DESIGN OF AN AGRICULTURAL UAV FOR CROP MONITORING
Eyes over the Fields
Abstract:
Unmanned Air Vehicles (UAVs) are unpiloted flying robots. Though they were initially developed and used by the military, now it has seen their wide applications in various sectors, including Agriculture. This project outlines the design of an agricultural UAV and how this technology can help the detection of plant disease and prevent it from spreading through early identification of plant-insect or disease symptoms. UAVs can skillfully travel up and down through endless field rows from a set position or even far over a tree canopy. It could be operated from difficult locations for people to enter.
Furthermore, it supplies the operator with high-resolution photographs to monitor and detect all the pests and pathogens. Also, it would help in isolating the infected area or the presence of rogue plants. Early detection of plant pest and disease incidents will render the response more manageable and reduce the effects of an outbreak. In this research, we are looking into the ways by which drones could support the agriculture sector in tackling these challenges. It also justifies why capturing and analysing aerial imagery is the best way to deal with this situation. There are multiple technologies available in the industry for assisting image capturing using a drone. This project involves installing specific cameras for multispectral and hyperspectral imaging, which can be installed in the UAVs to capture the image samples ranging from small plots to large-scale fields. Once the samples are collected, they should be processed to detect and predict the challenges. We calculate plant responses in the visible and near-infrared portions of the electromagnetic spectrum to track plant tension remotely from the samples. We will also be able to diagnose the tension of the illness before noticeable signs are evident.
TABLE OF CONTENTS
1.1 MOTIVATION AND BACKGROUND. 1
2.1 UAV Applications in Agriculture. 3
2.3 Current Designs and Technologies. 5
5.2.3 Electronic Speed Control 13
5.2.8 Crop imaging and Cameras used. 15
9.4 Landing gear and tire sizing. 24
10.1 Aerodynamic Calculations. 25
10.1.2 Thrust to weight ratio. 26
10.1.4 Parasitic Drag (Zero lift) 27
10.1.5 Drag due to lift(Induced drag) 27
10.3.2 Minimum thrust required for level flight 29
10.3.3 Minimum Power Required for level flight 29
10.3.4 UAV Climb and Descending. 30
10.3.5 UAV Take-off and Landing. 30
11. Finite Element Analysis. 32
12. Cost analysis and Feasibility. 34
12.3 Design Feasibility and Practicality. 35
15. Project Management Review. 38
APPENDIX A — UPDATED GANTT CHART. 1
1. INTRODUCTION
1.1 MOTIVATION AND BACKGROUND
In the current generation, humans are in a race to innovate and discover new technologies, forgetting how to link those technologies to industries which supports humans needs. Agriculture is one among those industries which must be given importance. Food is the main and basic need of a human being, and the only source for that is agriculture. Hence It is equally important to grow crops and protect them from external factors such as pests and bacteria. Due to rise in the global temperature’s scientists predict that it has increased both the number and the appetite of the insects which will make them eat and breed on the crops grown across the globe. Also, as predicted by the researchers this activity of pests if not controlled can destroy almost 30–50% of crops what farmers grow today. Taking the above situation into matter this project mainly deals with designing an Unmanned Aerial Vehicles (UAVs) or drones which is basically an aircraft without a human pilot on board. Over the past few years, they have been evolved and developed rapidly, after finding a wide usage in military and civil purposes. Though they were just limited to military purposes, now it has become clear that the UAVs can be used in lot of other areas. Where one among them is the agriculture. Coming from an agricultural background and having an exposure on plant health and growth, I was fortunate to monitor how the crops were affected due to pest and the fertility of the soil. Having a good interest in supporting agriculture, it has always been a dream to utilize the UAV technology to help and support the farmers to make their lives easier. This design of the drone will help the farmer to monitor the crop health and development, and determine the fertility of the soil, which will update the farmer for taking immediate measures.
1.2 AIMS AND OBJECTIVES
Scientific survey conducted by crop health experts across the globe has detected large crop losses occur due to pests and diseases. This project aims to design an agricultural UAV that will support the farmers by protecting the crops through regular monitoring of their health and detection of pests. Regular monitoring can help the farmers to take the immediate measures for protecting the crop from pests, dehydration, heat stress, plant damage etc.
· To define the project objectives and scope
· Identify the role of drone in agricultural use; determine, compare, and examine the practicality of various designs.
· To investigate and contour the technical characteristics of the existing designs and comparison with the design made.
· To understand the market demands and needs of the design.
· To research on the material and designs of the drones.
· To establish Conceptual planning and designing the drone.
· To determine whether the developed design is cost efficient and working
PROJECT PLAN
· The project starts with a deep literature review on UAV technology, existing designs, and the market needs. Following this, all the aerodynamic parameters are considered, and a detailed understanding of the UAV structure and design is obtained. Also, the cameras and sensors are selected for aerial imaging.
· Moving on, the UAV body frame is studied and analyzed which leads to the selection of materials and its component’s selection. Considering all the aerodynamic parameters and measurements the conceptual designs are sketched. Later the concepts are analyzed and compared to know which is efficient and reliable, and then the final design is been selected and processed for the detailed study and design.
· A detailed aerodynamic calculation is been worked for the final design. All the major sizing’s and measurements are obtained. Later the flights duration, flying range, power consumption and its capacity is been obtained.
· The final design is modelled using the CATIA-V5 software and the CFD is performed on the model. Last but not the least the designs cost analysis is performed and its future developments and worked and described.
2. LITERATURE REVIEW
2.1 UAV Applications in Agriculture
Farming in developing countries is primarily based on farmers’ conventional experience, with unscientific farming methods widely used, resulting in low production and resource depletion. Furthermore, farming has not adopted mechanization. Hence managing a farm and sustaining a field is a time-consuming and labor-intensive process. As a result, precision agriculture (PA) has a lot of space for growth. It allows a farmer to apply the correct amount of care at the right time and in the right place on the farm by using geographic information and communication technology (Geo-ICTs) concepts. However, drone-based sensing and image interpretation are needed to capture timely high-resolution images.
The solution for capturing timely images has been performed by the UAV’s, where the user can control remotely. These UAVs have been employed with specific cameras and sensors that collected timely data from the crop field to identify stressed areas in real-time. Having received this data, the farmer can carry out the healing measures says (Ram, 2020).
2.2 UAV
Since before the Wright Brothers’ ground-breaking flight, UAVs have been in progress. The first story dated from the American Civil War when an engineer patented an unmanned balloon that could be used to release bombs when a time-delay fuse system caused a basket to topple its contents. While this is a very primitive idea about what we now call “drones,” it demonstrates how the early man thought of unmanned aerial systems. Following the American Civil War, this technique continued to advance slowly; the first military aerial observation photographs were taken in 1898 during the Spanish-American War using a telescope fixed to a kite.
Then in 1970, the development of Scout and the pioneer gave a kick start to the production of the more well-known glider-type UAVs. It was from this design the predator drone was introduced.
These drones were advanced and are still in use, its autonomous control systems demonstrate how long they have come and how the technology progressed.
From the past two decades the structural design of the UAVs have evolved and developed to serve multiple purposes. As the requirements change, the design is upgraded to serve them. Though the designs change as per needs, there are few considerations that remain constant.
The degree of autonomy is the first of these feature requirements. Most of the early UAV prototypes were programmed to follow a predetermined course before they ran out of fuel. They had a camera aboard, which would be retrieved after the UAV touched down. Later, as the technology evolved the radio signals were used to control the UAVs from ground. (Scheve, n.d.)
UAV Types:
These UAV’s were further classified into two prominent categories:
Multirotor UAV’s: These are miniature UAV’s that work under the principal of rotor system, which consists of three or four propellers to provide lift. Multirotor are considered more reliable because they are easy to handle, short take off space and can hover over an area while carrying the payload. Due to the rotors being mounted on the wings, there is an enormous drag that is developed, which opposes the cruise flight. Hence the multirotor UAV’s are less suitable for long range and endurance flight.
· Fixed wing UAV’s: Fixed wing UAV’s are the ones which are powered by electric batteries which gives long range distance compared to the multi rotor systems which are powered by two or more generating rotors with fixed-pitch spinning blades that helps in generating lift.
Compared to the multi rotor the fixed wing drone are more logical to be used for fulfilling the missions which require long range and endurance. The fixed wing UAV’s gives longer flight
time and duration which brings more advantages to crop monitoring for flying across large areas of farms with longer duration. Hence Fixed wing UAV’s systems are preferably used in the operations such as farmlands and hilly areas.
Both varieties of UAV’s are controlled by the ground systems where a user operates it through the remote signal. (ÖzgürDündar, 2020) also suggested that this is true. Here are some comparisons between the fixed wing and multirotor UAV.
In this project, a fixed-wing UAV is preferred because of its simpler aerodynamics and controls, which increases the speed of the UAV. Fixed-wing UAV will also benefit agriculture as it can cover large areas in a short period, and it’s easy to access will help the user fly comfortably. Moreover, the fixed-wing UAVs carry enough weights, which acts as an advantage in this project.
2.3 Current Designs and Technologies
Currently, there are variety of UAV designs in the market to support the agriculture sector, which include the multirotor and the fixed wing. The multirotor drones include the tricopters, quadcopters, hexacopters and the octocopters. In fact, the multirotor drones are commonly used for agricultural purposes, as they are easy to handle and are manurable. The other variety is the fixed wing UAV, these are comparatively less preferred in the agriculture sector, as they require lot of work and space to operate. As each design has its own advantages, the fixed wing UAVs provide longer range in a smaller period which can be used to larger areas of lands. Some of the designs and technologies are:
· AGRAS T20: AGRAS T20 is a hexacopter, which has been specially manufactured and produced by DJI. This advanced technology is designed for crop protection and monitoring. The UAV comes with an FVP camera to provide real-time visuals and Real-Time NDVI
Mapping. Also, the multispectral sensors have been employed to provide actionable insights into crop health and formulate variable spraying and seeding maps. The design is navigated by 3D flight route planning, enabling it to perform real-time mapping and generate flight paths. Furthermore, for collision prevention, the UAV is implemented with an Omnidirectional Digital Radar system to detect obstacles from all horizontal directions. Apart from the technologies, the UAV can carry a payload of up to 20L(20kg) and cover 12 hectares per hour.( (DJI, 2019)
· Trinity F90+: This is a Fixed wing UAV, which offers Vertical Takeoff and Landing (VTOL) capabilities from flexible operational areas for expanded range and coverage. This UAV is employed with MICASENSE RedEDge-MX and RedEDge-MX MICASENSE Dual Camera Kit, which features a sensor that captures five narrow spectral bands and generates plant health indexes and RGB images. Apart from that, the UAV weighs 5kg with a cruise speed of 38MPH. IT has got a wingspan of 7.48 feet and can travel up to a range of 100km.( (Solutions, 2021)
2.4 Crop Imaging
Agriculture is a field evolved from the sedentary human civilization. The intense agriculture began in twentieth century which increased the productivity. As the cultivation expanded, the biggest challenge faced by the farmers was the difficulty in monitoring large crop fields. Lack of this surveillance led to decline in production and crop yield. Introduction of satellite imaging, manned aircraft system, and ground surveying helped to control the problem to an extent. Though these methods were effective for larger farm fields, small and medium-ranged farms could not attain the benefit of these technologies due to their high cost. Also, there were various factors like weather dependencies that toughened the problem.
Unmanned Air Vehicle (UAV) technology was proposed as an alternative to solve this challenge as these aircraft could fly low and can generate much more accurate data. The biggest advantage of this solution was that UAVs could be used for closer analysis compared to other solutions as the normal imaging of crops could showcase only the external properties that were within reach of the eyesight. To obtain more detailed information like plant stress, dehydration, and heat stress, multispectral sensors were implemented in the UAVs. The data received from these sensors are processed and analysed for early detection potential challenges.
These sensors are potentially expensive compared to alternatives like commercially available camera that are limited to imaging within the visible range. However, on a utilitarian perspective, usage of sensors in UAVs had lots of benefits. Primarily, the vegetation discriminating ability of sensors makes it a critical element for crop monitoring in diverse vegetations. Also, the low altitude UAVs increases
these benefits in supporting the discrimination of potential threats like weeds in a vegetation or early detection of a disease spread. Furthermore, increasing the resolution of cameras and integrating advanced technologies into the UAVs helps in mitigating the problem to a much larger and broader extend. (Bryson, 2010)
2.5 Design Principles
UAV design is a multidisciplinary process that starts with the concept of parameters and specifications, usually a list of the most crucial mission characteristics, including payload, endurance, altitude, and speed. Following that, an initial sizing based on similar aircraft designs is undertaken to narrow down the available airframe concepts, with the following steps being to evaluate the selected design’s aerodynamic performance.
· Obtain a geometrical design that provides sufficient volume for the systems.
· Determine the structural responses based on the projected loading.
· Selection of desired motors and batteries to propel the required thrust.
Hence as like the general aviation aircraft, the main aim of the final UAV design is to fly as effectively as possible. As a result, two of the most critical design considerations are to create flyable and controllable solutions and to strive for even improved results in the design (Austin, 2010).
Generally, the UAV’s have the same components as crewed aircraft, in terms of equipment design, except that there is no requirement for a cockpit or any environmental control or life support systems. Even though this saves weight, it is often reimbursed by the Advanced guidance, navigation, and control
systems needed, which can be very challenging depending on the size of the aircraft and the amount of mission autonomy requested. Also, in addition to this, the payload has been added, which specifies the purpose of UAVs and is typically comprised of different instructions and mission-specific objects, imposes a further load.
The payload mainly consists of EO/IR sensors, the multispectral and other specific cameras and communication systems in the agricultural UAV design. In contrast, different designs have payloads such as fertilizers and pesticides, etc.
Equations 1 and 2 depict the importance of a high-performance design, emphasizing how low structural weight, strong aerodynamics, and high engine efficiency can minimize fuel weight, increase range, and thus allow for even more helpful payload to be considered in the project. (Papageorgiou, 2019)
3. Design Constraints
Every engineering design made is a solution to real-time problems that emerge due to the advancements in technology. To achieve a balance between the design goal and the limitation, we consider certain constraints in advance. As this project aims to design a UAV for crop monitoring, general conditions like weight, safety, and cost are considered.
Below are some Important constraints specified:
· Size and weight: The UAVs payload should be capable of supporting the propulsion system, cameras, sensors, battery, and other electronic components. The actual weight of the payload should not be more than 3kg. Furthermore, all these components should fit inside the aircraft’s frame, without affecting the overall weight of the body. So that it doesn’t affect the flying time.
· Cost: Cost analysis has been performed so that it is in an acceptable range for the farmers.
· Safety:
- Flight Control: The flight controller should reach the origin point in case of communication loss to regain the connectivity.
- Power Source: The UAV is powered by a lithium battery. Therefore, no flammable liquids and substances are used to damages to humans and UAV
- Design and development: The UAV should be designed and developed well to avoid any structure damage, which might affect the mission.
· Aircraft:
- Battery: The UAV should be supported by a rechargeable battery, which can help an average flight of 15–20 minutes so that the flight can cover an area of 30–40 km with an added payload.
- Wingspan: The wingspan should be designed to a length of not less than 2m, so that it can give a required lift to the weight added.
- Payload: The UAVs payload should be able to support all its components, which should not be more than 2kg.
· Cameras:
- Mapping: The cameras should be able to map the crop fields and terrains to calculate the crop yield. It should also provide live video to the user for its location and damage spotting in the field.
- Photography: The cameras should take the required multispectral, thermal, and live pictures to help farmers gather information regarding crop health.
· Communication:
- Coverage: The coverage should include a minimum of 30 km from the origin to cover larger areas of the field without losing contact with the user.
- Data rate: The UAV system should support live streaming and data transfer using high data rates to obtain quality streaming.
4. Mission Specification:
4.1 General Flight
The aircraft must be operated with in the range of the transmitter and should be virtually observed by the live video. The UAV is advised to be used only during daylight hours and in good weather. The UAVs maximum altitude would be 400ft, with a standard flight height of 200–300 feet over agricultural fields.
4.2 Flight speed
This UAV’s preferred top speed is 40 mph. If the 40 mph speed limits the construction space so much, the speed can be further increased. The UAV will be flying at a speed of 35 mph when taking images. If the maximum speed is increased, the selected application’s airspeed will change as well.
4.3 Payload
The UAV will be carrying a load of 4 kg, which includes cameras, sensors, and all the other electronic equipment like battery, motor, etc.
4.4 Take-off and Landing
The UAV must be able to take and land on muddy roads close to the farm fields. Also, the aircraft must be able to During take-off, the runway would be restricted to 500 feet. The preferred landing distance is 1,000 feet, but if necessary, it can be raised.
4.5 Endurance
The take-off place for the UAV will be located 3 kilometres away from the field. This distance is used because the UAV must take pictures from the point where the crop start, which enables it to cover the entire field for mapping, pest detection of the crops.
4.6 Mission Profile
The mission consists of different stages with the tasks mentioned below:
5. System overview:
5.1 Block diagram
5.2 Battery
The battery is the primary power source for UAV operations. A 6000 MAH 6S Lithium Polymer (Li-Po) battery will power the UAV. Li-Po batteries are preferred compared to other batteries because of their numerous advantages: lighter weight, greater power, and faster discharge speeds.
The battery voltage and the number of cells is the two most essential parameters in the battery. For the motor to run, the voltage given by the battery must be at least equal to the voltage of the motor. The endurance of a battery, on the other hand, is an indicator of how much electricity the battery can carry. (Schneider, 2020)
5.2.1 Flight controller
The Flight Controller is a smaller circuit board that controls the servo motions in response to the input. It does that by collecting the user’s order and decides how to manipulate the servos accordingly.
The UAV is fitted with the latest Pixhawk flight controller in this project, which is an open hardware project that combines a processor with critical sensors to function the flight. The Pixhawk flight controller is equipped with a 168 MHz CPU and 256 KB RAM and a compass, 3-D accelerometer, and other connectors. This functionality gives an edge by allowing the user to install autopilot applications. Furthermore, it also meets the necessary condition in addition to its stability and reliability.
5.2.2 Motor
The UAV is equipped with a brushless DC motor, which is supported by the battery. The FC converts the electrical energy into a rotational force that rotates the propeller to provide mechanical torque. Brushless DC motors have several benefits, including highly accurate speed control, high performance, high stability, reduced noise, longer lifespan (no brush abrasion), and no ionizing sparks.
5.2.3 Electronic Speed Control
The electronic speed control is a circuit, which controls the speed of the electric motor. The ESC could also be capable of engine reversal and dynamic braking. The ECS consists of two main sets of connections. One will connect the battery, and the other one connects to the brushless motor.
5.2.4 Arduino
Arduino is an open-source electronics application that uses simple hardware and software to make it convenient to use. It consists of a circuit board that reads the sensor’s inputs and converts them into output. In this project, the sensors collect data regarding the atmosphere conditions, read by Arduino, and then send it to Raspberry pi through a USB serial port. (Anon., 2020)
5.2.5 Raspberry pi
Raspberry pi is a series of small board computers that is installed in the UAV. The Raspberry Pi is used to connect a webcam for online viewing, a GPS for location monitoring, and a 4G/3G USB connection between the UAV and the server. The Raspberry Pi 3 is the Raspberry Pi’s third generation. It has a 1.2GHz 64-bit quad-core processor, which will be included in this project based on a suggestion by a computer engineering student because it can do many tasks at once. Furthermore, the Raspberry Pi is significantly faster and has considerably more memory than the Arduino.
It has a video display for downloading, and the Raspberry Pi can conveniently run the Internet with a 4G USB stick. It has a video window for streaming, and a 4G USB stick can be used to connect to the Internet. (Anon., 2019)
5.2.6 Servo
The servos are the rotary actuator, which controls the angular and linear positions of the ailerons. The UAV is equipped with four servos, two for the wings and two for the tail ailerons. They generally consist of a cable connection that is connected to the flight controller through a USB port. On receiving the signal from the user, the flight controller directs the servos to rotate accordingly. The PWM ( Pulse Width Modulation ) principle governs the angle of rotation of a servo motor, which means the length of the pulse transmitted to its control PIN defines the angle of rotation. Servo motors are made up of a DC motor and several gears operated by a variable resistor (potentiometer).
5.2.7 Modem
The UAVs have cameras and sensors which constantly collect real-time data during the flight. The collected data is transmitted to the ground station or the user via a modem. A 3G/4G is preferred to perform the work of transferring the collected data.
5.2.8 Crop imaging and Cameras used
The Cameras play an essential role in this project. As the project aims to monitor the crops, specific cameras are implemented to determine the crop’s health, soil condition, water levels, and pest detection.
Multispectral Cameras:
Light from a narrow variety of wavelengths across the electromagnetic spectrum is detected by multispectral imaging. Multispectral photographs are taken by either special cameras that use filters to distinguish specific wavelengths or devices sensitive to wavelengths, like light, form frequencies that are not apparent to the naked eye (infrared and ultra-violet, for example).
The UAV is equipped with Multispectral Cameras. This camera allows the farmer to manage crops, soil, and fertilizing effectively. The camera consists of a remote sensing imaging technology that uses green, red, red edge, and Near-Infrared wavebands to capture both visible and invisible images of crops and vegetation. Once the images are obtained, they are integrated with specialized agricultural software that converts the output into a piece of meaningful information. This data helps the farmer to monitor, plan and manage the crops more effectively. (Castro, 2012)
In his project the UAV is equipped with M High-resolution RGB and multispectral camera.
This camera is used for dual purposes. First, It’s RGB camera captures high resolution images of the crops, which can be used for mapping of the fields, spotting malfunctioning irrigation lines and water management. Also, the camera can support live video streaming application.
Second, the multispectral camera takes multispectral photographs, which are extremely useful in determining the health of plants. Since the human eye has a narrow vision of plant and soil quality, multispectral equipment allows the farmer to see better than the naked eye. Some advantages of multispectral imaging include: (Corrigan, 2020)
· Crop yield estimation
· Identifying pests, pathogens, and weeds. Early identification will help he farmer to get the most out of pesticides and seed sprays.
· Determine plant population and spacing issues.
· Provide soil fertility information and improve fertilization by identifying nutrient deficiencies.
· Help in land management, such as deciding whether to put agricultural land into cultivation or rotate crops, and so on.
· Examine crop damage incurred by farm equipment and render required repairs or replacements.
· Recognizing the areas, where the risk of water stress is high and controlling crop irrigation.
6. Major Components
6.1 Fuselage
The fuselage is the aircraft’s main body section, which carries all the payload and embraces its components together. There are variety of fuselage shapes used in the UAV industry as shown in fig(17). But it mainly depends on the missions the UAV is commissioned to execute. The fuselage also helps align the control and stabilization surfaces with the lifting surfaces, which is essential for aircraft stability and maneuverability. As the UAV in this project is built to operate at low speeds a cylindrical shell with a spherical dome in the front was used.
6.1.1 Wing
The wings or an air foil play a major role in the UAV’s operation by providing lift and allowing the flight to fly. The aircraft’s roll performance is controlled by through the ailerons, which are attached to the trailing edges of the wings. In today’s aircraft designs, various wing designs are used based on the craft’s mission. The figure(18) shows the various wing configurations.
Apart from that, the aircraft’s speed also depends on the geometry of the aircraft. The existing UAV technologies use several wing geometry’s as shown in figure(19).
6.1.2 Empennage
The Empennage or the tail is an important structure in the UAV, which provides stability during the flight. The empennage is composed of the entire tail assembly that includes tailfin, tail plane, and its attachment to the fuselage. Fig (20) represents the parts of a general tail in an aircraft.
As shown in the above image the tail consists of a vertical stabilizer, and a horizontal stabilizer, which consists of rudder and a elevator respectively. The vertical stabilizer is used to reduce the aerodynamic side slip of the aircraft and provide directional stability, whereas the horizontal stabilizer provides stability to the entire aircraft. However, there are variety of designs and geometries of the tail that can be used in this design depending on the mission. The variety of tails used in the current designs are seen in Fig(21).
7. Design Alternatives
7.1 Overview
Specific restricting considerations have been considered to choose a design for this UAV, including the payload of electronic components that will be to be encased and protected somewhere inside the fuselage. Given that the UAV moves longer distances with the pay load, the options were further narrowed. After conducting research about the existing designs used and comparing them with the requirements of this project, it concluded that a fixed-wing design similar to that of a RC Plane would be preferred. As the UAV is set for longer rangers, the creation of the RC Plane seemed more suitable.
The design of the RC Plane was considered because, the design is suitable for sustaining long periods of flight due to its lift to weight ratio. Also, the lengthened wings of the aircraft can withstand more loads during the flight, which makes it more efficient for longer distances. Since these aircrafts come in a number of configurations, the following are some experimental prototypes that were considered before settling on the final version.
7.2 Design Alternative 1
The first conceptual design that was visualized at is shown in fig(22). This design has been equipped with a high wing attached to the fuselage. A high wing is preferred in this design because, firstly, the center of gravity of a high-wing aircraft is below the wing, which means the fuselage functions as a pendulum to improve roll stability when opposed to a low-wing UAV, whose center of gravity is balanced above the wing. Also, for high-wing aircraft, the tendency to experience a dangerous spiral descent is relatively more minor. This effect is highly preferred for UAVs that fly for a longer time with a minimal pilot workload.
Secondly, talking about the landing characteristics, the low-wing aircraft can “float” more quickly than the high-wing aircraft due to the more significant ground impact during the flare, which tends to soften the landing. However, this same ground impact will trigger ballooning during the flare, making accurate landings more difficult. Moreover, the UAV might require taking off and landing at the farm field. Hence high wing will not obstruct while taxing.
A T-tail design is preferred in the aircraft because it gives smoother airflow over the elevators, which reduces the drag. Furthermore, because of the endplate effect, where the proximity of a perpendicular surface (in this case, the horizontal tail and the fuselage) improves aerodynamic performance by reducing air pressure losses over the capped ends of the lifting surface, the T-tail increases the effective aspect ratio of the fin, resulting in the fin having a higher and more efficient aspect ratio.
While this concept satisfies the project’s specifications, it does have several flaws. The biggest drawback is in the design specifications themselves. The optimal position for the camera is at the UAV’s nose since it is intended to take images of the field from various angles. However, this configuration necessitates a front-cantered propeller, which will affect the electronics powering the camera and the camera itself.
7.3 Design Alternative 2
This second conceptual design that looked at is seen in fig(23). This concept suggests a swept wing with a configuration of mid-wing, with a fuselage rounded in the front to accommodate all of the electrical elements, then thins out until it reaches a T-tail that is used to balance the aircraft’s take-off. This design is highlighted by its narrow and long fuselage and its rigid swept-back wings, which give an outstanding aerodynamic capability.
The swept wing was preferred for this design because it gives more lateral stability to the aircraft, which is beneficial for the cameras to capture perfect pictures; also, as the wings are designed in a much thinner and finer way, less friction is acted on the UAV. Furthermore, the usage of swept-back wings causes less turbulence if the speed of the UAV abruptly changes. Finally, the extended wingspan gives greater lift with the least amount of drag.
This UAV consists of a v type tail, and it is preferred because; Firstly, it has got fewer surfaces, and a V-tail aircraft would have less drag and hence a higher cruising speed than a conventional tail aircraft with the same characteristics. Secondly, the most crucial advantage is how the vertical and horizontal tail surfaces interact during high-angle-of-attack maneuvers, including stalls and spins. However, considering the various positive points, the same issue remains, namely the position of the engine. Since the fuselage thins out too far at the back of the aircraft, it is possible to fit a propeller there. Although the aerodynamics of this design has been greatly improved, the fact that it still needs with front propeller is perplexing.
7.4 Design Alternative 3
The third design is seen in fig (24). This concept is widely used in many sectors that prefer UAVs. The design consists of a cylindrical fuselage that extends to a cone-shaped figure. Like the RC Plane straight and rigid wings are seen in this design. The structure consists of an inverted V-tail, which is connected to the wings through a bob. V-tail is preferred because it is lighter than the other conventional tails and has a less wetted area, thus producing less induced and parasitic drag. The distinction between this configuration and the RC Plane is the expanded fuselage, which allows for the use of a back-centered propeller. This is a significant change from previous concepts since it enables the camera and other electrical components to be mounted in the nose of the UAV without being obstructed by the propeller.
7.5 Proposed design
After Considering the conceptual designs that were worked on and comparing their advantages and disadvantages, it is decided that the 3rd design was the best design to be relied on. With its solid framework, lightweight, and propeller location suitability, this UAV design highly matched the design requirements.
8. Design Configuration
8.1 Design Take-off weight
The design take-off weight can be written as:
The gross take-off weight can be calculated by the eq (1). To assume the initial take-off weight, eq(1) must be further modified to make the battery and empty weights fraction of the total weight as shown in the eq(2). The payload weight depends on what cameras and sensors are attached for the UAV’s mission. In case of crew, the design consists of no crew, hence it is assumed to be zero and the empty weight is calculated by determining the weight of the components mentioned in table.
After all the calculations were made using the equations 1 and 2 the total take-off weight is estimated to be 3131.5.
8.2 Wing Configuration
Considering the qualitative observation, the NACA 4415 air foil is implemented in this design because of its high popularity in agricultural UAVs. The High wing position was preferred for several reasons; firstly, high wings are beneficial for small runways. Secondly, they prevent the ground impact from increasing the lift when the UAV reaches the ground and protects the wing from obstacles during take-off and landing. Furthermore, Raymer has suggested that the standard agricultural UAV’s aspect ratio is to be 7.5. The UAV is designed to fly at a speed of not more than 40mph, hence flat straight wings are preferred over the swept wings.
8.3 Tail Configuration
In this design, an inverted V-tail was preferred over the traditional methods. A hinged control surface also referred to as a ruddervator, is located on the aft edge of each twin surface and incorporates the features of both a rudder and elevators. Inverted v-tail was selected because it is lighter and has a less wetted surface area due to the fewer surfaces, which comparatively produces less induced and parasitic drag. The air foil preferred is NACA 0012 for both the sides of the tail, with a small degree of incidence, preferably 1 or 2 degrees, to account for the moment generated by the single-engine propeller. Both the sides of the tail will have an aspect ratio and taper ratio of 4 and 2, respectively.
9. Design Sizing
9.1 Fuselage
From the take-off weight calculated, the length of the fuselage is obtained from the eq(3) using the historical data for agricultural UAV.
The length of the fuselage and the radius is taken as 840mm and 3.13 respectively.
9.2 Wing
· Wing area = 0.2 m²
· Wingspan =1m
· Chord length = 200 mm
Since the wing is a straight wing, the mean aerodynamic chord is just the chord, with the chord’s position being half of the wing’s semi span.
9.3 Tail and Bob
The tail is sized based on the wing and fuselage sizing.
· Fin area = 0.0496 m²
· Area of each of the V tail = 0.017 m²
9.4 Landing gear and tire sizing
The front nose wheel and the aft wheels are the two components of the UAV. The nose wheel would be able to turn for land steering, but not the aft wheels. Furthermore, for UAVs with steerable nose wheels, the rake angles should not exceed 15 degrees, and the trail should be approximately 20%.
By using eq(4) and eq(5), the tire diameter and tire width are obtained respectively and as the tires are used on rough surfaces the tire sizes need to be increased by 20%.
10. UAV Calculations
10.1 Aerodynamic Calculations
10.1.1 Centre of gravity
The Centre of Gravity (CG) has been estimated at this stage using known or estimated weights for the major components of the UAV such as the wings, fuselage, and tail. The Nose of the aircraft was used as a datum for calculating X CG and the center line of the fuselage was used to calculate the Z CG positions. The CG in the Y plane is assumed to be zero. (Raymer, 1992)
Using eq(6) and eq(7) the CG of fuselage is found to be 442.82. From this considering the weights and moments of the wing, boom and tail the CG of the entire UAV is obtained.
Hence using the above values along with the CG of the UAV is found to be 640.62mm.
10.1.2 Thrust to weight ratio
It is important to note that while calculating thrust-to-weight ratio for the propeller UAV, power loading is used instead of the thrust. As suggested by Raymer for agricultural UAVs, it is estimated that power loading is 11lb/hp and the hp/W is 0.09. Hence for the propeller aircraft, the thrust is created by resulting in improvements to the thrust-to-weight ratio equation.
To evaluate a first approximation for P/W and T/W, statistical inference can be used. The historical considerations for agricultural aircraft are used in this mathematical estimation, as seen in eq (9)
Once the eq(8) is solved, the obtained value is substituted in eq(9) to get the thrust-to-weight ratio.
P/W and T/W are equal to 0.0569 and 0.6259 respectively.
10.1.3 Wetted area
The wetted areas are the exposed surfaces of the aircraft, which can be visualized as the area of the external parts of the aircraft that are exposed to sunlight. The wetted areas of wing and tail, and fuselage are to be calculated by eq(10) and eq(11) respectively.
Also, the internal volume of the fuselage can be obtained by the eq()
The values obtained are:
10.1.4 Parasitic Drag (Zero lift)
Parasitic drag is a form of drag which acts on the UAV while flying in the air. Since the UAV will be traveling at subsonic speeds, the parasitic drag will mostly be the skin friction drag plus a small separation drag. The parasitic drag can be calculated by two different methods, but we will be using the skin friction method as shown in eq(13).
According to Raymer the value of the skin friction for a light aircraft with single engine is 0.0055. The parasitic drag obtained is 0.0298.
10.1.5 Drag due to lift(Induced drag)
The induced drag or the lift-induced drag is a form of drag which is caused due to lift. According to conventional wing theory, the most powerful wing has an elliptical lift distribution, and any wing lacking one would have an increase in drag. Here the drag due to lift factor (K) is calculated by the classical method that is based upon the Oswald span efficiency factor (e).
From the eq(15), the drag due to lift was found to be 0.0625.
10.1.6 Drag Polar
The drag polar is the relation between the aircraft lift and its drag. The drag polar is calculated using the values of induced drag and parasitic drag by the following equation.
From eq(16) the polar drag is 0.0554.
10.2 Stability and Control
The stability and controls of the UAV deals with the rotational motions of the UAV that include pitch, yaw, and roll.
The static pitch moment of the fuselage is calculated by the eq(17), and the value obtained is 0.00166.
From the above equations, the lift coefficient is calculated, as shown in the eq(18), respectively.
The lift coefficient from the above equations were found to be 0.646.
10.3 Flight Mechanics
10.3.1 Steady level flight
The steady level flight is an essential factor in this project as the mission of the UAV is to capture photos of the farm field. A stable flight can support the camera to take proper images. Minimum thrust and power calculations and comparisons are considered to calculate the steady level flight. Also, the steady flight will be calculated based on the cruise speed of the UAV. It’s important to recall that the thrust should equal the drag, and the lift should equal the weight, which is expressed in the following equations.
Following that, the velocity and thrust to weight ratio for the steady flight is given by the eq(21) and (22).
According to eq(22), the criterion for minimum thrust at a given weight is also the requirement for the minimum lift to drag ratio. Hence to find the velocity at which the thrust is minimum and lift to drag ratio is maximum, the derivative of eq(23) has been set to zero, which is expressed in the following equation.
10.3.2 Minimum thrust required for level flight
The minimum velocity, drag and lift coefficients are expressed in the following equations.
The optimum lift coefficient is the minimum lift coefficient, which is determined solely by aerodynamic parameters. This implies that the aircraft will travel at the optimum lift coefficient by varying the velocity or air density.
10.3.3 Minimum Power Required for level flight
Raymer states that the conditions for minimum thrust and minimum power required are not the same, which is because the steady level flight is equal to the drag times the velocity as expressed in the equation.
The power from the above equation was found to be 50.6. The minimum power velocity, drag, and lift coefficients are expressed by the following equations.
10.3.4 UAV Climb and Descending
The climb conditions of the UAV are calculated under two conditions — Firstly, the rate of climb that provides the maximum vertical velocity. Secondly, the climb angle maximizes the angle of climb. These two conditions are related and are calculated. (Raymer, 1992)
First, the rate of climb velocity is obtained by using the eq(31).
The climb velocity and the climb angle are calculated by the following equations.
10.3.5 UAV Take-off and Landing
The take-off analysis is split into multiple segments and calculated.
· Ground roll:
During the ground roll, the forces that act on the aircraft are the thrust, drag and roll friction of the wheels. Hence these components are first calculated by the following equations.
The values of KT and KA obtained are 0.585 and -3.2057 respectively.
Substituting the KT and Ka values in eq(36)
The ground roll value was found to be . But the UAV is limited for a minimum take off distance 500 feet, which is comparatively less. Hence this is a Compact aircraft, according to Raymer the rotate distance is approximately the same as the take-off velocity, which is 1.1 sin times the stall velocity.
· Transition:
To calculate the transition distance, the radius of the transition arc must be first calculated by e(37).
The transition arc obtained is 555.28. Now, as the transition arc and climb angle are estimated, the transition take-off segment can be calculated by using the eq(38).
The height calculated is 14.69.
The UAV’s horizontal distance of the transmission segment and the horizontal climb distance is calculated using the eq(40) and eq(41).
Hence from the above calculations the take-off distance is obtained by eq(42).
Total take off distance is found to be 509.38.
The landing analyses id same as the take-off analyses, but in the reverse way. The landing distance is estimated to be 500ft. (Raymer, 1992)
11. Finite Element Analysis
The fluid flow over an object is an external flow over the outside of the body, wherein this design is the air foil and fuselage. The fluid flow moves around the air foil, which causes the flow to build up regular and parallel forces to the flow, and these forces are called the drag and lift force. In this project, as we have considered the air foil NACA 4412, the aerodynamic parameters like the pressure, velocity, and temperature acting on the air foil and fuselage were observed using the ANSYS fluent. (Escobar-Ruiz, 2019)
Velocity flow over an air foil:
The minimum and maximum velocity in this flow is 0 m/s and 17 m/s respectively.
Pressure Distribution over an air foil:
The turbulence acting on the air foil is shown in fig(30).
The total pressure acting on the air foil is shown in fig(31)
12. Cost analysis and Feasibility
12.1 Sub systems
The vital part of any design project is its cost analysis. Analyzing and detailing the design cost is a systematic approach to estimate the strengths and weaknesses of the alternatives used to determine options that provide the best method to achieving benefits while preserving savings. During the cost analysis it is also important to note that It makes no difference how well the aircraft performs if it is prohibitively costly to build. Below are the cost estimations of each product used in this project to complete the mission.
The prices mentioned above of the components are estimated based on each component’s current prices in the market. As every element cannot be manufactured from scratch, they are purchase from the local dealers. This also plays a vital role in design projects because the design parameters and measurements should qualify in installation and carrying the purchased equipment. The cost of it must be efficient to meet the designer needs if the UAVs are mass manufactured. Furthermore, as the UAV is used in crop fields, there might be damages or repair of the components, which might be the responsibility of the manufacturer to investigate the problem and fix it.
12.2 Major Components
The major components include the fuselage, wing, tail and the landing gear. The costs for manufacturing these components is shown in below table.
The total cost of the overall design was found to be 3889. Even though the costs are estimated, it does have some flaws. The current UAVs present in the market for agricultural purposes are available in a comparatively lesser price than the cost estimated for this design and on the other hand if the farmer employs a person for investigating the crops by patrolling rough the fields, might also be an cost efficient method. As the drone meets the market needs, it still might not be ac cost efficient as other technologies which will be discussed in the future work and development.
12.3 Design Feasibility and Practicality
Though the design proves to satisfy the goals and objectives, several other factors cause hindrance to the UAV design:
- As drone/UAV technologies serve agricultural purposes, it is easy to implement the crop monitoring technology to existing ones. This might raise uncertainty in the market requirements as to whether to certify the design or not.
- The designed UAV will be flying at higher speeds, and it also can’t hover in a particular area. This might limit the potential market to smaller farms.
- The higher cost of the design will make it less cost-efficient, limiting the market needs due to other cost-efficient methods.
13. Conclusion
Technological advancements in the UAV sector have been researched in recent decades. The prospect of a new agricultural UAV was conceived because of recent developments in UAV technology. As part of the project, I could explore further on different UAV’s and current technologies. Also, I was able to briefly explain the UAV’s major components and subsystems. Three conceptual designs were made, considering the necessities in the agricultural field, from which one final design was selected by comparing the advantages and considering the implications. The final UAV model was designed with the requirements of 1) carrying a maximum payload of 3 kg, 2) maximum cruise at 40mph, 3) take-off distance at 500ft etc. Furthermore, a detailed design of the UAV was established that includes the UAV sizing and measurements, design configuration, calculation of aerodynamic parameters and analysis. It is observed that the design can be implemented successfully and can bring a lot of innovations to the agriculture sector. Finally, the cost analysis was performed, and the costs of the overall drone was estimated to be 4,119£. The budget seems to be exceeding the initial estimates, but the advantages should be looked in an utilitarian perspective. Ultimately, the design can bring lots of benefits to the sector and even has the potential to improvise to further areas. Hence, I would like to conclude my analysis as a success as the model seems to be promising and had a huge potential for future developments.
14. Project Future Work
The aim of this project was to design an agricultural UAV with features like air crop monitoring and live streaming. The project’s primary goals and objectives have been achieved. However, this design can be further developed to extend its missions and improve its effectiveness.
The UAV in this project is designed to take off and land using a space-consuming runway, and the user needs flying skills to operate it. But this problem can be further developed by upgrading the design with (Vertical Take-Off and Landing) VTOL technology. This technology is a mixture of multirotor and fixed-wing applications, where the aircraft will consist of a fixed-wing and a multirotor. This can be easily implemented to the currently designed UAV as it seems practically possible and practical. This up-gradation will curb the usage of runways, and as the UAV can take off vertically, the design will be more convenient for use in terrain and hilly areas like rubber and tea plantation. Also, the fixed-wing UAV cannot pause and hover at a particular area, which can be rectified by using the VTOL technology that benefits the user to monitor the properties of the required site. The technology also helps the mission to carry heavier loads as the rotors can provide more lift than the fixed-wing UAV. Apart from this, the UAV can be equipped with an autopilot system, which will still require a runway for take-off and land. But the usage of autopilot makes it easy for the user without any previous experience to operate the aircraft.
The UAV designed is operated within the user’s eyesight, which limits the user from flying it to a farther distance, as it might lose the signal and fail the mission. This can be further rectified by using high range transmitters, where this will help the user to travel across estates and plantations to collect the required data. Also, during harsh weather conditions there are high chances for the UAV and the ground station to lose connectivity, where in this scenario the UAV must be able to comeback to the point of origin. This feature comes with the autopilot system, which controls the aircraft on loosing connection with the user.
The battery is an essential factor of the UAV for longer ranges to perform its operations. But due to the limited weight of the payload, the more extended missions are sometimes impossible. All the existing UAV technologies face this cause. Hence an alternative for this is to implement solar technology in the UAV. This is done by implementing the solar panels to the wing or the fuselage body’s upper surface. This futuristic development can back up the existing battery and can support long-range missions. Moreover, the usage of solar power also reduces the charging time by powering the batteries constantly.
The landing gear requires some future work. As the runway and landing surfaces in the farm fields are rough and dirty, the UAV might experience a rough landing which might directly affect the structure of the fuselage. Hence a future work is required on designing a effective landing gear for rough landings with the use of the shock absorbers. This will help the UAV land without any fracture.
15. Project Management Review
The project was spread across eight months, starting from September 30th to April 6th, where it was extended to 12th April. The project is worth 30 credits overall, and there are various factors to discuss in this part. The project plans and approaches to achieve goals have slightly deviated as the project has progressed. In addition to this, there is a dictionary of events that have had a huge impact on the project and other academics, which are described and discussed.
Firstly, there were multiple goals and deadlines set on the project timeline, where a few of them were not achieved as imagined. This is because of the increased focus on a particular section for more than the fixed time mentioned in Gantt chart. The initial plan started with providing a conceptual design idea by doing a good amount of literature review. This phase of the project had multiple hurdles with managing time. Because, as the project had begun along with other modules, it was challenging to keep a regular pace on the project. Also, some of the available resources on the internet were to be paid to refer, which included research papers and published books. Then came the project outline submission, which took several days to complete, as there was confusion in preparing the format of the outline. It was challenging to set an order and input the content. Once the conceptual designs were established, analysis was done on each concept to propose a final plan.
Then came the next submission, i.e., the progress review. The calculations were to be 50% completed by the original timeline, but it was challenging to focus on the project progress due to the semester exams. The Christmas break had started by that time, and the improvement was not up to mark. So, I took up the project work in holidays to work on the calculations. A detailed study related to its sizing, configuration, and aerodynamic measures were performed after proposing a final design. The timeline set for this phase of the project was not precise, as it consumed many days. The workload and pressure here were high because the semester B had just begun, and assignments were added up with deadlines closing by. This led to few changes in the Gantt chart, which is shown in APPENDIX.
Secondly, the Covid-19 outbreak and the national lockdown have significantly impacted the project and its progress. The national lockdown has had significant implications in every sector and industry, and the university had no exception. As the national lockdown was implemented before the start of the project, every meeting with the supervisor were virtual, except a few in the beginning. This bought a lack of interaction with the supervisor as it would have been comparatively better to meet the supervisor in person and discuss the progress. Also, due to the lockdown measures, the LRC’s capacity was limited, which restricted the usage of resources. Even though the teaching and the meetings were online, the university had worked tirelessly and did an incredible job offering the available resources. Also, my supervisor gave her best to support and encourage me throughout the project by conducting weekly meetings to set goals and timelines, reviewing the project work, and clearing my doubts. Due to this, the outputs of the project are largely unaffected. Moreover, all the project objectives were successfully achieved well within the deadline. It was motivating as the most reliable way to determine the success of project management is by determining whether the project goals and objectives has been achieved.
To summarize, the project objectives are as follows:
· To define the scope of the project
· Identify the role of UAV in agricultural use; determine, compare, and examine the practicality of various designs.
· To investigate and contour the technical characteristics of the existing designs and comparison with the design made.
· To understand the market demands and needs of the design.
· To research on the material and designs of the drones.
· To establish conceptual planning and designing the drone.
· To determine whether the developed design is cost efficient and working.
These were the objectives that were set at the initial phase of the project. As the project progressed, many inputs were added, and a lot of knowledge gained related to UAV designing. The inputs gained from the supervisor have led to the upgrading of the objectives along with the existing ones. Below are the objectives with their completed documentation within this report, in their respective areas.
· The projects objectives and scope are defined in the section().
· The theoretical review of the UAV, its use in agriculture, comparisons with the existing technologies is established in section ().
· The Market demands have been understood and the mission requirements have been derived in section()
· Research has been conducted on the drone designs and based on the requirements three initial designs have been presented in section()
· A final design has been proposed and a detailed design of the UAV has been performed in section()
· The cost analysis has been performed to know if the UAV designed is cost efficient or not, which is derived in section()
To summarize the project management analysis, it is relevant to conclude that certain choices made along the way affected the project’s outcome. Further decisions were made to reduce the detrimental consequences of the project’s goals and priorities. As the project nears completion, the COVID-19 pandemic had some major impact on the project. But, with effective planning and management, these challenges were handled and did not alter the project’s outcome. Despite of these challenges, it is safe to state that, all goals and priorities are met within the deadline, implying good project management.
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APPENDIX B– CAD MODELS
Fuselage:
· Empennage (Tail):
· Wing:
· Main Landing gear:
· Front Landing gear:
· Propeller
· Boom:
· Assembly
APPENDIX C -2D Drawings
