Brian Sanders

Aerodynamic and Aeroelastic Characteristics of Wings with Conformal Control Surfaces for Morphing Aircraft

Investigations are conducted on lifting surfaces with conventional and conformal trailing-edge control surfaces. The Sohngen inversion formula is used with the thin-airfoil integral equation to determine the aerodynamic pressure for various control surface chord-to-airfoil chord ratios. Comparisons to a conventional control surface show increases in lift and pitching moment of the airfoil with a conformal control surface. Aerodynamic pressure distributions acting on a wing with control surfaces are determined with the vortex lattice technique. Predicted aerodynamic pressures and roll moments are compared to available wind-tunnel data and provide a more general understanding of theaerodynamicbehavior observed there. Roll performance of a rectangular wing is determined for various control surface chord-to-wing chord ratios. It is found that the maximum roll rate is greater for a wing with a conformal control surface, but has a lower reversal dynamic pressure than the wing with a conventional control surface. The aerodynamic and aeroelastic results obtained from this investigation provide some insight for wings designed with conformal control surfaces.

Overview of the DARPA/AFRL/NASA Smart Wing program

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.

Defense Advanced Research Projects Agency – Smart Materials and Structures Demonstration Program Overview

IN 1993 the Defense Advanced Research Projects Agency (DARPA) recognized that smart materials and structures technology provides a specific opportunity for many technological breakthroughs. A twophased, 8-year program was initiated to develop new, affordable smart materials and structures and to demonstrate the performance gains achievable in system applications. The first phase of the program was focused on developing generic smart materials technology. The second phase of the DARPA program was to demonstrate the use of smart materials to achieve aerodynamic and hydrodynamic flow control and to reduce noise and vibration in a variety of structures. A portion of this second phase effort was also directed toward improving the authority of actuation materials and their use in actuators to expand the potential applications of the technology. The Smart Materials and Structures Demonstration Program was initiated to achieve cultural goals as well as technological goals. In order to reconsider how we think of aeronautical structures, this program developed active structural systems where the actuation and structure were wholly integrated. Indeed, in several designs the actuators were the structures and vice versa. Traditional aerospace structures are of fixed geometry and structural control is typically achieved via articulation of substructures that can be pinned at some revolute point (ailerons), or through mechanisms that revolve and translate (e.g., slats and flaps). While such systems change aircraft characteristics, they have deficiencies with regard to aerodynamic performance, added weight, and observability. At the pinnacle of this work are demonstration projects conducted by multidisciplinary teams to show how Smart Materials and Structures technology can be implemented to enable new capabilities for helicopter and aircraft systems. Three projects that are particularly noteworthy are The Smart Rotor Project, The Smart Aircraft and Marine Propulsion System demONstration (SAMPSON) Project, and The Smart Wing Project. These efforts target the application of smart structures technology for aerospace systems. The latter two, the Smart Wing Project and the SAMPSON project, are particularly concerned with shape adaptive structures for aircraft. The DARPA, Defense Sciences Office funded these efforts under the Smart Materials Demonstration Program. Other groups, including the DLR (Germany) (Moner et al., 1998), the Air Force Research Laboratory, and NASA, are also working on such structures for aircraft. A comprehensive review of the most significant work in this area is provided by Sater et al. (2000). This paper highlights some background information and concepts fundamental to smart materials and structures development, a few of the significant accomplishments of each demonstration project in actuation capabilities enabled by smart materials and challenges involved with their integration into engineering systems, and potential game changers that may result from advancements in this technology.

Mechanical properties of shape memory polymers for morphing aircraft applications

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.

Vibration and Flutter Characteristics of a Folding Wing

Studies are presented that characterize the dynamic aeroelastic aspects of a morphing aircraft design concept. The notion of interest is a folding wing design resulting in large-scale wing area changes. A finite element approach is used to investigate the sensitivity of natural frequencies and flutter instabilities to the wing position (e.g., fold angle), actuator stiffness, and vehicle weight. Sensitivities in these areas drive design requirements and raise flight envelope awareness issues. The study is presented in two parts as a comparison between two models of varying complexity. A simple folding wing model, based on the Goland wing, is analyzed and results are compared with a built-up structural model of the proposed full scale morphing vehicle.

Aerodynamic Performance of the Smart Wing Control Effectors

This paper presents and discusses the wind tunnel results obtained during Phase 1 and Phase 2 of the Smart Wing program. A series of four tests was conducted, two in each phase. The purpose of the tests was to evaluate the performance of smart material based control effectors in representative aerodynamic environments. In Phase 1, wing twist using a Shape Memory Alloy (SMA) torque tube and smoothly contoured trailing edge surfaces enabled by SMA wires were evaluated on a semi-span, 16% scale model of a typical fighter wing. The focus of Phase 2 was to address the design and demonstration of a high-frequency, large-deflection, and smoothly contoured trailing edge control surface capable of a spanwise variation in deflection. The actuation system for this control surface was based on piezoelectric (PZT) ultrasonic motors. A smoothly contoured leading edge control surface was also built and tested using SMA wires. These designs were evaluated on a 30%, full-span model of a representative Unmanned Combat Air Vehicle (UCAV). In each wind tunnel entry comparisons were made to the performance of conventional control surfaces. Successful results included: improved aileron effectiveness at high dynamic pressures; demonstrated improvements in lateral and longitudinal control effectiveness with smoothly contoured control surfaces over conventional hinged control surfaces; continuous spanwise shape control; and, large deflections at rates over 80°/s, which is well within the desired deflection aileron rates for control of fighter aircraft.

Topology Optimization Approach for the Determination of the Multiple-Configuration Morphing Wing Structure

The paper introduces an innovative topology optimization approach for determining the distribution of structural properties and actuators to design amorphing wing that is capable of achievingmultiple target shapes. The previous investigation by the authors demonstrated, using various problem formulations and a novel modeling concept, the fundamental topology synthesis of a simple two-configurationmorphingwing structure.Theprimary objective of the present investigation is therefore to introduce improvements and extensions to the previous concepts and problem formulations to those capable of accommodating the multiple-configuration definitions. The investigation includes the formulation of appropriate topology optimization problems and the development of effective modeling concepts. In addition, principal issues on the external load dependency and the reversibility of a design, as well as the appropriate selection of a reference configuration, are addressed in the investigation. The methodology to control actuator distributions and concentrations is also discussed. Finally, an examplemultiple-configuration problem that portrays the generic surveillance mission is solved to demonstrate the potential capabilities of the approach.

Large-Area Aerodynamic Control for High-Altitude Long- Endurance Sensor Platforms

The use of large-area aerodynamic control schemes to enable high-altitude long-endurance sensor platforms is investigated. The focus is on a vehicle with a joined-wing design. The vehicle has two performance shortcomings that are considered typical of the broader class of high-altitude long-endurance vehicles. The first is minimum roll rate at landing due to the large amount of roll damping associated with these configurations. It is shown that multiple distributed control surfaces can help meet the roll rate requirements. The second is sensitivity of takeoff gross weight to maximum lift-to-drag ratio. Notional mission requirements drive the fuel fraction to high levels and small changes in lift-to-drag ratio can enable large changes in the vehicle weight through reduced fuel requirements. It is shown that the same technology used to satisfy the roll requirement can also be used to actively control the twist and camber during cruise and can have a moderate impact on the vehicle weight or endurance.

Optimal actuator location within a morphing wing scissor mechanism configuration

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.

DARPA/AFRL/NASA Smart Wing program: final overview

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.