Foi realizada uma análise de estabilidade de voo, resultando em uma margem estática de 5,6% com o Cmnulus em condições de voo. Palavras-chave: UAV Solar, Processo Analítico Hierárquico, Ponto de Design, Baixo Número de Reynolds, Autonomia, Envelope de Voo.
Nomenclature
Glossary
Introduction
- Motivation
- UAVs in Contemporary Society
- UAV Operation Legislation
- Solar Powered UAVs
- Project Background
- Thesis Objectives
- Document Outline
Despite the setbacks, Google will continue to develop solar-powered stratospheric drones for Internet delivery. The second chapter addresses the selection of the airframe concept best suited to the LEEUAV mission.
LEEUAV Concept
- Project Requirements
- Mission Profile
- Airframe Concept Generation
- Rocket Configuration
- Lighter-Than-Air Configurations
- Rotary Wing Configurations
- Fixed Wing Configurations
- Conceptual Design Selection
- Prospective Aircraft Configurations
- Analytic Hierarchy Process Based Decision
- Discussion of Results
The conventional tractor placement, in Figure 2.7a, places the engine at the front of the hull, with the propeller in undisturbed air. The tail assembly in Figure 2.8 is an example that can be adapted to a double boom concept. Launch can also be achieved with a removable launch carriage, such as the example in Figure 2.12a, built in [58].
According to the arguments presented in Section 2.3, a total of 8 predicted aircraft configurations were selected, shown in Figure 2.13. Considering equation (2.1), the term L/D is directly related to aerodynamics and mbatterym to weight ratio.
Aircraft Initial Sizing
First Generation Prototype
Its wing splits into three sections for easy ground transportation, and each section has a C-shaped attachment with a torsion box to increase tolerance to maintenance damage. According to the results of the parametric study, a two-row field of solar collectors was considered to be the most efficient solution, which corresponded to the allowable middle chord of 33 cm according to the deflection of the aerodynamic profile. The hull can also be divided into three parts, which are the main body of the container, the tail arm and the rear axle support.
Storage space is minimized by making the horizontal tail removable, while the vertical tail and feather carrier are connected as one piece. Although the installation of solar arrays above the wing was not included in the manufacturing process, parametric calculations related to the power generation system showed the array of electric propulsion components in Table 3.2 as the most efficient alternative found for the mission [54].
Mass Prediction Model
- Communication Systems
- Control Actuators
- Propulsion System
- Empty Weight Estimation
The Thomas Scherrer, whose receiver is in Figure 3.5, is the long-range RC system of choice. Wind conditions, slow flight and autonomous landing are handled with the airspeed sensor, the components of which are shown in Figure 3.10. The design of the propulsion system has defined a solution that combines both lithium-polymer batteries and solar panels to provide power for the electric motor, as schematically illustrated in Figure 3.14 [55].
The scatter plot in Figure 3.17 shows the specified blank width of the shoulder and wing area of the aircraft under study. Looking exclusively at the finned wing aircraft in Figure 3.17, it was possible to obtain a regression equation relating empty weight to wing area.
LEEUAV Provisory General Characteristics
The few solar planes identified in Figure 3.17 also have finned wings, but none were used as a regression point because their weight values were considered optimistic. Considering the accuracy of the current empty weight model, overestimation is preferable to underestimation as it may later cause the endurance to fall below the 8 hour requirement, while ending up with less weight than predicted will only allow the UAV to exceed the required endurance. All in all, with the mass of all built-in components listed in this chapter, and the airframe weight, calculated by inserting the wing area of the preliminary size LEEUAV into equation (3.1), an estimate of the complete weight distribution was obtained in advance. a) Dimensions and weight distribution of the components.
The weight percentages shown in Figure 3.19 are converged values that resulted from the completion of the next phase, the preliminary project. It should be noted that the sum of the additional weight of the payload with the communication components gives a value close to the maximum load of 10 N specified in the mission requirements.
Preliminary Project
Aerodynamics
- Aerodynamic Software Accuracy
- Cruise Stage Computation
By analyzing the percentage difference between XFLR5 and STAR-CCM+R analysis results of the first generation LEEUAV cruise flight, illustrated in figure 4.4, it was observed that a grid with 1600 elements offers the best compromise between accuracy and computation time. Therefore, for those specific analysis results, in Figure 4.3, correction functions (4.1) and (4.2) were calculated, assuming the form Zx(α) =Cx(α)ST AR−CCM+/Cx(α)XF LR5, where either is light (L) or drag (D). Despite the mentioned incoherence, the practical purpose of this mission correction is achieved by improving the XFLR5 output margin of error while rearranging lift and drag predictions for angles of attack between -5o and 5.5o, more conservatively.
After determining the cruise speed and atmospheric data, the aerodynamic geometries (wing and tail) of the LEEUAV assumed from the initial sizing (Figure 3.18) went through VLM computer analyses. The entire process, shown in the flow diagram in Figure 4.5, was repeated until the MTOW equaled the aerodynamically calculated lift.
STOP
Stability and Control
- Static Stability
- Dynamic Stability
The overall moment coefficient as a function of the angle of attack, in figure 4.14a, proves that. The axis used to measure the longitudinal coordinates of CG and AC is taken from Figure 4.12. Looking at Figure 4.16a, given an initial condition of 9.6o, the pitch angle practically stabilizes after one second.
The same happens with the pitch rate, in Figure 4.16b, where the initial state takes a value of -47o/s. In Figure 4.18, its time response presents an initial overshoot before reaching its settling time, which happens faster for the roll rate than for the yaw rate.
Propulsion
- Required Power and Energy
- Propulsion Sub-system Summary
- Maximum Performance Regime
The flow diagram in Figure 4.21 summarizes how propulsion and energy studies related to climbing are incorporated into the iterative design process. It should be noted that in Figure 4.21, the energy required by the avionics, Eavionics, is also included. For example, the power supply module in Figure 3.7 has a maximum input voltage of 18V, which excludes 5S Lipo batteries.
As implied at the beginning of section 4.2, the series of iterations illustrated in Figure 4.21 emerged in two interwoven phases of the preparatory project. Knowing the maximum electrical power and efficiency of the engine, a single 2D function relating aircraft speed to thrust at maximum power is obtained by intersecting the surface in Figure 4.22 with the respective constant axis power plane.
Flight Envelope
The maneuvering speed, Umvr, occurs at the point where both the lift coefficient and the load factor simultaneously have the highest possible values. In other words, the maximum load factor at maneuvering speed ensures that the aircraft can execute the turn with a minimum radius and maximum angular speed. When a gust of wind occurs, the aircraft experiences an immediate change in angle of attack, leading to a sudden change in lift and therefore load factor.
Assuming that the aircraft is exposed only to symmetrical vertical gusts during level flight, the gust can be determined on a similar pattern to the maneuver envelope, except that the limits are determined by the incremental gust load factor added in Equation 4.13. Adding the effect of valve deflection to the shroud would increase the load factor at lower speeds, due to the increase in CLmax.
Design Point
This detail was not added because it is not critical to the true ultimate loads that the aircraft structure will experience. Upstream of the wing, the fuselage has been resized so that all components, including the RPV camera, are at the front. In addition, the span of the wingtips without panels has been reduced slightly to add some spatial tolerance in the center, between the solar arrays, which should help ensure a rigid wing-to-fuselage connection.
The ailerons and rudder springs were not drawn as their design involved mounting solutions not addressed at this stage of the project. The design point is clearly influenced by the solar energy collection subsystem, whose performance description is skipped in the document.
Solar Energy Management
- Solar Energy Sub-System
- Daily Irradiation Model
- Interaction of Solar Radiation with the Earth
- Solar Radiation Model r.sun MATLAB R Implementation
- Energy and Power Management
- Standard Mission Profile
- Reduced Climb Assumption
- Night Mission (non-rechargeable battery)
- Avionics Energy Requirements
- Discussion of Energy System Setup
Therefore, a correction factor is used that takes into account the variable solar distance. when calculating extraterrestrial radiationG0normal to the sun's ray angle. By applying the total efficiency of the solar collection system, ηenergy, to the irradiance profile, the solar energy harnessed through the solar panel area, Wsolar, was obtained. The number of 4200 mAh 3S LiPo batteries used in data processing varies from two, which is the standard airborne amount specified in Section 4.3.1, to three, assuming a third battery is included in the weight of the additional payload , i.e. , the weight of the aircraft does not change.
Looking at figure 5.6a, it can be seen that at the December solstice, the shortest day of the year, solar energy alone is not enough for cruising. During the June solstice, which is the longest sunny day of the year, solar energy surprisingly reaches optimal ratings.
Detailed Design Considerations
- Main Wing Break-Up
- Wing Loading Estimate
- Fuselage Layout
- Tail Assembly
In this case the tail is consumable, so the 3D Panel Method analysis was performed with the wing as the only geometry. The Cpwing distribution results at cruise speed are visible in Figure 6.2, where suction and pressure surfaces, responsible for the overall lift during cruise regime, are distinguished. This means approximately 2500 registered point forces, each corresponding to a panel in the mesh, will need to be inserted into the FEM analysis software.
For this reason it was divided into two parts, illustrated in figure 6.4, with a front part with a length of 1.16 meters and a back part where the stabilizers are installed together with the engine. The front of the fuselage is meant to support the wing and hold most of the components.
Conclusions
Project Achievements
In terms of endurance, the power and energy received by the arranged solar panels were determined for different seasons. A daily irradiance model was calculated for a single flight location using analytical relationships, bibliographically supported and historical irradiance data available online. Taking into account the established 8 hour requirement, it was verified that on the March equinox the endurance falls short with a grade of 7 and a half hours.
All dimensions of the airframe, which includes a dual array of 2x6 and 2x7 PV arrays on the wing, have been determined. As an additional basis for the future detailed design of the aircraft, the wing Cp distribution at cruise speed was obtained in XFLR5 by performing a 3D panel method analysis.
Future Work
It is therefore not expected that the design point of the LEEUAV will suffer repetitions due to the detailed design. Experimental techniques can also be arranged to verify the accuracy of FEM calculation analysis and to study the residual resistance of the prototype in the presence of defects. To avoid collisions with the tail while transitioning to air, a trolley geometry is proposed with support surfaces for each side of the wing and a third fuselage support area forward of the CG.
In terms of aerodynamics, it is possible to practically eliminate the uncertainty and limitations associated with the results obtained in XFLR5 if a computational CFD analysis is performed on the updated airframe geometry. Finally, an additional work of no significant consequence to the present project consists in the development of an improved radiation prediction model.
Bibliography
32] Regulation (EC) No 1592/2002 of the European Parliament and of the Council on common rules in civil aviation and establishing a European Aviation Safety Agency, July 2002.
Appendix A
ISA Data on Portuguese Landscape
Appendix B
Analytic Hierarchy Process Tables
A - Aerodynamics B - Structural Design C - Manufacturing and Maintenance D - Propulsion E - Stability and Control F - Solar Panels Integration G - RPV Integration. H - Payload Volume I - Takeoff and landing Adaptability J - Portable characteristics i - Quadcopter ii - Conventional aircraft iii - Tractor T-tail.
Appendix C
Database of Similar Aircraft
