Agricultural aircraft control system using the global positioning system

An aircraft control system for applying chemicals to an agricultural field in one of a plurality of flight patterns is provided. A global positioning system receiver receives radio frequency signals from satellites and the position of the aircraft is determined from the information contained in the received signals. An aircraft computer stores the surface coordinates of the field to be sprayed. The aircraft pilot enters the desired orientation, swath width and track width of the flight pattern into the computer. Based on the aforementioned information, the computer produces a flight pattern having the desired orientation and generates, via a pilot headset, audible signals representative of amount and direction of deviation from the desired flight pattern. The computer means may also automatically activate and deactivate chemical spraying upon entering and exiting, respectfully, the airspace above the field.

BACKGROUND OF THE INVENTION 
The present invention relates generally to chemical spraying of 
agricultural fields from an aircraft and, more particularly, to a control 
system and method for applying chemicals to an agricultural field wherein 
the chemicals are automatically released over the field as the aircraft 
travels along an appropriate flight pattern. Radio frequency signals from 
global positioning satellites are used to determine the instantaneous 
position of the aircraft relative to the flight pattern and the field. 
Chemical spraying of field crops and orchards has long been widespread in 
the agricultural industry. During aerial spraying of chemicals on an 
agricultural field, the aircraft makes numerous sequential, adjacent 
passes, spraying a swath across the field during each pass. The aircraft 
pilot must carefully guide the aircraft to ensure that each of the 
successive traverses over the field is laterally spaced from the adjacent 
traverse by the proper distance in order to avoid either gaps or overlaps 
in spraying coverage. As will be appreciated, overlaps in spraying 
coverage result in spraying more chemicals on the field than desired. This 
is costly and may cause crop damage. Gaps between swaths, on the other 
hand, leave untreated areas in which crop growth may be poor. 
Several methods for controlling swath width and placement have been devised 
in the past. For instance, commonly assigned U.S. Pat. No. 4,225,226 
issued to Davidson et al discloses a laser guidance system for crop 
spraying aircraft. The crop spraying aircraft carries a rotating laser 
transmitter and receiver to transmit a laser beam onto a plurality of 
ground reflectors located at known positions relative to each other and to 
detect the subsequently reflected laser beams. The angular position of the 
aircraft is then determined by a microprocessor based on the reflected 
laser beams. Any deviation from a predetermined spraying path results in a 
microprocessor-generated error signal. 
Other methods for controlling swath width and Location include using ground 
personnel holding flags at either end of the field to provide visual 
guidance to the aircraft pilot and dropping materials on the field from a 
dispenser mounted on the aircraft to provide a visual ground reference for 
the aircraft pilot on the next traverse. Numerous problems exist with the 
above described methods. The high chemical concentrations used by modern 
crop spraying aircraft, which allow such aircraft to cover larger areas 
with a given payload, have increased the health hazards associated with 
using ground personnel in close proximity to the chemical spraying. 
Further, overlapping of these higher concentration chemicals can damage or 
destroy crops to a greater degree. 
Additional problems with previous systems involve the requirement of 
adjacent traverses and the manual operation of the chemical spraying 
device. To make sequential, adjacent traverses of a field, the pilot is 
required to execute a key-hole turn at the end of each pass. A key-hole 
turn consists, for example, of a 45 degree left turn, a 270 degree right 
turn and another 45 degree left turn in succession. The short radius turns 
and sharp turning angles required in previous methods significantly 
increase the possibility of aircraft aerodynamic stall. 
Prior chemical spraying systems also require that the aircraft pilot 
identify the proper time to release the chemicals at the beginning of the 
swath and the proper time to shut off the spraying device at the end of 
the swath. Typically, these judgments are made based on visual perception 
of the aircraft pilot. Failure to turn the spraying device on or off 
correctly results in unsprayed crops or overspraying into neighboring 
land. 
Accordingly, the need exists in the art for an improved control system and 
method for applying chemicals to an agricultural field by aircraft which 
dynamically detects position changes of the aircraft, automatically 
activates and deactivates the chemical spraying at the beginning and 
ending boundaries of the field, permits increases in the radius turn and 
turning angle of the flight paths, provides more accurate swath path 
control, allows alteration of the directional orientation of the swaths 
for optimal spraying coverage, and provides increased swath control to 
ensure uniform chemical coverage throughout the field. 
SUMMARY OF THE INVENTION 
The aforementioned need is met by the aircraft control system and method 
for applying chemicals to an agricultural field in one of a plurality of 
flight patterns in accordance with the present invention. The control 
system includes a global positioning system receiver for continuously 
determining aircraft position and a computer for automatically activating 
and deactivating the chemical spraying system of the aircraft when the 
aircraft traverses the field in the desired flight pattern. 
In accordance with one aspect of the present invention, a aircraft control 
system for use in an agricultural aircraft for applying chemicals to an 
agricultural field in one of a plurality of flight patterns, such as an 
oval pattern and a keyhole pattern, comprises a global positioning 
receiver means for receiving radio frequency signals from a plurality of 
satellites. A computer means, responsive to the global positioning 
receiver means, stores the surface coordinates of the boundary of the 
agricultural field and the one of the plurality of flight patterns. The 
radio frequency signals are decoded by the computer means to determine 
continuously the position of the aircraft. The actual position of the 
aircraft is then compared to the desired flight pattern. In addition, the 
computer means automatically activates at least one dispenser valve, 
contained in the aircraft, when the aircraft is flying within the boundary 
of the agricultural field whereby the chemicals are applied to the 
agricultural field. Preferably, the computer means also includes means for 
recording aircraft flight data during an application of the chemicals to 
the agricultural field. 
A pilot interface means, responsive to the computer means, indicates 
deviations in position of the aircraft from the one of the plurality of 
flight patterns to a pilot of the aircraft. Preferably, the pilot 
interface means comprises an audible signal means for transmitting an 
audible signal representative of amount and direction of deviation of the 
aircraft from the one of the plurality of flight patterns to the pilot of 
the aircraft 
The aircraft control system is preferably operated fin the differential 
mode to compensate for errors in the satellite radio frequency signals. In 
the differential mode, the global positioning receiver means receives a 
correction radio frequency signal from a stationary differential ground 
station representative of the aforementioned frequency fluctuations in the 
radio frequency signals. The computer means includes means for decoding 
the correction radio frequency signal and uses the decoded correction 
radio frequency signal to compensate for frequency fluctuations in the 
radio frequency signals to determine continuously the position of the 
aircraft. 
To increase fuel and time efficiency, the computer means may include means 
for determining the most direct flight path from a takeoff point of the 
aircraft to the agricultural field based on surface position of the 
agricultural field and the takeoff point. The computer means preferably 
includes means for monitoring the level of the chemicals in the reservoir 
and closes the dispenser valve upon complete dispersion of the chemicals. 
The stop position of the aircraft when the dispenser valve is closed is 
then stored. The computer means then reopens the dispenser valves 
automatically upon refilling the reservoir and upon the aircraft resuming 
the one of the plurality of flight patterns and traversing the stop 
position. 
In accordance with another embodiment of the present invention, an aircraft 
control system for use in an agricultural aircraft for applying chemicals 
to an agricultural field in one of a plurality of flight patterns having 
at least one dispenser valve for releasing the chemicals from a reservoir 
is provided. The aircraft control system comprises global positioning 
receiver means for receiving the radio frequency signals from a plurality 
of global positioning satellites and for generating position signals 
representative of the radio frequency signals. 
A computer means, responsive to the global positioning means, stores 
surface coordinates of the boundary of the agricultural field, selects the 
one of the plurality of flight patterns of the aircraft, orients the one 
of the plurality of flight patterns in response to the orientation signal, 
decodes the position signals to determine continuously the position of the 
aircraft. 
A pilot interface means, responsive to the computer means, indicates 
deviations of the aircraft from the one of the plurality of flight 
patterns to a pilot of the aircraft and provides an orientation signal 
representative of desired flight path orientation of the one of the 
plurality of flight patterns in response to the pilot selection such that 
the pilot guides the aircraft along the one of the plurality of flight 
patterns to apply the chemicals to the agricultural field. 
Preferably, the computer means includes means for automatically activating 
the at least one dispenser valve when the aircraft is flying within the 
boundary of the agricultural field whereby the chemicals are applied to 
the agricultural field. The computer means may also include means for 
determining a sequence of paths of flights in the one of the plurality of 
flight patterns based on a desired swath width and a desired track width. 
In accordance with yet another embodiment of the present invention a method 
for controlling application of chemicals to an agricultural field using an 
agricultural aircraft having at least one dispenser valve for containing 
and releasing the chemicals is provided. The method comprises the steps 
of: providing surface coordinates of the boundary of the agricultural 
field; selecting one of a plurality of flight patterns; receiving radio 
frequency signals from a plurality of satellites; decoding the radio 
frequency signals to determine continuously the position of the aircraft 
relative to the agricultural field and the one of the plurality of flight 
patterns; indicating to a pilot of the aircraft deviations in position of 
the aircraft from the one of the plurality of flight patterns; and 
automatically activating the at least one dispenser valve when the 
aircraft is flying within the boundary of the agricultural field whereby 
the chemicals are applied to the agricultural field. 
Preferably, the method for controlling an agricultural aircraft further 
comprises the steps of: receiving correction radio frequency signals from 
a stationary differential ground station; decoding the correction radio 
frequency signals; and using the decoded correction signals to compensate 
for errors in the radio frequency signals to determine continuously the 
position of the aircraft. 
The step of indicating to an pilot of the aircraft may comprise the steps 
of: generating an audible signal representative of amount and direction of 
deviation of the aircraft from the one of the plurality of flight 
patterns; and transmitting the audible signal to the pilot of the 
aircraft. 
The method for controlling an agricultural aircraft preferably further 
comprises the steps of: providing a desired swath width and a desired 
track width; determining a sequence of paths of flight of the aircraft in 
the one of the plurality of the flight patterns based on the desired swath 
width and the desired track width; and indicating deviations of the 
aircraft from the sequence of the paths of flight to the pilot. 
It is thus a feature of the present invention to provide an aircraft 
control system and method for applying chemicals to an agricultural field 
in one of a plurality of flight patterns wherein the chemicals are 
automatically released as the aircraft traverses the field. 
Other features and advantages of the present invention will be apparent 
from the following description, the accompanying drawings and the appended 
claims.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIG. 1, a block diagram of an aircraft control system 100 
and a differential global positioning system (GPS) ground station 102 for 
applying chemicals to an agricultural field in one of a plurality of 
flight patterns is shown in accordance with the present invention. The 
aircraft control system 100 includes a global positioning receiver means, 
which comprises satellite antenna 104 and GPS receiver 106, for receiving 
radio frequency signals from satellites. The satellite antenna 104 may be 
one of a number of well known antenna designs, such as a fixed radiation 
pattern antenna or an adaptive array antenna. Computer means 108 receives 
position signals over signal path 110 from the GPS receiver 106 indicative 
of the received radio frequency signals and determines the position of the 
aircraft from the position signals. 
Based on the thus determined position of the aircraft and the surface 
coordinates of the field to be sprayed, which are stored in an electronic 
memory (not shown), the computer means 108 controls pilot interface means, 
comprising a display and operator interface 112 and an audio signal means, 
shown as headset 114, to indicate the proper flight path to the aircraft 
pilot. The computer means 108 also controls the operation of a dispenser 
valve 116 to release chemicals from a reservoir 118 when the aircraft is 
flying over the field in the correct flight path. The global positioning 
receiver means further includes a correction antenna 113 and a telemetry 
receiver 114 for receiving correction signals from the differential GPS 
ground station 102 during differential operation of the aircraft control 
system 100. 
The process of receiving and decoding radio frequency signals from 
satellites to determine the position of an aircraft or other object is 
well known in the art. Since the structure and philosophy of the GPS 
receiver are not important to present invention beyond the generation of 
position signals, details of such receivers will not be further disclosed 
herein. Those desiring additional information regarding GPS receivers and 
the GPS system in general are referred to the NATO publication entitled 
"Navstar GPS User Equipment" distributed by the U.S. Coast Guard, GPS 
information Center which is incorporated herein by reference. 
As is well known in the art, the radio frequency signals transmitted by the 
GPS satellites contain various pseudorandom frequency fluctuations which 
may be intentionally produced, such as for security purposes, or are 
caused by ionospheric interference. The differential GPS ground station 
102 is used to detect and compensate for these fluctuations. Since the 
operation of differential GPS systems is well known in the art and is 
extensively discussed in the aforementioned NATO publication, only a 
general description of the operation of the ground station 102 will now be 
given. 
The differential GPS ground station 102 is operated at a previously 
surveyed location. A stationary satellite antenna 120 receives radio 
frequency signals from GPS satellites and a stationary GPS receiver 122, 
similar no the GPS receiver 106, conditions the received radio frequency 
signals for input into a computer 124. The computer 124 then determines 
the position of the ground station 102 based on the received radio 
frequency signals. This determined position of the ground station 102 is 
compared to the surveyed position of the ground station 102 and a 
correction signal is generated indicative of this comparison. In response 
to the correction signal, a telemetry transmitter 126 transmits a 
correction radio frequency signal via a differential antenna 128. 
The correction radio frequency signal is received by the correction antenna 
113 and conditioned by the telemetry receiver 114 for proper receipt by 
the computer means 108. The computer means 108 uses the correction signal 
to compensate for frequency fluctuations in the radio frequency signals 
transmitted by the GPS satellites. 
The operation of the present invention will now be described in detail with 
reference to FIGS. 2 through 4. Initially, the agricultural field to be 
sprayed, shown at 208 in FIGS. 2 and 3, is premapped by driving a GPS 
receiver equipped vehicle around the perimeter of the field. During the 
traverse of the perimeter, the surface coordinates of the field are 
detected and translated into an appropriate coordinate system. These 
coordinates are then stored in storage device, such as a computer. The 
coordinates are then downloaded into the computer means 108 of the 
aircraft prior to a spraying operation. It should be appreciated that the 
coordinates of more than one field may be downloaded into the computer 
means 108. Thereafter, the aircraft pilot accesses the coordinates of a 
particular field before spraying. 
In addition, the computer means 108 stores a plurality of flight patterns 
in which the airplane may traverse the field. FIG. 2 shows an aircraft 200 
executing a key-hole turn flight pattern 202 having successively adjacent 
swaths or flight paths 204 over the field 208. The aircraft 200 executes a 
turn 206 at the end of each swath 204 so as to traverse the field 208 in 
an adjacent swath 204. An oval or race track flight pattern 300 is 
illustrated in FIG. 3 having first, second and third flight paths 302, 304 
and 306. 
Once the coordinates of the field 208 to be sprayed has been selected, the 
computer means 108 determines the most direct flight path from the takeoff 
point 308 of the aircraft 200 to the field 208 based on the surface 
position of the field 208. Upon reaching the field 208, the pilot 
determines the desired orientation of the swaths. The pilot determines 
this orientation based on a number of factors including wind, obstructions 
and approach angle. After determining the appropriate swath orientation, 
the pilot enters the selected orientation into the computer means 108 via 
an appropriate input device. The pilot also enters the desired swath width 
and track width (width of the oval pattern). The pilot interface means 
provides an orientation signal representative of the desired flight path 
orientation to the computer means 108 in response to the pilot selection. 
The computer means 108 then orients the flight pattern in accordance with 
the orientation signal. 
Based on the aforesaid information, the computer means 108 automatically 
determines the sequential paths of flight of the aircraft over the field 
208 based on the orientation of the flight pattern, the desired swath 
width and the desired track width. Since the oval flight pattern allows 
larger turning radiuses and lesser turning angles, thereby reducing the 
risk of aircraft aerodynamic stall, the flight paths will usually be in 
oval configurations, as shown in FIG. 3. As the aircraft 200 traverses the 
field 208, an audible signal representative of amount and direction of 
deviation of the aircraft from the flight pattern is continually given to 
the pilot via headset 114. 
When the aircraft is following the desired flight path, no audio signal is 
produced. An audio tone of increasing frequency is produced as the amount 
of deviation from the desired path increases. The direction of deviation 
from the desired path is communicated to the pilot through the use of a 
continuous tone for one direction and a pulsed tone for the other 
direction. Consequently, the audible signal indicates both amount and 
direction of deviation to the pilot. By providing steering information in 
audio format, the pilot can guide the aircraft without impairing the 
vision and seat-of-the-pants senses. The steering information may also be 
presented to the pilot using a conventional heads up display. The heads up 
display presents the information on the windshield of the aircraft to 
provide visual instructions to the pilot. 
On approach to the field 208, the pilot guides the aircraft 200 using the 
above described audio signal. As the aircraft crosses one boundary of the 
field 208, the computer means 108 automatically releases the chemicals via 
the dispenser valve 116 and the reservoir 118. At the end of a swath, such 
as first swath 302 of FIG. 3, the aircraft 200 crosses the opposite 
boundary and the computer means 108 automatically turns off the sprayer 
system. As will be readily comprehended by those skilled in the art, the 
spraying procedure may alternatively be operated manually by the pilot 
based on visual perception as is well known in the art. 
After completing the first swath 302, the pilot indicates to the computer 
means 108 that a second swath 304 in the opposite direction is commencing. 
Alternatively, the computer means 108 may be programmed to automatically 
commence the second swath 304. For example, the computer means 108 may be 
programmed to commence the next swath whenever the aircraft experiences a 
90 degree deviation from the preceding swath direction. Thus, the computer 
means 108 would automatically detect when the aircraft is turning to 
proceed with a new swath. 
Upon completion of the second swath 304, a third swath 306 is identified 
adjacent to the first swath 302 and spaced at the appropriate swath width. 
The computer means 108 records the aircraft flight data, including 
direction, speed and altitude, for the spraying operation. The spraying 
operation is executed in this manner until the field is completely sprayed 
or the chemicals are exhausted. 
In the latter case, the position of the aircraft when the chemicals are 
exhausted is stored and, upon returning with additional chemicals, the 
flight path is recalled. As the aircraft 200 approaches the point of the 
prior chemical cut-off, the chemicals are automatically released and the 
spraying is continued substantially without overspray or a gap in 
coverage. 
Pilot interface 400 will now be described with reference to FIG. 4. A slot 
402 accepts a digitally encoded magnetic card (not shown for ease of 
illustration) to download field data into the computer means 108 of the 
aircraft. A switch assembly is provided comprising an outer rotary switch 
404 and a concentric inner rotary switch. Around the periphery of the 
outer rotary switch 404 is located a set of laser diode indicator lights. 
Each of the respective indicator lights has an associated function 
including field identification 406, navigate 408, swath width 410, swath 
course 412, track width 414, recover last pass 416 and auto spray 418. 
After loading the chemicals into the reservoir 118 of the aircraft 200, the 
control system is activated via on/off switch 420. After downloading and 
saving the data for the particular field to be sprayed by inserting the 
magnetic card into the slot 402, the aircraft 200 is taxied over a 
predetermined calibration point and the GPS receiver is calibrated into a 
predetermined coordinate system via calibration switch 422. 
Each field has an unique, four digit identification number which is entered 
into memory during downloading. The four digit identification number may 
be visually presented on a display 424 by selecting the field ID position 
406 of the outer rotary switch 404. The most direct route to the field is 
communicated to the pilot via an audible signal when the outer rotary 
switch 404 is rotated to the navigate position 408. When the aircraft is 
approaching the field, the swath width 410, the swath course 412 (or 
orientation of the flight pattern) and the track width 414 (width of the 
oval) is entered by the pilot via the appropriate rotary switch 404 
selection. Lastly, the auto spray function 418 is activated to permit the 
computer means 108 to automatically release the chemicals over the field 
208. 
If a prior load of chemicals has been dispensed and the field is not 
completely covered, the recover last pass function 416 allows the pilot to 
being spraying at the depletion point after refilling the reservoir 118. 
The computer means 108 monitors the level of the chemicals in the 
reservoir 118 and closes the dispenser valve 116 upon complete dispersion 
of the chemicals. The computer means 108 then stores the stop position of 
the aircraft when the dispenser valve is closed (and the chemicals are 
completely dispersed) and reopens the dispenser valve upon the aircraft 
resuming the flight pattern and traversing the stop position. 
Having thus described the aircraft control apparatus and method for 
applying chemicals to an agricultural field in accordance with the present 
invention in detail by way of reference to preferred embodiments thereof, 
it will be apparent that other modifications and variations are possible 
without departing from the scope of the invention defined in the appended 
claims.