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

Shape morphing of aircraft wing: Status and challenges

The recently completed DARPA/AFRL/NASA Smart Wing program, performed by a team led by Northrop Grumman Corporation (NGC), addressed the development and demonstration of smart materials based concep...

Overview of the DARPA Smart Wing Project

A state-of-the-art review is presented regarding the research and development of in situ fibre optic damage detection and assessment systems (FODDAS) embedded in fibre-reinforced composite structures. Representative individual fibre optic strain sensors and distributed sensor networks are briefly described. A major emphasis is placed on their capabilities for detecting damage, determining damage location and assessing the nature of damage, arising primarily from specific events such as impacts or quasi-static stress overloads. The main features of such systems as custom-built and structure-specific units with minimal human involvement are highlighted. Issues that could affect the validity of the performance of such strain sensors are discussed. Fracture and non-fracture of fibre optic sensors are identified as two fundamentally different approaches for damage detection and their primary features are discussed in relation to location determination and evaluation of the nature of damage. The major advantages and limitations of each approach are discussed. Directions and areas of potential future research in the development of related FODDAS are highlighted.

http://iopscience.iop.org/article/10.1088/0964-1726/11/6/314/pdf

Damage detection and assessment in fibre-reinforced composite structures with embedded fibre optic sensors-review

With increasing size of wind turbines, new approaches to load control are required to reduce the stresses in blades. Experimental and numerical studies in the fields of helicopter and wind turbine blade research have shown the potential of shape morphing in reducing blade loads. However, because of the large size of modern wind turbine blades, more similarities can be found with wing morphing research than with helicopter blades. Morphing technologies are currently receiving significant interest from the wind turbine community because of their potential high aerodynamic efficiency, simple construction and low weight. However, for actuator forces to be kept low, a compliant structure is needed. This is in apparent contradiction to the requirement for the blade to be load carrying and stiff. This highlights the key challenge for morphing structures in replacing the stiff and strong design of current blades with more compliant structures. Although not comprehensive, this review gives a concise list of the most relevant concepts for morphing structures and materials that achieve compliant shape adaptation for wind turbine blades.

Review of morphing concepts and materials for wind turbine blade applications

The DARPA/AFRL/NASA Smart Wing program, led by Northrop Grumman Corporation (NGC) under the DARPA Smart Materials and Structures initiative, addressed the development of smart technologies and demonstration of relevant concepts to improve the aerodynamic performance of military aircraft. In Phase 2, Test 2 of the program, the main objective was to demonstrate high-rate actuation of hingeless, spanwise, and chordwise deformable control surfaces using smart materials-based actuators on a 30% scale, full span wind tunnel model of a proposed NGC uninhabited combat air vehicle (UCAV). A minimum actuation rate of 25° flap deflection in 0.33 s, producing a slew rate of 75°/s, was desired. This slew rate is representative of many operational military aircrafts with hinged control surfaces. Numerous trade studies were performed on a variety of smart materials and flexible structure configurations before arriving at the final trailing edge structure design that consisted of a flexcore center and elastomeric outer s...

Development of High-rate, Adaptive Trailing Edge Control Surface for the Smart Wing Phase 2 Wind Tunnel Model:

Northrop Grumman Corporation built and twice tested a 30 percent scale wind tunnel model of a proposed uninhabited combat air vehicle under the DARPA/AFRL Smart Materials and Structures Development - Smart Wing Phase 2 program to demonstrate the applicability of smart control surfaces on advanced aircraft configurations. The model constructed was a full span, sting mounted model with smart leading and trailing edge control surfaces on the right wing and conventional, hinged trailing edge control surfaces on the left wing. Among the performance benefits that were quantified were increased pitching moment, increased rolling moment and improved pressure distribution of the smart wing over the conventional wing. This paper present an overview of the result from the wind tunnel test performed at NASA Langley Research Center's Transonic Dynamic Tunnel in March 2000 and May 2001. Successful results included: (1) improved aileron effectiveness at high dynamic pressures, (2) demonstrated improvements in lateral and longitudinal effectiveness with smooth contoured smart trailing edge over conventional hinged control surfaces, (3) chordwise and spanwise shape control of the smart trailing edge control surface, and (4) smart trailing edge control surface deflection rates over 80 deg/sec.

DARPA/AFRL Smart Wing Phase 2 wind tunnel test results

The main goal of the Smart Wing Phase 2 Test 2 was to demonstrate high-rate actuation of hingeless, spanwise deflection variable control surfaces using smart material- based actuators. Requirement goals of 25-degree flap deflection in 0.33 sec, producing a sweep rate of 75 deg/sec, were desired. This sweep rate is similar to those specified for many of the existing military platforms with hinged control surfaces. Numerous studies were performed on many different smart material and flexible structure configurations before arriving at the final design which used an a flexcore-elastomeric skin trailing edge structure with eccentuation using high power ultrasonic motors. The final trailing edge control surface was made up of 10 eccentuator-driven segments connected together by a continuous outer skin and a flexible hinge pin at the trailing edge tip. This pin allowed the segments partial freedom to rotate about each other, but constrained any lateral motion thus giving a smooth trailing edge shape for non-uniform spanwise deflections. To control the ten segments of trailing edge, a VME-based control system with high speed, simultaneously sampled A/D and D/A boards and a dedicated DSP board was developed. This paper describes the analysis and design of the flex structure, ultrasonic motor selection and performance, element and coupon test to verify analysis, instrumentation to measure deflection, and control system development and integration that led to a highly successful test.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Development, control, and test results of high-rate hingeless trailing edge-control surface for the Smart Wing Phase 2 wind tunnel model

The use of smart materials technologies can provide unique capabilities in improving aircraft aerodynamic performance. Northrop Grumman built and tested a 16% scale semi-span wind tunnel model of the F/A -18 E/F for the on-going DARPA/WL Smart Materials and Structures - Smart Wing Program. Aerodynamic performance gains to be validated included increase in the lift to drag ratio, increased pitching moment (C m ), increased rolling moment (C l ) and improved pressure distribution These performance gains were obtained using hingeless, contoured trailing edge control surfaces with embedded shape memory alloy (SMA) wires and spanwise wing twist via a SMA torque tube and are compared to a conventional wind tunnel model with hinged control surfaces. This paper presents an overview of the results from the first wind tunnel test performed at the NASA Langley's 16ft Transonic Dynamic Tunnel (TDT). Among the benefits demonstrated are 8-12% increase in rolling moment due to wing twist, a 10-15% increase in rolling moment due to contoured aileron, and approximately 8% increase in lift due to contoured flap, and improved pressure distribution due to trailing edge control surface contouring.

Smart wing wind tunnel test results

To optimize military fleet readiness, life cycle tracking of aircraft is required under the Air Force Aircraft Structural Integrity Program. Improvements in aircraft inspection and maintenance procedures are essential in today's climate of increasingly complex aircraft and decreasing defense outlays, forcing life extension programs for current aircraft. Automated structural health monitoring incorporating remote damage detection, load/environment tracking, and structural integrity assessment could provide significant cost savings over the life of an airframe. This paper presents the design requirements for development of an aircraft structural health monitoring system (SHMS). Design of a SHMS requires careful analysis of structural geometry, operational environment, expected damage modes, etc., to determine sensor categories and locations. Additionally, the task of integrating data collection, processing, and storage hardware into the airframe must be addressed. Sensors and sensing technologies are discussed along with specific requirements for monitoring system hardware and software. Anticipated life cycle savings versus implementation costs are also presented for the ideal SHMS.

Mark N. West

Papers

Development of High-rate, Adaptive Trailing Edge Control Surface for the Smart Wing Phase 2 Wind Tunnel Model:

DARPA/AFRL Smart Wing Phase 2 wind tunnel test results

Development, control, and test results of high-rate hingeless trailing edge-control surface for the Smart Wing Phase 2 wind tunnel model

Smart wing wind tunnel test results

Design requirements and system payoffs for an on-board structural health monitoring system (SHMS)