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

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

Soft robotics and its related technologies enable robot abilities in several robotics domains including, but not exclusively related to, manipulation, manufacturing, human–robot interaction and locomotion. Although field applications have emerged for soft manipulation and human–robot interaction, mobile soft robots appear to remain in the research stage, involving the somehow conflictual goals of having a deformable body and exerting forces on the environment to achieve locomotion. This paper aims to provide a reference guide for researchers approaching mobile soft robotics, to describe the underlying principles of soft robot locomotion with its pros and cons, and to envisage applications and further developments for mobile soft robotics.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsif.2017.0101

Fundamentals of soft robot locomotion.

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:

A key objective of the Smart Wing Phase 2, Test 2 is to demonstrate high-rate actuation of hingeless control surfaces using smart material-based actuators. Actuation rates resulting in a minimum of 20 degree(s) flap deflection in 0.33 sec, producing a sweep rate of at least 60 degree(s)/sec, are desired. This sweep rate is similar to those specified for many of the existing military platforms with hinged control surfaces. The ability to deploy control surfaces without discrete hingeline would, however, enhance platform mission by reducing radar cross section and improving aerodynamic performance. Studies on numerous actuation concepts and flexible structures were executed during the early and mid phase of the program in an effort to satisfy these goals. In the first study, several actuation concepts with different transducers were modeled and analyzed. These concepts included distributed piezoelectric stack actuators with and without hydraulic amplifiers and pumps, antagonistic tendon actuation, and eccentuation. The transducers selected for the trade studies included piezoelectric ultrasonic motors, actively cooled SMA, ferromagnetic SMA, and stacks made from piezoelectric ceramic wafer, piezoelectric single crystal wafer, irradiated PVDF-TrFE film, and dielectric elastomer film. Although many of the technologies are not fully mature, they provide a glimpse of what improvements could be possible with their successful development. The studies showed that distributed polymer stacks provided the most elegant solution, but eccentuation was deemed the most realistic and lowest risk approach to attaining the program goals. A common issue to all the concepts was the structural stiffness that the actuators worked against. This was resolved in the second study by developing a flexcore- elastomeric skin trailing edge structure with eccentuation using high power ultrasonic motors. This paper describes the two studies and the final concept in detail.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Development of high-rate large-deflection hingeless trailing-edge control surface for the Smart Wing wind tunnel model

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

Shape estimation of deforming structures

Based on the current operational and sustainment trends in the United States Air Force (USAF), modern airframes with high composite content in primary structures will likely undergo a service life extension program (SLEP) in the future. However, unlike for metallic airframes, the USAF currently has no experience in SLEP of composites, with few enabling technical tools. One such tool is a lifing method for assessing fatigue life used and remaining for bolted joints. Virtually all of the composite airframes currently in service in USAF are assembled with fasteners. Structural integrity requirements dictate that these joints remain functional—i.e., capable of transferring load–over the design service life. One approach to meeting this requirement is to limit the hole elongation to a maximum value—e.g., 4%-relative to the nominal hole diameter. The certification process for such joints must demonstrate that detrimental hole wear does not occur during the design service life. However, if the aircraft mission changes or service life must be increased or both, the USAF must assure that these joints will remain structurally functional. In order to recertify the composite joints for use beyond the original design service life without resorting to extensive testing, an analytical method for predicting fastener hole elongation is necessary. This paper details the development and initial verification of an engineering approach for predicting bolt hole elongation that was performed under “Assess Technology for Performing a Structural Life Extension Program for Advanced Composite Airframe Structures” program funded by the Air Force Research Laboratory (AFRL). A total of 63 bearing specimens were excised from several 36-ply, 0.187 inch thick, [44/44/11] laminates made from IM7/9773 unidirectional tape. These specimens were tested in a double lap shear configuration with 1⁄4-inch high-strength (220 ksi Ftu) stainless steel bolts. Twenty two (22) constant amplitude (CA) bearing fatigue tests were conducted at a frequency of 2.0 Hz with a stress ratio of R = 1 at six peak stress levels (Pmax), ranging from 63 ksi to 132 ksi. Percent hole elongation vs. cyles (%e-N) curves and normalized local residual stiffness vs hole elongation (k/ko-%e) per Pmax were extracted from these CA fatigue tests and used to develop a lifing method for this composite bolted joint design. The proposed lifing method estimates the cycle-by-cycle hole elongation by incrementally moving along the appropriate CA %e-N curve from a damageequivalent initial elongation state determined from residual joint stiffness data, k/ko-%e. Nineteen (19) specimens were tested under various CA block and spectrum fatigue loading to verify the lifing method. Comparison of predictions and test data showed sufficient performance by the proposed enigeering lifing approach relative to trend and consistency.

Donny P. Wang

Papers

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

Development of high-rate large-deflection hingeless trailing-edge control surface for the Smart Wing wind tunnel model

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

Shape estimation of deforming structures

A Method for Predicting Fastener Hole Elongation in Composite Joints due to Cyclic Loading