8. Subset Selection in Regression (Monographs on Statistics and Applied Probability, no. 40). By A. J. Miller. ISBN 0 412 35380 6. Chapman and Hall, London, 1990. 240 pp. £25.00.

Subset Selection in Regression

Aircraft wings are a compromise that allows the aircraft to fly at a range of flight conditions, but the performance at each condition is sub-optimal. The ability of a wing surface to change its geometry during flight has interested researchers and designers over the years as this reduces the design compromises required. Morphing is the short form for metamorphose; however, there is neither an exact definition nor an agreement between the researchers about the type or the extent of the geometrical changes necessary to qualify an aircraft for the title ‘shape morphing.’ Geometrical parameters that can be affected by morphing solutions can be categorized into: planform alteration (span, sweep, and chord), out-of-plane transformation (twist, dihedral/gull, and span-wise bending), and airfoil adjustment (camber and thickness). Changing the wing shape or geometry is not new. Historically, morphing solutions always led to penalties in terms of cost, complexity, or weight, although in certain circumstances, thes...

A Review of Morphing Aircraft

http://michael.friswell.com/PDF_Files/C348.pdf

Morphing aircraft: the need for a new design philosophy

The continuous drive for increased fuel efficiency and sustained innovation in the automobile industry requires the adoption of radically new technological advances. Road vehicle aerodynamic design...

https://journals.sagepub.com/doi/pdf/10.1177/0954407013496557

Review of shape-morphing automobile structures: concepts and outlook

A bistable airfoil with the actuator system and the aerodynamic loads coupled to the structure is designed to understand the aeroelastic characteristics of the system. The bistable flap consists of a stack of six bistable prestressed buckled laminates with the plates having dimensions of 100 × 100 mm made from Hexcel 913 glass fiber. The bistable plates attached to a spar situated at 85% chord on the rotor blade. The foam tape placed between each of the plates at the trailing edge making the airfoil weather tight. The bistable plate spar is parallel to the direction of motion of the moving crosshead of the test machine. For the flap to be in equilibrium without any actuator input, the sum of the work done on the structure by the aerodynamic loads W f and the work done on the aerodynamic loads by the structure W b is zero. The modulus function shows that the work needs to be done on the structure to rotate the flap in either direction from an equilibrium point whereas the work done on the aerodynamic loads is dependant on direction.

Aeroelastic Study of Bistable Composite Airfoils

An investigation of truss structures for the purpose of creating a continuously variable camber trailing edge device for an aircraft wing is presented. By creating structures that are both statically and kinematically determinate and then substituting truss elements for actuators, it is possible to impose structural deflection without inducing member stress. A limited number of actuators with limited strain capabilities are located within the structure in order to achieve a target deflected shape starting from an initially symmetric profile. Two objective functions are used to achieve this: a geometric objective for which the target displacement is fixed and a shape objective for which the target displacement is dependent on the surface shape of the targeted aerofoil. The proposed shape objective function is able to offer improvements over the geometric objective by removing some of the constraints applied to the targeted structure joint locations. Four methods for selecting the location of a set of actuators are compared, namely exhaustive search, a genetic algorithm, stepwise forward selection (SFS) and incremental forward selection (IFS). Both SFS and IFS are variations of regression methods for subset selection; in each case an approach has been created to allow the imposing of upper and lower bounds on the search space. It is shown that the genetic algorithm is well suited to addressing the problem of optimally locating a set of actuators; however, regression methods, particularly IFS, can provide a rapid tool suitable for addressing large selection problems.

/pdf/determinate-structures-for-wing-camber-control-5cwbmd12gp.pdf

Determinate structures for wing camber control

Morphing aircraft are flight vehicles that change their shape to effect both a change in the mission of the aircraft and to perform flight control without the use of conventional control surfaces. The key to morphing aircraft is the full integration of the shape control into the wing structure, and this is most easily achieved using composite structures. The design of these vehicles must take full account of the aerodynamic loads and must carefully consider the power requirements for shape control to ensure an overall performance benefit. This paper overviews three possible methods to achieve the required structural compliance that are under investigation at Bristol. The first is the design of the internal structure to produce a compliant mechanism that achieves the required aerofoil deformation using a small number of actuators. The second is the use of stiffness tailoring, incorporating the performance objectives, together with material constraints such as buckling and manufacturing requirements. The final approach is the use of multi-stable structures to perform large shape changes. For these structures, no force is required to maintain their stable configurations. The general features of these approaches will be described and illustrated using simulated and experimental results.

/pdf/compliant-structures-for-morphing-aircraft-156ldyabxb.pdf

Compliant Structures for Morphing Aircraft

Many structures, both man made and in nature, are hierarchical in the sense that there are structures on more than one length scale and the performance is enhanced by the optimization of such a system. The length scales involved can go down to the micro and nano scales, for example considering the crystal structure of solids. However the emphasis in this paper is the macro length scale and the use of hierarchical designs to morph aircraft wings. Two examples will be given, namely the optimization of the composite lay-up to enhance a structure’s anisotropic properties and the optimization of truss and skin elements in a compliant mechanism approach to morphing aircraft.

/pdf/the-optimisation-of-hierarchical-structures-with-5cgu6u4r1u.pdf

The optimisation of hierarchical structures with applications to morphing aircraft

A method of distributing a limited amount of material in a frame type structure with the objective of creating a compliant morphing aerofoil is presented. The approach applies the Method of Moving Asymptotes (MMA) optimisation algorithm to an initial ground structure. By tailoring the cross sectional properties of the frame members the surface displacement of the structure when subjected to applied actuator and aerodynamic loading is controlled. A multi-criteria objective function is formulated that provides control of the surface form of the structure without instilling predefined nodal displacements together with addressing the conflicting issues of adequate stiffness and flexibility. Local failure conditions are incorporated into the algorithm in the form of maximum, minimum and buckling stress constraints.

/pdf/design-of-a-compliant-aerofoil-using-topology-optimisation-3xs5aned4e.pdf

Design of a compliant aerofoil using topology optimisation

Morphing aircraft structures present a possibility to adapt to changing flight conditions and objectives in order to achieve an optimised configuration along with providing a replacement of conventional aircraft control devices. This paper presents a concept for active wing morphing in the form of variable camber control by the application of a variable geometry truss structure. The Kagome truss pattern is shown to offer a geometry that after modification satisfies the requirements of static and kinematic determinacy; thus by replacing selected members with linear actuators structural form may be altered without resistance. Analysis of available deflection is provided with a linear, elastic model coupled to an aerodynamic panel method allowing the effect of aeroelastic loads to be considered. Further challenges including the construction of an effective skin design and model development are considered.

Active Truss Structures for Wing Morphing

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