Pedro Gamboa

Optimization of a Morphing Wing Based on Coupled Aerodynamic and Structural Constraints

This paper presents the work done in designing a morphing wing concept for a small experimental unmanned aerial vehicle to improve the vehicles performance over its intended speed range. The wing is designed with a multidisciplinary design optimization tool, in which an aerodynamic shape optimization code coupled with a structural morphing model is used to obtain a set of optimal wing shapes for minimum drag at different flight speeds. The optimization procedure is described as well as the structural model. The aerodynamic shape optimization code, that uses a viscous two-dimensional panel method formulation coupled with a nonlinear lifting-line algorithm and a sequential quadratic programming optimization algorithm, is suitable for preliminary wing design optimization tasks. The morphing concept, based on changes in wing-planform shape and wing-section shape achieved by extending spars and telescopic ribs, is explained in detail. Comparisons between optimized fixed wing performance, optimal morphing wing performance, and the performance of the wing obtained from the coupled aerodynamic-structural solution are presented. Estimates for the performance enhancements achieved by the unmanned aerial vehicles when fitted with this new morphing wing are also presented. Some conclusions on this concept are addressed with comments on the benefits and drawbacks of the morphing mechanism design.

Design of a Morphing Airfoil Using Aerodynamic Shape Optimization

An in-house high-fidelity aerodynamic shape optimization computer program based on a computational fluid dynamics solver with the Spalart-Allmaras turbulence model and a sequential-quadratic-programming algorithm is used to obtain a set of optimal airfoils at the different flight conditions of a light unmanned air vehicle. For this study, the airfoil requirements at stall, takeoff run, climb gradient, rate of climb, cruise, and loiter conditions are obtained. Then, the aerodynamic shape optimization program is used to obtain the airfoil that has the optimal aerodynamic characteristics at each one of these flight conditions. Once the optimal airfoils at each flight condition are obtained, the results are analyzed to gain a better understanding of the most efficient initial airfoil configuration and the possible mechanisms that could be used to morph the single element airfoil. The results show that a very thin airfoil could be used as the initial configuration. Furthermore, a morphing mechanism that controls the camber and leading-edge thickness of the airfoil will almost suffice to obtain the optimal airfoil at most operating conditions. Lastly, the use of the optimal airfoils at the different flight conditions significantly reduces the installed power requirements, thus enabling a greater flexibility in the mission profile of the unmanned air vehicle.

Design of a Morphing Airfoil for a Light Unmanned Aerial Vehicle Using High-Fidelity Aerodynamics Shape Optimization

An in -house high -fidelity aerodynamic shape optimization computer program based on a computational fluid dynamics solver with the Spalart -Allmaras turbulence model and a sequential quadratic programming algorithm is used in order t o obtain a set of optimal airfoils at the different stages of flight of a light unmanned air vehicle. For this study, the airfoil requirements at stall, takeoff run, climb gradient, rate of climb, cruise and loiter conditions are obtained . Then, t he aerody namic shape optimization program is used to obtain the airfoil that has the optimal aerodynamic characteristics at each one of the se stages of flight. Once the optimal airfoils at each stage of flight are obtained, the results are analyzed in order to gain a better understanding of the most efficient initial airfoil configuration and the possible mechanisms that could be used to morph the single element airfoil. The results show that a very thin airfoil could be used as the initial configuration. Furthermor e, a morphing mechanism that controls the camber and leading edge thickness of the airfoil will almost suffice to obtain the optimal airfoil at most operating conditions. Lastly, the use of the optimal airfoils at the different stages of flight significant ly reduce s the installed power requirements, thus enabling a greater flexibility in the mission profile of the unmanned air vehicle.

Design Optimization of a Variable-Span Morphing Wing for a Small UAV

The present work focuses on the study, design and validation of a variable-span morphing wing to be fitted to a mini UAV. An in-house aerodynamic shape optimization code, which uses a viscous two-dimensional panel method formulation coupled with a non-linear lifting-line algorithm or a non-linear VLM algorithm and a sequential quadratic programming optimization routine, is used to solve a drag minimization problem to determine the optimal values of wing span for the whole vehicle’s flight speed envelope while subject to geometric constraints. A simple weight representation model based on empirical data obtained from a wing prototype was used to estimate the variable-span wing weight. The UAV flies in the speed range 12m/s to 35m/s. Near its maximum speed it is possible to obtain a 20% wing drag reduction with the variable-span wing in comparison with the original fixed wing. An analysis is also performed to estimate the roll rate available with asymmetric span control showing that the variable-span wing matches the aileron in terms of roll power. An electro-mechanical actuation mechanism is developed using an aluminum rack and pinion system. The wing model is designed with the help of graphical CAD/CAM tools and then a full scale model is built for bench preliminary testing the wing/actuator system.

Multidisciplinary Design Optimization of a Morphing Wing for an Experimental UAV

§The aim of this work is to design a morphing wing concept for a small unmanned aerial vehicle (UAV), in order to improve the vehicle’s performance over its intended speed range. The wing is designed using a multidisciplinary design optimization framework where an aerodynamic shape optimization code coupled with a structural morphing model environment is setup to obtain a set of optimal wing shapes for minimum drag at different flight speeds. The optimization procedure is described as well as structural modelling. The aerodynamic shape optimization code, which uses an inviscid/viscous 2-dimensional panel method formulation coupled with a non-linear lifting-line algorithm and an sequential quadratic programming (SQP) optimization algorithm is suitable for preliminary wing design optimization tasks, although its robustness still needs further improvements. The morphing concept, based on changes in wing planform shape and wing section shape achieved by extending spars and telescopic ribs, is explained in detail. Comparisons between initial wing performance, optimal morphing wing performance and the performance of the wing obtained as the coupled aerodynamic-structural solution are presented. Estimates for the performance enhancements achieved by the UAV when fitted with this new morphing wing are also included. Some conclusions on this concept are addressed with comments on the benefits and drawbacks of the morphing mechanism design.

Evaluation of a Variable-Span Morphing Wing for a Small UAV

This paper describes the development and ground validation of a variable-span morphing wing intended be fitted to a small UAV prototype. The vehicle flies in the speed range 11m/s to 40m/s. The wing model is designed with the help of graphical CAD/CAM tools and then a full scale prototype is built for preliminary bench testing the wing/actuator system. The wing is built in composite materials and is made of two parts. The inboard part is fixed to the fuselage and uses a monocoque skin construction. The outboard part slides inside the inboard part to change the span of the wing and uses a typical structure made of spar, ribs and thin skin. An electro-mechanical actuation mechanism is developed using an aluminum rack and pinion system driven by two servomotors placed at center of the wings. Bench tests, performed to evaluate wing under load, showed that the system is capable of performing the required extension/retraction cycles and is suitable to be installed on a small UAV prototype.

Design of a Variable Camber Flap for Minimum Drag and Improved Energy Efficiency

A variable camber flap concept is optimized to reduce the drag of a low speed light UAV between its stall and cruise speeds using an in-house aerodynamic shape optimization code. The flap, which maintains continuity on the upper surface, was analyzed both numerically and experimentally and was shown to provide important reductions in drag when compared to the clean wing/airfoil in the lower speed range (2.7% on average for the wing) and to have significant actuation energy savings when compared to a conventional plain flap (in the order of 40%). Although the concept uses current actuator technology and materials it is a good option for improving flight endurance/range at low speed over other more complex and advanced morphing concepts.

Variable-span wing development for improved flight performance:

This paper describes the development and testing of a variable-span wing (VSW) concept. An aerodynamic shape optimisation code, which uses a viscous two-dimensional panel method formulation coupled with a non-linear vortex lattice algorithm and a sequential quadratic programming optimisation routine, is used to solve a drag minimisation problem to determine the optimal values of wing span for various speeds of the vehicle’s flight envelope while subject to geometric constraints. Structural design is performed using the finite element method for static analysis where the particular interface between wing parts is conveniently modelled. A full-scale prototype is built for ground testing the wing/actuator system. The wing is built in composite materials and an electro-mechanical actuation mechanism is developed using an aluminium rack and pinion system driven by two servomotors. Bench tests, performed to evaluate wing under load, showed that the system is capable of performing the required extension/retraction cycles and is suitable to be installed on a UAV airframe fully instrumented for evaluating the VSW concept prototype in flight. The data collected from the performed flights showed full functionality of the VSW and its aerodynamic improvements over a conventional fixed wing for the higher speed end of the flight envelope.

Telescopic Wing-Box for a Morphing Wing

This paper describes the design and testing of a wing-box capable of producing wingspan changes for flight speed adaptation developed within the CHANGE project. One of the goals of CHANGE was to design and implement a morphing wing that could combine more than one morphing concept. The capabilities adopted for this wing are span change and leading edge (LE) and trailing edge (TE) camber changes. The last two can produce combinations of positive and negative chordwise camber changes and even spanwise twist. A modular design philosophy was adopted for this wing such that the individual systems producing span change, LE change or TE change can be separately developed and then integrated into the overall wing system. This approach facilitated the development of each required mechanism and made the integration of all components easier. The structure was designed for strength, stiffness and low weight using a structural finite element model. A prototype telescopic wingbox section of 0.6 m in span but with full scale cross-section was manufactured and fitted with the actuation system before full development of the wing system. This prototype was used to validate both the structural design through actual loading and the actuation system’s proper functioning through hundreds of span extension/retraction cycles under load. Results from design and experimental tests demonstrated full functional capability of the telescopic wing-box system.

Cork: Is It a Good Material for Aerospace Structures?

Cork is a natural material with remarkable energy absorption properties, which make it an ideal candidate material when thermal insulation or vibration suppression are major design requirements. However, little work has been done towards the use of cork based materials in structural components. This paper envisages assessing the feasibility of using cork composites with improved specific strength and damage tolerant properties for aerospace applications. A review of some results and conclusions about the mechanical behavior of cork composites will be done based on existing literature and other previous works of the authors on this subject. In particular, two types of materials were considered: 1) a sandwich structure with a cork-epoxy agglomerate core; 2) a carbon-epoxy laminate with embedded cork granulates. In both cases, a set of static and dynamic tests were carried out to characterize the mechanical behavior of the material with a special emphasis on its damage tolerant properties. These tests were replicated using a benchmark core material commonly used in aerospace applications in order to confirm the comparative benefits of cork based composites. A final part of this work seeks to evaluate the advantages of combining the natural damping characteristics of cork with high performance composites aiming at improving the aeroelastic behavior of aerospace components. In particular, the critical flutter speed of a cork based sandwich plate was compared with other conventional materials through a computational analysis. Regardless the type of application, results are encouraging about the use of cork based materials in aerospace components due to their noticeable damage tolerant and high energy absorption properties under different loading scenarios.