The addition of energy harvesting is investigated to determine the benefits of its integration into a small unmanned air
vehicle (UAV). Specifically, solar and piezoelectric energy harvesting techniques were selected and their basic functions
analyzed. The initial investigation involved using a fundamental law of thermodynamics, entropy generation, to analyze
the small UAV with and without energy harvesting. A notional mission was developed for the comparison that involved
the aircraft performing a reconnaissance mission. The analysis showed that the UAV with energy harvesting generated
less entropy. However, the UAV without energy harvesting outperformed the other UAV in total flight time at the target.
The analysis further looked at future energy harvesting technologies and their effect on the energy harvesting UAV to
conduct the mission. The results of the mission using the advanced solar technology showed that the effectiveness of the
energy harvesting vehicle would increase. Designs for integrating energy harvesting into the small UAV system were
also developed and tests were conducted to show how the energy harvesting designs would perform. It was demonstrated
that the addition of the solar and piezoelectric devices would supply usable power for charging batteries and sensors and
that it would be advantageous to implement them into a small UAV.
In this paper, the topology optimization methodology for the synthesis of distributed actuation system with specific applications to the morphing air vehicle is discussed. The main emphasis is placed on the topology optimization problem formulations and the development of computational modeling concepts. For demonstration purposes, the inplane morphing wing model is presented. The analysis model is developed to meet several important criteria: It must allow large rigid-body displacements, as well as variation in planform area, with minimum strain on structural members while retaining acceptable numerical stability for finite element analysis. Preliminary work has indicated that addressed modeling concept meets the criteria and may be suitable for the purpose. Topology optimization is performed on the ground structure based on this modeling concept with design variables that control the system configuration. In other words, states of each element in the model are design variables and they are to be determined through optimization process. In effect, the optimization process assigns morphing members as 'soft' elements, non-morphing load-bearing
members as 'stiff' elements, and non-existent members as 'voids.' In addition, the optimization process determines the location and relative force intensities of distributed actuators, which is represented computationally as equal and opposite nodal forces with soft axial stiffness. Several different optimization problem formulations are investigated to understand their potential benefits in solution quality, as well as meaningfulness of formulation itself. Sample in-plane morphing problems are solved to demonstrate the potential capability of the methodology introduced in this paper.
In this paper, the optimal location of a distributed network of actuators within a scissor wing mechanism is investigated. The analysis begins by developing a mechanical understanding of a single cell representation of the mechanism. This cell contains four linkages connected by pin joints, a single actuator, two springs to represent the bidirectional behavior of a flexible skin, and an external load. Equilibrium equations are developed using static analysis and the principle of virtual work equations. An objective function is developed to maximize the efficiency of the unit cell model. It is defined as useful work over input work. There are two constraints imposed on this problem. The first is placed on force transferred from the external source to the actuator. It should be less than the blocked actuator force. The other is to require the ratio of output displacement over input displacement, i.e., geometrical advantage (GA), of the cell to be larger than a prescribed value. Sequential quadratic programming is used to solve the optimization problem. This process suggests a systematic approach to identify an optimum location of an actuator and to avoid the selection of location by trial and error. Preliminary results show that optimum locations of an actuator can be selected out of feasible regions according to the requirements of the problem such as a higher GA, a higher efficiency, or a smaller transferred force from external force. Results include analysis of single and multiple cell wing structures and some experimental comparisons.
This investigation addresses basic characterization of a shape memory polymer (SMP) as a suitable structural material for morphing aircraft applications. Tests were performed for monotonic loading in high shear at constant temperature, well below, or just above the glass transition temperature. The SMP properties were time-and temperature-dependent. Recovery by the SMP to its original shape needed to be unfettered. Based on the testing SMPs appear to be an attractive and promising component in the solution for a skin material of a morphing aircraft. Their multiple state abilities allow them to easily change shape and, once cooled, resist large loads.
This paper represents a "work-in-progress" status report on shape determination and sensing methods for deforming structures utilizing embedded sensors. This work is part of a larger effort in morphing aircraft structures at the Air Force Research Laboratory. The two critical issues involved in the present work are the determination of the number and placement of embedded sensors, and algorithms for transforming the sensor data into displacements to define the shape of the structure. These issues are addressed in the context of a laboratory experiment, which demonstrate many of the challenges
inherent in the problem.
The research in this study develops an analysis technique for mechanized solid-state actuators. The methodology's strength stems from the fact that it can be applied to a single solid-state actuator or an actuator that is coupled to a compliant mechanism (mechanized). The technique couples the actuator to any compliant mechanism and it takes into account interactions between the mechanized actuator and its load. Thus the methodology can be applied to a myriad of loaded systems. The analysis technique is rooted in thermodynamics and thus can be expanded to a wide range of systems (piezoelectric, electrohydraulic, electrostrictive, magnetostrictive, etc.). The methodology uses energy transfer as a medium to develop analytical relationships between input parameters and output parameters. Results of the technique are consistent with existing energy-based techniques and experimental data.
Morphing as an independent variable is addressed. Potential missions to demonstrate the value of morphing are presented and discussed. The effects of morphing on vehicle kinematics is demonstrated for takeoff, landing, and turn rate. At the system level, the effects of variable lift-to-drag ratio and specific fuel consumption on vehicle weight are examined for cruising flight. An example mission is presented to demonstrate how morphing can be implemented in constraint and sizing analyses, which are at the core of the aircraft conceptual design process. A comparison of morphing and non-morphing aircraft weights is made. It is demonstrated in some cases morphing adds weight due to requiring a structure to complete two missions. The requirement for new structural concepts is briefly discussed.
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.
The recently completed DARPA/AFRL/NASA Smart Wing Program, performed by Northrop Grumman Corporation, addressed the development and demonstration of smart materials based concepts to improve the aerodynamic and aeroelastic performance of military aircraft. This paper present a final overview of the program.
A wind tunnel demonstration was conducted on a scale model of an unmanned combat air vehicle (UCAV). The model was configured with traditional hinged control surfaces and control surfaces manufactured with embedded shape memory alloys. Control surfaces constructed with SMA wires enable a smooth and continuous deformation in both the spanwise and cordwise directions. This continuous shape results in some unique aerodynamic effects. Additionally, the stiffness distribution of the model was selected to understand the aeroelastic behavior of a wing designed with these control surfaces. The wind tunnel experiments showed that the aerodynamic performance of a wing constructed with these control surfaces is significantly improved. However, care must be taken when aeroelastic effects are considered since the wing will show a more rapid reduction in the roll moment due to increased moment arm about the elastic axis. It is shown, experimentally, that this adverse effect is easily counteracted using leading edge control surfaces.
The DARPA/AFRL/NASA Smart Wing program, conducted by a team led by Northrop Grumman Corporation (NGC) under the DARPA Smart Materials and Structures initiative, addresses the development of smart technologies and demonstration of relevant concepts to improve the aerodynamic performance of military aircraft. This paper presents an overview of the smart wing program. The program is divided into two phases. Under Phase 1, (1995 - 1999) the NGC team developed adaptive wing structures with integrated actuation mechanisms to replace standard hinged control surfaces and provide variable, optimal aerodynamic shapes for a variety of flight regimes. Two half-span 16% scale wind tunnel models, representative of an advanced military aircraft wing, one with conventional control surfaces and the other with shape memory alloy (SMA) actuated smart control surfaces, were fabricated and tested in the NASA Langley Research Center (LaRC) Transonic Dynamics Tunnel (TDT) wind tunnel during two series of tests, conducted in May 1996 and June 1998, respectively. Details of the Phase 1 effort are documented in several papers. The on-going Phase 2 effort discussed here was started in January 1997 and includes several significant improvements over Phase 1: 1) a much larger, full-span model; 2) both leading edge (LE) and trailing edge (TE) smart control surfaces; 3) high-band width actuation systems; and 4) wind tunnel tests at transonic Mach numbers and high dynamic pressures (up to 300 psf.) representative of operational flight regimes. Phase 2 includes two wind tunnel tests, both at the NASA LaRC TDT - the first one was completed in March 2000 and the second (and final) test is scheduled for April 2001. The first test-demonstrated roll-effectiveness over a wide range of Mach numbers achieved using a combination of hingeless, smoothly contoured, SMA actuated, LE and TE control surfaces. The second test addresses the development and demonstration of high bandwidth actuation. An overview of the Phase 2 effort is presented here; detailed discussions of the wind tunnel testing, model design and fabrication, and actuation system development are given in companion papers.
The DARPA/AFRL/NASA Smart Wing program, conducted by a team led by Northrop Grumman Corp. under the DARPA Smart Materials and Structures initiative, addresses the development of smart technologies and demonstration of relevant concepts to improve the aerodynamic performance of military aircraft. This paper present an overview of the smart wing program.