Guiding lights
Efficient evacuation of passengers from an airliner in an emergency and in low- or zero-light conditions is an integral part of flight safety. One of the basic elements of achieving that safety is to ensure that passengers can find the emergency exits. Floorpaths using unpowered photoluminescent (PL) technology can help achieve that end, and now Boeing is to install such a system—produced by a small UK company—in its future B737 and B757 aircraft.
 After exposure to cabin lighting for only 30-45 min, the SafTGlo system is approved to perform for 12 h in total darkness. |
STG Aerospace Ltd, which employs only 19 people, has won a six-year contract from Boeing worth some $6 million. Its SafTGlo PL systems can indicate evacuation routes even after total aircraft power failure. Other manufacturers and airlines are already using SafTGlo systems, but Boeing's commitment is a major advance for the company's patented technology. The PL material "glows brightly and has greater longevity than electric-powered alternatives," according to STG. The FAA and UK Civil Aviation Authority (CAA) have both approved it as well as more than 30 other international regulatory bodies. SafTGlo has been installed in some 1500 aircraft, and Embraer has selected it for its ERJ-170 and -190 regional jets.
STG's Technical Director, Peter Bodle, says he first considered the potential for a PL system (the basic technology has been long established) in the 1980s, following an air accident in which exit indicators failed to function in a fire. During the 1990s, the PL system was researched and developed until it reached required international standards, and STG found that only specially activated strontium aluminate was appropriate for aircraft cabin use. Stable, non-radioactive, and non-toxic, it had the required length "after-glow" characteristics. STG worked with PL pigment manufacturers to combine new methods of processing. The resultant material has the ability to emit an "intense glow far in excess of the perceptive limits of the human eye." The material can totally replace conventional electrically lit floor-path emergency lighting and requires only occasional cleaning.
PL technology uses the natural properties of some materials to emit a glow after absorbing energy from a light source. The company explains that after exposure to cabin lighting for 30-45 minutes, the SafTGlo system is approved to perform for 12 h in total darkness. The luminescence occurs when electrons in the atoms of the absorbing material are excited by light energy and "jump" from the inner, lower-energy orbits to outer, higher-energy orbits. When the excitation light is extinguished, each electron falls back to its original state and gives up its stored energy as a photon of light.
According to STG, its system meets all requirements for use in PL technology in aircraft safety applications. There is no limit to the number of times it can be charged and it "never loses" its PL qualities, stated STG. The PL strip, which is of low weight and requires virtually no maintenance except cleaning, can be incorporated into four different mounting systems: three floorpath track systems that are installed in carpeted areas on aircraft, and a specially designed non-slip galley strip.
- Stuart Birch
Litening up
The Zeiss Optronik Litening combined targeting and navigation pod is to be integrated into the multi-role Saab-BAE Systems' Gripen as an option. Litening has forward-looking infrared (FLIR) and laser designation capabilities. The FLIR image can overlay the real world in Gripen's wide-angle diffractive optics head-up display (HUD). It will be fitted to the side fuselage pylon and will not reduce Gripen's ability to carry a heavy and varied load of air-to-air and air-to-surface missiles, said Saab. Litening combines a third generation focal-plane array FLIR with a CCD camera for full day and night use. Its laser designator and rangefinder also have spot detector/tracker/marker functions. The system will enhance Gripen's low-level night navigation. Litening is of modular construction.
- Stuart Birch
Ames Lab studies processing methods
Most materials scientists follow tried-and-true methods for melting, cooling, and shaping various materials into usable forms, even though the science behind those methods is not always fully understood. An effort is underway at the Materials Preparation Center (MPC), part of the U.S. Department of Energy's (DOE) Ames Laboratory, to delve more deeply into the mysteries of processing science - the methods by which metals, alloys, polymers, and ceramics are synthesized to give them specific properties. Ames Lab scientists hope to better understand existing processing methods and develop techniques for making advanced materials for future technologies.
A new program called the Process Science Initiative (PSI) offers a limited pool of competitive funding for two types of materials-processing projects: those that lead to an improved fundamental understanding of existing processing techniques, and those that explore new techniques for producing novel materials. The DOE provides funds for the PSI program; MPC and Ames Lab provide the research facilities. The MPC is a designated DOE national user facility that specializes in preparing small samples of high-purity, novel materials that are not available from commercial sources.
It is critical that scientists understand what happens to a material when it goes from a liquid to a solid state because most metals and alloys are made of tiny crystals. The way in which the liquid crystallizes to form the microstructure of the solid determines the material's properties, such as its strength and formability. Subsequent secondary processing, such as rolling or extruding, also affects a material's properties.
"In a lot of the recent research, we've focused heavily on the properties of materials without really understanding how we arrived at, or control, the microstructure," said Brian Gleeson, Assistant Professor of Materials Science and Engineering at Iowa State University and PSI Program Manager. "Materials scientists see the need for research that will give them this type of information."
Larry Jones, Director of the MPC, said determining how to synthesize metals and alloys is a difficult task. "The materials we're dealing with today often have high melting points, or they may easily pick up impurities from the crucibles we melt them in," he said. "And they may need to be cooled in a very regimented way to produce the desired microstructure."
With most complex materials, scientists have a limited understanding of what happens to the metal or alloy while it's being processed. "You have to know the conditions—such as the temperatures, forces, and amount of deformation—affecting that material during processing," Jones said. "Accurately measuring those parameters is not easy when you're dealing with temperatures of 1800°C (3272°F), which is an aggressive thermal environment."
The PSI program is the only known initiative to focus specifically on improving the science of materials processing, according to Gleeson. In fiscal year 2000, four projects received $141,000 in PSI funds. The DOE authorized an increase of the PSI budget to $250,000 for the current fiscal year, which began October 1. Four projects have already been selected to share approximately $175,000 of those funds, with the remaining $75,000 to be allocated later in the year.
Among the projects receiving PSI funds is one in which Ames Lab scientists are studying the properties of liquid/solid interfaces. "In alloy systems, there's a range of solidification where the liquid and solid phases of the material coexist," Gleeson said. "It's the coexistence of the solid and the liquid that really sets the stage for the final product."
The scientists built a rig that enables them to reach and maintain the liquid/solid coexistence, then measure the properties of the interface between the two phases. "This is very fundamental knowledge that could be applicable to a range of other alloy systems," Gleeson said.
Another project that received funding for the current year involves synthesizing and characterizing polymer gels that respond to pH or temperature changes. The goal is to develop polymer gels that would either swell or contract in response to specific pH or temperature changes. "This is a formidable materials-synthesis challenge, but success would be of both fundamental and practical significance."
- Jean L. Broge
