13:30
Adaptive structures 2
Chair: Sergio Ricci
13:30
30 mins
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Preliminary investigation of the superelastic monostable spoiler for dynamic gust loads alleviation
Andrea Castrichini, Federica Siotto, Xiaoyang Sun, Josh Coppin, Raul Lozano Vargas, ignacio Ballesteros Ruiz, Enzo Cosentino, Michael Hadjipantelis
Abstract: Much effort has been made to design aircraft to optimise fuel consumption through reduction of aerodynamic drag. A sizable contribution to the overall drag is lift-induced drag, which could be reduced by increasing the wing span, but such a design solution has well defined limits since it often results in the increment of structural loads, especially in terms of wing bending moment, and consequently wing weight.
Aircraft flight and ground loads are the key elements in carrying out the aircraft structural sizing and therefore determining its weight. In order to minimise costs and fuel consumption, aircraft designers aim to achieve minimum structural weight, whilst ensuring that failure cannot occur at any point of an aircraft’s operation and in-service life due to excessive stresses or deflections.
Aircraft load alleviation strategies are of particular interest since they allow the mitigation of critical load cases thus preventing oversizing the structure.
This paper investigates a novel load alleviation technology named “superelastic mono stable spoiler”. This consists in a passive load alleviation system given by a monostable surface that is passively deployed when the local structural strain is higher than a given threshold value and passively stow back when the strain is reduced.
Such a surface, when located on the top part of the aerodynamic airfoil, is supposed to obstruct the incoming aerodynamic flow leading to local flow separation and consequently lift reduction.
Such a working mechanism allows the “superelastic mono stable spoiler” (SMS) to act as a passive loads alleviation system that passively pops up only when needed and it is supposed to be not activated in normal cruise conditions.
This paper will present a number of trade studies looking at the impact of different activation thresholds and deflection rate of the “superelastic mono stable spoiler” on the aircraft gust dynamic response. A representative civil aviation model will be used and all the analyses will be done using a linear time marching unsteady gust simulation formulation based on doublet lattice method for the aerodynamics and modal condensation for the structure.
Initial preliminary results show promising loads alleviation capability in a one minus cosine gust encounter.
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14:00
30 mins
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Investigation of multibody flight dynamic modes of an aircraft with flexible folding wing tips
Amir Hossein Modarres Aval, Vadim Maltsev, Zhuoneng Li, Declan Clifford, Andrea dr Da Ronch
Abstract: It is always tempting to improve the aerodynamic efficiency of an aircraft by increasing the aspect ratio of its wings. However, there are mainly two issues: first regarding the size to meet airport gate limitations, and second the increased structural weight to make the wing resilient enough to the extra aerodynamic load produced by an increment in the aspect ratio of the wing. To address these issues, the semi-aeroelastic hinge concept has been recently proposed and it has attracted the attention of many researchers. Unlike conventional folding wing tips, as used on the 777-X, previous studies [1, 2] demonstrated that the use of semi-aeroelastic hinge devices in aircraft incorporating high-aspect-ratio wings allows not only to fit the vehicle into airport gates but also to alleviate aerodynamic loads by enabling floating wing tips to be used in-flight.
This work is part recent effort led by Airbus in the frame of the Out of cycle NExt generation highly efficient air transport (ONEheart) project [3] and “we”, as a research group at the University of Southampton develop technology bricks to enable overall aircraft design. In this study, we investigate how flight modes and handling qualities of the vehicle are affected by the added flexibility to the wing. A representative civil jet aircraft with articulated wings is used to explore the effect of introducing a wing-tip device, connected to the wings with an elastic hinge, on the flight dynamic modes of the vehicle.
Using a multibody dynamic simulation, an aircraft with articulated wings has been mathematically modeled, with the aircraft being composed of three rigid parts. This multibody formulation enables one to account for finite rotations of rigid folding wing tips in addition to the traditional flight dynamic modes. For sufficiently soft discrete structural hinges, substantial coupling between flexible and rigid modes occurs, leading to the potential to modify the flight dynamic behavior through structural flexibility. Using a multibody flight dynamics simulation tool with a nonlinear quasi-steady aerodynamic representation, different structural-hinge elastic properties, orientation, wing tip weight, and location on the aircraft are examined. It is also desirable to evaluate the transient and steady-state behavior of forces and moments that act as a constraint at hinges. In this regard, the time history of the constraint forces and moments on the hinge in different flight regimes have been also evaluated.
The orientations of the hinges are symmetric to the x-z plane of the aircraft. However, sideslip can easily cause an asymmetry in the hinge orientation which may have an important effect on the flight dynamic response of the vehicle, therefore one of our primary goals in this study is to investigate the side-slip effect.
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14:30
30 mins
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Parametric nonlinear flutter analysis of the semi-aeroelastic hinges during manoeuvres and gust encounters
Paolo Mastracci, Andrea Castrichini, Thomas Wilson
Abstract: A recent consideration in aircraft design is the use of semi-aeroelastic hinges, with
the aim of enabling higher aspect ratio wings with less induced drag but also meeting airport gate limitations. Of particular interest is the concept of using in-flight free-floating wingtips in order to reduce aircraft gust and manoeuvre loads. On a previous work, a multibody formulation was introduced to account for finite rotations of rigid folding wingtips attached through flared hinges on a flexible airframe structure including aerodynamic follower forces for the folding wingtip components. This study uses the same formulation to investigate the effect of geometric nonlinearities on the aircraft aeroelastic stability. A time marching flutter analysis is used to depict how the stability of the aircraft varies during static and dynamic conditions like manoeuvres and gusts. It is shown that the aeroelastic stability of the aicraft is strongly influenced by the aicraft deformed shape leading to a reduction of stability the higher the tips coasting angles. Preliminary results show the emergence of unstable flutter mechanisms which have the tendency to become more and more unstable the higher the wing deformation and wingtip coasting angle. The aim of the paper is to show in which scenarios, such a degradation might be critical.
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15:00
30 mins
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Constrained flexible wing with folding wingtip dynamics model based on Lagrange's method
Lina Dehmlow, Pedro González, Gerrit Stavorinus, Flávio Silvestre
Abstract: One way of reducing an aircraft’s induced drag while meeting airport gate limitations is increasing the wingspan and introducing a folding wingtip. By making the hinge flexible and rotating it’s axis outboard the folding wingtip could be used to reduce gust loads. As aircraft are becoming more flexible, the flexibility is another important factor that needs to be considered. In the following a set of equations of motion describing a constrained flexible wing with a flared folding wingtip, that considers follower forces of the wing and folding wingtip as well as the geometric exact angle of attack is derived using Lagrange’s method considering the folding wingtip as separate body. The formulation is used to set up an aeroelastic model in MATLAB/Simulink. The model is tested on the TU-Flex wing with a hinge introduced at 80% span and compared to the original wing. It can be shown that the folding wingtip dynamics have an influence on the stability of the system reducing the damping of the modes and introducing a new lower frequency mode.
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