An experimental investigation of the wake of an Unmanned Aerial Vehicle (UAV) model using flow visualization techniques and a 3D Laser Doppler Anemometry (LDA) system is presented in this work. Emphasis is given on the flow field at the wingtip and the investigation of the tip vortices. A comparison of the velocity field is made with and without winglet devices installed at the wingtips. The experiments are carried out in a closed-circuit subsonic wind tunnel. The flow visualization techniques include smoke-wire and smoke-probe experiments to identify the flow phenomena, whereas for accurately measuring the velocity field point measurements are conducted using the LDA system. Apart from the measured velocities, vorticity and circulation quantities are also calculated and compared for the two cases. The results help to provide a more detailed view of the flow field around the UAV and indicate the winglets’ significant contribution to the deconstruction of wing-tip vortex structures.

Purpose: The purpose of this paper is to present the preliminary design of a medium altitude long endurance (MALE) unmanned aerial vehicle (UAV), focusing on the interaction between the aerodynamic and the structural design studies. Design/methodology/approach: The classic layout theory was used, adjusted for the needs of unmanned aircraft, including aerodynamic calculations, presizing methods and CFD, to estimate key aerodynamic and stability coefficients. Considering the structural aspects, a combination of layout, finite element methods and custom parameterized design tools were used, allowing automatic reshapes of the skin and the internal structural parts, which are mainly made of composite materials. Interaction loops were defined between the aforementioned studies to optimize the performance of the aerial vehicle, maximize the aerodynamic efficiency and reduce the structural weight. Findings: The complete design procedure of a UAV is shown, starting from the final stages of conceptual design, up to the point where the detail design and mechanical drawings initiated. Practical implications: This paper presents a complete view of a design study of a MALE UAV, which was successfully constructed and flight-tested. Originality/value: This study presents a complete, synergetic approach between the configuration layout, aerodynamic and structural aspects of a MALE UAV.

The current study provides a thorough analysis and evaluation of fixed-wing UAV correlations with respect to NATO classification, region of production, entry-into-service (EIS) date and other operational specifications. A set of 202 existing fixed-wing platforms is used to populate an in-house database. A screening of the corresponding data is conducted using a correlations matrix, and a statistical analysis of the key UAV design parameters is, in turn, performed. The results are presented using a wide variety of charts and statistical coefficients, to provide as much information as possible for future UAV design and performance assessment studies. Correlations for each mission type are provided, followed by a detailed evaluation of the key design parameters and design ratios (wingspan, gross takeoff weight, empty weight, payload weight, endurance, and operational speeds) with respect to NATO classification and region of origin. These key parameters are then plotted as a function of EIS date for every NATO category to identify any underlying trends and, finally, the platforms are classified in regard to some qualitative attributes, such as mission type and low observability. The results suggest that the trendlines extracted for each category significantly deviate from the generic trends. Therefore, omitting the classification in terms of region, size and weight can lead to misleading outcomes and should be avoided. Another conclusion lies in the fact that, apart from the average trendline, the design engineers should also have an indication of the data variance, due to the high dispersion observed in the datasets of several design parameters.

The current study investigated the effect of leading-edge slats on the longitudinal stability at high angles of attack of a Blended-Wing-Body (BWB) Unmanned Air Vehicle (UAV). Using a Design of Experiments (DOE) approach and, specifically, the Taguchi method, four leading-edge slat design parameters were investigated on three different levels. These parameters were the slat semi-span, the rotation of the slat element, the extension forward of the leading edge and the downward drop below the leading edge. An L₉ orthogonal array (OA) was used to investigate the influence of these key design parameters using three performance criteria, namely the angle at which pitch break occurs, the corresponding speed and the distance between the Neutral point of each configuration and the Neutral point of the reference platform. The investigation was conducted by using high-fidelity Computational Fluid Dynamics (CFD) methods for each of the nine configurations defined by the L₉ OA, over a range of angles of attack between −4 and 16 degrees. Based on these results, and using a Signal-to-Noise ratio (SNR) analysis, two combinations were eventually derived, one that optimized pitch break angle and speed and one that optimized longitudinal stability. Finally, the Pareto Analysis of Variance (ANOVA) technique was conducted to define the contribution of each of the six design parameters on the selected performance criteria. More specifically, the semi-span seemed to have the most significant effect on pitch break angle and speed, whereas the rotation of the slat element was the most important parameter with regard to static stability.

The current study presents a low-fidelity, quasi-3D aerodynamic analysis method for Blended-Wing-Body (BWB) Unmanned Aerial Vehicle (UAV) configurations. A tactical BWB UAV experimental prototype is used as a reference platform. The method utilizes 2D panel method analyses and theoretical aerodynamic calculations to rapidly compute lift and pitching moment coefficients. The philosophy and the underlying theoretical and semi-empirical equations of the proposed method are extensively described. Corrections related to control surfaces deflection and ground effect are also suggested, so that the BWB pitching stability and trimming calculations can be supported. The method is validated against low-fidelity 3D aerodynamic analysis methods and high-fidelity, Computational Fluid Dynamics (CFD) results for various BWB configurations. The validation procedures show that the proposed method is considerably more accurate than existing low-fidelity ones, can provide predictions for both lift and pitching moment coefficients and requires far less computational resources and time when compared to CFD modeling. Hence, it can serve as a valuable aerodynamics and stability analysis tool for BWB UAV configurations.

The current work investigates the effect of canard geometric characteristics on the performance of a lightweight flying wing Unmanned Aerial Vehicle (UAV), capable of both conventional and Vertical Take-Off and Landing (VTOL) flight. The canards are sized as horizontal stabilizers to enhance the UAV’s longitudinal stability and minimize trimming requirements during cruise. Using a Design of Experiments (DOE) approach and, specifically, the Taguchi method, six canards’ design parameters are investigated on three different levels. These parameters are the sweep angle (Λ), aspect ratio (AR), taper ratio (λ), vertical position in relation to the main wing (v_pos), incidence angle (i_c), and dihedral angle (Γ). An L₂₇ orthogonal array (OA) is used to investigate the influence of these key design parameters using two performance criteria, namely the Lift-to-Drag ratio (L/D) and the pitching moment coefficient (C_m), at cruise conditions (designated as L/D_cruise and |C_m|_cruise). The investigation is conducted by using high-fidelity Computational Fluid Dynamics (CFD) methods for each of the 27 configurations defined by the L₂₇ OA, over a range of angles of attack. Based on the CFD results, two distinct combinations are derived for maximum L/D_cruise and minimum |C_m|_cruise using the Signal-to-Noise ratio (SNR) analysis. The optimal design parameter combinations for the two performance criteria are A₂B₁C₁D₁E₁F₁ and A₂B₂C₁D₂E₂F₃, respectively. Finally, the Pareto Analysis of Variance (ANOVA) technique is conducted to define the contribution of each of the six design parameters on the L/D_cruise and the |C_m|_cruise. More specifically, i_c seems to have the most significant effect on L/D_cruise, whereas Λ is the most important parameter for |C_m|_cruise.