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This article presents an experimental evaluation of a morphing leading edge demonstrator by investigating its morphed shape, the level of induced strains in the airfoil skin, the actuation force, and the morphing mechanism’s capability to lock and transfer the applied loads. In addition, a finite element model of the demonstrator is assembled comprising an elastic morphing skin and a kinematic morphing mechanism. The obtained results are used to assess whether the demonstrator performs according to the design objectives, such as the target shape, the character of the morphing deformation and the morphing mechanism locking, applied during the design process. The comparison between experimental and numerical results yielded a good agreement in terms of observed morphed shape and pertaining strains. The average difference in morphed shape was less than 0.08% chord at the maximum actuator extension. The observed difference in the respective strains was less than 400 micro-strains. A significant difference, up to 70%, was observed in the actuation force, which was attributed to the modelling assumptions and to the force measurement technique employed in the experiment. Nevertheless, both results show good qualitative agreement showing similar trends.

Morphing offers an attractive alternative compared to conventional hinged, multi-element high lift devices. In the present work, morphed shapes of a NACA 64A010 airfoil are optimized for maximum lift characteristics. Deformed shapes of the leading and trailing edge are represented through Bezier curves derived from locally defined control points. The optimization process employs the fast Foil2w in-house viscous-inviscid interaction solver for the calculation of aerodynamic characteristics. Transitional flow results indicate that combined leading and trailing edge morphing may increase maximum lift in the order of 100%. A 60–80% increase is achieved when morphing is applied to leading edge only—the so-called droop nose—while a 45% increase is obtained with trailing edge morphing. Out of the stochastic optimization algorithms tested, the Genetic Algorithm, the Evolution Strategies, and the Particle Swarm Optimizer, the latter performs best. It produces the designs of maximum lift increase with the lowest computational cost. For the optimum morphed designs, verification simulations using the high fidelity MaPFlow CFD solver ensure that the high lift requirements set by the optimization process are met. Although the deformed droop nose increases drag, the aerodynamic performance is improved ensuring the overall effectiveness of the airfoil design during take-off and landing.

This paper provides an overview of research into a morphing wing leading edge allowing smooth and continuous shape changes. Together with high-lift technologies investigated in the Collaborative Research Center 880 over the past nine years, the morphing droop nose has the potential to generate very high lift coefficients with low noise. Multiple design strategies were explored over the course of research and summarized here. Design features include novel, multifunctional, hybrid tailored composites comprising fiberglass and elastomeric materials, integral stringers to facilitate the flow of internal and external forces, and the use of optimization chains to synthesize the numerous design variables. The results of experimental tests show in general the suitability of the design methods, as well as a number of lessons learned, including the need for tighter aerodynamic-structural coupling, that are useful for future work.

The numerical three-dimensional structural design of a large-displacement flexible morphing wing leading edge, otherwise known as a droop nose, is presented in this article. The droop nose is an essential component of a novel internally blown high-lift system for a transport aircraft to delay stall and reduce internal compressor requirements. A design chain consisting of optimization procedures was used to arrive at the structural design of the droop nose composed of a composite fiberglass skin with integral stringers and supporting kinematic mechanisms. The optimization tools aim to produce a design with minimal error to the critical target shapes. A maximum final error of 10.09 mm between calculated and target trajectories of the stringers was found after the kinematic optimization stage. After inputting the kinematic optimization results into the skin optimization stage and solving, a maximum error in the order of 13 mm and curvature difference 0.0028 1/mm were calculated, occurring in the outboard region. Prior two-dimensional analyses with similar shape deviations showed 0.4% lift reduction though further three-dimensional investigations are required. Concepts for integrating industrial requirements abrasion and lightning strike protection and in-flight de-icing into a multifunctional skin show promise and the resulting aerodynamic surface quality was found to be adequate.

A morphing droop-nose wing tip with span of 1.3 m and target 2 deg droop was designed, manufactured, and tested as part of the European project Novel Air Vehicle Configurations: From Fluttering Wings to Morphing Flight. The morphing droop-nose device featured a fiberglass composite skin with optimized three-dimensional thickness distribution, which was supported by topology-optimized superelastic nickel titanium and aluminum internal compliant mechanisms. The tests included ground and low-speed wind-tunnel tests (55 m/s) with the aim of assessing the structural performance and the design chain through measurements of shape, strains, surface pressures, and total forces/moments on the model. Comparisons with the experimental results were used for validation of the computational models and optimization tools. The morphing device was able to change shape while resisting the external loads, and it was identified that the distribution of strain and shape accuracy may be improved through the use of a concurrent as opposed to sequential design chain and other developments to the optimization tools. The use of a superelastic material facilitated the high-strain displacement, exceeding 2% strain in the design case and measured up to 4.54%, making it highly suitable for compliant mechanism applications. This paper explains the insights made from the experimental tests and recommendations for the future design of morphing structures.

A design for a new high lift system that features a morphing wing leading edge &ldquo, droop nose&rdquo, has the potential to generate high lift coefficients whilst mitigating airframe noise emissions. This seamless, continuous, and stepless flexible droop nose potentially offers improvements to stall and compressor requirements for an internally-blown active Coandă trailing edge flap. A full-scale, span-trimmed three-dimensional droop nose was manufactured and ground-tested based on results obtained from new design synthesis tools. A new component of the droop nose is the hybrid fiberglass-elastomeric skin that is tailored in stiffness to meet morphing curvature requirements and spanwise bending resistance. A manufacturing concept of the novel skin was established that led to an adequate manufacturing quality. The skin was driven and supported by two optimized kinematic ribs and conventional actuators and overall shape results show good agreement apart from the region closest to the leading edge. Kinematic trajectory measurements showed that the kinematics met the target trajectories well, with and without the influence of the skin, and it was deemed that the error in curvature is due to a higher than expected skin stiffness in the hybrid layer. Calculated actuator torque levels and strain measurements corroborate this inference. The lessons learned show that means of adjustment post-assembly are needed, and a reduction of torque, energy and a better curvature distribution may be achieved if the skin at the spar junction is allowed to move relative to the main wing. Careful aerodynamic, structural, actuation and manufacturing trade-off studies would be needed to determine the overall performance benefit.

Morphing is a technology with high potential to reduce emissions in aviation by adapting the shape of the wings to varying external operating conditions. This paper is presenting results from the EU FP7 funded CHANGE project, where different concepts to adapt a UAV wing airfoil to different demands were investigated. The paper is concentrating on the design and experimental testing of a droop nose, which transforms the leading edge part of the 60 cm chord airfoil from a NACA 6510 shape for loiter and low speed to a NACA 2510 shape for a high speed mission. This paper is presenting the use of an especially soft skin, which reduces the needed force for morphing. That way the requirements for the servos driving the droop nose could be reduced significantly. This paper is showing the implications of such a soft design on the accuracy of the shape generated. For such a skin design, the driving mechanism of the system is designed as a compliant mechanism, which was generated by topology optimization, taking into account aerodynamic loads. For easy manufacturing reasons, thermoplastic polylactic acid (PLA) with zero warp property was used for the manufacturing of this compliant mechanism. Finally deformation measurements of the morphing skin were carried out in a series of lab tests. The match between measured and numerically derived section is quite good, especially in the root region of the wing. Finally an example of an alternative concept to the soft approach is presented. It is the metal based compliant mechanism with a rather stiff GFRP skin. A discussion on the use of different materials and the way forward towards 3D skin optimization is wrapping up the paper.

In a wind tunnel experiment a morphing wing with span extension and camber morphing was investigated. The considered aircraft is an unmanned aerial vehicle (UAV) with a span of 4 m. During the investigations a half wing model was analysed with pressure and structural measurement. The half wing model has three different morphing mechanisms. The focus is on the morphing leading edge concept, which will be shortly described with the main objectives. First of all the morphing leading edge will be described. Afterwards the results of the wind tunnel measurement for pressure distribution, balance and deformation measurement will be presented and discussed.

For the application of laminar flow on commercial aircraft wings the high-lift devices at the leading edge play a major role. Since conventional leading edge devices like slats do not comply with the high surface quality requirements needed for laminar flow, alternative concepts must be developed. Besides the conventional Krueger device which enables laminar flow on the upper side of the airfoil and additionally implicates an insect shielding functionality, smart droop nose devices are currently under investigation. However, the research on such morphing devices which can deform to a given target shape and provide a smooth, high-quality surface has to give answers to questions of fundamental industrial requirements like erosion protection, anti/de-icing, lightning strike protection and bird strike protection. The integration of these functionalities into a given baseline-design of a morphing structure is a key challenge for the realization of such devices in the future. This paper focuses on the design drivers, System interdependencies and effects of the integration of the mentioned functionalities into a smart droop nose device developed in the European project SARISTU. The paper presents the concept and design procedure for the enhanced adaptive droop nose with focus on the integration of additional functionalities. It gives an overview on the functional demonstrators realized in the framework of the project and the setup and results of the large-scale ground test.

The use of active flow control in high-lift systems is a promising solution to improve aircraft low-speed capabilities and reduce noise emissions during landing. To date, however, the system power requirements have been too high in relation to the achieved lift gains, to allow a large use of these technologies in the aeronautical industry. The present work addresses this problem by developing and testing a leading-edge device to increase the efficiency of an internally-blown Coanda-flap configuration. The main objectives are the increase of the stall angle of attack and the reduction of the jet momentum requirements. A 2D sensitivity analysis is performed to explore the effects of varying the airfoil camber and thickness in the first 20% of the airfoil chord. The resulting droop-nose configuration yields a reduction of 32% of the jet momentum required to achieve a target maximum lift coefficient of 5.0, while improving the stall angle by 10°. As the modified leading edge geometry presents different stall mechanisms, the aerodynamic response to variations of jet momentum is also different. In particular, for a jet momentum coefficient above 0.035 the stall angle of attack increases with jet momentum, in contrast to the behavior observed with the baseline leading-edge configuration. Subsequent to the 2D study, the results are tested on a wing-body configuration with a circulation controlled plain flap, which is deflected by 65°. Therefore, calculations at an identical blowing coefficient are performed on the clean-nose and droop-nose configurations. The comparison of the 3D results verifies the stall delay observed in 2D. The outboard leading edge stall seen on the clean-nose configuration is successfully suppressed. In contrast, the maximum lift of the droop-nose configuration is limited due to fuselage-wing integration effects. As a result, the increase of the maximum lift coefficient is limited to 3%, whereas the maximum angle of attack is raised by 10°.

A full scale morphing wing tip demonstrator with a droop-nose adaptive morphing wingtip was wind tunnel tested as part of the European FP7 project NOVEMOR. This demonstrator features a flexible fiberglass skin and an aluminium internal compliant mechanism. The tests were carried out to assess the performance of compliant mechanism and skin under aerodynamic loading. The results show that strains in the mechanism are mainly from the actuation showing adequate stiffness in the mechanism. In addition to strains, pressure data was taken to determine aerodynamic loading. The Finite element and computational fluid dynamics simulations performed showed good agreement with the experimental values.

The permanently increasing demands on performance and noise reduction in today's aircraft high lift systems enforces the study of adaptive technologies to overcome the restrictions of state of the art fully passive technologies. As an alternative to conventional slats and flaps, an active blown Coanda-flap based high lift system is investigated within the German national Collaborative Research Centre 880 to improve on the mentioned limitations. One key feature is provided by an adaptive gapless droop nose with an exceedingly high grade of leading edge morphing. The construction of this component is based on a structural optimization framework, developed at DLR. The framework consists of two hierarchical design steps, an optimization of the skin layout with discrete joints to the inner actuation mechanism and the topology optimization of the latter. In this paper, the methodology of the second step and its application to the droop nose is discussed. For efficiency reasons, the design of the inner mechanism is completely implemented in the matrix software environment MATLAB. A key component is given by a Finite Element based non-linear solver for the static calculation of the stiffness distribution on a regular grid. As part of the inner loop of this design process, this solver must be implemented as efficient as possible. Due to the lack of sensitivity information in commercial Finite Element programs, the direct implementation of the elasticity equations is further enforced. A main focus of this article concentrates on the underlying assembly approach for the needed system matrices. Finally the application of the tool chain to the droop nose compliant mechanism is presented.

A demonstrator morphing leading edge was designed and manufactured as an intermediary step in preparation for wind tunnel testing of a droop-nose adaptive morphing wingtip (AMWT) as part of the European FP7 project NOVEMOR. This demonstrator features a flexible fiberglass skin and a monolithic aluminum internal compliant mechanism and support structure for lightweight design. The design process involves the design of the skin via a structural optimization tool, followed by continuum gradient-based topology optimization of first the compliant mechanism and then the support structure. The skin was manufactured using prepreg Hexcel HexPly® 913 plies, the aluminum internal structure was laser cut from stock plate material and the compliant region was driven by a linear stepper motor actuator. Displacements and strains were measured and compared with target values and that of finite element computations and overall show good agreement; however issues such as grey-areas and hinge-regions in the topology optimization need to be addressed for the final wind tunnel design for better post-processing and reduced stress concentrations.

Morphing is a technology with high potential to reduce emissions in aviation, since it enables wings to adapt their shape to operate at a higher efficiency over the full range of flight conditions. This paper is presenting a concept to adapt camber by drooping the nose. The scope is the setup and bench top testing of a full scale wing tip leading edge wind tunnel model with a morphing droop nose. The complete model features a span of 1.3 m and a strong taper from the root to the tip. For completeness, the design approach is covered as well. The design comprises a GFRP skin to be drooped by two compliant mechanisms, which are driven by linear motors. The compliant morphing devices are “designed-through-optimization”, with the optimization algorithms including Simplex optimization for composite compliant skin design, continuum-based and load path representation topology optimization methods for compliant internal substructure design. The compliant mechanism is manufactured by nickel-titanium alloy to allow high strains in the order of several percent, which is shown to be critical in the design of such compliant mechanisms. In order to validate the models, strains within the mechanisms are measured while drooping the nose in the bench top test. This is done after installing the mechanisms into the leading edge skin. It can be shown, that the simulation for the inboard mechanism is close to the experimental results. The comparison of strain levels in the skin and in the mechanism during droop reveals that the stiffness distribution between these two components is quite different. As a result this ratio can be taken into account in future design processes in order to distribute strains more evenly. Moreover the 3D shapes of the morphed and clean skin are measured and their comparison with the target shapes is presented as well. Finally, the bench top tests are a proof of concept for the overall concept and design which resultes in a “go” for the following low speed subsonic wind tunnel tests.Copyright © 2015 by ASME

The future generation of high lift devices for transport aircrafts has to contribute to the reduction of noise during landing and a reduction of drag during cruise flight. Also it has to be compatible with affords for natural laminar flow on the wing. A smart gapless droop nose would be an alternative to today’s slats and promises to contribute to those goals. A consortium of Airbus, EADS-IW, CASSIDIAN and DLR developed such a smart leading edge in the framework of the fourth German national research program in aeronautics. This paper describes a 1:1 3D fiber reinforced flexible smart droop nose and its ground test. The results of these tests will finally be compared with the results of the finite element simulation.