18-01-2013, 10:33 AM
Stealth Technology
Stealth Technology.doc (Size: 173.5 KB / Downloads: 44)
ABSTRACT
Stealth is the technique of making a plane (or any other object) less visible to the enemy by reducing its radar and IR (infra red, heat) visibility. Reducing the IR image of a plane can be accomplished by directing the hot exhaust gasses to the top of the plane and mix them with cold air (the B-2 uses this technique). Reducing radar visibility can be accompli^ed by deflecting the radar waves in such a direction that they don't go back to the emitting radar (F-117 uses faceting, the B-2 uses continues curving) or making use of less radar reflecting materials (composite material, plastic) and/or radar absorbing coatings. A study of radar absorbing materials is also made. The seminar also deals with plasma stealth technology
INTRODUCTION
Stealth is the technique of making a plane (or any other object) less visible to the enemy by reducing its radar and IR (infra red, heat) visibility. Reducing the IR image of a plane can be accomplished by directing the hot exhaust gasses to the top of the plane and mix them with cold air (the B-2 uses this technique). Reducing radar visibility can be accompliced by deflecting the radar waves in such a direction that they don't go back to the emitting radar (F-117 uses faceting, the B-2 uses continues curving) or making use of less radar reflecting materials (composite material, plastic) and/or radar absorbing coatings (e.g. B-2). The active substance in these coatings are mostly metal ions. Because of this most of the radar absorbing coatings aren't very water-resistant.
Stealth technology, designs and materials engineered for the military purpose of avoiding detection by radar or any other electronic system. Stealth, or anti detection, technology is applied to vehicles (e.g., tanks), missiles, ships, and aircraft with the goal of making the object more difficult to detect at closer and closer ranges. Since radar is the most difficult form of detection to elude, avoidance is generally accomplished by reducing the radar cross section (RCS) of the object to within the level of background noise; for example, the reported goal of U.S. military designers is to make a fighter plane with an RCS the size of a bird. The RCS is the area of an imaginary perfect reflector that would reflect the same amount of energy back to the receiving radar antenna, as does the actual target, which may be much larger or even smaller than the RCS. A pickup truck, for example, with its flat surfaces and sharp edges has an RCS of approximately 200 sq m, but a smooth-edged fighter jet has an RCS of only 2 to 4 sq m. The RCS of any given object, however, differs at various angles and radar frequencies. Much about stealth technology remains classified, but among the anti detection techniques used in the U.S. Air Force F-117 Stealth fighter plane (which probably has an RCS of 1 sq m or less) are a low profile with no flat surfaces to reflect radar directly back.
COMPONENT DESIGN
When the basic aircraft signature is reduced to a very low level, detail design becomes very important. Access panel and door edges, for example, have the potential to be major contributors to radar cross-section unless measures are taken to suppress them. Based on the discussion of simple flat plates, it is clear that it is generally unsatisfactory to have a door edge at right angles to the direction of flight.
REDUCING IR VISIBILITY
There is two significant sources of infrared radiation from air breathing propulsion systems: hot parts and jet wakes. The fundamental variables available for reducing radiation are temperature and emissivity, and the basic tool available is line of sight masking. Recently some interesting progress has been made in directed energy, particularly for multiple bounce situations, but that subject will not be discussed further here. Emissivity can be a double-edged sword, particularly inside a duct. While a low emissivity surface will reduce the emitted energy, it will also enhance reflected energy that may be coming from a hotter internal region. Thus, a careful optimization must be made to determine the preferred emissivity pattern inside a jet engine exhaust pipe. This pattern must be played against the frequency range available to detectors, which typically covers a band from one to 12 microns. The short wavelengths are particularly effective at high temperatures, while the long wavelengths are most effective at typical ambient atmospheric temperatures. The required emissivity pattern as a function of frequency and spatial dispersion having been determined, the next issue is how to make materials that fit the bill. The first inclination of the infrared coating designer is to throw some metal flakes into a transparent binder. Coming up with a transparent binder over the frequency range of interest is not easy, and the radar coating man probably won't like the effects of the metal particles on his favorite observable. The next move is usually to come up with a multi layer material, where the same cancellation approach that was discussed earlier regarding radar suppressant coatings is used. The dimensions now are in angstroms rather than millimeters.
STEALTH MATERIALS AND COATINGS
Typical materials for reduced-observable treatments include, but are not limited to, the following categories:
i.There are two kinds of conductive fillers: conductive fibers, which look like very light whiskers 2 to 6 mm long, are made of carbon, metals, or conductive-material coated glass fibers; and conductive-material coated particles, which may look like colored sand.
ii.Sprays include conductive inks or paints, which normally contain silver,
copper, zinc, bronze, or gold as the base ingredient. They appear black, metallic gray,
copper, bronze, or gold in color.
iii.Small cell foams, both open and closed, are painted, or loaded, with absorbing inks and paints. These foams resemble flexible foam rubber sheetsor air conditioning filters. They can be single-layered or noticeably multi-layered, with glue lines separating the strata. A ground plane, if applied, can consist of a metallic paint, a metallic sheet (aluminum foil or metalized thin plastic), or undetectable sprayed inks. Some manufacturers may mark the front of these foams with lettering saying "front" or with serial numbers if the ground plane is not obvious. Some foam may contain composite fiber to make them more rigid or even structural.
PLASMA STEALTH
Plasma stealth technology is what can be called as "Active stealth technology" in scientific terms. This technology was first developed by the Russians. It is a milestone in the field of stealth technology. The technology behind this not at all new. The plasma thrust technology was used in the Soviet / Russian space program. Later the same engine was used to power the American Deep Space 1 probe.
In plasma stealth, the aircraft injects a stream of plasma in front of the aircraft. The plasma is ionized gas particles. The plasma will cover the entire body of the fighter and will absorb most of the electromagnetic energy of the radar waves, thus making the aircraft difficult to detect. The same method is used in Magneto Hydro Dynamics. Using Magneto Hydro Dynamics, an aircraft can propel itself to great speeds.
Plasma stealth will be incorporated in the MiG-35 "Super Fulcrum / Raptor Killer". This is a fighter which is an advanced derivative of the MiG-29 "Fulcrum / Baaz". Initial trials have been conducted on this technology, but most of the results have proved to be fruitful.
CONCLUSION
The development of stealthy airplanes teaches several important lessons about technology. The first is that often many different technologies must be combined to achieve a desired outcome. An advance in one field, such as materials or aerodynamics, must be accompanied by advances in other fields, such as computing or electromagnetic theory. The second lesson is that sometimes trial and error techniques are insufficient and advances in mathematical theory are necessary in order to achieve significant advances. Finally, stealth teaches the lesson that technology is never static - a "stealth breakthrough" may only last for a few years before an adversary finds a means of countering it.