Search Results (20)

Despite the tremendous advances in aircraft design that led to successful powered flights of aircraft as heavy as the Antonov An-225 Mriya, which weighs 640 tons, or as fast as the NASA-X-43A, which reached a record of Mach 9.6, many characteristics of bird flight have yet to be utilized in aircraft designs. These characteristics enable various species of birds to fly efficiently in gusty environments and rapidly change their momentum in flight without having modern thrust vector control (TVC) systems. Vultures and seagulls, as examples of expert gliding birds, can fly for hours, covering more than 100 miles, without a single flap of their wings. Inspired by the Great Black-Backed Gull (GBBG), this paper presents “CGull”, a non-flapping unmanned aerial vehicle (UAV) with wing and tail morphing capabilities. A coupled two degree-of-freedom (DOF) morphing mechanism is used in CGull’s wings to sweep the middle wing forward and the outer feathered wing backward, replicating the GBBG’s wing deformation. A modular two DOF mechanism enables CGull to pitch and tilt its tail. A computational model was first developed in MachUpX to study the effects of wing and tail morphing on the generated forces and moments. Following the biological construction of birds’ feathers and bones, CGull’s structure is mainly constructed from carbon-fiber composite shells. The successful flight test of the proof-of-concept physical model proved the effectiveness of the proposed morphing mechanisms in controlling the UAV’s path. Full article

Bird wings are exquisite mechanisms integrated with multiple morphological deformation joints. The larger avian species are particularly adept at utilizing their wings’ flapping, folding, and twisting motions to control the wing angle and area. These motions mainly involve different types of spanwise folding and chordwise twisting. It is wondered whether the agile maneuverability of birds is based on the complex coupling of these wing morphing changes. To investigate this issue, we designed a two-section wing structure ornithopter capable of simultaneously controlling both spanwise folding and chordwise twisting and applied it to research on heading control. The experimental data collected from outdoor flights describe the differing flight capabilities between the conventional and two-section active twist wing states, indicating that incorporating an active twist structure enhances the agility and maneuverability of this novel flapping aircraft. In the experiments on yaw control, we observed some peculiar phenomena: although the twisting motion of the active twist ornithopter wings resembles that of a fixed-wing aileron control, due to the intricate coupling of the wing flapping and folding, the ornithopter, under the control of active twist structures, exhibited a yaw direction opposite to the expected direction (directly applying the logic assumed by the fixed-wing aileron control). Addressing this specific phenomenon, we provide a plausible model explanation. In summary, our study with active twist mechanisms on ornithopters corroborates the positive impact of active deformation on their attitude agility, which is beneficial for the design of similar bio-inspired aircraft in the future. Full article

A novel concept of morphing airfoils, capable of changing camber and thickness, is proposed. A variable airfoil shape, defined by six input parameters, is achieved by allowing the three spinal points (at fixed axial positions) to slide vertically, while the upper and lower surfaces are determined by the lengths of the three corresponding ribs that are perpendicular to the spine. Thus, it is possible to find the most appropriate geometric configuration for a wide range of possible operating conditions often present with contemporary unmanned aerial vehicles. Shape optimizations for different Reynolds numbers and different cost functions are performed by coupling a genetic algorithm with simple panel method flow calculations. The obtained airfoils are presented and compared, whereas the proposed concept is validated by more advanced flow simulations. It appears that improvements in aerodynamic performance of nearly 20% can be expected at Re ranging from 0.05 × 10⁶ to 0.1 × 10⁶. The proposed methodology shows promise and can be applied to different types of lifting surfaces, including wing, tail or propeller blade segments. To check the viability of this method for producing airfoils that can be used in a practical sense, structural analysis of one of the obtained geometries using a simplified 1D finite element method as well as a more detailed 3D analysis are performed. The model is then 3D-printed on a fused deposition modeling (FDM) printer with a polyethylene terephthalate glycol (PETG) filament, and the capability of the airfoil to adequately morph between the two desired geometries is experimentally shown. Full article

The influence of trailing edge deformation on the aerodynamic characteristics of camber morphing wings is an important topic in the aviation field. In this paper, a new memory alloy actuator is proposed to realize trailing edge deformation, and computational fluid dynamics (CFD) and wind tunnel experiments are used to study the influence of trailing edge deformation on the aerodynamic characteristics of the camber morphing wings. The experiments was carried out in a transonic wind tunnel with Mach numbers ranging from 0.4 to 0.8 and angles of attack ranging from 0° to 6°. The external flow fields and aerodynamic force coefficients with and without deformation were calculated using the CFD method. A loose coupled method based on data exchange was used to achieve a fluid–structure interaction (FSI) analysis. The research results indicate that when the trailing edge is deflected downwards, the phenomenon of shock wave forward movement reduces the negative pressure area on the upper wing surface, increases the pressure on the lower wing surface, and ultimately increases the total lift. This work provides a new approach for the implementation of trailing edge deformation and a powerful data reference for the design of camber morphing wings. Full article

The current morphing technologies are mostly regarded as auxiliary tools, providing additional control torques to enhance the flight maneuverability of unmanned aerial vehicles (UAVs), and they cannot exist independently of the traditional control surfaces. In this paper, we propose a tandem-wing micro aerial vehicle (MAV) with multiple variable-sweep wings, which can reduce the additional inertia forces and moments and weaken the dynamic coupling between longitudinal and lateral motion while the MAV morphs symmetrically for pitch control or asymmetrically for roll control, thereby flying without the traditional aileron and elevator. First, load experiments were conducted on the MAV to verify the structural strength of the multiple variable sweep wings, and the control moments caused by the morphing of the MAV were presented through numerical simulations. Then, the effects caused by symmetric and asymmetric morphing were investigated via dynamic response simulations based on the Kane dynamic model of the MAV, and the generated additional inertia forces and moments were also analyzed during morphing. Finally, dynamic response experiments and open-loop flight experiments were conducted. The experimental results demonstrated that the morphing mode in this study could weaken the coupling between the longitudinal and lateral dynamics and that it was feasible for attitude control without the traditional aileron and elevator while flying. Full article

A multi-dimensional morphing wing skeleton mechanism is proposed with double-sided triangular pyramid units, which can realize continuous variable span-wise bend, span-wise twist, and sweep. A lockable morphing unit is designed, and its mechanism/structure characteristics, degree of freedom, and the deformable function of its deformable wing skeleton mechanism are analyzed. One kind of flexible skin is proposed to meet the performance requirements, consisting of an internal metastructure and a flexible surface bonded on both sides. The morphing wing skeleton mechanism and the equivalent treated metastructure flexible skin are then combined. Subsequently, a two-way fluid–structure interaction analysis is conducted to investigate the influence of aerodynamic loads on the flexible skin and skeleton mechanism in different deformation states, including the influence of structural passive deformation on the aerodynamic characteristics of the morphing wing. The computational fluid dynamics method is employed to analyze the aerodynamic characteristics of the morphing wing in its initial state, as well as in three deformation states, and to study its aerodynamic performance in different flight environments. Full article

In this study, a novel framework for the flight control of a morphing unmanned aerial vehicle (UAV) based on linear parameter-varying (LPV) methods is proposed. A high-fidelity nonlinear model and LPV model of an asymmetric variable-span morphing UAV were obtained using the NASA generic transport model. The left and right wing span variation ratios were decomposed into symmetric and asymmetric morphing parameters, which were then used as the scheduling parameter and the control input, respectively. LPV-based control augmentation systems were designed to track the normal acceleration, angle of sideslip, and roll rate commands. The span morphing strategy was investigated considering the effects of morphing on various factors to aid the intended maneuver. Autopilots were designed using LPV methods to track commands for airspeed, altitude, angle of sideslip, and roll angle. A nonlinear guidance law was coupled with the autopilots for three-dimensional trajectory tracking. A numerical simulation was performed to demonstrate the effectiveness of the proposed scheme. Full article

Morphing wings are a typical application of shape-adaptive structures in aviation, which play an important role in improving the comprehensive performance of an aircraft. However, traditional morphing wings based on purely mechanical, rigid-flexible coupling, or purely flexible structures usually cannot achieve a distributed morphing ability and have limitations in weight, intelligence level, and reliability. In this paper, a distributed morphing lattice structure based on variable geometry digital metamaterials is proposed. The innovative structural concept consists of three types of fundamental cells featuring remarkably different mechanical properties and three other types of derived cells. One type of the derived cells embedded with micro-actuators, named an active cell, can autonomously extend or contract. All these cells can be reversibly assembled in a random sequence to form an active distributed morphing lattice structure with the ability to realize different target aerodynamic contours. In addition, taking a simplified variable thickness wing as a designing case, this paper develops a cell combination optimization methodology on the basis of a heuristic algorithm to determine the optimal combination sequence of the six types of basic cells and the actuator inputs of active cells collaboratively. Final results show that the optimized lattice structure can morph its outer surface into a predefined aerodynamic contour with a maximum deviation of 3 mm. Full article

This work presents an aerodynamic and structural optimization for a Droop Nose Leading Edge Morphing airfoil as a high lift device for the UAS-S45. The results were obtained using three optimization algorithms: coupled Particle Swarm Optimization-Pattern Search, Genetic Algorithm, and Black Widow Optimization algorithm. The lift-to-drag ratio was used as the fitness function, and the impact of the choice of optimization algorithm selection on the fitness function was evaluated. The optimization was carried out at various Mach numbers of 0.08, 0.1, and 0.15, respectively, and at the cruise and take-off flight conditions. All these optimization algorithms obtained effectively comparable lift-to-drag ratio results with differences of less than 0.03% and similar airfoil geometries and pressure distributions. In addition, an unsteady analysis of a Variable Morphing Leading Edge airfoil with a dynamic meshing scheme was carried out to study its flow behaviour at different angles of attack and the feasibility of leading-edge downward deflection as a stall control mechanism. The numerical results showed that the variable morphing leading edge reduces the flow separation areas over an airfoil and increases the stall angle of attack. Furthermore, a preliminary investigation was conducted into the design and sensitivity analysis of a morphing leading-edge structure of the UAS-S45 wing integrated with an internal actuation mechanism. The correlation and determination matrices were computed for the composite wing geometry for sensitivity analysis to obtain the parameters with the highest correlation coefficients. The parameters include the composite material qualities, thickness, ply angles, and the ply stacking sequence. These findings can be utilized to design the flexible skin optimization framework, obtain the target droop nose deflections for the morphing leading edge, and design an improved model. Full article

Evaluating the impact of morphing devices in terms of actuation energy is a promising approach to quantify, from the earliest stages of wing design, the convenience of active camber morphing compared to the use of conventional control surfaces. A morphing wing device consists of an adaptive structure coupled with an actuation system. The starting point for the design of the adaptive structure is a three-dimensional parametric-geometry-representation technique working on the definition of the external morphing shape. The morphing shape is defined to be feasible from the structural point of view and able to meet the aerodynamic design requirements. The new method presented here enables the computation of the actuation energy as a combination of strain energy and external aerodynamic work. The former is the energy required to deform the skin and can be computed in an analytical way, based on the same quantities used by the parameterization technique. The latter is used to compute the energy needed to counteract the external aerodynamic loads during the deformation. This method is applied to the design optimization of a morphing aileron which is installed on a 24 m span wing, starts at 65% of both the chord and the semi-span and extends for one third of the span. A parametric study shows the superiority of the morphing aileron, compared with an equivalent hinged aileron, in terms of energy saving, weight penalty reduction and ease of on-board installation. The morphing aileron is more compact and requires a lower actuation energy combined with a lower deflection, while providing the same roll moment. Full article

The mission performance of future advanced aerospace structures can be synthetically improved via active shape control utilizing piezoelectric materials. Multiple work modes are required. Bending/twisting mode control receives special attention for many classic aerospace structures, such as active reflector systems, active blades, and compliant morphing wings. Piezoelectric fiber composite (Piezocomposite) material features in-plane anisotropic actuation, which is very suitable for multiple work modes. In this study, two identical macro-fiber composite (MFC) actuators of the F1 type were bonded to the base plate structure in an “antisymmetric angle-ply bimorph configuration” in order to achieve independent bending/twisting shape control. In terms of the finite element model and homogenization strategy, the locations of bimorph MFCs were determined by considering the effect of trade-off control capabilities on the bending and twisting shapes. The modal characteristics were investigated via both experimental and theoretical approaches. The experimental tests implied that the shape control accuracy was heavily reduced due to various uncertainties and nonlinearities, including hysteresis and the creep effect of the actuators, model errors, and external disturbances. A multi-mode feedback control law was designed and the experimental tests indicated that synthetic (independent and coupled) bending/twisting deformations were achieved with improved shape accuracy. This study provides a feasible multi-mode shape control approach with high surface accuracy, especially by employing piezocomposite materials. Full article

A morphing wing concept allowing for coupled twist-camber shape adaptation is proposed. The design is based on an optimized thickness distribution both spanwise and chordwise to be able to morph the wing sections into targeted airfoil shapes. Simultaneously, the spanwise twist is affected by the actuation. The concept provides a higher degree of control on the lift distribution which can be used for roll control, drag minimization, and active load alleviation. Static deformation and flight tests have been performed to evaluate and quantify the performance of the proposed mechanism. The ground tests include mapped actuated wing shapes, and wing mass and actuation power requirements. Roll authority, load alleviation, and aerodynamic efficiency estimates for different configurations were calculated using a lifting line theory coupled with viscous 2D airfoil data. Roll authority was estimated to be low when compared to a general aviation aircraft while the load alleviation capability was found to be high. Differences between the lift to drag ratio between the reference and morphing wing configurations are considerable. Mass and actuation energy present challenges that can be mitigated. The flight tests were used to qualitatively assess the roll control capability of the prototype, which was found to be adequate. Full article

Migratory birds have the ability to save energy during flight by arranging themselves in a V-formation. This arrangement enables an increase in the overall efficiency of the group because the wake vortices shed by each of the birds provide additional lift and thrust to every member. Therefore, the aerodynamic advantages of such a flight arrangement can be exploited in the design process of micro air vehicles. One significant difference when comparing the anatomy of birds to the design of most micro air vehicles is that bird wings are not completely rigid. Birds have the ability to actively morph their wings during the flapping cycle. Given these aspects of avian flight, the objective of this work is to incorporate active bending and torsion into multiple pairs of flapping wings arranged in a V-formation and to investigate their aerodynamic behavior using the unsteady vortex lattice method. To do so, the first two bending and torsional mode shapes of a cantilever beam are considered and the aerodynamic characteristics of morphed wings for a range of V-formation angles, while changing the group size in order to determine the optimal configuration that results in maximum propulsive efficiency, are examined. The aerodynamic simulator incorporating the prescribed morphing is qualitatively verified using experimental data taken from trained kestrel flights. The simulation results demonstrate that coupled bending and twisting of the first mode shape yields the highest propulsive efficiency over a range of formation angles. Furthermore, the optimal configuration in terms of propulsive efficiency is found to be a five-body V-formation incorporating coupled bending and twisting of the first mode at a formation angle of 140 degrees. These results indicate the potential improvement in the aerodynamic performance of the formation flight when introducing active morphing and bioinspiration. Full article

A smart structure to actuate a morphing trailing edge based on the super critical airfoil NASA sc-0714(2) was designed and verified in a transonic wind tunnel. The pressure distribution over the wing was measured to evaluate the structure ability and effects of trailing edge deflections on the aerodynamic characteristics. In the experiment, Mach number was from 0.4 to 0.8, and the angle of attack was from 0° to 6°. The results showed that the smart structure based on shape memory alloy could carry aerodynamic loads under transonic flow and deflect the trailing edge. When the driving force was constant, deformation would be influenced by the Mach number and angle of attack. Increasing the Mach number weakened the actuation capability of the smart structure, which decreased the deflection angle and rate of the trailing edge. The influence of the angle of attack is more complex, and couples with the influence of the Mach number. The higher the Mach number, the stronger the influence of the angles of attack. Additionally, the trailing edge deflection would dramatically change the flow structure over the airfoil, such as the shock wave position and strength. If separation was caused by the trailing edge deflection, the limitation of the smart structure would be further found. Full article

Aircraft winglets are well-established devices that improve aircraft fuel efficiency by enabling a higher lift over drag ratios and lower induced drag. Retrofitting winglets to existing aircraft also increases aircraft payload/range by the same order of the fuel burn savings, although the additional loads and moments imparted to the wing may impact structural interfaces, adding more weight to the wing. Winglet installation on aircraft wing influences numerous design parameters and requires a proper balance between aerodynamics and weight efficiency. Advanced dynamic aeroelastic analyses of the wing/winglet structure are also crucial for this assessment. Within the scope of the Clean Sky 2 REG IADP Airgreen 2 project, targeting novel technologies for next-generation regional aircraft, this paper deals with the integrated design of a full-scale morphing winglet for the purpose of improving aircraft aerodynamic efficiency in off-design flight conditions, lowering wing-bending moments due to maneuvers and increasing aircraft flight stability through morphing technology. A fault-tolerant morphing winglet architecture, based on two independent and asynchronous control surfaces with variable camber and differential settings, is presented. The system is designed to face different flight situations by a proper action on the movable control tabs. The potential for reducing wing and winglet loads by means of the winglet control surfaces is numerically assessed, along with the expected aerodynamic performance and the actuation systems’ integration in the winglet surface geometry. Such a device was designed by CIRA for regional aircraft installation, whereas the aerodynamic benefits and performance were estimated by ONERA on the natural laminar flow wing. An active load controller was developed by PoliMI and UniNA performed aeroelastic trade-offs and flutter calculations due to the coupling of winglet movable harmonics and aircraft wing bending and torsion. Full article