Active Flow Control Demonstrated on “Airborne Wind Tunnel”

A research team uses synthetic jets to manipulate the wake behind an external pod.

AFRL engineers, collaborating with aerospace manufacturers and other Air Force groups, recently demonstrated the first-ever airborne active flow control system when they manipulated the airflow behind an F-16 external pod. They significantly altered the turbulent wake using small, electrically controlled, piezoelectric synthetic jet (PESJ) actuators. This demonstration is just one part of AFRL’s multiphase Aeroelastic Load Control program aimed at reducing the weight, complexity, and signature of air vehicles through the introduction of active control technologies.

Posted in: Briefs, Mechanical Components, Aerodynamics

Coordination of Autonomous Unmanned Air Vehicles

Researchers are developing mathematical algorithms for autonomous unmanned air vehicle cooperative control.


Future autonomous unmanned air vehicles (UAV) will need to work in teams to share information and coordinate activities in much the same way as current manned air systems. Funded by AFRL, Professor Hugh Durrant-Whyte and his research staff (see Figure 1) at the Australian Research Council’s Center of Excellence for Autonomous Systems have been developing mathematical models and simulation studies to understand—and ultimately provide— this future UAV capability.

The team’s research focuses on coordination and cooperation for teams of autonomous UAVs engaged in information gathering and data fusion tasks, including cooperative tracking, ground picture compilation, area exploration, and target search. The underlying mathematical model for coordination and cooperation employs quantitative probabilistic and information-theoretic models of platform and sensor abilities. This information-theoretic approach builds on established principles for distributed data fusion in sensor networks, extending these ideas to problems in the distributed control of sensing resources. The researchers have made substantial progress towards formulating, solving, and demonstrating these methods for multi-UAV systems. In particular, they have developed distributed algorithms that enable UAV team-based search and exploration operations. These search and exploration algorithms can incorporate realistic constraints on platforms and sensors—a priori constraints from the environment and weak information from external sources. To date, Prof Durrant-Whyte’s research team has successfully demonstrated these algorithms on a flight simulator of midlevel fidelity (see Figure 2).

Recently, the team presented its findings to AFRL researchers at Wright- Patterson Air Force Base (AFB), Ohio, and Eglin AFB, Florida. Based on the promising results of this research effort, AFRL is funding two additional projects to further explore the mathematical aspects of the technology and facilitate real-world application through demonstrations. The first round of demonstrations will involve high-fidelity, hardware-in-the-loop simulations, culminating in a large-scale demonstration involving a UAV fleet operated by the University of Sydney (see Figure 3). AFRL’s two research projects will provide significant scientific and technical advancement in the cooperative control of autonomous systems.

The availability of autonomous UAV teams capable of complex cooperative behavior will enable warfighters to execute highly complex missions effectively and safely removed from harms way (i.e., remotely). In addition to providing these advantages, the UAV technology’s imaging and atmospheric sampling capabilities have the potential to support both homeland security emergency scenarios and real-time forest fire monitoring tasks.

Dr. Tae-Woo Park, of the Air Force Research Laboratory’s Air Force Office of Scientific Research, and Prof Hugh Durrant-Whyte, of the University of Sydney (Australian Research Council Federation Fellow), wrote this article. For more information, contact TECH CONNECT at (800) 203-6451 or place a request at http://www.afrl.af.mil/techconn/index.htm. Reference document OSR-H-05-06.

Posted in: Briefs, Information Sciences, Mathematical models, Simulation and modeling, Unmanned aerial vehicles

Surface-Emitting Laser Arrays Bring Light to the Top

Novel techniques for improving the efficiency and functionality of high-powered laser diodes

Laser diodes are an integral part of everyday life, incorporated into commonplace items as diverse in function as laser pointers, fiber-optic communications systems, and DVD players. Manufacturers make most laser diodes by layering specially doped semiconductor materials on a wafer. By slicing tiny chips from these wafers to attain two perfectly smooth, parallel edges, they create very thin (tens of microns) waveguides. These waveguides define a resonating cavity that causes stimulated light to combine in a way that embodies a “laser” and propagates its lasing action. Although this process represents a highly successful and wellengineered means for producing semiconductor lasers, the lasers do not produce an optimum beam. Beam emission occurs from the small rectangular opening at the end of the chip, a configuration that results in an elliptically distorted beam as well as the loss of output efficiency. In addition, the output aperture’s relatively small size can lead to destruction of the cleaved and polished end facet during the laser’s high-power operation. Laser diodes produced using this process are also susceptible to substantial fluctuations in output wavelength and beam quality as a function of temperature. Furthermore, since the chip emits beam output from an edge instead of its top or bottom surface, manufacturers experience difficulty both in packaging various diode configurations and in combining the output beams of multiple laser diodes.

Posted in: Briefs, Photonics, Fiber optics, Lasers, Fiber optics, Lasers


General-purpose imagery viewer supports a variety of visualization requirements for government and commercial applications.

Visualization of geospatially correct, remotely sensed data is a key element of many government and commercial applications. It enables a user to analyze and assess ground activities and other conditions of interest. Because remotely sensed data can include a diversity of data types reflecting many different data formats, users may experience difficulty visualizing and interpreting these varying data types and formats due to data structure complexity. In addition, important supplemental information often accompanies the data. This supplemental information—or metadata— may include pertinent information of significant value to the user with respect to where, when, and how data collection occurred. Whereas some applications require metadata to support geospatial analysis functions such as positioning and measurement, many others are unable to interpret such metadata and it may thus go unnoticed. Multiband data and motion imagery further compound the task of visualization with spectral components and complex video streams interlaced with other geospatial information.

Posted in: Briefs, Software, Data acquisition and handling, Imaging, Imaging and visualization, Data acquisition and handling, Imaging, Imaging and visualization

New Capability to Characterize the Mechanical Properties of Explosive Materials

Engineers develop a tool for testing materials at extremely high strain rates.

Improved targeting accuracy and the long-standing desire to minimize collateral damage are causing current and future munitions to become much smaller. As munitions size decreases, the explosive materials packed within bomb cases begin to carry a significant portion of the structural loads experienced by the warhead. In an ongoing program effort to determine the mechanical properties of explosives and other energetic materials, scientists at AFRL’s High Explosives Research and Development (HERD) facility (Eglin Air Force Base, Florida) acquired a miniaturized split Hopkinson pressure bar (MSHPB) (see Figure 1). Designed and built by Mr. Clive Siviour under the guidance of Drs. John Field, Bill Proud, and Stephen Walley (of the United Kingdom’s University of Cambridge, Physics and Chemistry of Solids Group), the MSHPB is capable of strain rates up to 105 s-1 in material samples. AFRL’s European Office of Aerospace Research and Development sponsored the project.

Posted in: Briefs, Materials, Materials properties, Hazardous materials

Ceramic Matrix Composites Research

Ceramic matrix composites research advances the development of high-temperature structures for aerospace applications.

AFRL scientists characterized and evaluated the high-temperature mechanical behavior of fiber-reinforced ceramic matrix composite (CMC) materials used in aerospace structural applications. Researchers examined four principal characteristics of a porous matrix composite that General Electric developed for the aerospace industry. Their evaluations resulted in an increased understanding of the materials and their potential for applications in military and commercial aerospace products.

Posted in: Briefs, Materials, Research and development, Ceramics, Composite materials

Characterizing Mechanical Properties at the Microscale

Scientists employ focused ion beam milling to prepare micron-size single-crystal test specimens and use a nanoindenter device to record stress-strain curves.

Scientists from AFRL, Pratt & Whitney Aircraft, and General Electric Aircraft Engines, working under the Defense Advanced Research Projects Agency’s Accelerated Insertion of Materials (AIM) program, have invented a new method for characterizing the single-crystal properties of aerospace alloys using micron-size test samples. The research team based the new characterization method on focused ion beam (FIB) microscopy and a commercially available nanoindentation-based test instrument. Further development of these methodologies, in conjunction with their continued integration with simulation methods devised under the AIM program, will enable engineers to consider local changes in material microstructure and their effect on properties in the design process. The integration of advanced mechanical property measurements, materials representation, and simulation methods will dramatically decrease the time required for new materials insertion and will transform microstructure into a design variable for engineered systems. These advancements will directly benefit combat systems and readiness.

A deformed single crystal of pure nickel after measurement of critical resolved shear stress under single-slip conditionsA primary challenge to the rapid insertion of new materials into the design cycle is the need to understand both the intrinsic properties of an engineering material at the microscopic level and the influence of defects on these properties at the macroscopic level. Historically, scientists have been unable to develop model parameters or validate continuum materials behavior models that are based upon discrete microstructural information. Continuum crystal plasticity models are at the frontier of techniques that incorporate direct microstructural information. However, a major deficiency of these models is the need to obtain required input information: the single-crystal mechanical properties of individual grains, or microconstituents. Acquiring this information is particularly difficult when such parameters must reflect the subtleties of material process history or the local influence of material defects.

Under the AIM program, AFRL researchers have sought to measure the single-crystal mechanical properties, such as the critical resolved shear stresses and strain hardening rates, of micro- and nanoscale samples extracted from relevantly processed structural alloys (see figure). Scientists are currently developing direct methods to automatically and rapidly characterize both the mechanical response of relevant microstructural elements and the stochastic nature of material property variation to establish the mechanical properties of a material’s representative volume elements (RVE).

It is essential for scientists building continuum models to quickly determine the mechanical properties of RVEs in order to quantify the inherent variability in material properties, the observed variability in experimental measurements, and the uncertainty in predicted properties. They can then establish “confidence metrics” for the data they incorporate into the designer’s knowledge base. Without such confidence, scientists can add new materials (or old materials in new applications) to the knowledge base only after extremely difficult and costly testing.

The new characterization method uses FIB milling to isolate and prepare single-crystal mechanical test specimens from individual grains, or precipitates, of a conventionally processed alloy. Scientists then move the prepared specimens to a conventional nanoindenter device outfitted with a flatpunch indentation tip. The nanoindenter imposes uniaxial compression on the microsamples and records highfidelity load-displacement measurements as the samples deform. With the development of this novel mechanical behavior test capability, researchers now envisage sampling the local mechanical effects of material microstructure and statistically incorporating these results in improved constitutive response surfaces, which could be used in simulations of critical component features.

Dr. Dennis M. Dimiduk, Dr. Michael D. Uchic, and Dr. Peter S. Meltzer (Anteon Corporation), of the Air Force Research Laboratory’s Materials and Manufacturing Directorate, wrote this article. For more information, contact TECH CONNECT at (800) 203-6451 or place a request at http://www.afrl.af.mil/techconn/index.htm. Reference document ML-H-04-10.

Posted in: Briefs, Materials

Switching Chassis Enables Ethernet Control of 3U Modules in LXI Environment

Designed to enable the use of PXI test modules in a LAN extensions for Instrumentation (LXI) environment, Pickering Interfaces’ (Woburn, MA) 60-100 and 60-101 chassis are fully compliant with Functional Class C of the LXI standard. They allow 3U PXI switching modules to be supported in a LXI-compliant environment. The 60- 100 is suitable for modules occupying 7 or fewer slots, and the 60-101 can support up to 13 slots.

Posted in: Products, Products, Electronics & Computers

A Software Development Process for Small-Scale Embedded Systems

Developing software for small-scale embedded applications is different from developing large-scale software applications. Large-scale applications use commercially available ‘one fits all’ software development solutions that are difficult to scale downward and usually miss the desired process goals. In many cases, developing a small-scale software application development process within an existing corporate environment is quicker, less expensive, and results in superior developer productivity and product quality.

Posted in: Articles, Articles, Electronics & Computers, Software, Embedded software, Embedded software, Product development

Choosing Among ZigBee RF Power Options for Your Wireless Application

While often associated with home automation, the new ZigBee wireless data standard is making fast inroads into industrial, military, and aerospace applications. By supplying highly reliable, wireless mesh networking at very low cost, ZigBee enables improvements to traditional sensing and monitoring applications, and enables new applications that would otherwise be impractical.

Posted in: Articles, Articles, Electronics & Computers, Power electronics, Wireless communication systems, Power electronics, Wireless communication systems