Stealth aircraft

Given titaniums lightness, strength, and resistance to corrosion and high temperatures, its most common use is in ahoys with other metals for constructing aircraft, jet engines, and missiles. Its alloys also make exceUent armor plates for tanks and warships. It is the major metal used for constructing the stealth aircraft that are difficult to detect by radar. 

The word stealth comes for ancient roots meaning to steal. There are a number of stealth aircraft in operation today with others coming on line. To be stealthy, a plane should ... 

The most common mode of aircraft detection is radar. Essentially, radar is the detection of radio waves that have been thrown out and which bounce off objects returning to the site of origin. Today s radar, if properly used, can help identify the location, speed, and identity of the aircraft. The radar cross-section (RCS) of an aircraft is how much echo the plane sends from radar. Birds have an RCS of about 0.01 m. The Stealth Bomber has an RCS of 0.75 m. The Stealth Bomber and many stealth aircraft gain their stealth character from both the shape of the aircraft and the presence of radar absorbing material (RAM), which is made to absorb and eliminate radio waves rather than reflect them. Most of the RAM materials are polymeric. 

Stealth aircraft are often painted a medium gray or bluish gray that matches the sky so that it does not stand out. Coatings are composed of RAM that penetrates cracks reducing the number of minor repairs and use of special tape for repair. Every screw, panel, seam, and gap is covered with a special tape or the RAM coating adding to the bomber s stealthiness. 

Epoxy/cyanate ester thermoset blend-based composites have low dielectric constant desirable for advanced radomes, microwave anteimas, and stealth aircraft composite applications. Other applications include its use in copper clad laminates, semiconductor devices, and fire-resistant aircraft structural composites. 

In 2003, the United States initiated the Future Combat Systems (PCS) program, which is the largest and most ambitious planned acquisition program in the US Army s history. This PCS system covers almost every field application, as shown in Pigure 16.11, and every field is based on the use of an advanced energy storage system, so far mostly lithium-ion batteries. These applications include satellites, drones, stealth aircraft, UAVs, warships, aircraft carriers, AUVs, and integrated battle systems for individual soldiers. 

A major contribution from chemistry and chemical engineering has been the development of materials with important military applications. Chemists and chemical engineers, working with experts from areas such as electronics, materials science, and physics, have contributed to such developments as new explosives and propellants, reactive armor (a complex material with an explosive layer that can reduce the penetration of an incoming projectile), and stealth materials that reduce the detectability of aircraft by radar. 

Composite materials have been acclaimed as the Materials of the Future. A key question is whether composite materials will always remain the materials of the future or if the future is here. Advanced polymer composites, once destined for stealth military aircraft or aerospace uses, are beginning to be used in down-to-earth structures, such as bridges, buildings, and highways. However, there are still considerable impediments to wider use, and composite manufacturers need to make great strides in the development and manufacturing of composite materials. 

The destabilization (mixing) of a jet flow is desirable in many applications, including combustion, noise suppression at jet engine exhaust, infrared signature reduction of engine exhaust for platform stealth, and employment of a lighter and cheaper material for the lift flap such as that used in C-17 aircraft. 

Nevertheless, several general papers have been published on stealth technology applied to aircraft such as LOCKHEED F 117 [5,6] or others [7,8,9]. The description of radar absorbing materials is restricted to iron or ferrite loaded paints or elastomers except the case of retinyl Schiff base salts [10,11]. This molecule attracted interest of many scientists in 1987. In fact this material which is a charge transfer salt derived from the A vitamin, never exhibited high-frequency dielectric constant due to its intrinsic conductivity, despite its beautiful orange colour Moreover, reference books as the one of Knott el al. [12] do not mention the use of conductive polymers for this purpose. 

Many of the materials, processes and manufacturing methods discussed earlier in the chapter have been implemented in their construction. Another interesting relatively new field of development in the military aircraft sphere is that of stealth , a concept that requires the designer to achieve the smallest possible radar cross-section to reduce the chances of early detection by defending radar sets. The essential compound curvature of the airframe with constant change of radius is much easier to form in... 

Other fibers and polymers have also been used, and the trend is toward increased utilization of composites in automobiles and aircraft. For example, a composite of graphite fibers in a polymer matrix is used in the construction of the F-117 Stealth fighter and other military aircraft. Graphite-polymer composites are used in a number of sporting goods such as golf club shafts, tennis racquets, fishing rods, and skis. The F-16 military aircraft was the first... 

Composite materials have been used extensively in the military aircraft B-2 stealth bomber [12]. Most of this aircraft s body is made from composite materials designed to absorb radio waves. Currently composites are being used in aircraft and boat propellers, helicopter rotors, and in wind turbines. They are also replacing the use of finished metals in materials applications for missiles, spacecraft, automobile parts, golf clubs, and bicycles. 

FIGURE 2 Advanced combat aircraft must retain high aeroperformance while emphasizing affordability and stealth. Source 2002 by Lockheed Martin. Published with permission. 

The B2 Spirit stealth bomber, a U.S. military aircraft representing sophisticated applied physics, has a unit cost of more than US 1.15 billion (as of 2003). 

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