26-09-2013, 04:46 PM
A SEMINAR REPORT ON STEALTH TECHNOLOGY
[attachment=58388]
ABSTRACT
Stealth aircraft’s are aircraft that use stealth technology to make it harder to be detected by radar and other means than conventional aircraft by employing a combination of features to reduce visibility in the visual, audio, infrared and radio frequency (RF) spectrum. Well known examples include the United States' F-117 Nighthawk (1980s-2008), the B-2 Spirit "Stealth Bomber," and the F-22 Raptor.While no aircraft is totally invisible to radar, stealth aircraft limit current conventional radar's abilities to detect or track them effectively enough to prevent an attack. Stealth is accomplished by using a complex design philosophy to reduce the ability of an opponent's sensors to detect, track and attack an aircraft. Modern stealth aircraft first became possible when a mathematician working for Lockheed Aircraft during the 1970s adopted a mathematical model developed by Petr Ufimtsev, a Russian scientist, to develop a computer program called Echo 1. Echo made it possible to predict the radar signature an aircraft made with flat panels, called facets. In 1975, engineers at Lockheed Skunk Works found that an airplane made with faceted surfaces could have a very low radar signature because the surfaces would radiate almost all of the radar energy away from the receiver.Reduced radar cross section is only one of five factors that designers addressed to create a truly stealthy design. Designers also addressed making the aircraft less visible to the naked eye, controlling radio transmissions, and noise abatement.
INTRODUCTION
Stealth technology also termed LO technology (low observable technology) is a sub-discipline of military tactics and passive electronic countermeasures, which cover a range of techniques used with personnel, aircraft, ships, submarines, and missiles, to make them less visible (ideally invisible) to radar, infrared, sonar and other detection methods. Development in the United States occurred in 1958, where earlier attempts in preventing radar tracking of its U-2 spy planes during the Cold War by the Soviet Union had been unsuccessful.
Designers turned to develop a particular shape for planes that tended to reduce detection, by redirecting electromagnetic waves from radars. Radar-absorbent material was also tested and made to reduce or block radar signals that reflect off from the surface of planes. Such changes to shape and surface composition form stealth technology as currently used on the Northrop Grumman B-2 Spirit "Stealth Bomber". The concept of stealth is to operate or hide without giving enemy forces any indications as to the presence of friendly forces. This concept was first explored through camouflage by blending into the background visual clutter. As the potency of detection and interception technologies (radar, IRST, surface-to-air missiles etc.) have increased over time, so too has the extent to which the design and operation of military personnel and vehicles have been affected in response. Some military uniforms are treated with chemicals to reduce their infrared signature. A modern "stealth" vehicle will generally have been designed from the outset to have reduced or controlled signature. Varying degrees of stealth can be achieved. The exact level and nature of stealth embodied in a particular design is determined by the prediction of likely threat capabilities.
HISTORY
In England, irregular units of gamekeepers in the 17th century were the first to adopt drab colors (common in the 16th century Irish units) as a form of camouflage, following examples from the continent.
Yehudi lights were successfully employed in World War II by RAF Shorts Sunderland aircraft in attacks on U-boats. In 1945 a Grumman Avenger with Yehudi lights got within 3,000 yards (2,700 m) of a ship before being sighted. This ability was rendered obsolete by the radar of the time.
One of the earliest stealth aircraft seems to have been the Hornet Ho 229 flying wing. It included carbon powder in the glue to absorb radio waves.Some prototypes were built, but it was never used in action.
In 1958, the CIA requested funding for a reconnaissance aircraft, to replace U-2 spy planes in which Lockheed secured contractual rights to produce the aircraft. "Kelly" Johnson and his team at Lockheed's Skunk Works were assigned to produce the A-12 or OXCART the first of the former top secret classified Blackbird series which operated at high altitude of 70,000 to 80,000 ft and speed of Mach 3.2 to avoid radar detection. Radar absorbent material had already been introduced on U-2 spy planes, and various plane shapes had been developed in earlier prototypes named A1 to A11 to reduce its detection from radar. Later in 1964, using prior models, an optimal plane shape taking into account compactness was developed where another "Blackbird", the SR-71, was produced, surpassing prior models in both altitude of 90,000 ft and speed of Mach 3.3.
RCS (RADAR CROSS SECTION):
Almost since the invention of radar, various methods have been tried to minimize detection. Rapid development of radar during WWII led to equally rapid development of numerous counter radar measures during the period; a notable example of this was the use of chaff.The term "stealth" in reference to reduced radar signature aircraft became popular during the late eighties when the Lockheed Martin F-117 stealth fighter became widely known. The first large scale (and public) use of the F-117 was during the Gulf War in 1991.
RCS MINIMISATION:
There are two broad aspects of RCS minimization techniques. One falls under the effort to shape the airframe, and covers the geometric design considerations that are taken into account when aiming for a low RCS. The other principle is referred to as “radar-absorbent materials” and is concerned with the materials that help to reduce the reflectivity of the airframe, as well as the structures that will support these materials and integrate them into the airframe (often referred to as “Radar-absorbent structures”. These two axes are of course not taken in isolation during the design; trade-offs often have to be made between them.
NON-METALLIC AIRFRAME:
Dielectric composites are more transparent to radar, whereas electrically conductive materials such as metals and carbon fibers reflect electromagnetic energy incident on the material's surface. Composites may also contain ferrites to optimize the dielectric and magnetic properties of a material for its application.
RADAR ABSORBING SURFACE:
RAS (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.
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 0° to 90°, the amount of light that is reflected in the direction of the light beam is more. At 90°, 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 90° and as it proceeds to 180°, the amount of light reflected in the same direction decreases drastically. This makes the aircraft like F-117 stealthy
RADAR-ABSORBING MATERIAL:
Radar-absorbent materials (RAM), often as paints, are used especially on the edges of metal surfaces. While the material and thickness of RAM coatings is classified, the material seeks to absorb radiated energy from a ground or airs based radar station into the coating and convert it to heat rather than reflect it back.
Radar absorbent surfaces absorb the incoming radar waves rather than deflecting it in another direction. RAS totally depends on the material with which the surface of the aircraft is made. The F-117 extensively uses RAM to reduce its radar signature or its radar cross section.
The RAS is believed to be silicon based inorganic compound. This is assumed by the information that the RAM coating on the B-2 is not water proof. This is just a supposition and may not be true. What we know is that 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.
ACOUSTICS:
Acoustic stealth plays a primary role in submarine stealth as well as for ground vehicles. Submarines use extensive rubber mountings to isolate and avoid mechanical noises that could reveal locations to underwater passive sonar arrays.
Early stealth observation aircraft used slow-turning propellers to avoid being heard by enemy troops below. Stealth aircraft that stay subsonic can avoid being tracked by sonic boom. The presence of supersonic and jet-powered stealth aircraft such as the SR-71 Blackbird indicates that acoustic signature is not always a major driver in aircraft design, although the Blackbird relied more on its extremely high speed and altitude.
VISIBILITY:
The simplest stealth technology is simply camouflage; the use of paint or other materials to color and break up the lines of the vehicle or person.
Most stealth aircraft use matte paint and dark colors, and operate only at night. Lately, interest in daylight Stealth (especially by the USAF) has emphasized the use of gray paint in disruptive schemes, and it is assumed that Yehudi lights could be used in the future to mask shadows in the airframe (in daylight, against the clear background of the sky, dark tones are easier to detect than light ones) or as a sort of active camouflage.
CONCLUSION
The development of stealthy airplanes teaches several important lessons abouttechnology. The first is that often many different technologies must be combined to achieve adesired outcome. An advance in one field, such as materials or aerodynamics, must beaccompanied by advances in other fields, such as computing or electromagnetic theory. Thesecond lesson is that sometimes trial and error techniques are insufficient and advances inmathematical theory are necessary in order to achieve significant advances. Finally, stealthteaches 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.
[attachment=58388]
ABSTRACT
Stealth aircraft’s are aircraft that use stealth technology to make it harder to be detected by radar and other means than conventional aircraft by employing a combination of features to reduce visibility in the visual, audio, infrared and radio frequency (RF) spectrum. Well known examples include the United States' F-117 Nighthawk (1980s-2008), the B-2 Spirit "Stealth Bomber," and the F-22 Raptor.While no aircraft is totally invisible to radar, stealth aircraft limit current conventional radar's abilities to detect or track them effectively enough to prevent an attack. Stealth is accomplished by using a complex design philosophy to reduce the ability of an opponent's sensors to detect, track and attack an aircraft. Modern stealth aircraft first became possible when a mathematician working for Lockheed Aircraft during the 1970s adopted a mathematical model developed by Petr Ufimtsev, a Russian scientist, to develop a computer program called Echo 1. Echo made it possible to predict the radar signature an aircraft made with flat panels, called facets. In 1975, engineers at Lockheed Skunk Works found that an airplane made with faceted surfaces could have a very low radar signature because the surfaces would radiate almost all of the radar energy away from the receiver.Reduced radar cross section is only one of five factors that designers addressed to create a truly stealthy design. Designers also addressed making the aircraft less visible to the naked eye, controlling radio transmissions, and noise abatement.
INTRODUCTION
Stealth technology also termed LO technology (low observable technology) is a sub-discipline of military tactics and passive electronic countermeasures, which cover a range of techniques used with personnel, aircraft, ships, submarines, and missiles, to make them less visible (ideally invisible) to radar, infrared, sonar and other detection methods. Development in the United States occurred in 1958, where earlier attempts in preventing radar tracking of its U-2 spy planes during the Cold War by the Soviet Union had been unsuccessful.
Designers turned to develop a particular shape for planes that tended to reduce detection, by redirecting electromagnetic waves from radars. Radar-absorbent material was also tested and made to reduce or block radar signals that reflect off from the surface of planes. Such changes to shape and surface composition form stealth technology as currently used on the Northrop Grumman B-2 Spirit "Stealth Bomber". The concept of stealth is to operate or hide without giving enemy forces any indications as to the presence of friendly forces. This concept was first explored through camouflage by blending into the background visual clutter. As the potency of detection and interception technologies (radar, IRST, surface-to-air missiles etc.) have increased over time, so too has the extent to which the design and operation of military personnel and vehicles have been affected in response. Some military uniforms are treated with chemicals to reduce their infrared signature. A modern "stealth" vehicle will generally have been designed from the outset to have reduced or controlled signature. Varying degrees of stealth can be achieved. The exact level and nature of stealth embodied in a particular design is determined by the prediction of likely threat capabilities.
HISTORY
In England, irregular units of gamekeepers in the 17th century were the first to adopt drab colors (common in the 16th century Irish units) as a form of camouflage, following examples from the continent.
Yehudi lights were successfully employed in World War II by RAF Shorts Sunderland aircraft in attacks on U-boats. In 1945 a Grumman Avenger with Yehudi lights got within 3,000 yards (2,700 m) of a ship before being sighted. This ability was rendered obsolete by the radar of the time.
One of the earliest stealth aircraft seems to have been the Hornet Ho 229 flying wing. It included carbon powder in the glue to absorb radio waves.Some prototypes were built, but it was never used in action.
In 1958, the CIA requested funding for a reconnaissance aircraft, to replace U-2 spy planes in which Lockheed secured contractual rights to produce the aircraft. "Kelly" Johnson and his team at Lockheed's Skunk Works were assigned to produce the A-12 or OXCART the first of the former top secret classified Blackbird series which operated at high altitude of 70,000 to 80,000 ft and speed of Mach 3.2 to avoid radar detection. Radar absorbent material had already been introduced on U-2 spy planes, and various plane shapes had been developed in earlier prototypes named A1 to A11 to reduce its detection from radar. Later in 1964, using prior models, an optimal plane shape taking into account compactness was developed where another "Blackbird", the SR-71, was produced, surpassing prior models in both altitude of 90,000 ft and speed of Mach 3.3.
RCS (RADAR CROSS SECTION):
Almost since the invention of radar, various methods have been tried to minimize detection. Rapid development of radar during WWII led to equally rapid development of numerous counter radar measures during the period; a notable example of this was the use of chaff.The term "stealth" in reference to reduced radar signature aircraft became popular during the late eighties when the Lockheed Martin F-117 stealth fighter became widely known. The first large scale (and public) use of the F-117 was during the Gulf War in 1991.
RCS MINIMISATION:
There are two broad aspects of RCS minimization techniques. One falls under the effort to shape the airframe, and covers the geometric design considerations that are taken into account when aiming for a low RCS. The other principle is referred to as “radar-absorbent materials” and is concerned with the materials that help to reduce the reflectivity of the airframe, as well as the structures that will support these materials and integrate them into the airframe (often referred to as “Radar-absorbent structures”. These two axes are of course not taken in isolation during the design; trade-offs often have to be made between them.
NON-METALLIC AIRFRAME:
Dielectric composites are more transparent to radar, whereas electrically conductive materials such as metals and carbon fibers reflect electromagnetic energy incident on the material's surface. Composites may also contain ferrites to optimize the dielectric and magnetic properties of a material for its application.
RADAR ABSORBING SURFACE:
RAS (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.
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 0° to 90°, the amount of light that is reflected in the direction of the light beam is more. At 90°, 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 90° and as it proceeds to 180°, the amount of light reflected in the same direction decreases drastically. This makes the aircraft like F-117 stealthy
RADAR-ABSORBING MATERIAL:
Radar-absorbent materials (RAM), often as paints, are used especially on the edges of metal surfaces. While the material and thickness of RAM coatings is classified, the material seeks to absorb radiated energy from a ground or airs based radar station into the coating and convert it to heat rather than reflect it back.
Radar absorbent surfaces absorb the incoming radar waves rather than deflecting it in another direction. RAS totally depends on the material with which the surface of the aircraft is made. The F-117 extensively uses RAM to reduce its radar signature or its radar cross section.
The RAS is believed to be silicon based inorganic compound. This is assumed by the information that the RAM coating on the B-2 is not water proof. This is just a supposition and may not be true. What we know is that 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.
ACOUSTICS:
Acoustic stealth plays a primary role in submarine stealth as well as for ground vehicles. Submarines use extensive rubber mountings to isolate and avoid mechanical noises that could reveal locations to underwater passive sonar arrays.
Early stealth observation aircraft used slow-turning propellers to avoid being heard by enemy troops below. Stealth aircraft that stay subsonic can avoid being tracked by sonic boom. The presence of supersonic and jet-powered stealth aircraft such as the SR-71 Blackbird indicates that acoustic signature is not always a major driver in aircraft design, although the Blackbird relied more on its extremely high speed and altitude.
VISIBILITY:
The simplest stealth technology is simply camouflage; the use of paint or other materials to color and break up the lines of the vehicle or person.
Most stealth aircraft use matte paint and dark colors, and operate only at night. Lately, interest in daylight Stealth (especially by the USAF) has emphasized the use of gray paint in disruptive schemes, and it is assumed that Yehudi lights could be used in the future to mask shadows in the airframe (in daylight, against the clear background of the sky, dark tones are easier to detect than light ones) or as a sort of active camouflage.
CONCLUSION
The development of stealthy airplanes teaches several important lessons abouttechnology. The first is that often many different technologies must be combined to achieve adesired outcome. An advance in one field, such as materials or aerodynamics, must beaccompanied by advances in other fields, such as computing or electromagnetic theory. Thesecond lesson is that sometimes trial and error techniques are insufficient and advances inmathematical theory are necessary in order to achieve significant advances. Finally, stealthteaches 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.