Span morphing using the GNATSpar wing

Rigid wings usually fly at sub-optimal conditions generating unnecessary aerodynamic loses represented in flight time, fuel consumption, and unfavourable operational characteristics. High aspect ratio wings have good range and fuel efficiency, but lack manoeuvrability. On the other hand, low aspect ratio wings fly faster and are more manoeuvrable, but have poor aerodynamic performance. Span morphing technology allows integrating both features in a single wing design and allows continuously adjusting the wingspan to match the instantaneous flight conditions and mission objectives. This paper develops, a novel span morphing concept, the Gear driveN Autonomous Twin Spar (GNATSpar) for a mini-UAV. The GNATSpar can be used to achieve span extensions up to 100% but for demonstration purposes it is used here to achieve span extensions up to 20% to reduce induced drag and increase flight endurance. The GNATSpar is superior to conventional telescopic and articulated structures as it uses the space available in the opposite sides of the wing instead of relying on overlapping structures and bearings. In addition, it has a self-locking actuation mechanism due to the low lead angle of the driving worm gear. Following the preliminary aero-structural sizing of the concept, a physical prototype is developed and tested in the 7?×5? wind-tunnel at the University of Southampton. Finally, benefits and drawbacks of the design are highlighted and analysed

PE-HD fatigue damage accumulation under variable loading based on various damage models

Despite numerous studies on fatigue of polymer materials under variable loading, there is little work on highdensity polyethylene (PE-HD). In this context, an experimental analysis for determining the fatigue strength of PE-100, under constant and variable amplitude loading is presented. Further, the cumulative fatigue damage behavior of PE-100 was experimentally investigated. First, the fatigue curve (S-N: stress vs. number of cycles) was obtained in order to establish the fatigue life of PE-100 subjected to constant stress amplitude. Secondly, Miner’s fatigue rule as well as stress-based and energy-based fatigue damage models were used to estimate the cumulative variable amplitude fatigue damage. Comparison between predictions and experimental results showed different trends depending on the choice of prediction model used implying careful fatigue damage consideration when designing under variable amplitude loading

Span morphing using the GNAT spar for a mini-UAV: designing and testing

Rigid wings usually fly at sub-optimal conditions which generates unnecessary aerodynamic loses represented in flight time, fuel consumption, and unfavourable operational characteristics. Large wingspans allow for good range and fuel efficiency, but lack manoeuvrability; on the other hand, low aspect ratio wings fly faster and are more manoeuvrable, but suffer from poor aerodynamic performance. Span morphing technology allows integrating both features in a single wing design and allows continuously adjusting the wingspan to match the instantaneous flight conditions and mission objectives. This paper develops a novel span morphing concept called the Gear driveN Autonomous Twin (GNAT) spar for a mini-UAV. The GNAT spar allows span extension up to 25% of the original span to reduce induced drag and increase flight endurance. The GNAT is superior to conventional telescopic structures as it uses the extra space available in the other side of the wing instead of relying on overlapping structures associated with telescopic spars. In addition, it has a self-locking capability due to the low lead angle of the driving worm gear of its actuation mechanism. Aero-structural sizing and design of the concept is performed using low fidelity aerodynamics (XFLR5) and high-fidelity FE solver (SolidWorks). Furthermore a physical prototype of the concept is developed, followed by the integration of Latex flexible skin to provide the aerodynamic shape of the wing. Following from this, the design of robust control system using the Arduino Uno R3 microcontroller is discussed. Finally, benefits and drawbacks of the design are highlighted and analysed

Twist morphing using the variable cross section spar: a feasibility study

This paper presents the variable cross section spar (VCSpar) concept that facilitates varying the shear center position relative to the aerodynamic center, allowing the external aerodynamic loads to twist the structure and maintain its deformed shape. The VCSpar is considered in this paper as integrated within the wing of a representative unmanned aerial vehicle (UAV) to enhance its flight performance and control authority. A preliminary design study was conducted to assess the potential benefits of the concept using a low-fidelity design tool. Then, aeroelastic modeling of the concept was performed where the VCSpar was modeled as a two-dimensional equivalent aerofoil using bending and torsion shape functions to express the equations of motion in terms of the twist angle and plunge displacement at the wingtip. The aerodynamic lift and moment acting on the equivalent aerofoil were modeled using Theodorsen’s unsteady aerodynamic theory. A low-dimensional state-space representation of an empirical Theodorsen’s transfer function was adopted to allow time-domain analyses

Mechanical properties of hybrid carbon fiber reinforced polyethylene and epoxy composites

In this work, a hybrid polyethylene/epoxy combination matrix is reinforced with carbon fiber fabric. The objective is to develop a composite material with better tensile and impact properties. Three ratios of high molecular weight polyethylene powder were used as an additive to the epoxy matrix system. These composite materials were manufactured using hand-layup and vacuum bagging technique. The study carried out here is to find the effect of polyethylene weight fraction on tensile and impact properties of the carbon fabric reinforced epoxy composite material. The results show the tensile strength has been improved by the lowest used ratio of polyethylene additive while, all the hybrid composites exhibit higher tensile ductility. On the other hand, the Izod impact strength shows degradation in impact properties for the hybrid composites. Several suggestions are made about ways to improve the behavior of such materials

MECHANICAL PROPERTIES OF HYBRID CARBON FIBER REINFORCED POLYETHYLENE AND EPOXY COMPOSITES

ABSTRACT In this work, a hybrid polyethylene/epoxy combination matrix is reinforced with carbon fiber fabric. The objective is to develop a composite material with better tensile and impact properties. Three ratios of high molecular weight polyethylene powder were used as an additive to the epoxy matrix system. These composite materials were manufactured using hand-layup and vacuum bagging technique. The study carried out here is to find the effect of polyethylene weight fraction on tensile and impact properties of the carbon fabric reinforced epoxy composite material. The results show the tensile strength has been improved by the lowest used ratio of polyethylene additive while, all the hybrid composites exhibit higher tensile ductility. On the other hand, the Izod impact strength shows degradation in impact properties for the hybrid composites. Several suggestions are made about ways to improve the behavior of such materials