Jayanth N. Kudva

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

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 skin actuated by high-power ultrasonic motors using an eccentric motion. The trailing edge control surface fitted onto the wind tunnel model comprised 10 eccentric-driven segments connected together by a continuous outer skin and a flexible hinge pin at the trailing edge tip. This pinned configuration allowed the segments partial freedom to rotate about each other, but constrained any lateral motion thus giving a smooth trailing edge shape for nonuniform spanwise deflections. To control the 10 segments of the 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 tests to verify analysis, control system development, model integration, and results from the wind tunnel test.

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.

Qualitative assessment of smart skins and avionic/structures integration

Current military aircraft employ multiple single function antennas installed at different locations to provide communications, navigation and identification (CNI), electronic warfare and radar and weapon delivery in the .15 to 18 GHz frequency bands. The smart skins concept, wherein several antennas are integrated into one (or a few) multifunction apertures conformal to the outer geometry of the aircraft, promises considerable benefits. These include extended antenna coverage, efficient use of aircraft realestate, quick installation and replacement and structural weight savings. However, to realize these payoffs, several disparate technical and operational issues such as development of multifunction apertures, integration of the radiating elements and repackaging the electronics into load-bearing structure, antenna isolation and resource management, and tolerance to low velocity impact damage, need to be resolved. Potential payoffs and the technical challenges of smart skins implementation and avionics repackaging is discussed in quantized transitional states from black box avionics traditional packaging to structurally integrated avionics of the future. Qualitative assessments of related smart skin technologies and risk reduction approaches, which could transition the technology to current and future aircraft, are proposed, and preliminary cost estimates presented.

Shape memory alloy TiNi actuators for twist control of smart wing designs

On high performance military aircraft, small changes in both wing twist and wing camber have the potential to provide substantial payoffs in terms of additional lift and enhanced maneuverability. To achieve the required wing shape, actuators made of smart materials are currently being studied under an ARPA/WL contract for a subscale model of a fighter aircraft. The use of the shape memory alloy TiNi for wing twist actuation was investigated using shape memory effect (SME) torque tube actuator configurations. The actuator configurations were sized to fit inside a 16% scale model of an aircraft wing and the torques supplied to the wing were similarly calculated from full-scale requirements. The actuator systems were tested in a conventional laboratory setting. Design and calibration of the actuators for wing twist are discussed.

Smart Skin Conformal Load-bearing Antenna and Other Smart Structures Developments

Developmental research efforts are underway investigating the use of innovative materials and design methodologies to enhance aircraft performance. This research discipline is commonly referred to as smart structures and materials. In general terms, smart structures utilize conventional and smart materials to sense their operating environments, analyze the resulting information, and actuate the structure in response to the sensed input. Research in the smart structures arena may be further divided into three distinct components: smart skins, vibration suppression, and adaptive structures. All components share the common purpose of enhancing vehicle performance and/or eliminating structural dynamics problems associated with current and future aircraft. Under the smart skins specialty, the primary technology discussed is the embedment of radio frequency antenna elements within conformal load bearing structures such as aircraft wing and fuselage skins to improve avionics and structural performance while reducing airframe maintenance costs, weight, signature, and drag. The role of conformal load bearing antennas as a key facilitator for smart skins is presented hi some detail with projections for near term technology applications. The other key smart structures initiatives are also covered to complete the picture.

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.

Acoustic-emission sensing in an on-board smart structural health monitoring system for military aircraft

A smart structural health monitoring system (SHMS) requires various sensing technologies to detect and locate flaws, and assess their criticality to the structural integrity of the aircraft. To realize its full potential, a SHMS must be capable of remotely sensing flaw growth and location. Acoustic emission (AE) is one of the few sensing technologies that is capable of direct and remote sensing of flaw growth. Currently, there are two AE sensing techniques used for monitoring, detecting and locating flaw growth in structural components. In one technique, specific AE event parameters are captured by narrowband transducers and are studied to identify their source and location. The other technique studies the whole AE waves captured by wideband transducers and then detects and locates flaw growth based on waveform analysis and the wave propagation characteristics of the structure being monitored. This paper investigates both AE techniques, establishes their limitations, and defines the goals that need to be achieved in AE technology before it can successfully be implemented into a SHMS.

Smart structures concepts for aircraft structural health monitoring

Automated smart systems to monitor the structural health of military aircraft have the potential to reduce life cycle costs, improve turnaround times, and enhance survivability. However, before on-board structural health monitoring systems (SHMS) can be a reality, further advances in several technology areas, as well as careful integration of the component technologies, are required. This paper presents an assessment of the component technologies and discusses the requirements, architecture, technology integration, feasibility, and payoffs of SHMS for military aircraft.

Overview of the DARPA/AFRL/NASA Smart Wing Phase II program

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.

Smart wing wind tunnel test results

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 (Cm), increased rolling moment (Cl) 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 Langleys 16 ft Transonic Dynamic Tunnel. 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.