a full
opening of the feeder valve with a hand crank operated at about 30
revolutions per minute emptied the hopper in approximately 2 miles,
depending on the speed at which the plane was flown. In other words,
it was necessary to take at each trip a strip of about 60 feet of cotton
if the poundage of dust utilized per acre was not to exceed that dis-
tributed by the ground machines. Any additional width which could
be taken of course constituted a reduction in the poundage per acre
delivered.
These figures were obtained by straightaway flights with the
_ feeder operating continuously from the start until the hopper was
empty. When this hand-crank hopper was placed in service in
actually dusting cotton fields, a serious difficulty developed, due to
variations in the rate of flying speed of the plane as it crossed back
_ and forth over the fields. In turning to enter a field the plane would
_ be flying probably 100 feet or more in the air. It would be man-
euvered into position and then would glide downward with a throt-
tled motor into the edge of the field. It was often still descending
for perhaps the first 100 feet after crossing the edge of the cotton,
especially if any obstructions intervened along that margin of the
field. The feeder would be opened and the crank started almost as
soon as the plane passed the edge of the cotton. The dust would be
blown out behind the plane for some distance, but often for about
150 feet after the plane entered the field it was still gliding down-
ward, and thus traveling at a reduced ground speed. The result
_ was that the dust being put out at the normal rate spread over a
_ rather wide strip at the edge of the field. Then the motor was grad-
_ ually speeded up as the pilot neared the elevation he desired, and
field.
when he reached this point he “ gave her the gun” to maintain a
safe flying speed at the low level across the field. This rapid in-
crease in speed, with no change in the rate at which the dust was
_ delivered, resulted in a very wide strip being treated at the edge of
the field, the margins being pulled in rapidly to a much narrower
strip across the center of the field, where the plane was traveling at
full speed. Then, when the plane reached the far edge of the field,
it zoomed upward quickly and blew back into the field the dust
which was delivered as the feeder was being cut off. This practi-
cally reversed the conditions experienced while entering the field.
The zooming not only decreased the ground speed of the plane but
blew the dust downward and backward from a distance beyond the
An outline of the dust cloud produced by this trip across the field
presented somewhat the shape of an hour glass, wide at both ends
and narrowing rapidly to the middle. To avoid leaving untreated
28 BULLETIN 1204, U. §. DEPARTMENT OF AGRICULTURE.
cotton with a dust cloud so shaped, it was necessary to take only
narrow strips. This results in much overlapping of poisoning near
the ends of the rows if the strips are spaced close enough to give a
thorough application at the middle. The waste of poison is enormous.
Theoretically this overlapping could be compensated by varying
the rate of cranking as the speed of the plane changes. This was
attempted but proved impracticable, because it depends on the per-
sonal equation and the judgment of the human. When moving at
the rate of from 75 to 90 miles an hour, as is the case in this dusting
work, ground is being covered so rapidly that the slightest error in
caleulation on the part of the operator of the crank is tremendously
magnified. Although attempted by several individuals it proved im-
possible to compensate accurately for the change of speed.
The need for a feeder which would perform this function auto-
matically resulted in the construction of the air-suction hopper. In
this device the dust is carried from the hopper by means of air suc-
tion, created by the stream of air flowing down through the hopper.
Since this air is collected by a funnel pointing forward over the
plane wing, its velocity is determined by the plane’s speed, and the
amount of suction created is thus in turn proportional to the speed
of the plane.
To test this principle, a series of straightaway flights were made
over a stretch of fields, with as much variation as possible in the
speed of the plane. The same amount of dust (120 pounds) was
loaded into the hopper for each flight and the flights were started
at the same point. The time requirement for emptying the hopper
was varied from 45 seconds to 2 minutes and 22 seconds. In every
instance the hopper was emptied in the same distance, namely 5,470
feet. The ground speed therefore ranged from 31.2 to 90 miles an
hour. The fact that the hopper discharge lasted exactly the same
distance indicates that, in straightaway flights at least, the use of
air suction for dust delivery provides an automatic compensation
for variation in plane speed. ‘These figures were of course made
with the feeder valve wide open and the dust delivery at the heaviest
rate provided in any of the experimental work. More erratic figures
probably would be obtained on reduced deliveries, but this point was
not tested. The records obtained indicate that to treat cotton at the
rate of 6 pounds per acre it is necessary for the plane to cover a
swath 160 feet wide, or if this figure is reduced to 2 pounds per acre
it will be necessary to treat 480 feet at each trip.
These figures are very satisfactory for straightaway flights, but
when short flights were made, with the plane operating back and forth
over the field, somewhat different results were obtained. In fact,
variation in the feed was noted to some extent in the straightaway
flights. When first opened, with a full load of dust in the hopper,
the feed was not very heavy, but as this dust quantity became
reduced somewhat the feed increased until it quickly reached a
maximum delivery, which was maintained throughout practically the
remainder of the flight. In other words, the dust delivery was to a
slight extent dependent on the amount in the hopper, even in
straightaway flying. In flying back and forth over a field where
the strips were rarely more than 600 to 700 feet long, this undesirable
feature was more accentuated. Not only was the dust feed lighter
vee ee ae
;
|
|
|
DUSTING COTTON FROM AIRPLANES. 29
when the hopper was full, but usually when the valve was thrown
open it took a few seconds for the dust to reach its maximum
delivery, and in those few seconds the plane traveled a considerable
distance.
While these two hoppers were being tested and developed, the
one which had been used in dusting the catalpa trees in Ohio
arrived. This was immediately attached to a plane and tested in a
few trial flights, but was found to be less suitable for cotton dusting
than those which had already been constructed. The Dayton hopper
had obviously been built to put out a large quantity of dust in a
minimum time, without much regard to the regularity of delivery.
When tried over a cotton field it was found that it at first fed rather
slowly, and then, when perhaps one-fourth of the hopper’s contents
- had been emptied out, it suddenly fed out the remainder in an
enormous burst, providing a very inefficient distribution when regu-
lar field flights are attempted. Furthermore, hanging this hopper
on the side of the plane made the plane slightly side-heavy for suc
low flying, and since the hopper presented square corners to the
air current and was not stream-lined in the slightest, it caused an
unequal drag on one side of the plane. This interfered with flying
somewhat, and was especially undesirable in that the interference
was not regular in making turns, depending on which way the plane
was banking. = Further work with this type of hopper was therefore
abandoned. —
DIRECTING PLANE OPERATION.
In operating a plane the pilot is forced to keep a keen lookout for-
ward and has very little chance to judge whether all portions of the
field are being thoroughly treated, while the hopper operator is un-
able to converse with the pilot when in flight and can not give any
elaborate directions. Special arrangements were therefore made for
directing the flight from the ground, and when actual field poison-
ing was in progress one or more men were always placed in the cot-
ton field which was being treated, provided with white flags 3 feet
square attached to handles about 6 feet long. A system of wigwag
signals was then used, by means of which the men on the ground
gave the pilots directions for each crossing, and specified the exact
points at which the crossing should be made. This seemed the only
expedient which could be employed in the preliminary work.
The method of directing the plane for effective dusting will al-
ways be one of the most difficult problems in any attempt to use the
airplane in commercial work, especially since a slight error in the
airplane flight means so much cotton field area improperly treated.
This problem will require a considerable amount of experimentation
before it will be solved satisfactorily. Probably the care and effi-
ciency of the pilot will always be a very important factor in deter-
mining thoroughness of treatment.
LEAFWORM CONTROL GPERATIONS.
In the treatments of the cotton fields for leafworm control, those
first infested received applications varying in amount, and the re-
sultant leafworm mortality served as a basis for later plans, the
width of swath varying widely, depending on the field being treated,
30 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE. :
elevations flown, air conditions, regularity of hopper operation, and
other considerations. Some flights were made at a reduced feed,
using deliberately narrow strips, while others were made at a higher —
feed, widening these strips as much as possible.
As a result of these studies and the observations on the leafworm
control effected, it was found that by properly controlling the dust
delivery it was possible to give effective treatment to strips varying
from 25 to approximately 500 feet in. width. Of course in the
smaller fields, especially in those immediately adjoining obstructions,
where definite direction of the dust was particularly desirable, the
narrow strips were utilized, while in the larger fields, where it was
desirable to take as much area at a time as possible, the feed was in-
creased to take care of wide strips. These wide strips are possible
only under favorable air conditions, and are especially suitable when
the plants are moist. As the breeze increases later in the day and the
plants become dry, the poisoning can be better controlled and the
applications made more thorough and accurate by taking narrower
strips at a reduced rate of dust delivery.
In all this field work it was almost the universal rule that ex-
cessive applications were made, as compared with the treatments
desired in each instance, because in operating over practically every
field it was necessary to repeat some flights to correct faulty dust
delivery through the feeder. For instance, the feeder might choke
for only a second or two about the middle of a field, and with the
crude system of signaling available, it would often be necessary
to have the pilot make one or more trips completely across this
field to make sure of treating the area which had been skipped. In
addition, owing to flimsy construction, it was impossible to shut
off the feeder completely, and consequently there was great waste
| of material in banking through the turns outside the field.
For these reasons the figures which were obtained on poundage
delivery should not be taken too seriously, though they are in a way
rather striking. In using the standard calcium arsenate for leaf-
worm control, following various methods, the poundage delivered to
the different fields varied from shghtly less than 2 pounds per
acre to about 11 pounds peracre. After fairly standardized methods
had been worked out, however, and had been checked by the amount
| required for leafworm control, it was found that from 2 to 4 pounds
of calcium arsenate per acre was sufficient for the maximum effect.
The results of these dosages so far as leafworm control was con-
cerned, were quite equal to those obtained from the use of ordinary
dusting machines applying the poison at the rate of 6 or 7 pounds
er acre.
‘ In every instance the effect of the application on the worm was
very carefully watched, with respect to the mortality not only of
the worms in the field at the time, but also of those which hatched
later from the eggs then present. As with any form of dusting
apparatus, it was difficult to control infestation when the plants had
been rather thoroughly skeletonized before treatment and provided
very little leaf surface on which the poison could adhere. On the
other hand, the control which resulted from airplane dusting on
such fields was fully equal to that which followed the use of the
most efficient hand guns or wheel traction machines, ordinarily used
for boll-weevil dusting. Under conditions more favorable for con-
:
‘ya ye F
4 ae tl 6 alae | a sath h nit ad!
DUSTING COTTON FROM AIRPLANES. 31
. trol, where the worm infestation had not progressed quite so far,
the results were of course much more satisfactory.
It was quite noticeable, however, that the distribution of the
material in the path of the plane was not absolutely uniform
throughout the width of the strip. In several instances a single
application was made in a fairly heavily infested field containing
many eggs which hatched later and were then allowed to develop
without further treatment. Perfect control was always obtained in
a strip from 25 to 50 feet wide directly under the plane, but beyond
this strip the dosage of poison was somewhat lghter and more of
the worms hatching from the eggs managed to survive, so that the
fields treated in this manner with very wide swaths presented
alternating strips thoroughly and partially controlled. On the
other hand, sufficient control was exerted to prevent really serious
commercial damage to any of the cotton, and where two applica-
tions were made in such fields, practically complete control was
secured.
This experience was compared with the work which was being
done at the same time on other properties in controlling the leaf-
worm with calcium arsenate with different types of ground machines,
and it was found that to control this unusually heavy infestation
two applications of calcium arsenate were usually necessary. As
nearly as could be determined, about 2 pounds of calcium arsenate
per acre delivered from the airplane proved as effective as 5 pounds
per acre delivered from a ground machine. Of course the effective-
ness of this application was measured only by leafworm control,
and is by no means settled as regards the boll weevil.
TESTS OF VARIOUS INSECTICIDES.
DIFFERENT CALCIUM ARSENATES.
To contrast with the results secured from calcium arsenate of the
usual type a number of other varieties were utilized. By a slight
variation in manufacturing methods, calcium arsenate can be pro-
duced with practically the same chemical analysis, but with a great
range in the physical characteristics. For example, its volume may
range from 40 to 250 cubic inches to the pound, and the material
ordinarily found on the market varies from 60 to 150 cubic inches to
the pound. This difference is largely due to difference in the size
of particles.
To determine the behavior of these different dusts in the air, flights
were made with a product testing about 60 and another about 135
cubic inches to the pound. The heavier material (60 cubic inches)
did not behave very well in the air and dropped nearly directly to
the ground from the plane, not being as subject to the influence of
the slip stream as the standard material (90 cubic inches). The light
material behaved very differently. It had been feared that it was so
exceedingly light that when released in the air it would float away
and never reach the plants, but it proved to be subject to the influence
of the slip stream and made a beautifully controlled cloud. Unfor-
tunately it was not possible to make determinations of adhesion of
this material, but as far as visual observation was possible it seemed
_ to work fully as well as the standard material.
/
32 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE.
LEAD ARSENATE,
A few tests were made with arsenate of lead. The material used
had a volume of about 80 cubic inches to the pound, which was fairly
close to that of the standard calcium arsenate, but the physical char-
acteristics of the particles were rather radically different. The lead
arsenate proved to be only a fair dusting material. It was not as
satisfactory as either the standard or the light calcium arsenates used,
so far as could be judged from the dust cloud formed. Two cuts of
cotton on Shirley were treated solely with lead arsenate for compari-
son with calcium arsenate in leafworm control, and the mortality
resulting was hardly as satisfactory as that from similar applications
of calcium arsenate. This was probably to be expected, as lead
arsenate is usually less toxic to the worm than calcium arsenate.
PARIS GREEN.
Other tests were made with Paris green. This material differs
greatly from either of the arsenates tested, being only 33 cubic inches
to the pound and possessing almost no adhesion between particles.
This material flowed so readily through openings that the valves
which had been constructed for using calcium arsenate allowed the
Paris green to leak through even when completely closed. This was
corrected as well as possible by packing. It was found at the outset
that even the slightest opening of the valve gave such a heavy deliv-
ery of the Paris ; green that an excessive dosage resulted. In fact, | in
the first trips made the material poured out at a rapid rate and w
whipped directly to the ground without spreading over any a
ciable width. Paris green, if used unadulterated and at a heavy
dosage, is injurious to the cotton plants because of the free arsenic
pr esent, and the day following the flights which had been made with
straight Paris green it was noted that wherever the plane had passed
over the cotton there was a row of plants perhaps 10 feet wide
directly under the plane which had been almost completely burned
up by the poison. This row was very definitely marked and illus-
trated the lack of spread of the material.
Following this experience the Paris green was mixed in varying
proportions swith air-slaked lime, and the following were the charac-
teristics of the mixtures tested:
Cubie
Says Parts inches
green lime. per
pound.
1 1 54
1 3 63
1 5 66
These three materials were then tested from a plane and behaved
considerably better than the straight Paris green, as far as delivery
from the plane and spread in the air are concerned. Still they were
not satisfactory. The lime flowed too fast through the valves and
when blown into the air seemed to separate from the Paris green.
A very peculiar condition resulted. The Paris green was blown
down over a strip of plants more or less directly “under the plane,
DUSTING COTTON FROM AIRPLANES. a3 %
while the lime did not usually reach the same plants so heavily but
spread through the cotton at some distance from the line of flight
of the plane.
As these difficulties were evidently due entirely to lack of adhesion
of the materials, still another preparation was made. This included
one part Paris green, one-half part lime, and five parts white flour.
This combination worked very satisfactorily in the plane and spread
through the cotton and adhered to the plants very well. The ad-
hesive qualities provided by the flour seemed to hold the material
together fairly well in the air.
So far as worm control is concerned, the effect of the Paris green
was much more pronounced than that of any other chemical used.
In every instance practically complete control was secured im-
mediately after such applications, and it was thus shown that prob-
ably the instances of partial control with either calcium arsenate or
lead arsenate were due to the lower toxicity of these materials rather
than to faulty distribution. In ordinary field leafworm control
work, a mixture of about 5 to 10 parts of lime to 1 of Paris green
is always used, and is distributed at the rate of from 2 to 5 pounds
per acre. In the airplane work with the flour mixture, the Paris
green was used at the rate of approximately 14 pounds per acre, and
practically complete worm control was found in every field treated.
OBSERVATIONS ON BOLL WEEVIL CONTROL.
Only casual observation was made on the effect of these poisons
on the cotton boll weevil. Neither of these properties had been
poisoned for boll weevil control during the season, and weevils were
exceedingly abundant on both. For fully two weeks before the first
airplane poisoning was done the weevils had so thoroughly infested
both plantations that not a cotton bloom was visible. This condi-
tion persisted during the beginning of the experiments, but by the
time the fields on the two properties had nearly all received one or
two applications of calcium arsenate for leafworm control, it was
suddenly noted that cotton squares not infested with boll weevils
were becoming fairly common, and by the end of the experimental
eriod both plantations were blooming rather freely wherever the
poisoning had been done.
This can not be positively accredited to the dusting, since it fre-
quently happens that when the weevils have very heavily infested
a field for a few weeks they leave this field in search of new food
and give it a period of rest, during which a few blooms may struggle
through to opening. Considerable weevil control had certainly been
accomplished, however, since the blooming on these properties was
_ much more pronounced than on others adjoining, where no applica-
tions had been made. Furthermore, this late blooming did not ap-
pear on the few fields which had never developed sufficient leafworm
infestation to require poisoning. |
GENERAL CONSIDERATIONS OF AIRPLANE DUSTING.
The foregoing pages have been devoted to description of the test
work. Positive data on the economics of airplane dusting are not
available, but some incidental observations bearing on this phase of
the problem were made, and the following pages indicate some of the
problems now to be solved.
~%
34 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE.
ACREAGE DUSTED PER HOUR.
The number of acres that can be dusted in an hour by means of
planes is rather a complicated question, and the information ob-
tained is only suggestive. As the hoppers used held only about 125
pounds of poison, frequent landings were necessary. The treatment
of small areas at a time further restricted the speed. Generally
speaking, in the work on these two properties, the plane spent from
6 to 12 minutes in the air at each flight. Much of this time was
spent in maneuvering, and a certain amount in going to and from the
landing field. To avoid loss of time, provisions were made for load-
ing the hopper fairly quickly when the planes landed, but this opera-
tion could be greatly expedited by more elaborate loading equipment.
Counting both flying and ground time, the airplanes averaged 6 or
7 flights an hour, emptying a hopper of dust during each flight.
At least 240 acres were being treated per hour.
Other records based on straightaway flights, with more definite
efforts for acquiring speed in operation, usually showed between
400 and 500 acres dusted per hour. Since only a small portion of
this time is spent in actually delivering the dust, and much is con-
sumed in going back and forth for new loads, undoubtedly the
acreage capacity of a plane can be greatly increased with larger
hoppers constructed to hold approximately the maximum carrying
capacity of the plane.
ADVANTAGE OF AIRPLANES AFTER RAINFALL.
Airplanes are not in the slightest dependent on ground conditions,
so long as the landing field is solid enough to permit landing and
taking off, and with a sodded field reasonably well drained this is
possible almost any time. An interesting illustration of this fact
developed during the work. The leafworm infestation became heavy
about August 25 in many fields on both plantations, and on the
25th and 26th all infested fields were carefully treated. Just as the
planes were returning from the last flight on the afternoon of the
26th a heavy storm came up and it rained about 3 inches in the next
hour. This caused all of the poison which had just been distributed
over the cotton fields to be washed from the plants. The worms
eat at a tremendously rapid rate and a delay of 24 hours in poisoning
them frequently results in the fields being stripped of foliage. The
next morning the worms were working actively and the fields were
so muddy that it would have been impossible to operate any ground
dusting machines. The landing field was dry enough for airplane
operation, however, and both planes were put into service to catch
up with the infestation. In less than one hour all acreage requiring
poisoning had been treated and the crops were thus again protected
from damage. For instance, on Hermione plantation 111 acres
needed poisoning very badly. These were treated between 11.23
a.m. and 12.09 p. m., or in a period of 46 minutes, using 549 pounds
of calcium arsenate on the area, or an average of 4.9 pounds per
acre. This was a rather heavy dosage, but the applications were
made practically at midday, and the wind velocity was rather high,
so that it was deemed desirable to use an extra quantity in the
emergency.
_ lt
DUSTING COTTON FROM AIRPLANES. 35.
SUITABILITY OF TERRAIN.
The contour and environment of cotton fields are particularly im-
portant in low flying such as is required for cotton dusting, and will
really determine the safety of the fields for airplane operation. At
the same time, many obstructions to low flying can be eliminated with
- comparative ease. For instance, snags can usually be removed with
_ little trouble. Again, if cotton were planted with a view to airplane
- dusting, the fields could easily be arranged in continuous tiers most
convenient for the operation of the plane in long, straight flights.
Of course there are many hilly sections of the Cotton Belt in which
it would be too dangerous to use the planes as a regular operation,
but throughout the flat country, such as the Mississippi Delta, or
large areas in Texas, the conditions are ideal for flying. The ground
is perfectly level and meadows provide landing fields on every prop-
erty. Commercial use of the planes could never be developed if the
flying should prove unduly dangerous to the pilots, but under the
conditions prevailing in these districts low flying is not seriously
dangerous. Forced landings can be made at any point, and even
_ though the motor should be cut off while flying over the fields, if
_ sufficient speed were maintained to bring the plane to a level, it could
be landed in the corn or cotton with very little danger to the pulot,
although of course some damage would be done to the plane.
Yet the conditions around Tallulah are not abnormally favorable
for airplane dusting. The Parish of Madison, in which Tallulah is
located, is probably from 15 to 20 per cent cleared. Swamp lakes
occur throughout the Parish. These have heavily timbered margins,
the woods usually extending for some distance around them, since
_ it is impossible to drain the land for cultivation anywhere near them.
* The cultivated fields therefore, follow the contour of the land rather
_ than being consolidated in cleared areas.
_ _ As such conditions are not the most favorable for airplane opera-
_ tion, a few tests under more favorable flying conditions were made
~ at Scott, Miss., where the planes were kept for two days, and used in
special tests of straightaway flights. Scott is in Bolivar County,
which is one of the most important cotton-producing counties in the
United States. The county has been rather thoroughly drained by
large drainage projects and this has rendered possible an extreme
consolidation of cleared area. A deliberate effort has been made to
clear up the small timbered areas and throw the open fields together
as a means of reducing weevil damage.
The newly cleared fields about Scott presented a particularly
interesting condition. Following the drainage, which at many
points was provided only a few years ago, large areas on a few plan-
tations have been very recentl7 cleared and put into cultivation.
Timber is so heavy in this territory that it is not financially prac-
_ ticable to clear the stumps from the field and they must be left to
rot out. Many of the plantations in this district have large areas
of such so-called “new ground,” where cotton is planted in a very
heavy stand of stumps from 4 to 5 feet high. The majority of the
plantations are now poisoning for weevil control by means of the
ordinary ground dusting machines, and these stumpy fields present
a very serious obstacle. In the first place the stumps provide hiber-
nation quarters for the weevil, and thus the fields receive an unusu-
ee ee ee ee ee ee me ay WN aS Oy
36 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE.
ally heavy infestation in the early spring, requiring more poisoning
than the older fields farther out in the open. On the other hand, if
weevil control can be effected, these fields are the most profitable
for cotton because of their oreater fertility, and consequent higher
potential yield. In using ground dusting machines it is a serious
problem to take care of any considerable acreage of this sort, be-
cause the larger machines can not be operated under such conditions,
owing especially to the necessity of night poisoning, and they would
be broken up by striking the stumps.
These stumps, of course, presented not the slighest obstacle for
the airplane, except to provide an element of danger if forced land-
ings should be necessary, and with the planes it was possible to pro-
duce a much more thorough application than has ever been accom-
plished in ground work. ~The plane, operating above the stumps,
is not requir red to dodge them, and consequently can thoroughly dust
every cotton plant.
The possibilities of straightaway flying and the acreage capacity
of a plane were found to be much greater in the territory around
Scott than Tallulah. In the large cleared areas in continuous cot-
ton it was found that strips from 1 to 6 or 8 miles long could be
treated in a straightaway flight, reducing the loss of time in turning
which is unavoidable in working small individual fields.
Only a few records were obtained under such conditions, but cer-
tainly the plane capacity can be increased beyond that indicated for
the Tallulah neighborhood, and it seems quite possible, judging from
the present fragmentary figures, that with a hopper designed for the
maximum carrying capacity of the plane, a single plane can treat
as much as from 700 to 1,000 acres in an hour. With such capacity,
of course, the area which could be allotted to a plane for each sea-
son’s work could be greatly increased. Much more definite data must
be obtained, however, before any really accurate figures can be pro-
vided on the subject.
CONTROL OF DUST SPREAD.
At the beginning it was considered possible that the use of the
plane might result in indiscriminate poisoning of every object on
the property, including the cabins and everything in them, but as
the work progressed it became apparent that no more promiscuous
dusting of surroundings was done with the planes than with ground
machines as ordinarily operated. It is true that cabins frequently
were subjected to a cloud of dust, but this is equally true in the ease
of ground machines, and the latter have been used for several years
without any apparent damage or danger. The poison, except where
it is being delivered directly on the cotton plant, is so thinly dis-
tributed that the portion drifting to any other point does not settle
in injurious quantities.
Many have feared danger from poisoning cotton fields adjoining
meadows or corn, the produce from which is to be fed to stock.
However, poisoning under such conditions has been done innumerable
times for a number of years with ground machines, which permit
fully as much drift of poison as the planes, and not the shghtest
evidence of danger has ever been noted. Considered from this view-
point there is no apparent reason why airplane dusting should be any
more dangerous than the ordinary operation.
|
|
7
;
.
DUSTING COTTON FROM AIRPLANES. 37
SUGGESTIONS FOR FUTURE INVESTIGATIONS.
Before any attempt at commercial airplane dusting can be made
various other problems must be considered. For example, the de-
sign of the plane should permit a hopper of the maximum carrying
capacity. The most efficient dust delivery must be determined. Pos-
sibly this will not be through the bottom of the fuselage. As the
velocity of the slip stream varies widely at different points around
the plane, the propeller effect should be thoroughly charted and the
most efficient point of delivery of the dust located. At a point as
far forward as the observer’s cockpit, where the dust is being de-
livered, the air stream from the propeller is a comparatively few
feet in diameter, so that when the dust is dropped into it, this dust
has only a short distance to fall before it reaches quiet air. If this
distance could be increased, the effect of the air on the powder would
be greater, and probably more of the pellets of material adhering
together could be broken up into individual particles. It might be
possible to accomplish this by the use of conduits which would de-
liver the dust into the air at a point near the tail of the plane,
where the diameter of the stream is greater. Such questions can be
answered only by experiment.
Possibly the exhaust from either one or both banks of cylinders
could be piped through a conduit which would not give back pressure
on the motor and which would still connect with the dust outlet to
break up and dry out the dust. A more efficient spread might be
secured by using a bifurcated device, delivering the dust on both sides
of the fuselage; or stream-line conduits might be arranged along the
trailing edges of the wings to carry the dust for delivery either at the
wing tips or at intervals on the wings. All such work would require
careful designing and the cooperation of skilled airplane engineers
who could appreciate and measure the hazards involved.
The type of plane most desirable for dusting is still to be deter-
mined. One important item will be to increase, just as much as is
safe, the dust load which can be carried at any time by the plane,
in order to increase flying time and decrease ground time and thus
correspondingly increase the acreage allotment of a plane. In the
experiments conducted the pilot was concerned only with flying the
plane, and the dust was delivered entirely by the hopper operator,
who rode in the observer’s cockpit. Equipment could be arranged,
however, so that it would not be nesessary to carry this hopper opera-
tor, and poison could be substituted for his weight. Automatically
operated hoppers can be easily developed with a very simple control
beside the pilot, and he could start and stop the flow of poison
whenever desired. The pilot is in a better position to do this than
the observer, because-he is better protected from the blast of the
propeller, and as his view is not obstructed by the lower wings he
has a better view of the fields. The development of special dusts
for airplane work depends entirely on the perfecting of a regular
delivery. If it were found possible to deliver dust uniformly and
under thorough control with comparatively lght doses, the ideal
poison would be a highly concentrated form, which might be shghtly
- more expensive per pound than any other, but would more than
compensate for this by the greater acreage handled by a single
charge and a single flight of the plane. On the other hand, if it
does not prove possible to perfect dust delivery to this degree, and
38 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE.
irregular clouds must be used, thus requiring.more or less overlap-
ping, the development of the dust would naturally tend toward a
diluted form which would be comparatively inexpensive and could
be used at a higher poundage per acre and to make sure of absolutely
complete covering of all spots.
CHARACTERISTICS OF AIRPLANES USED.
The dusting planes used in these tests were those commonly
termed the “ Curtis H,” or, more properly, Curtis JN6H. They are
commonly used for training observers and will safely carry about |
350 pounds: besides the pilot. This probably means that the maxi-
mum dust capacity of one of these planes, with the hopper con-
structed in the plane, would not exceed 250 pounds. These planes
had the Hispano, 150-horsepower, 8-cylinder, V-type motor. The
ordinary number of revolutions per minute at flying speed is about
1,400 with the heavy propeller, while it 1s about 1,500 with the
hghter propeller, commonly known as the “ toothpick.” The mini-
mum safe ground speed of this plane is about 50 miles an hour, and
its maximum speed depends of course on the wind direction and
velocity, but is at best little over 90 miles an hour.
This plane has a main tank capacity of 21 to 22 gallons of gaso-
line, with an emergency tank holding 7 gallons. Normal consump-
tion usually approximates 10 gallons an hour, so that the safe fly-
ing time on one filling is not more than 2 hours in the air, and when
frequent landings are necessary, the small amount which would be
saved while filling the hopper is compensated for by the extra gas
used for taking off. Gassing and oiling the plane will require about
15 minutes, and in figuring on the operation of the plane this time
should be allowed after every 2 hours. The motor holds 16 quarts
of oil and will require about 6 quarts per hour of operation. All oil
must be drained from the motor every 5 flying hours and replaced.
The gasoline used should be special aviation gasoline, testing from
68 to 74, and the oil should be a special quality of extra heavy oil.
Both of these items are thus more expensive than for ordinary
motors.
In commercial operation, the length of life of a plane will be a
very important item. The following figures are probably fair aver-
ages. The life of the plane itself will be about 200 flying hours, at
the end of which time it must be overhauled. This overhauling will
possibly add 150 flying hours to its life. These planes deteriorate
in storage, and their period of life would probably not vary greatly,
whether or not they were subjected to maximum use. The motor
life depends largely on the human element, but the average time
will be about 80 to 100 hours. It must be then completely over-
hauled, and at the end of two overhaulings practically a new motor
has been constructed; thus a total motor life in a plane will be
from 240 to 300 hours. Such flying as is done in dusting is un-
usually hard on the motor. It is necessary for the pilot to main-
tain an excessive speed for safety at the low altitude, and in ad-
dition the air temperature is so high near the ground that the motor
heats more rapidly than when flying higher.
Another type of plane available for study was the “ De Haviland
4B,” or, as it is commonly nicknamed, the “ D. H.” ‘This plane is’
equipped with a 420-horsepower Liberty motor, a 12-cylinder V-
h ng
DUSTING COTTON FROM AIRPLANES. 39.
type, with the speed of the propellor ordinarily ranging from 1,480
to 1.550 R. P. M. The main gasoline tank holds 78 gallons and the
emergency tank holds 9. The gasoline consumed is from about
20 to 25 gallons an hour, so that such a plane would have a dusting
time of about 34 hours on a single filling. The motor holds about 8
gallons of oil and consumes practically 2 gallons per hour, and it
also should be drained after every 5 hours of flying time and new
oil added. The minimum safe ground speed of the D. H. plane
is about 65 miles, and the maximum speed is about 120 miles per
hour. The greater power and lift of this plane makes it possible
to climb much more rapidly, and thus it could more easily avoid ob-
structions than the Curtis. On the other hand in some flying its
much larger size might prove a handicap. One decided advantage
it would possess is the fact that it has a carrying capacity of be-
tween 500 and 700 pounds, which would permit a much longer time
in the air for dusting from each filling of the hopper.
These two types of planes are the only ones studied. Other models
should by all means be considered, since both of these were developed
several years ago and the more recent models probably have more
desirable characteristics for this type of flying.
COST OF OPERATION.
A few calculations relating to costs of operation are presented
for what they are worth.
Each plane should have one or more pilots and two mechanics. In
fact, since a plane would find favorable flying conditions about 7 or 8
hours a day, and it would be difficult for a pilot to stand more than 4
hours of such flying each day, the most economical arrangement
might be to provide two pilots for each plane. These pilots would
cost at least $300 a month each, and the mechanics would cost $150 a
month each.
In the following computations a day’s work of one pilot and a
plane has been figured at 4 hours. The pilot would probably fly
about 5 days a week, and in cotton dusting would have about 6 weeks
to fly, or a total of 120 flying hours yearly on this particular assign-
ment. It would of course be necessary to pay his salary for the
entire year. At $3,600 a year, this would make a charge of $30 per
flying hour for the pilot. One mechanic would be charged to each
_ pilot, and a three months’ flying period only charged, because this
mechanic could always be used on other duties the remainder of the
_ year. Consequently, the charge is $450 for each season, or $3.75 per
- hour for each plane.
Summarizing these figures, we have the following costs for a
4-hour day operation of a Curtis plane:
Le eS ere apes ey ee rs eee * Sips yee BIG
ED DA Se BS 2 ee SE ee ee SP ag eee oe 15
4 40 gallons of gasoline at 25 cents_____ 4 2 Ls = 10
9 Se oatlietin OF OL) At-o lee 2 Set! te 4 2 06 eee 8
Ja, TREO TRS Re yea seks BVT Pe eee ee, Ma eee eRe Ena SeS One See EE TE 155
3 These figures would probably be reduced considerably if the opera-
4 tion were placed on a commercial basis, but they compare very favor-
_ ably with ordinary dusting machine figures. The figures available
indicate that one plane operating 4 hours a day would take care of
40 BULLETIN 1204, U. S. DEPARTMENT OF AGRICULTURE.
-
as much area for the season as at least 40 cart dusting machines,
which have the greatest acreage capacity of any machines now
used in cotton dusting. To operate these dusting machines of course _
requires considerable + supervision, and a number of special expenses,
_such as fuel for lights, etc., but, considering only the value of man
labor and mules alone, it would cost $236 a night to operate these
machines. On this basis considerable economy in favor of the plane
would be indicated. The cost of the plane and its upkeep in repairs
would apparently figure no more than the original cost plus up-
keep of the dusting machines which it would replace. Consequently,
it seems possible that the cost of equipment, if each is allowed full
acreage, would be about the same as for ground dusting machines,
and the operating expenses would be hghter with the airplanes than
with the ground machines. Furthermore, all work which has been
conducted seems to indicate that the poison required per acre can
be greatly reduced with a plane as compared with the ground ma-
chines, and this would be a very important item, since ‘the cost of
poison is by far the heaviest expenditure involved in dusting cotton.
CONCLUSIONS.
The studies which have been described are far from deciding on
the practicability of using the airplane for applying insecticides,
but they have shown that the dust can be blown down among the
plants from the air above them and that this dust can be made to
adhere to the plants under daytime conditions when plane operation
is feasible. The planes can be manipulated so that all portions of the
field are treated. In fact, the cotton leafworm was controlled with a
poison allowance considerably below that necessary when using or-
dinary dusting machines. Whether this application was sufficiently
thorough to control the boll weevil is quite another question, since
weevil control requires a much more thorough application than is
necessary to control the leafworm, but all records bearing on this
question appear to furnish decidedly favorable indications of success.
Financially the use of the airplane does not seem to be out of the
question, and in fact there is considerable possibility of pronounced
economy as compared with the ground machines. It has the advan-
tage of centralizing the control “of the operation and placing it on
a more skilled basis, which would undoubtedly greatly tend to in-
crease the quality of the results secured. On the other hand, no
farmer can afford to buy a single plane and figure on dusting his ‘cot-
ton, since it is not safe to place all of the eggs in one basket in this
manner. Motors will go wrong, and cotton poisoning is an opera-
tion which can not be delay ed when needed. The operation could be
only considered as a community affair or for planters whose acreage
would be large enough to justify purchasing more than one plane.
In reality, to or ganize in safety, one plane should be provided in re-
serve for every one or two which are kept in flight.
All of these are questions which can be worked out only by time
and trial, but many districts in the South have now reached the point
in public sentiment where the desirability of community weevil con-
trol can be seen, and it is only by some such method as the use of the
airplane that such community poisoning can be attempted in the near
future.
WASHINGTON : GOVERNMENT PRINTING OFFICE :! 1923
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