Www.123seminarsonly.com



Introducing Stealth technologyStealth technology also known as LOT (Low Observability Technology) is a technologies which covers a range of techniques used with aircraft, ships and missiles, in order to make them less visible (ideally invisible) to radar, infrared and other detection methods.[1]From the late years of World War II to today's computer enabled design changes, stealth has been a major factor in the improvement of reconnaissance and attack aircraft. The term "stealth", is thought to have been coined in 1966 by Charles E. "Chuck" Myers, combat pilot and later an exec at Lockheed. When we think of stealth today, immediately images of the B-2 bomber or the F-117A Nighthawk fighter come to mind. In simple terms, stealth technology allows an aircraft to be partially invisible to Radar or any other means of detection. This doesn't allow the aircraft to be fully invisible on radar. Stealth technology cannot make the aircraft invisible to enemy or friendly radar. All it can do is to reduce the detection range or an aircraft. This is similar to the camouflage tactics used by soldiers in jungle warfare. Unless the soldier comes near you, you can't see him. Though this gives a clear and safe striking distance for the aircraft, there is still a threat from radar systems, which can detect stealth aircraft.[1]Stealth technology is expanded into each of those areas which seek to detect the aircraft, ships & missiles. Thus it is essential to develop visual, infrared acoustic and radar stealth. However many countries have announced that they have developed counter-stealth techniques that allow them to negate stealth. [2]Stealth principleThe concept behind the stealth technology is very simple. As a matter of fact it is totally the principle of reflection and absorption that makes aircraft "stealthy". Deflecting the incoming radar waves into another direction and thus reducing the number of waves does this, which returns to the radar. Another concept that is followed is to absorb the incoming radar waves totally and to redirect the absorbed electromagnetic energy in another direction. What ever may be the method used, the level of stealth an aircraft can achieve depends totally on the design and the substance with which it is made of. [2]2.1 The key features of Stealth -Unusual Design -Outer Paint -Reduce Heat Exhaust Signatures -Eliminate High Altitude Contrails -Eliminate Brown ExhaustFig.2.1.1: T-50 STEALTH fighter [3]Introduction TO RADIO detection and rangingRadar is a system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships.A radar system has a transmitter that emits either microwaves or radio waves that are reflected by the target and detected by a receiver, typically in the same location as the transmitter. Although the signal returned is usually very weak, the signal can be amplified. This enables radar to detect objects at ranges where other emissions, such as sound or visible light, would be too weak to detect. Radar is used in many contexts, including meteorological detection of precipitation, measuring ocean surface waves, air traffic control, police detection of speeding traffic, and by the military. [4]Fig.3.1: DETTECTION AN AIRCRAFT USING RADAR 3.1 PRINCIPLEA radar dish or antenna sends out pulses of radio waves or microwaves. These waves bounce off any object in their path, and return to the dish, which detects them. The time it takes for the reflected waves to return to the dish enables a computer to calculate how far away the object is, its radial velocity and other characteristics. [4]3.2 Distance MeasurementOne way to measure the distance to an object is to transmit a short pulse of radio signal (electromagnetic radiation), and measure the time it takes for the reflection to return .The distance target is one half the product of the time taken by the radiated signal to travel to the target and back to the receiver and the speed of the signal radiated.[4]3.3 Frequency modulationAnother form of distance measuring radar is based on frequency modulation. Frequency comparison between two signals is considerably more accurate, even with older electronics, than timing the signal. By changing the frequency of the returned signal and comparing that with the original, the difference can be easily measured.[4]3.4 Speed measurementSpeed is the change in distance to an object with respect to time. Speed measurement is done by using the technique of droppler effect. The radar beam is fired at the moving target. As it recedes from the radar source, each successive wave has to travel further to reach the car, before being reflected and re detected near the source. As each wave has to move further the gap between each wave increases. This shows a change in the spectrum of the waves. [4]3.5 Size measurementThe size of targets image on radar is measured by the radar cross section (RCS) measured in Square meters .This does not equal geometric area .A perfectly Conducting sphere of projected cross-sectional area 1 m2. RADAR wavelength much less than the diameter of the sphere .RCS is independent of frequency , Conversely ,a flat plate of area 1 m2 will have an RCs of almost 14000 m2 at 10GHz if the radar is perpendicular to the flat surface since it will reflect the signal right back to the radar antenna from where it came. By reflecting much of the radiation away from the antenna or absorbing it altogether, the target achievers smaller radar cross section. [4]Stealth shipA stealth ship is a ship which employs stealth technology construction techniques in an effort to ensure that it is harder to detect by one or more of radar, visual, sonar, and infrared methods. These techniques borrow from stealth aircraft technology, although some aspects such as wake and acoustic signature reduction are unique to stealth ships' design.Reduction of radar cross section (RCS), visibility and noise is not unique to stealth ships; visual masking has been employed for over two centuries and RCS reduction traces back to American and Soviet ships of the Cold War. One common feature is the inward-sloping tumblehome hull design that significantly reduces the RCS. [5]Fig.4.1: STEALTH ship [6]4.1 ShapingIn designing a ship with reduced radar signature, the main concerns are radar beams originating near or slightly above the horizon (as seen from the ship) coming from distant patrol aircraft, other ships or sea-skimming anti-ship missiles with active radar seekers. Therefore, the shape of the ship avoids vertical surfaces, which would perfectly reflect any such beams directly back to the emitter. Retro-reflective right angles are eliminated to avoid causing the cat's eye effect. A stealthy ship shape can be achieved by constructing the hull and superstructure with a series of slightly protruding and retruding surfaces. This design was developed by several German shipyards, and is thus extensively applied on ships of the German Navy.[5]RASRAS or Radar absorbent surfaces are the surfaces on the aircraft, which can deflect the incoming radar waves and reduce the detection range. RAS works due to the angles at which the structures on the aircraft's fuselage or the fuselage itself are placed. These structures can be anything from wings to a refueling boom on the aircraft. The extensive use of RAS is clearly visible in the F-117 "Night Hawk". Due to the facets (as they are called) on the fuselage, most of the incoming radar waves are reflected to another direction. Due to these facets on the fuselage, the F-117 is a very unstable aircraft.[1]centercenterFig. 5.1: Conventional and Stealth aircraft [8]The concept behind the RAS is that of reflecting a light beam from a torch with a mirror. The angle at which the reflection takes place is also more important. When we consider a mirror being rotated from 0o to 90o, the amount of light that is reflected in the direction of the light beam is more. At 90o, maximum amount of light that is reflected back to same direction as the light beam's source. On the other hand when the mirror is tilted above 90o and as it proceeds to 180o, the amount of light reflected in the same direction decreases drastically. This makes the aircraft like F-117 stealthy.[1]RAMRadar absorbent surfaces absorb the incoming radar waves rather than deflecting it in another direction. ‘Radar absorbent Material’ totally depends on the surface of the aircraft is made. Though the composition of this material is a top secret. The F-117 extensively uses RAM to reduce its radar signature or its radar cross section. [1]Fig.6.1.1 RADAR absorbent material [7]The RAS is believed to be silicon based inorganic compound. The RAM coating over the B-2 is placed like wrapping a cloth over the plane. When radar sends a beam in the direction of the B-2, the radar waves are absorbed by the plane’s surface and are redirected to another direction after it is absorbed. This reduces the radar signature of the aircraft. A Jaumann absorber or Jaumann layer is a radar absorbent device. The Foam absorber is applied to the chamber walls with the tips of the pyramids pointing inward or toward the radar. As a radar wave strikes a pyramid, it experiences a gradual transition from free space at the tip of the pyramid to absorbing foam at the base. [1]Methods of avoiding detectionDesign for stealth requires the integration of many techniques and materials. The types of stealth that a maximally stealthy aircraft & ships seeks to achieve can be categorized as visual, infrared, acoustic, and Radar.7.1 Visual stealthLow visibility is desirable for all military aircraft and is essential for stealth aircraft. It is achieved by coloring the aircraft so that it tends to blend in with its environment. For instance, reconnaissance planes designed to operate at very high altitudes, where the sky is black, are painted black. (Black is also a low visibility color at night, at any altitude.) Conventional daytime fighter aircraft are painted a shade of blue known as "air-superiority blue-gray," to blend in with the sky. Stealth aircraft are flown at night for maximum visual stealth, and so are painted black or dark gray. Chameleon or "smart skin" technology that would enable an aircraft to change its appearance to mimic its background is being researched.[9]FIG.7.1.1 VISUAL stealth plane-Hawk GB [11] 7.2 Infrared stealthAnother important factor that influences the stealth capability of an aircraft is the IR (i.e. Infrared, electromagnetic waves in the. 72–1000 micron range of the spectrum) signature given out by the plane. Usually planes are visible in thermal imaging systems because of the high temperature exhaust they give out. This is a great disadvantage to stealth aircraft as missiles also [9]have IR guidance system. The IR signatures of stealth aircraft are minute when compared to the signature of a conventional fighter or any other military aircraft. Fig.7.2.1 Thermal infrared image - US Military F117 Stealth [14]Engines for stealth aircraft are specifically built to have a very low IR signature. Another main aspect that reduces the IR signature of a stealth aircraft is to place the engines deep into the fuselage. This is done in stealth aircraft like the B-2, F-22 and the JSF. The IR reduction scheme used in F-117 is very much different from the others. The engines are placed deep within the aircraft like any stealth aircraft and at the outlet; a section of the fuselage deflects the exhaust to another direction. This is useful for deflecting the hot exhaust gases in another direction.[10]Infrared radiation are emitted by all matter above absolute zero; hot materials, such as engine exhaust gases or wing surfaces heated by friction with the air, emit more infrared radiation than cooler materials. Heat-seeking missiles and other weapons zero in on the infrared glow of hot aircraft parts. Infrared stealth, therefore, requires that aircraft parts and emissions, particularly those associated with engines, be kept as cool as possible. [9]7.3 Acoustic stealthAlthough sound moves too slowly to be an effective locating signal for antiaircraft weapons, for low-altitude flying it is still best to be inaudible to ground observers. Several ultra-quiet, low-altitude reconnaissance aircraft, such as Lockheed's QT-2 and YO-3A, have been developed since the 1960s. Aircraft of this type are ultra light, run on small internal combustion engines quieted by silencer-suppressor mufflers, and are driven by large, often wooden propellers. They make about as much sound as gliders and have very low infrared emissions as well because of their low energy consumption. The U.S. F-117 stealth fighter, which is designed to fly at high speed at very low altitudes, also incorporates acoustic-stealth measures, including sound-absorbent linings inside its engine intake and exhaust cowlings. [9]Fig. 7.3.1 acoustic stealth aircraft [12]7.4 Radar stealthRadar stealth or invisibility requires that a craft absorbs incident radar pulses, actively cancel them by emitting inverse waveforms, deflect them away from receiving antennas, or all of the above. Absorption and deflection treated below are the most important prerequisites of radar stealth. [9]7.5 ABSORPTIONMetallic surfaces reflect RADAR; therefore, stealth aircraft parts must either be coated with RADAR-absorbing materials or made out of them to begin with. The latter is preferable because an aircraft whose parts are intrinsically RADAR-absorbing derives aerodynamic as well as stealth function from them, whereas a RADAR-absorbent coating is, aerodynamically speaking, dead weight. The F-117 stealth aircraft is built mostly out of a RADAR-absorbent material termed Fibaloy, which consists of glass fibers embedded in plastic, and of carbon fibers, which are used mostly for hot spots like leading wing-edges and panels covering the jet engines. [9]Deflection Most RADAR are monostatic, that is, for reception they use either the same antenna as for sending or a separate receiving antenna colocated with the sending antenna; deflection therefore means reflecting RADAR pulses in any direction other than the one they came from. This in turn requires that stealth aircraft lack flat, vertical surfaces that could act as simple RADAR mirrors. [9] Fig.7.6.1.Deflectin of radar because of the stealth design [13]RADAR can also be strongly reflected wherever three planar surfaces meet at a corner. Planes such as the B-52 bomber, which have many flat, vertical surfaces and RADAR-reflecting corners, are notorious for their RADAR-reflecting abilities; stealth aircraft, in contrast, tend to be highly angled and streamlined, presenting no flat surfaces at all to an observer that is not directly above or below them. The B-2 bomber, for example, is shaped like a boomerang. [9]Plasma StealthPlasma 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. [16]In plasma stealth, the aircraft injects a stream of plasma in front of the aircraft. 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. [15]Fig.8.1 Plasma Stealth Aircraft [20]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 .Initial trials have been conducted on this technology, but most of the results have proved to be fruitful. [16] Counter-stealthWhenever a technology is developed for military purposes, another technology is also developed to counter that technology. There are strong efforts to develop a system that can counter the low Observability of the fifth generation stealth aircraft. There are ways of detection and elimination of a low observable aircraft but this doesn't give a 100% success rage at present. On a radar screen, aircraft will have their radar cross sections with respect to their size. This helps the radar to identify that the radar contact it has made is an aircraft. Conventional aircraft are visible on the radar screen because of its relative size. On the other hand, the relative size of a stealth aircraft on the radar screen will be that of a large bird. This is how stealth aircraft are ignored by radar and thus detection is avoided. [17]A proven method to detect and destroy stealth aircraft is to triangulate its location with a network of radar systems. This was done while the F-117 was shot down during the NATO offensive over Yugoslavia. A new method of detecting low observable aircraft is just over the horizon. Scientists have found a method to detect stealth aircraft with the help of microwaves similar to the ones emitted by the cell phone towers. Nothing much is known about this technology, but the US military seems to be very keen about doing more research on this. [18]Furthermore, every jet aircraft leaves swirls of air—vortices—in its wake. Doppler radar, which can image wind velocities, might pinpoint such disturbances if it could be made sufficiently high-resolution.Other anti-stealth techniques could include the detection of aircraft-caused disturbances in the Earth's magnetic field (magnetic anomaly detection), networks of low frequency radio links to detect stealth aircraft by interruptions in transmission, the use of specially shaped RADAR pulses that resist absorption, and netted RADAR. Netted RADAR is the use of more than one receiver, and possibly more than one transmitter, in a network. Since stealth aircraft rely partly on deflecting RADAR pulses, receivers located off the line of pulse transmission might be able to detected deflected echoes. By illuminating a target area using multiple transmitters and linking multiple receivers into a coordinated network, it should be possible to greatly increase one's chances of detecting a stealthy target. No single receiver may record a strong or steady echo from any single transmitter, but the network as a whole might collect enough information to track a stealth target. [17]The politics of stealthAs defensive weaponry has become ever more accurate and therefore more lethal, offensive delivery platforms (ships, aircraft, missiles, etc) have become increasingly dependent upon on various forms of stealth to achieve mission objectives. This trend of deploying stealthy offensive weapons platforms has disturbing political consequences. Political restraint is largely based on the perceived risk/reward ratio of military action. And stealth technology has the effect of lowering the perceived political risk of belligerent behavior. Therefore a government in possession of stealth weapons platforms is far more likely to embark upon a course of aggression. When viewed from this perspective, it becomes apparent that stealth technology represents a shift away from traditional military defense, to a more offensive military posture. As a consequence, the widely held belief that stealth technology enhances pilot safety and mission survivability is false. Since any added margin of safety provided by stealth technology is more than offset by the tendency of political leaders and military planners to employ stealth aircraft on missions and in environments that would be considered suicidal for any conventional aircraft. Even a cursory examination of America's deployment and use of stealth technology lends ample credence to these conclusions. [19]Stealth in wartimeStealthy jet aircraft have been used for surveillance since the 1950s, but dedicated-design stealth warplanes were not used in combat prior to the first Gulf War (1991). In that war, F-117s—which first became operational in 1982—made some 1,300 sorties and were the only aircraft to bomb targets in downtown Baghdad? B-2 bombers were first used in combat in the Kosovo conflict in 1999, flying bombing sorties from Missouri to Yugoslavia (with midflight refueling over the Atlantic). F-117s were also used in the Kosovo conflict; one was shot down and two were damaged by enemy fire. The first overseas combat deployment of B-2 bombers occurred in 2003, during Operation Iraqi Freedom.Stealth technology is also employed in U.S. cruise missiles such as the Tomahawk and the AGM-129A. The Tomahawk, a tactical weapon that can carry either nuclear or conventional warheads, has been deployed in four versions, including air-, sea-, and ground-launched types, and was used extensively in combat in both Gulf Wars and in Afghanistan in 2002. The AGM-129A is stealthier than the 1970s-vintage Tomahawk; it carries the W80 250-kiloton nuclear warhead and is designed to be fired from under the wings of the B-52H Stratofortress strategic bomber. The AGM-129A has not been used in combat. [21]Benefits of Stealth Technology A smaller number of stealth aircraft may replace fleet of conventional attacks jets with the same or increased combat efficiency.Possibly resulting in longer term savings in the military budget.A Stealth aircraft strike capability may deter potential enemies from taking action and keep them in constant fear of strikes, since they can never know if the attack planes are already underway.The production of a stealth combat aircraft design may force an opponent to pursue the same aim, possibly resulting in significant weakening of the economically inferior party.Stationing stealth aircraft in a friendly country is a powerful diplomatic gesture as stealth planes incorporate high technology and military secrets. [1] [2] [5] [9] [10]Disadvantages Of stealth technologyStealth technology has its own disadvantages like other technologies. Stealth aircraft cannot fly as fast or is not maneuverable like conventional aircraft. The F-22 and the aircraft of its category proved this wrong up to an extent. Though the F-22 may be fast or maneuverable or fast, it can't go beyond Mach 2 and cannot make turns like the Su-37. Another serious disadvantage with the stealth aircraft is the reduced amount of payload it can carry. As most of the payload is carried internally in a stealth aircraft to reduce the radar signature, weapons can only occupy a less amount of space internally. On the other hand a conventional aircraft can carry much more payload than any stealth aircraft of its class. Whatever may be the disadvantage a stealth aircraft can have, the biggest of all disadvantages that it faces is its sheer cost. Stealth aircraft literally costs its weight in gold. Fighters in service and in development for the USAF like the B-2 ($2 billion), F-117 ($70 million) and the F-22 ($100 million) are the costliest planes in the world. After the cold war, the number of B-2 bombers was reduced sharply because of its staggering price tag and maintenance charges.The B-2 Spirit carries a large bomb load, but it has relatively slow speed, resulting in 18 to 24 hour long missions when it flies half way around the globe to attack overseas targets. Therefore advance planning and receiving intelligence in a timely manner is of paramount importance.Stealth aircraft are vulnerable to detection immediately before, during and after using their weaponry. since reduced RCS bombs and cruiseMissiles are yet not available; all armament must be carried internally to avoid increasing the radar cross section. As soon as the bomb bay doors opened, the planes RCS will be multiplied.Another problem with incorporating "stealth" technology into an aircraft is a wing shape that does not provide the optimum amount of lift. The resulting increase in drag reduces flight performance. "Stealth" shapes, such as the "faceting" found on Lockheed's F-117 "stealth" fighter, also tend to be aerodynamically destabilizing. This is brought under control only through the use of highly sophisticated computers that serve to electronically balance the aircraft in flight through its autopilot and control system.All of these modifications, however, hurt the plane's performance, adding weight, affecting aerodynamics, and altering the structure of the aircraft. The advantages of stealth technology must always be weighed against its disadvantages.[1] [2] [5][6] [9] [10] [22]Stealth technology of yester-years, today and tomorrow Stealth technology is a concept that is not at all new. During the Second World War, allied aircraft used tin and aluminum foils in huge numbers to confuse German radar installations. This acted as a cover for allied bombers to conduct air raids. This method was later used as chaffs by aircrafts to dodge radar guided missiles. The first stealth aircraft was the F-117 developed by Lockheed Martin. It was a top-secret project developed by its Skunk Works unit. The F-117 was only revealed during the late 80s and then saw action in the Persian Gulf. In due course of time the B-2 was developed as a successor to the B-2. Though both of them serve different purposes, the B-2 went a step ahead of the F-117. Stealth technology became famous with the ATF contest. The Boeing-Lockheed YF-22 and the McDonell Douglas-Grumman YF-23 fought for the milti-billion contracts to build the fighter that would take the USAF into the fifth generation fighter era. The Boeing-Lockheed won the contract and the F-22 was approved to be the replacement for the F-15 "Eagle" interceptor. America now has a competitors, Russia decided to respond to the development of the F-22 by making the Su-47 (S-37) "Berkut" and the MiG-35 "Super Fulcrum / Raptor Killer". These fighters were developed by the two leading aviation firms in Russia Sukhoi and Mikhoyan Gurevich (MiG). The future of these projects totally depends on the funding which will be provided to the Russian defense sector. There are some hopes of increase in the funding to these projects as countries like India have started providing funds and technical assistance for these projects. [23]ConclusionTill date stealth aircraft have been used in several low and moderate intensity conflicts, including operation Desert Storm. Operation Allied Force and the 2003 invasion of Iraq .In each Case they were employed to strike high value targets which were either out of range of conventional aircraft or which were too heavily defended for conventional aircraft to strike without a high risk of loss. In addition ,because The stealth aircraft aren’t going to be dodging surface to air missiles and anti-aircraft artillery over the target they can aim more carefully and thus are more likely to hit the high value targets early in the campaign (or even for it) ,Before other aircraft had the opportunity to degrade the opposing air defense.However, given the increasing prevalence of excellent Russion-biltSurface –to-air missile (SAM) system on the open market, stealth aircraft are likely to be very important in a high intensity conflict in order to gain and maintain air supremacy. Stealth technology .in future, would be required for clearing the way for deeper strikes , which conventional aircraft would find very difficult .For example ,China license-builds a wide range of SAM systems in quantity and would be able to heavily defend important strategic and tactical targets in the event of some kind of conflict .Even if anti-radiation weapons are used in an attempt to destroy the SAM radars of such systems, these SAMs are capable of shooting down weapons fired against them. The surprise of a stealth attack may become the only reasonable way of making a safe corridor for conventional bombers. It would then be possible for the less-stealth force with superior weaponry to suppress the remaining systems and gain air superiority.16. REFRENCES[1] [2] [3] =UTF-8&sa=N&tab=wi [4] [5] [6] [7] [8] [9] [10] [11] htp://hitechweb.genezis.eu/stealth4f_soubory/image013.jpg [12] [13] reflecting.gif [14] htp://library/thermal/pdm/ir_thermography.htm [15] [16] [17] [18] [19] POLITICS+OF+STEALTH+technology&source=bl&ots=UGriQoglNp&sig=C2Q1o3i8ybgd4HHjaKZFmUHjhKI&hl=en&ei=HzrUSc36FMiBkQXcn5T4Dg&sa=X&oi=book_result&ct=result&resnum=1 [20] [21] [22] [23] ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download