3.Hybrid UAV

The hybrid UAV is also known as a VTOL UAV since it can take off and land vertically utilizing a rotary mechanism, much like a fixed-wing aircraft. Their control system consists of three controllers: one for horizontal mode, one for vertical mode, and one for transition mode. The detection and control systems are housed within the fuselage.

## *5.3.3 Concept evaluation*

Hybrid This UAV combines the features of a fixed-winged and rotary-winged UAV, making it more suitable for carrying the imaging system, however it is slightly more expensive to produce. As a result of **Table 4**, it is evident that the hybrid UAV outperformed all of their conceptions, and the hybrid UAV will be developed throughout the design development phase.


#### **Table 4.**

*UAV feasibility analysis [14].*

#### **6. UAV design development**

#### **6.1 Mission requirements and parameter estimation**

The flight profile mission must be determined before any design vehicles are considered. Because this vehicle will be classified as a mini-VTOL UAV, the mission profiles will be limited. The UAV's range must be at least 10 kilometers, as estimated by statistical analysis of existing VTOLs such as the Bluebird Skylite, AV RQ-11B Raven, AV Switchblade, and AV UAS: Wasp AE. Hovering is the stage where the aircraft transitions from VTOL to fixed-wing mode. The UAV must be able to cruise at a maximum altitude of 60 meters, as most IR thermographies, such as the Hikvision thermal Bi-spectrum network bullet camera and the Flir Duo Pro thermal camera, have a maximum capturing distance or altitude of 60 meters. The UAV's endurance must also be at least one hour (**Figure 4**).

Initial weight estimation and weight build-up is given as below:

$$\mathbf{W}\_{\rm TO} = \mathbf{W}\_{\rm struct} + \mathbf{W}\_{\rm avi} + \mathbf{W}\_{\rm prop} + \mathbf{W}\_{\rm fuel} + \mathbf{W}\_{\rm misc} + \mathbf{W}\_{\rm panload} \tag{1}$$

where *Wstruct* is the airframe structures + motor casing + tilt rotor mechanism + the landing gear, *Wavi* is the weight of Servos + Sensors, *Wprop* is the weight of the propulsion system, *Wfuel* is the weight of fuel cells and/or batteries, *Wmisc* are the miscellaneous Weights such as in connecting wires, fasteners and *Wpauload* is the payload that is the detection system.


From the constraint analysis the marked region in red is the region of operation at stall. At this region for various speeds of stall the optimum wing loading is around 164*N=m*2.

**Figure 4.** *Mission profile.*

*Unmanned Aerial Vehicle for Agriculture Surveillance DOI: http://dx.doi.org/10.5772/intechopen.104476*

#### **6.2 Wing design**

Dihedral is not necessary because the wing attachment on the UAV is to be high wing and made roll stable. As a result, the dihedral angle is **0***<sup>o</sup>* . The UAV is not designed for high speed, and the motor mechanism will be located near the tip of the wing, with a taper ratio of one. The Mach number sweep is 0o since the UAV is not meant to achieve high Mach numbers and does not face drag divergence. The wing loading range obtained yielded a wing surface area of 1.221 *m***<sup>2</sup>**. The span (b) is 3.127 meters, while the chord (c) is 0.25 meters.

#### *6.2.1 Airfoil selection*

The airfoil was chosen by comparing the NACA 4 series to the other NACA series, which are the 5 and 6 numbers, because the NACA 4 series is thought to have a higher maximum lift coefficient, as Raymer proved. As a result, the lift, drag, and pitch moment coefficients of three NACA 4 series airfoils, the NACA 0012, 2412, and 4412, were compared. In the event of an air gale or other disturbance, a negative moment coefficient is desirable to aid maintain level flying. However, if this moment is sufficiently negative, the aircraft may be difficult to control. The NACA 4412 airfoil was ruled out due to its huge negative moment coefficient (**Figures 5** and **6**).

The NACA 2412 airfoil has a relatively small negative moment coefficient at practically all angles of attack, as seen in **Figure 7**. As a result of the analysis, the NACA 2412 has been chosen as the airfoil for the UAV since it possesses the required properties.

#### **6.3 Tail design**

The main aim of the empennage is to provide stability and counter moments caused by the wing. Horizontal and vertical stabilizers make up the empennage. A conventional tail was chosen because of its simplicity, which makes it simple to construct, as well as the fact that it meets both longitudinal and directional trim and stability criteria. The tail volume coefficients are used to design the empennage.

**Figure 6.** *Clmax vs. percent thickness to chord.*

**Figure 7.** *Airfoil selection parameters.*

Vertical tail volume coefficient is given by:

$$V\_v = \frac{I\_{wt} \mathcal{S}\_w}{\mathcal{S}\_w b\_w}$$

Horizontal tail volume coefficient is given by:

$$\mathbf{V}\_h = \frac{l\_{ht}\mathbf{S}\_{ht}}{\mathbf{S}\_w \mathbf{\overline{c}}\_w}$$

According to Raymer, the horizontal and vertical tail volume coefficients for an agricultural UAV are chosen to be 0.5 and 0.04 respectively (**Table 5**) [15].

#### **6.4 Control system design**

The ranges shown in **Figure 8** were used to size the control system.

#### **6.5 Propulsion system selection**

#### *6.5.1 Fuselage design*

Given the thickness of the detection system, the diameter was determined to be 500 mm. The detection system (camera), batteries, servos, and control system were all designed to fit inside the fuselage. The fuselage length was then calculated to be 75% of the wingspan, followed by the lofting process. The fuselage is lofted in order to


#### **Table 5.**

*Geometrical parameters of designed empennage.*


#### **Figure 8.**

*Control surface design parameters (Table 6) [16].*

increase the fuselage's overall aerodynamic performance. This entails reducing fuselage drag and generating a reasonable amount of lift from the fuselage. A rounded rectangle was initially chosen because to its ease of fabrication and component housing, however it had a bigger frontal area and wetted surface area, resulting in significant drag. In order to reduce drag and optimize the design, an oval cross-section with a small frontal area was chosen. In addition, an effort was made to limit the amount of wetted surface area. Because there were no components in the aft part of the fuselage,


#### **Table 6.**

*Battery and motor specification.*

the volume was reduced and a boom was used. This resulted in a large reduction in overall wetted surface area and, as a result, a significant reduction in parasitic drag.
