European Research Council Morphing Project at Swansea (2010-2015)
Professor Friswell was awarded a prestigious 2.5M euro grant from the European Research Council to continue to develop in flight morphing of aircraft wings. The project title was the Optimisation of Multi-scale Structures with Applications to Morphing Aircraft and started on 1 May 2010 for 5 years.
Flight, and the design of aircraft, has been a great success story. Early pioneers were inspired by the natural world, and early aircraft, such as the Wright Flyer, twisted a compliant wing for roll control. The demand for higher payloads and faster cruise speeds required stiffer wing structures. Controlling the aircraft by deforming the wings was replaced by discrete aerodynamic surfaces. However, modern aircraft wings are a compromise that allows the aircraft to fly at a range of flight conditions, but the performance at each condition is inevitably 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. Concepts based on mechanisms, for example variable sweep, have been successful, but concepts based on the compliance of the structure have met with limited success. Such compliant concepts, often termed morphing aircraft, were the subject of this ERC project.
The design of efficient morphing aircraft requires advances in system level modelling and performance assessment, innovative and novel structural concepts, and improved components such as compliant skins. All of these aspects were considered in the project and some highlights are summarised below.
The key requirement for the adoption of morphing technology is the demonstration of the potential performance benefits. This requires a system level analysis that considers not only the aerodynamics of the aircraft, but also the sizing and weight estimation for both the structure and actuators, and how the vehicle will be operated. For example, detailed analysis has been performed on aircraft with variable span for combined dash and loiter missions, to determine if the improved aerodynamic performance is able to offset the weight penalty.
Novel configurations investigated include the biologically inspired FishBAC compliant variable camber device, consisting of a chordwise spine with stringers to support a pre-tensioned elastomeric skin. A significant improvement in aerodynamic efficiency (the ratio of lift to drag) has been demonstrated in simulation and wind tunnel testing, for a relatively small increase in weight. A novel span extension concept with a compliant skin has been designed and extensively modelled.
The structures that comprise a morphing aircraft must be understood to enable the system level performance optimisation. Equivalent models are used to capture their characteristics at the system level and must allow for changes in dimensions and geometry. Skins are vital components, and are typically anisotropic to combine stiffness to support the aerodynamic loads, and flexibility to enable deformation. Corrugated and reinforced elastomer skins have been a particular focus within the project.
The design of morphing aircraft continues to be a huge challenge, and this project has made significant advances in understanding the key requirements in the design process. However, modern aircraft are lightweight and highly optimised, and more research is required before morphing can be routinely considered as a design option for commercial aircraft.
The efficient design of morphing aircraft requires the integration of many disciplines, and the introduction of new structural concepts. Hence the project has made progress in a number of directions that will now be outlined briefly. Only an outline can be provided here, and the published papers give further details.
System Level Optimization
Multi-objective system level optimization of morphing aircraft. Modern aircraft are lightweight and highly optimized; morphing concepts usually add weight and hence the performance benefits must be sufficient to counteract this penalty. Conventional aircraft have the advantage of significant experience to enable low fidelity conceptual design; for morphing aircraft this knowledge is limited and hence low fidelity prediction tools must be used. One of the core objectives of the project was to improve, integrate and validate these low fidelity tools for morphing solutions. The concepts considered included variable span, active winglets, adaptive torsion and variable camber. Objectives included global metrics such as range and endurance, as well as more local metrics such as the lift-to-drag ratio.
- RM Ajaj, CS Beaverstock & MI Friswell, Morphing Aircraft: The Need for a New Design Philosophy. Aerospace Science and Technology, 49, February 2016, 154-166.
- CS Beaverstock, BKS Woods, JHS Fincham & MI Friswell, Performance Comparison between Optimised Camber and Span for a Morphing Wing. Aerospace, 2(3), 2015, 524-554.
- JHS Fincham & MI Friswell, Aerodynamic Optimisation of a Camber Morphing Aerofoil. Aerospace Science and Technology, 43, June 2015, 245-255.
- RM Ajaj, MI Friswell & EI Saavedra Flores, On the Effectiveness of Active Aeroelastic Structures for Morphing Aircraft. The Aeronautical Journal, 117(1197), November 2013, paper number 3916, 1165-1174.
- RM Ajaj, MI Friswell, WG Dettmer, G Allegri & AT Isikveren, Performance and Control Optimisations using the Adaptive Torsion Wing. The Aeronautical Journal, 116(1184), October 2012, paper number 3775, 1061-1077.
Novel Morphing Concepts
The FishBAC compliant variable camber device is a biological inspired concept consisting of a chordwise spine with stringers to support a pre-tensioned elastomeric skin. This concept was extensively modelled and optimized, and the models were validated using wind tunnel and bench top tests. The FishBAC provides a lightweight solution that is aerodynamically efficient, and has generated significant interest in industry for both fixed wing and rotary wing applications. The AdAR (Adaptive Aspect Ratio) concept uses a compliant skin and allows span extensions of 100%. The novel internal structure comprises a telescopic spar, sliding ribs, an elastomer skin and a tensioned strap drive. The key problem is the weight of the actuation mechanism, and this was modelled extensively.
FishBAC Active Camber
- BKS Woods & MI Friswell, Multi-objective Geometry Optimization of the Fish Bone Active Camber Morphing Airfoil. Journal of Intelligent Material Systems and Structures, 27(6), April 2016, 808-819.
- BKS Woods, I Dayyani & MI Friswell, Fluid-Structure Interaction Analysis of the Fish Bone Active Camber Concept. Journal of Aircraft, 52(1), January 2015, 307-319.
- BKS Woods, O Bilgen & MI Friswell, Wind Tunnel Testing of the Fish Bone Active Camber Morphing Concept. Journal of Intelligent Material Systems and Structures, 25(7), May 2014, 772-785.
Active Camber using Piezoelectric Actuators
- O Bilgen & MI Friswell, Piezoceramic Composite Actuators for a Solid-State Variable-Camber Wing. Journal of Intelligent Material Systems and Structures, 25(7), May 2014, 806-817.
- O Bilgen & MI Friswell, Implementation of a Continuous-Inextensible-Surface Piezocomposite Airfoil. Journal of Aircraft, 50(2), March 2013, 508-518.
- O Bilgen, MI Friswell & DJ Inman, Theoretical and Experimental Analysis of Hysteresis in Piezocomposite Airfoils using the Classical Preisach Model. Journal of Aircraft, 48(6), November-December 2011, 1935-1947.
- BKS Woods & MI Friswell, The Adaptive Aspect Ratio Morphing Wing: Design Concept and Low Fidelity Skin Optimization. Aerospace Science and Technology, 42, April-May 2015, 209-217.
- RM Ajaj, MI Friswell, M Bourchak & W Harasani, Span Morphing using the GNATSpar Wing. Aerospace Science and Technology, 53, June 2016, 38-46.
- RM Ajaj, EI Saavedra Flores, MI Friswell & FA Diaz de la O, Span Morphing using the Compliant Spar. Journal of Aerospace Engineering, 28(4), July 2015, paper 04014108.
- RM Ajaj, EI Saavedra Flores, MI Friswell, G Allegri, BKS Woods, AT Isikveren & WG Dettmer, The Zigzag Wingbox for a Span Morphing Wing. Aerospace Science and Technology, 28(1), July 2013, 364-375.
- RM Ajaj, MI Friswell, EI Saavedra Flores, AJ Keane, AT Isikveren, G Allegri & S Adhikari, An Integrated Conceptual Design Study using Span Morphing Technology. Journal of Intelligent Material Systems and Structures, 25(8), May 2014, 989-1008.
- RM Ajaj, MI Friswell, WG Dettmer, G Allegri & AT Isikveren, Dynamic Modelling and Actuation of the Adaptive Torsion Wing. Journal of Intelligent Material Systems and Structures, 24(16), November 2013, 2045-2057.
- RM Ajaj, MI Friswell, DG Dettmer, AT Isikveren & G Allegri, Roll Control of a MALE UAV using the Adaptive Torsion Wing. The Aeronautical Journal, 117(1189), March 2013, paper number 3809, 299-314.
As part of the analysis equivalent models of structural components, such as skins, must be obtained. These models must retain their dependence on the physical geometry of the structure so that they may be integrated into the low fidelity tools for system level optimization. Corrugated panels used for skins on morphing aircraft were a particular focus, because their anisotropic properties which are stiff in one direction to support the aerodynamic loads and flexible in the orthogonal direction to allow deformation. Other aspects considered were bio-inspired materials, honeycombs and fibre reinforced elastomers.
- Y Xia, MI Friswell & EI Saavedra Flores, Equivalent Models of Corrugated Panels. International Journal of Solids and Structures, 49(13), June 2012, 1453-1462.
- I Dayyani, S Ziaei-Rad & MI Friswell, The Mechanical Behavior of Composite Corrugated Core Coated with Elastomer for Morphing Skins. Journal of Composite Materials, 48(13), June 2014, 1623-1636.
- I Dayyani, MI Friswell, S Ziaei-Rad & EI Saavedra Flores, Equivalent Models of Composite Corrugated Cores with Elastomeric Coatings for Morphing Structures. Composite Structures, 104, October 2013, 281-292.
General Homogenization and Bio-inspiration
- EI Saavedra Flores, MI Friswell & Y Xia, Variable Stiffness Biological and Bio-inspired Materials. Journal of Intelligent Material Systems and Structures, 24(5), March 2013, 529-540.
- I Dayyani, MI Friswell & EI Saavedra Flores, A General Super Element for a Curved Beam. International Journal of Solids and Structures, 51(17), 15 August 2014, 2931-2939.
- EI Saavedra Flores & MI Friswell, Multi-scale Finite Element Models for a New Material Inspired by the Mechanics and Structure of Wood Cell-walls. Journal of the Mechanics and Physics of Solids, 60(7), July 2012, 1296-1309.
- MS Murugan, BKS Woods & MI Friswell, Hierarchical Modeling and Optimization of Camber Morphing Airfoil. Aerospace Science and Technology, 42, April-May 2015, 31-38.
- SM Murugan & MI Friswell, Morphing Wing Flexible Skins with Curved Fiber Composites. Composite Structures, 99, May 2013, 69-75.
- EI Saavedra Flores, FA Diaz De la O, MI Friswell & J Sienz, A Computational Multi-Scale Approach for the Stochastic Mechanical Response of Foam-Filled Honeycomb Cores. Composite Structures, 94(5), April 2012, 1861-1870.
- SM Murugan, EI Saavedra Flores, S Adhikari & MI Friswell, Optimal Design of Variable Fiber Spacing Composites for Morphing Aircraft Skins. Composite Structures, 94(5), April 2012, 1626-1633.
- EI Saavedra Flores, SM Murugan, MI Friswell & EA de Souza Neto, Reorientation of Fibres and Local Mechanisms of Deformation in a Wood-Inspired Composite. Journal of Multiscale Modeling, 4(1), March 2012, Article ID 1250003, 15 pages.
Skins are a key component that were modelled and analyzed extensively. Bistable structures were also considered for load alleviation and also for large geometry changes. A novel control technique was developed using the structural resonance to activate the snap through with low power requirements. Uncertainty analysis was also performed for composite structures, for example corrugated panels, to ensure their robust performance.
Actuation for Morphing
- BKS Woods & MI Friswell, Spiral Pulley Negative Stiffness Mechanism for Passive Energy Balancing. Journal of Intelligent Material Systems and Structures, 27(12), July 2016, 1673-1686.
- BKS Woods, MI Friswell & NM Wereley, Advanced Kinematics for Morphing Aircraft Actuation. AIAA Journal, 52(4), April 2014, 788-798.
- O Bilgen, MA Karami, DJ Inman & MI Friswell, Actuation Characterization of Cantilevered Unimorph Beams with Single Crystal Piezoelectric Materials. Smart Materials and Structures, 20(5), May 2011, paper 055024.
Actuation of Bistable Structures
- AF Arrieta, O Bilgen, MI Friswell & P Ermanni, Modelling and Configuration Control of Wing-shaped Bi-stable Piezoelectric Composites under Aerodynamic Loads. Aerospace Science and Technology, 29(1), August 2013, 453-461.
- O Bilgen, AF Arrieta, MI Friswell & P Hagedorn, Dynamic Control of a Bistable Wing under Aerodynamic Loading. Smart Materials and Structures, 22(2), February 2013, paper 025020.
- AF Arrieta, O Bilgen, MI Friswell & P Hagedorn, Dynamic Control for Morphing of Bi-stable Composites. Journal of Intelligent Material Systems and Structures, 24(3), February 2013, 266-273.
- AF Arrieta, O Bilgen, MI Friswell & P Hagedorn, Passive Load Alleviation Bi-stable Morphing Concept. AIP Advances, 2(3), September 2012, paper 032118.
- I Dayyani, AD Shaw, EI Saavedra Flores & MI Friswell, The Mechanics of Composite Corrugated Structures: A Review with Applications in Morphing Aircraft. Composite Structures, 133, December 2015, 358-380.
- Y Xia, O Bilgen & MI Friswell, The Effect of Corrugated Skins on Aerodynamic Performance. Journal of Intelligent Material Systems and Structures, 25(7), May 2014, 786-794.
- I Dayyani, H Haddad Khodaparast, BKS Woods & MI Friswell, The Design of a Coated Composite Corrugated Skin for the Camber Morphing Airfoil. Journal of Intelligent Material Systems and Structures, 26(13), September 2015, 1592-1608.
- AD Shaw, I Dayyani & MI Friswell, Optimisation of Composite Corrugated Skins for Buckling in Morphing Aircraft. Composite Structures, 119, January 2015, 227-237.