Hindawi International Journal of Aerospace Engineering Volume 2018, Article ID 2820717, 10 pages https://doi.org/10.1155/2018/2820717 Research Article Development of Design Methodology for a Small Solar-Powered Unmanned Aerial Vehicle 1 2 Parvathy Rajendran and Howard Smith 1School of Aerospace Engineering, Universiti Sains Malaysia, Penang, Malaysia 2Aircraft Design Group, School of Aerospace, Transport and Manufacture Engineering, Cranfield University, Cranfield, UK Correspondence should be addressed to Parvathy Rajendran; [email protected] Received 7 August 2017; Revised 4 January 2018; Accepted 14 January 2018; Published 27 March 2018 Academic Editor: Mauro Pontani Copyright © 2018 Parvathy Rajendran and Howard Smith. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Existing mathematical design models for small solar-powered electric unmanned aerial vehicles (UAVs) only focus on mass, performance, and aerodynamic analyses. Presently, UAV designs have low endurance. The current study aims to improve the shortcomings of existing UAV design models. Three new design aspects (i.e., electric propulsion, sensitivity, and trend analysis), three improved design properties (i.e., mass, aerodynamics, and mission profile), and a design feature (i.e., solar irradiance) are incorporated to enhance the existing small solar UAV design model. A design validation experiment established that the use of the proposed mathematical design model may at least improve power consumption-to-take-off mass ratio by 25% than that of previously designed UAVs. UAVs powered by solar (solar and battery) and nonsolar (battery-only) energy were also compared, showing that nonsolar UAVs can generally carry more payloads at a particular time and place than solar UAVs with sufficient endurance requirement. The investigation also identified that the payload results in the highest effect on the maximum take-off weight, followed by the battery, structure, and propulsion weight with the three new design aspects (i.e., electric propulsion, sensitivity, and trend analysis) for sizing consideration to optimize UAV designs. 1. Introduction prominent researcher in this field, Noth [14, 20] developed a mathematical design model for sizing solar-powered elec- In recent years, awareness of the potential of unmanned tric UAVs. However, this mathematical design model focuses aerial vehicles (UAVs) for multiple missions has increased only on the conceptual design stage in estimating the general the level of research into improving UAV design and tech- sizing of UAV configurations. nologies. Studies found that electric- or fossil fuel-powered Noth [14, 20] focused on the 3 sizing elements of mass, UAVs have inadequate flying hours for various tasks. aerodynamics, and performance. Design characteristics, Increased focus has been placed recently on developing such as aircraft power consumption and cruise speed, must hybrid-powered electric UAVs, especially with the combina- also be optimized to ensure that the required long endur- tion of solar energy and battery or fuel cells in a battery- ance of the UAVs for 24 hours of real surveillance and powered system. The current study considers the pros and mapping applications is achieved. The current study aims cons of various power systems [1–6] and examines the design to improve the design properties, which requires further and development of solar cells in battery-powered UAVs. in-depth work, such as solar irradiance, mission profile, For more than a decade, small solar- and battery-powered and aerodynamic characteristics. Research gaps in electric electric UAVs were the subject of research and development propulsion sizing, sensitivity studies, and trend analysis [1, 5–19]. Seven small solar UAVs (i.e., So Long, Sky-Sailor, have also been identified. Sun-Sailor, Sun Surfer, AtlantikSolar AS-2, University of A synthesized UAV mathematical design model suitable Minnesota’s SUAV, and Cranfield University’s Solar UAV) for sizing and configuration design of small solar-powered weighing less than 20 kg have been developed to date. As a and battery-powered electric systems was developed to fulfill 2 International Journal of Aerospace Engineering Start UAV design program Solar irradiance Solar irradiance (9) Mission Electric profile propulsion Aircraf parameters Parameter initialization Altitude = 0 meter Mass Stability estimation & control Velocity = 2 km/hr Design AOA & tail incidence angle = 0° model Maximum take‐of mass = 3 kg Total power guess = 10 Watts Structure mass-to-wing area ratio = 0.34 kg/m2 Aerodynamic Sensitivity estimation studies Standard atmosphere Performance Trend Airfoil section analysis analysis Aerodynamics ((4)—(8)) Figure 1: Solar-powered electric UAV design element. Stability & control ((12)—(15)) — the previously mentioned requirements. This comprehensive Performance ((10) and (23) (32)) expansion work, based on various studies [21–23], considers nine design properties (i.e., mass sizing, aerodynamics, per- Mission profle (11) formance, stability and control, mission profile, solar irradi- Mass estimation ((1)—(3)) ance, electric propulsion, sensitivity studies, and trend analysis) to improve the current design model. No The proposed mathematical model was initially quasi- Iteration of validated using existing UAV data via rigorous computer Diference between initialized initialized and estimated ≤ 10%? modeling and analyses. The validity of the mathematical parameters model was deemed satisfactory after achieving a lower error Yes in the model’s conceptual design than in the actual UAV Electric propulsion ((17)—(22)) design using the empirical database. An actual solar- powered electric UAV [1] was also designed, developed, Outputs: various data in tables and flight-tested to further quasi-validate this model. The comprehensive design model is developed in this study to UAV design program ends further minimize assumptions and simplify previous designs. Figure 2: UAV design algorithm flowchart. 2. Mathematical Design Model because a pure electric UAV does not have a variable weight The developed solar-powered electric UAV mathematical during flight. design model and its algorithm flowchart are illustrated in Figures 1 and 2, respectively. The model contains the nine W = W + W + W + W TOmax Struct Batt Solar Electric 1 design components mentioned earlier. Three design compo- + WCtrl + WPay Max, nents, namely, mass estimation, aerodynamic estimation, and performance analysis, were initially developed by Noth WTOmax = WEmpty + WPay Max 2 [14]. Performance analysis is the only design component that was maintained based on the specifications developed The relevant coefficient in predicting the empty weight of by Noth. an electric UAV that weighs less than 15 kg is given in (3). In the mass estimation, the study by Mueller et al. [22] This equation is determined using regression analysis by was further adopted. The component mass was divided into collecting all possible measurements of 83 small electric the following basic elements, namely, structure, battery, UAVs. These 83 small UAVs, including solar-, battery-, fuel solar, electric propulsion, control system, and payload, as cell-, and hydrogen-powered electric UAVs, weigh less than shown in (1), respectively. The aircraft’s total take-off weight 14 kg. The parameters gathered include weights, wing area WTOmax may be expressed as a combination of the empty (S), wing span (b), aspect ratio (AR), height, total length, weight and payload weight, as shown in (2), respectively, root, and tip chord length of both the wing and tail surfaces. International Journal of Aerospace Engineering 3 18 9012 −9 4755 −9 4558 0 99 The amount of solar irradiance Ir that strikes the WEmpty =079 × b S AR W 3 max TOmax Earth, as given in (9), is critical in designing a solar- Similarly, in aerodynamic estimation, specific lift and powered UAV. The power available through the solar drag coefficient estimation was performed based on various module facilitates the sufficiency of the solar energy har- wing and horizontal tail airfoil characteristics [21]. However, nessed for the power required. The equation is adopted from the fuselage and vertical tail characteristics have yet to be [23–27], which begins by determining the input parameters, incorporated in this study. Additional power is incorporated including the day of the year, latitude, longitude, and altitude into the mission power requirement, specifically by defin- of the place of interest. ing the maximum power consumption during maneuver π π P at total mission power, compensating for the drag 1+0033cos 0 017203DN /180 sin SOLALT /180 Maneuver Irmax = increment that remains unaccounted due to the fuselage and 3 6 1000/4 8708 vertical tail. 9 The Reynolds number (RN) is a major factor in aerody- namic analysis. The RN range for an aircraft depends on No previous work has estimated in detail the UAV solar the mean aerodynamic chord length (c), airspeed (V), air power usage of the mission profile (i.e., not only cruise but density ρ , and viscosity μ . Equation (4) [21] defines the also the other mission profile phases, such as climb, loiter/ relation between these parameters. maneuver, and descent). The effects of gust wind speed and ρ direction were disregarded. The power required PRequired Vc fl fi RN = μ 4 for a level ight determined by the de nition of the wing area is shown in (10) [21]. This calculation