Stealth & Military Camouflage: Techniques & Materials

A Seminar Report On

STEALTH AND CAMOUFLAGE: TECHNIQUES AND MATERIALS Presented By SACHIN SANJAY KUMBHAR Exam Seat no. T120520887 T.E. (Mechanical)

Guided By

Prof. Pandurang Chopade

Department of Mechanical Engineering,

INDIRA COLLEGE OF ENGINEERING AND MANAGEMENT, PUNE – 410506 [2015-16] I

Shree Chanakya Education Society’s

Indira College of Engineering & Management, Pune.

CERTIFICATE This is to certify that SACHIN S. KUMBHAR (53187) has successfully completed the Seminar work entitled “Stealth & Military Camouflage: Techniques & Materials” in the partial fulfillment of T.E (Mechanical) for Savitribai Phule Pune University

Prof. Pandurang Chopade Guide

Prof. M. K. Landage TE Coordinator

External Examiner

Date: Place:

II

Prof. M.G. Bhong HOD, Mechanical

Seal:

Acknowledgement

With immense pleasure, I am presenting this seminar report as a part of the curriculum of T.E. (Mechanical). I wish to thank all the people who gave me endless support right from the stage the idea was conceived. I would like to thank Prof. Mahesh Bhong (HOD, Mechanical Department), & Prof. Milind K. Landage (TE Coordinator) for giving me opportunity to deliver a seminar on this interesting topic. I am heartily thankful to Prof. Pandurang Chopade whose encouragement, guidance and support from the initial to the final level enabled me to develop an understanding of the subject. This seminar would not be possible without help of our internet department & library department who helped me gathering the information from various sources. Lastly, I offer my regards and blessings to all of those who supported me in any respect during the completion of the seminar.

SACHIN S. KUMBHAR T.E. (Mechanical) Exam Seat no. T120520887

III

Abstract Since its introduction into war fighting in the early years of the twentieth century, air power has become a major determinant of success or failure of military forces. The effectiveness of air forces and their equipment is driven more by technology than of other military forces used in conduct of conventional warfare. An air force with a major technological advantage over its opposing air force has usually prevailed over its technologically inferior opponent in conventional warfare During the last decades, stealth technology has proven to be one of the most effective approaches as far as the endeavour to hide from radar systems is concerned. Especially for military aircraft, “stealth” or “low observable” technology has become ubiquitous: all new aircraft types are designed taking into account low observable principles and techniques, while existing jet fighters are considered for modification in order to reduce their radar signature. Low radar signature for a target means that it is detected and tracked at a shorter distance from a radar. In the past few decades’ advent of stealth technology has been one of the most important developments in military aviation technology. This technology has played a key role in the currently sole global superpower, America's, ability to shape the world order to its desires. In the past decade stealth technology has started to percolate to other nations quite rapidly. Apart from the US, Russia, China and India have active stealth aircraft programs underway. The concept of camouflage is as old as nature, and it has been an integral part of it. All animals, small and big, are found to employ several methods of concealment and disguise for self-preservation, both in defence and offence. Practically no animal is safe, since for every animal there is a predator. Both the predator and the prey have to adopt strategies for their survival. Thus there is an evolutionary arms race between different species and also within the same species.

IV

List of Figures Figure 3-1 Radar Antenna ................................................................................................... 7 Figure 3-2 Basic Principle of RADAR [5] ......................................................................... 8 Figure 3-3 Avoiding detection by RADAR [5] .................................................................. 9 Figure 3-4 Radar Absorbing Material Illustration [4]....................................................... 10 Figure 3-5 Four Thick Radar Absorbing Material Foams and Two Samples of Thin Radar Absorbent Sheets [4] ......................................................................................................... 11 Figure 4-1 A white cock against a white background - CounterShading ......................... 17 Figure 4-2 Disruptive Colouring Example ....................................................................... 18 Figure 6-1 Difference in images generated by LIDAR & Radar [10] .............................. 24

V

Table of Contents List of Figures ................................................................................................................................... V 1

INTRODUCTION ........................................................................................................................ 1

2

LITERATURE SURVEY ................................................................................................................ 2

3

2.1

History .............................................................................................................................. 2

2.2

The Reasons for use of Stealth Technology and Camouflage .......................................... 4

2.3

Military objects requiring Stealth .................................................................................... 5

STEALTH TECHNIQUES ............................................................................................................. 6 3.1

4

3.1.1

RADAR ...................................................................................................................... 6

3.1.2

Simple Radar System................................................................................................ 7

3.1.3

Shape of the Aircraft ................................................................................................ 9

3.1.4

Radar Absorbent Material (RAM) .......................................................................... 10

3.2

Infrared Signature and Infrared Stealth ......................................................................... 11

3.3

Acoustic Signature ......................................................................................................... 13

3.4

Visual Signature ............................................................................................................. 13

3.4.1

Size and Shape ....................................................................................................... 14

3.4.2

Camouflage Paints ................................................................................................. 14

3.4.3

Active Visual Camouflage ....................................................................................... 14

3.4.4

Condensation trails (Contrails) and Exhaust Smoke .............................................. 15

CAMOUFLAGE AND DECEPTION ............................................................................................ 16 4.1

Concealment .................................................................................................................. 16

4.1.1

Colour Matching..................................................................................................... 16

4.1.2

Countershading ...................................................................................................... 17

4.1.3

Disruptive Coloration ............................................................................................. 18

4.1.4

Shadow suppression .............................................................................................. 18

4.2 5

Stealth and Radar............................................................................................................. 6

R&D Work on Camouflage & Deception ........................................................................ 19

MATERIALS USED IN STEALTH, CAMOUFLAGE AND DETECTION TECHNIQUES. .................... 20 5.1

RAM................................................................................................................................ 20

5.2

Composites .................................................................................................................... 20

6

5.2.1

Polymer Matrix Composites (PMC’s) ..................................................................... 21

5.2.2

Metal Matrix Composites (MMC’s) ........................................................................ 21

5.2.3

Ceramic Matrix Composites (CMC’s) ..................................................................... 21

5.2.4

Carbon-Carbon Composites ................................................................................... 22

DIS-ADVANTAGES OF STEALTH AND CAMOUFLAGE.............................................................. 23 6.1

Stealth Aircraft: Cost Vs Numbers ................................................................................. 23

6.2

Counter-Stealth Technologies........................................................................................ 23

6.3

Introduction of LIDAR – Light detection and Ranging.................................................... 24

6.4

Other mentionable drawbacks ...................................................................................... 24

7

HOW TO OVERCOME THE DRAWBACKS ................................................................................ 26

8

CONCLUSION.......................................................................................................................... 27

9

BIBLIOGRAPHY ....................................................................................................................... 28

Nomenclature L.O.

Low Observable

WWII

World War II

RF

Radio Frequency

EM

Electro Magnetic

RADAR

RAdio Detection And Ranging

RAM

Radar Absorbent Material

RCC

Reinforced Carbon Carbon

IR

Infrared

RCS

Radar Cross Section

WVR

Within Visible Range

DRDO

Defence Research and Development Organization

DMSRDE

Defence Materials and Stores Research and Development Establishment

C/C

Carbon Carbon

LIDAR

LIght Detection And Ranging

Stealth and Camouflage: Techniques and Materials

1

INTRODUCTION

“Stealth” as a concept is not new to warfare. Stealth used as a noun means the act of moving, proceeding, or acting in a covert way; the quality or characteristic of being furtive or covert, the act or characteristic of moving with extreme care and quietness, especially as to avoid detection or, to avoid notice. Taken in a military sense stealth could be used to mean the method(s) of avoiding notice of one’s own forces by the enemy so that these forces that have evaded notice by the enemy can be deployed in a manner that the enemy, unaware of the forces’ existence and / or location is surprised at the strategic or tactical level to his disadvantage in battle. A complete and comprehensive definition of stealth technology could be as follows: “Stealth technology also termed Low Observable (LO) technology covers a range of techniques used with personnel, aircraft, ships, submarines, missiles and satellites to make them less visible (ideally invisible) to radar, infrared, sonar and other detection methods. It corresponds to camouflage for these parts of the electromagnetic spectrum.” In more recent times “Stealth Technology has come to be associated more with military aircraft able to evade radar and other sensors designed to detect and engage aircraft. [1] On the other hand, the word ‘camouflage’ has its origin in the French word ‘camoufler’ which means ‘to disguise’. When the word entered the English dictionary initially, it had a limited meaning, implying concealment or disguise of military objects in order to prevent detection by the enemy. The only sensor available in the early days was the human eye. The means to camouflage a military object were foliage and other locally available material. [2] Human civilization, beginning with primitive man, has been using camouflage, concealment and deception in various forms for different purposes, particularly in wars. The basic philosophy remaining one and the same, the changes that have come are in the methodology of application and the levels of sophistication. [2]

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2 2.1

LITERATURE SURVEY

History Man has always tried to evade the enemy by keeping his profile or “signature”

low. In the past, that meant to take care and hide from the eyes of the enemy, i.e., to take into account the optical region. From the time of appearance and development of the radar systems, the meaning of hiding expanded also to other parts of the electromagnetic spectrum. Today, all military equipment takes into account L.O. principles trying to be discreet at all aspects, reducing acoustic, radio, radar and infrared emissions, as well as in the optical region, trying to blend into the surrounding environment. Historically, the first attempt towards the construction of an aircraft with L.O. characteristics is considered to be the German Horten Ho-229(fig. 2-1), built a little before the end of WWII. That aircraft, which never saw operational action, is said to incorporate some special graphite paint

Figure 2-1 German Horten Ho-229

Figure 2-2 B-2 Stealth Bomber

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Stealth and Camouflage: Techniques and Materials absorbing radar waves. Its special “flying wing” shape is supposed to have inspired Northrop to design later the B-2 stealth bomber (fig. 2-2) [3] Until the '70s, among the aircraft types which exhibited, intentionally or not, L.O. characteristics, one would include the British Avro Vulcan and two planes by Lockheed, the U-2 Dragon Lady and most notably the impressive, Mach 3+, SR-71 Blackbird. Despite the efforts mainly of the U.S., none of these aircraft was really difficult to detect by radar. [3] As ‘V. Kapur’ has explained in his book viz. “Stealth Technology & it’s Effect”, At a more tactical level ground forces have used camouflage (fig. 2-3) through modifications of their equipment to reduce their detectability since armies first seriously applied their minds towards delaying detection of their troops in order to gain tactical and / or strategic advantage over the enemy. Surprise was achieved when forces the enemy had not seen earlier unexpectedly entered combat. At a much more basic level in the animal kingdom predators such as the big cats (lions, tigers, panthers etc.) conceal their approach from prey by staying downwind of the prey to conceal their odour and use vegetation in the area coupled with their natural colouring and patterns to reduce visual detection until it is too late for the prey to escape (fig. 2-4). All these measures were intended to delay the detectability of friendly forces by the enemy in order to surprise the enemy. [1]

Figure 2-3 Camouflagic Uniform

Figure 2-4 Animal Camouflage

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Stealth and Camouflage: Techniques and Materials The theoretical studies aimed at delaying / denying detection were later taken up for operationalisation, when it was found that tactical means alone were inadequate for the task of achieving adequately delayed detection of flying machines. As aviation continued to be a very high technology enterprise, the application of the concept of delaying detection to aerial platforms received considerable attention and the word “stealth” entered common usage in the 1980s and 1990s as a demonstration of application of very high technology to war fighting. [1] 2.2

The Reasons for use of Stealth Technology and Camouflage ‘S. Cadirci’ has explained in his report named “RF Stealth & Counter RF

Technologies” that air operations have provided many advantages in warfare, resulting in the extensive use of aircraft to dominate the battlefield. Stealth aircraft are specifically designed with the aforementioned features and performance qualities to increase survivability, which means accomplishing the mission objectives and returning home safely. Thus, stealth capability has a very high importance in the battlefield. Further, stealth aircraft are able to accomplish and survive missions where other assets cannot. Their operational flexibility provides users the ability to penetrate even the most well defended zones with relatively little risk. Though it is not possible to become completely stealthy, either delaying the detection or lessening an opponent’s ability to track target course after detection provides a major advantage to low observable users. With stealth technology, defenders might not be able to respond at all. Another advantage of stealth technology is optimizing the force and ammunition. Because low observables have greater survivability in deployed airfields and they are safer to penetrate into deep enemy zones, they can also get closer to high value, but strongly defended targets. For example, one or two stealth aircraft can accomplish a mission while repeated sorties with many conventional aircrafts may be required. Moreover, stealth aircraft increases the operational success rate of precision bombs by allowing their deployment closer to the target.

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Stealth and Camouflage: Techniques and Materials To summarize, stealth technologies provide flexibility in tactics and mission planning. They reduce the risks of operations against heavily defended targets in enemy territory with their enhancements to survivability. Additionally, stealth aircraft maintain the sudden attack advantage in the battlefield, and they maintain the ability to escape from defensive fire before, during and after a mission. Thus an air force needs stealth technology to neutralize enemy air defences and to destroy high value, strategic targets while improving friendly forces’ air superiority. An air force with these capabilities will control the airfields and operate safely while reaching and penetrating into an enemy’s deepest territories. [4] 2.3

Military objects requiring Stealth ‘J.R. Rao’ has stated in his Book named “Introduction to Camouflage & Deception”

that in general, any military vehicle in flight, in air, sea surface or sub-surface and land, which cannot be camouflaged by convention methods need the cover of stealth. Jet fighters and bombers are two important classes of aircraft requiring stealth as they are under constant exposure to fighter planes and ground-to-air missiles. F- 117A Stealth Fighter Aircraft developed by Lockheed, and B-2 Stealth Bomber developed by Northrop for US Air Force, are two such examples. Besides the aircraft proper, antennas employed in these aircraft for their own radar systems, such as Slotted Planner Array and Conformal Phased Array type, as well as radomes which cover radar and microwave antennas, need stealth protection. In general, stealth can be applied to any military object. The relative importance of the object and its vulnerability to the various sensors and the effectiveness of stealth and cost are the factors which must be taken into consideration. [2]

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3

STEALTH TECHNIQUES

Stealth is all about using technology to defeat detection systems that operate using the EM spectrum. Ability to defeat such detection systems would deliver the benefit of surprising then enemy (as the enemy would be unaware of the presence and location of stealth enabled weapon systems). Such surprise, by achieving a high level of stealth, would be delivered primarily through application of technology. To be considered stealthy in practice an aircraft should have minimal signatures in the following areas of the EM spectrum: i.

Radar

ii.

Infra-Red

iii.

Acoustics

iv.

Visual These four factors, from the point of view of the methods of reducing detectability in

these parts of the EM spectrum, will now be discussed in brief. [1] 3.1

Stealth and Radar

3.1.1

RADAR

In order to understand how stealth technology works against radar it is essential to understand the basic simplified working principles of radars. Radar has become the most important sensor in aerial warfare since its development during WW-II. This is primarily because radar can pick up aircraft and other radar reflective objects in all weather, by day and night and at larger distances than any other sensor currently in use.

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Stealth and Camouflage: Techniques and Materials

Figure 3-1 Radar Antenna Radar also gives very precise information on target parameters (including azimuth /elevation, range and target vector etc.) thus enabling effective engagement of the target. 3.1.2

Simple Radar System

All radar systems work in much the same way. EM energy is generated in a device called a magnetron or in a Travelling Wave Tube (TWT). This energy is modulated suitably and then channelled to a directional antenna. The modulated radar energy is then transmitted into space by the directional antenna, which focuses the radar energy into a conical beam. When a reflective object blocks part of this beam, that part of the beam is reflected in many different directions. The scattering of the beam is near random and some energy will be reflected back in the direction of the radar antenna that transmitted the radar energy in the first place. Complex time sharing algorithms are used to stagger the transmission of radar energy and leave the radar antenna silent (not transmitting), i.e. in receive mode, to enable the same antenna to be used for both transmission and reception. The idea is for the radar antenna to send out a burst of radio energy, which is then reflected back by any object it happens to encounter (fig. 3-1). The radar antenna measures the time it takes for the reflection to arrive, and with that information can tell how far away

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Stealth and Camouflage: Techniques and Materials the object is. The metal body of an airplane is very good at reflecting radar signals, and this makes it easy to find and track airplanes with radar equipment. The goal of stealth technology is to make an airplane invisible to radar. There are two different ways to create invisibility: i.

The airplane can be shaped so that any radar signals it reflects are reflected away from the radar equipment.

ii.

The airplane can be covered in materials that absorb radar signals. Most conventional aircraft have a rounded shape. This shape makes them

aerodynamic, but it also creates a very efficient radar reflector. [5] The round shape means that no matter where the radar signal hits the plane, some of the signal gets reflected back. A stealth aircraft, on the other hand, is made up of completely flat surfaces and very sharp edges. When a radar signal hits a stealth plane, the signal reflects away at an angle, like this: (fig. 3-2)

Figure 3-2 Basic Principle of RADAR [5]

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Stealth and Camouflage: Techniques and Materials In addition, surfaces on a stealth aircraft can be treated so they absorb radar energy as well. The overall result is that a stealth aircraft like an F-117A can have the radar signature of a small bird rather than an airplane. The only exception is when the plane banks -- there

Figure 3-3 Avoiding detection by RADAR [5] will often be a moment when one of the panels of the plane will perfectly reflect a burst of radar energy back to the antenna. (Fig. 3-3) 3.1.3

Shape of the Aircraft

As most radar waves impinge on an aircraft at near horizontal angles, vertical surfaces on the aircraft have to be eliminated completely or at least kept to the minimum in order to reduce radar reflections. The design is not quite so simple. Any uniformly curved surface would act as part of a sphere and reflect energy randomly, some of it towards the radar site we are trying to avoid. Therefore, the curved surfaces on a stealth aircraft have to be such that they form the surface of a sphere of ever changing radius, the radii tailored to reflect the incident energy away from the radar site (such a design would require powerful supercomputers to design the spread and magnitude of the ever changing radii to ensure that reflected radar energy is directed as desired). Such a design process could be expected to be and actually is very complex and costly. In addition to the external shape of the aircraft the substructure of its construction materials, especially in areas of high radar

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Stealth and Camouflage: Techniques and Materials reflectivity, can be designed to capture and deplete the energy of the radar beams incident upon the aircraft. [1] 3.1.4

Radar Absorbent Material (RAM)

There are some materials which are inherently radar absorbent. RAMs feature free electrons in their atomic structure40. When RAMs are illuminated by a radar beam, the free electrons in the RAM’s atomic structure are forced to oscillate at the frequency of the incident radar wave. The friction and inertia of the oscillating free electrons convert the radar energy into heat and thus help to weaken it. Many carbon fibre composites such as Re-Enforced Carbon-Carbon (RCC) have very high strength in addition to being radar absorbent and thus can be used as part of the aircraft’s structure itself rather than just as coatings. [1] Generally, composites are not metal and their RF signal reflection properties are very poor, thus non-metallic airframes are considered to not show up on radar. However, the non-reflected RF signals penetrate the non-metallic airframe and this time the reflection occurs from inside which results from the radar images of engines, fuel pumps, electrical wiring and all other components. Coating or painting the surfaces of airframes with special metallic finishing is the preferred way to prevent the penetration of RF signals through composites. [4]

Figure 3-4 Radar Absorbing Material Illustration [4]

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Stealth and Camouflage: Techniques and Materials RAM includes many types of materials. Six RAM examples, low dielectric foam (epoxy); lightweight lossy foam (urethane); thermoplastic foam (polytherimide); sprayable lightweight foam (urethane); thin MAGRAM silicone resin sheet; and resistive card (R-card) made of metalized Kapton, can be seen in (Fig. 3-5) in the order of clockwise from upper left. Another example, a ferrite-based paint, which is called “iron ball”, was used on the U-2 and SR-71 to reduce the RCS. [4]

Figure 3-5 Four Thick Radar Absorbing Material Foams and Two Samples of Thin Radar Absorbent Sheets [4]

3.2

Infrared Signature and Infrared Stealth All substances with a temperature above absolute zero (0° K, or -273.15° C, or -

459.67° F), emit electromagnetic waves. The heat content of a material produces molecular vibrations which cause electron oscillations. These oscillations provide electromagnetic coupling that produces an emission of energy. This emission is called infrared radiation (IR). IR has a wavelength spectrum of 0.7 to 14 micrometres, and the amount of radiation emitted is primarily dependent on the physical temperature of the associated object (proportionally). The emissivity characteristics of an object are related to the material’s molecular structure and the surface conditions of the object. IR energy that comes from another body is either absorbed or reradiated by the object according to its emissivity properties.

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Stealth and Camouflage: Techniques and Materials As with visible light, IR energy also travels in a straight line at speed of light. Similarly, IR energy is either reflected or absorbed and converted to heat when it hits the surface of an object. These absorption and reflection qualities change with material specifications. For example, polished surfaces reflect more IR energy but also have a much lower emissivity than matte surfaces. IR energy considerations are important to stealth designers, because IR detectors, also known as infrared homing devices, such as passive missile guidance systems, can use IR emissions from a target to track it. Detector systems, especially missile guiding seekers, which detect the radiated infrared signals of their target, are often referred to as "heat-seekers". IR signal reduction is focused on engine exhausts. The back side of an engine is the major source of IR radiation in an aircraft, and when the afterburner is applied, the heat increases significantly, by nearly fifty times, since IR energy emitted from the engines is proportional to the fourth power of absolute temperature. Thus, the second generation stealth F-117 Nighthawk and the third generation strategic stealth bomber B-2 Spirit have non-afterburning engines. On the other hand, the fourth generation stealth F-22 Raptor has the ability to cruise at supersonic speeds, but without afterburner. One method to decrease the IR signature of the engines is to use exhaust masking. This is accomplished by placing the engines on top of the body and the wings. This is the reason the F-117 A and B-2 exhausts cannot be seen from below. Another technique to decrease the IR signature is using the aircraft’s aft fuselage and vertical surfaces to shield the jet pipes from view over as large a part of this rear sector as possible. After engine heat, kinetic heating of the aircraft body is the second major source of IR radiation. Some closed-loop cooling systems and special materials, such as IR signal absorbent material, can be used to dissipate the heat from the body as well as the engine and exhaust parts. However, this method has some disadvantages; such as increased weight and special maintenance requirements, similar to RCS reduction oriented RAMs. [4]

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Stealth and Camouflage: Techniques and Materials 3.3

Acoustic Signature Aircraft noise is another means of its detection. Aircraft engines are the primary source

of this signature. Application of civilian technologies, driven by noise pollution laws, to military aircraft may serve to reduce the acoustic signature. This is already underway as seen in the shift in military jet engines from pure turbojets to turbofans with ever increasing bypass ratios. Other design changes to reduce noise are also finding their way from civil engines to military engines. Jet engine noise is caused primarily by the high speed movement of high pressure air. Attempts to shape the engine’s air flow passages to reduce this noise are underway. Control of the pressure distribution inside the engine as well as the redesign of the jet nozzles is reportedly to be a promising way forward. Another source of noise is the sonic footprint of an aircraft flying at supersonic speeds. The “sonic bang” is the noise heard as the pressure discontinuity which is the shock wave caused by supersonic flight crosses over the observer’s position. With adequate listening posts deployed it could be possible to track an aircraft in supersonic flight through this noise signature alone, especially as the sonic shock waves are directional. A stealthy aircraft would usually operate at subsonic speeds. Its supersonic capability, if any, would be reserved for the escape or die / kill situations where survival or the need to secure a victory in combat over an opponent outweighs the need for stealth. Both the B-2 “Spirit” and F-117A “Nighthawk”, the two longest in service stealth aircraft, are definitely subsonic. Newer designs such as the F-22, F-35, J-20, J-31 and PAK FA have supersonic capability (this supersonic capability is expected to be coupled with very high agility for success in tactical engagements). [1] 3.4

Visual Signature Visual detection was all that was available to detect aircraft in the infancy of the

military use of aircraft in WW-I. Detection of an aircraft by the human eye still remains important, especially at the close ranges typical of Within Visual Range (WVR) aerial combat and for use of lightweight Man Portable Air Defence Systems (MANPADS) such as the “Stinger”, RBS-70, Mistral, and SAM-16 “Igla” anti-aircraft missile systems. This is because of the possibility that even a Beyond Visual Range (BVR) air combat may

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Stealth and Camouflage: Techniques and Materials terminate in a WVR engagement. Additionally, in case sensors such as radar and IR fail to pick up an opposing aircraft it may, at closer ranges, be acquired and engaged visually. Several anti-aircraft weapon systems also use optical tracking. [1] The main factors in the visual signature of an aircraft are: i.

Size and shape.

ii.

Camouflage paints.

iii.

Active camouflage.

iv.

Contrails and exhaust smoke.

3.4.1

Size and Shape

The effects of size and shape are self-explanatory. The smaller the size and the smoother the contours of an aircraft the less likely is its visual detection. The Gnat, MiG21, and JAS-39 “Gripen” due to their smaller size compared to their contemporaries, are excellent examples of aircraft with low visual signatures. 3.4.2

Camouflage Paints

The aim of camouflage paints is to reduce the contrast between the aircraft and the background that it is viewed against. Another function of camouflage paints is to help break up the distinctive shape of the aircraft. Carefully selected paints are used to paint the aircraft surface with the aim that it matches the background that it is most likely to be viewed against. [1] 3.4.3

Active Visual Camouflage

A little reflection will remind the reader that when scanning the skies to pick up aircraft the first visual acquisition of the aircraft is as a small dark speck against the sky and it is only later at much closer ranges that the actual aircraft can be clearly seen complete with its paint scheme. Obviously the delay in initial acquisition of this dark speck at a distance is desirable as only through this first step is the visual tracking of the aircraft maintainable.

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Stealth and Camouflage: Techniques and Materials If not picked up early enough it may not be possible to acquire the aircraft visually in time to take necessary action against it. A technique dubbed “active visual camouflage” is being experimented with to achieve this aim. Active visual camouflage utilises a combination of photoelectric sensors and bright lights arranged around the airframe. The sensors and lights are linked through a central electronic processing unit. The photoelectric sensors measure the illumination on their side of the aircraft. This information is processed by the electronic processing unit which then commands the powerful lights set in the aircraft on the side opposite to the sensors to illuminate to give the same intensity as picked up by the diametrically opposed sensors. Thus, the airframe is lit up to match the ambient background illumination that it can be viewed against from all directions. [1] 3.4.4

Condensation trails (Contrails) and Exhaust Smoke

Aircraft engines burn hydrocarbon fuels. The by-products of combustion of the fuel include carbon oxides and water vapour and these are ejected from the exhaust along with other waste gases. At certain ambient conditions the water vapour in the exhaust gases condenses into a thick cloud like white trail called a condensation trail (contrail). Two methods exist to avoid the formation of contrails. The first is to avoid flying between the minimum trail (mintra) and maximum trail (maxtra) levels. This would in effect limit the operating envelope of an aircraft. The second method is to use chemical additives that change the size of water droplets present in the exhaust gases Smoke is present in the exhaust due to incomplete or inefficient combustion of fuel in the combustion chamber. Any power plant considered for use in a stealth aircraft would have to be smokeless. This can be achieved by electronic air-fuel mixture control and good combustion chamber designed for efficient combustion. [1]

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Stealth and Camouflage: Techniques and Materials

4

CAMOUFLAGE AND DECEPTION

As applied to nature, camouflage may be defined as the means by which animals escape the notice of predators or as a device or expedient designed to conceal or deceive. Whatever be the strategy adopted, deception is inherent in all of them since the true appearance of the animal is replaced by a false one. [2] 4.1

Concealment Concealment is a widely adopted method of camouflage. In nature, there are a variety

of backgrounds characterised by homogeneity and heterogeneity in colour, and structural simplicity and complexity. The predominant colours of various backgrounds are green and brown, besides sea blue and grey. These colours occur either singly or in combination, along with tonal and hue variations. Forests, woodlands, mountainous and rocky regions are complex backgrounds while deserts, seas and snow regions are simple. Cott gives an excellent account of camouflage in nature in his book, 'Adaptive Coloration in Animals'. The various principles that are found to operate by which different animals are concealed in their respective backgrounds are: [2] i.

Colour matching

ii.

Countershading

iii.

Disruptive colouration

iv.

Shadow suppression

4.1.1

Colour Matching

The first and the foremost requirement for an animal to blend with its background is to have on its body the prevailing colour of the environment. Several varieties of caterpillars, butterflies, grasshoppers, mantis, frogs, and birds are predominantly green in colour, which reduces their probability of detection in their green background. Lizards and several other species living on boughs, tree trunks and barks are usually brown in colour.

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Stealth and Camouflage: Techniques and Materials Animals living in deserts have on their bodies dusty brown coats. In snow-bound areas white colour is predominantly seen on birds and mammals. Fishes which dwell in water have transparent bodies. Those living on sea shore and sea bottom bear on their bodies appropriate colours harmonising with their backgrounds. Multicolours are found on species which Eve on flowers. Thus concealment is attained in animals in nature, broadly, by bearing colour resemblance to their respective environment. [2] 4.1.2

Countershading

The principle of countershading is also found to be operative in the camouflage scheme of animals. Figure 4-1 shows a white cock against white background; yet, it is conspicuously seen and recognized.

Figure 4-1 A white cock against a white background - CounterShading Although countershading in nature gives a degree of invisibility to the animal, further studies are needed to establish its role and value. [2]

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Stealth and Camouflage: Techniques and Materials 4.1.3

Disruptive Coloration

The two important characteristics by which any object is recognised are specific surface area and specific contour by which it is bounded. These two characteristics fix the size and shape of the object by which it is recognised. So, if these two characteristics are destroyed, recognition is not possible. This is what is accomplished in disruptive colouration. Figure 4-2 shows example of the same. [2]

Figure 4-2 Disruptive Colouring Example 4.1.4

Shadow suppression

An animal which is otherwise well camouflaged by the methods mentioned above can still be recognised indirectly by its shadow cast on the ground under the action of sunlight. The probability of recognition by the shadow depends on the nature of the surface on which it is cast. If the surface is smooth, the shadow is well defined; if the surface is uneven or irregular, the shadow is distorted or broken, making recognition difficult. Shadow

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Stealth and Camouflage: Techniques and Materials suppression becomes more important in the case of animals such as lizards, birds, butterflies, moths, etc. whose habitats are relatively flat and even, and exposed to sunlight. Butterflies compress their shadow into unrecognisable form by resting with their wings folded and orient their body with respect to the direction of sunlight in such a way that the shadow gets reduced practically into a line. Some butterflies tilt their bodies or wings in such a way that their shadow is hidden. Moths keep their body and wings depressed to the surface and crouch low. In some categories of animals, the dark elements in their disruptive patterns and the shadow together make recognition difficult. [2] 4.2

R&D Work on Camouflage & Deception The Defence Research and Development Organisation (DRDO) has been giving

special emphasis in recent years to research and development in the field of camouflage and deception. DMSRDE has been working on the development of camouflage paints and synthetic nets. The laboratory has developed paints and pre-garnished light weight synthetic camouflage nets for visible and NIR regions, conforming to colour schemes/patterns suitable for green belt areas, desert terrains and coastal areas. It has also developed polystyrene emulsions, polystyrene solvents and silicate based camouflage paints for effectively camouflaging runways and taxi tracks. DMSRDE and DW have been carrying out R&D on development of multi-spectral camouflage materials. DW has synthesised a large number of materials such as conducting polymers, liquid crystals, liquid foam and materials for anti-reflective coatings. DMSRDE has initiated a programme for developing a multi-spectral camouflage system which should be able to cater for visible, NIR, thermal IR and centimetre and millimetre wave radar regions. [2]

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5

5.1

MATERIALS USED IN STEALTH, CAMOUFLAGE AND DETECTION TECHNIQUES.

RAM Radiation-absorbent material, usually known as RAM, is a material which has been

specially designed and shaped to absorb incident RF radiation (also known as non-ionising radiation), as effectively as possible, from as many incident directions as possible. To be sufficiently lossy, RAM can be neither a good electrical conductor nor a good electrical insulator as neither type actually absorbs any power. Typically, pyramidal RAM will comprise a rubberized foam material impregnated with controlled mixtures of carbon and iron. [6] A material's absorbency at a given frequency of radar wave depends upon its composition. RAM cannot perfectly absorb radar at any frequency, but any given composition does have greater absorbency at some frequencies than others; no one RAM is suited to absorption of all radar frequencies. [6] A common misunderstanding is that RAM makes an object invisible to radar. A radarabsorbent material can significantly reduce an object's radar cross-section in specific radar frequencies, but it does not result in "invisibility" on any frequency. Bad weather may contribute to deficiencies in stealth capability. [6] 5.2

Composites Dielectric composites are transparent to radar. Composites may also contain ferrites to

optimize the dielectric and magnetic properties of a material for its application. Composites are combinations of two materials in which one of the materials, called the reinforcing phase, is in the form of fibres, sheets, or particles, and are embedded in the other materials called the matrix phase. The reinforcing material and the matrix material can be metal, ceramic, or polymer. [7]

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Stealth and Camouflage: Techniques and Materials One may conveniently speak of four generations of composites: 1st generation (1940s):

2nd generation (1960s):

Glass Fiber Reinforced Composites

High Performance Composites in the postSputnik era 4th generation (1990s):

3rd generation (1970s & 1980s):

The Search for New Markets and the Hybrid Materials, Nano composites and Synergy of Properties Biomimetic Strategies

5.2.1

Polymer Matrix Composites (PMC’s)

Polymer matrix composites are the most commonly used of the advanced composite materials. These materials can be fashioned into a variety of shapes and sizes. They provide great strength and stiffness along with a resistance to corrosion. The organic polymer matrix can be thermosetting or thermoplastic and gains its strength from fibres of carbon or boron. 5.2.2

Metal Matrix Composites (MMC’s)

Although heavier than PMC’s, metal matrix composites possess greater tensile strength, higher melting points, smaller coefficients of expansion, higher ductility and increased toughness. At the present time the focus seems to be on the development of matrices of aluminium, magnesium and titanium. 5.2.3

Ceramic Matrix Composites (CMC’s)

Naturally resistant to high temperatures, ceramic materials have a tendency to be brittle and fracture. Composites successfully made with ceramic matrices are reinforced with silicon carbide fibres. These composites offer the same high temperature tolerance of super alloys but without such a high density. The brittle nature of ceramics makes composite fabrication difficult. Usually most CMC production procedures involve starting materials in powder form.

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Stealth and Camouflage: Techniques and Materials 5.2.4

Carbon-Carbon Composites

Coveted for superior strength-to-density ratios at temperatures in excess of 1200K, carbon-carbon composites are excellent structural materials. Availability of carbon fibres in the late 1950s led to development of improved materials now known as carbon-carbon (C/C) composites. These composites are a family of materials which consist of a carbon (or graphite) matrix reinforced with carbon (or graphite) fibres. Thus the attractive properties of carbon are combined with the high strength, versatility and toughness of composites. The C/C family is unique in that it is the only elemental composite. Carbon-carbon composites range from simple unidirectional fibre reinforced structures to complex woven 3-dimensional structures. The variety of carbon fibres and multidirectional weaving techniques now available allow tailoring of C/C composites to meet complex design requirements. By selection of fibre-type, lay-up (or fibre-weave), matrix and composite heat treatment, the properties can be suited to different applications. [8]

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Stealth and Camouflage: Techniques and Materials

6 6.1

DIS-ADVANTAGES OF STEALTH AND CAMOUFLAGE

Stealth Aircraft: Cost Vs Numbers Stealth aircraft prove that stealth comes at a high cost. The high cost of development

of stealth aircraft as well as the high cost of manufacturing these aircraft has led even the US to curtail the numbers built. For instance, the US built only 21 B-2 (20 aircraft for USAF service and one for test and evaluation) and has capped its F-22 purchase at just 187 aircraft. Stealth technology is unlikely to be able to make up for numbers entirely and vice versa. Though, stealth aircraft technology is not a replacement for numbers per se, availability of stealth aircraft does enable an air force to do more with less especially in an offensive campaign. [1] A single unit of a B-2 Stealth Bomber cost approximately $1.1 Billion & its operating cost for 1 hour is around $130,159. 6.2

Counter-Stealth Technologies An aircraft cannot be made truly invisible. For example, no matter how cool the

exhaust vents of an aircraft are kept, the same amount of heat is always liberated by burning a given amount of fuel, and this heat must be left behind the aircraft as a trail of warm air. Infrared-detecting devices might be devised that could image this heat trail as it formed, tracking a stealth aircraft. 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. Anti-Stealth/ counter stealth can be achieved: [9] i.

By triangulating its location with a network of radar systems.

ii.

With the help of microwaves similar to the ones emitted by the cell phone towers.

iii.

By using over the horizon radar, ultra-wide band (impulse) radar, bi-static radar, imaging radar and IR imaging seekers.

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Stealth and Camouflage: Techniques and Materials 6.3

Introduction of LIDAR – Light detection and Ranging LIDAR is a Multi-Band and Multi-Static anti-stealth technology. Laser radar can

detect stealth targets efficiently because it has short wavelength, high beam quality, high directionality and high measuring accuracy, which helps functions of target identifying, posture displaying and orbit recording. Apart from these, LIDAR holds higher resolution and counter -jamming ability due to its coherence property and ultimately high frequency. The below Fig. illustrates the difference in image generated using LIDAR and RADAR [10]

Figure 6-1Difference in images generated by LIDAR & Radar [10]

6.4

Other mentionable drawbacks

i.

Stealth aircraft cannot fly as fast or is not manoeuvrable like conventional aircraft.

ii.

Another serious drawback 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.

iii.

Since the radar cross-section of an aircraft depends on the angle from which it is viewed, an aircraft will typically have a much smaller RCS when viewed from the

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Stealth and Camouflage: Techniques and Materials front or rear than when viewed from the side or from above. In general stealth aircraft are designed to minimize their frontal RCS. But it is not possible to contour the surface of an aircraft to reduce the RCS equally in all directions, and reductions in the frontal RCS may lead to a larger RCS from above. iv.

Another drawback of stealth aircraft is their vulnerability to detection by bi-static radars. [9]

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Stealth and Camouflage: Techniques and Materials

7

HOW TO OVERCOME THE DRAWBACKS

The drawback of this technology can be overcome by the following methods: i.

Aircraft designed primarily to supplement and replace by incorporating new stealth features and propulsion technology. These advances include its angular design, use of radar-absorbent composite materials, and the ability to "super cruise" at supersonic speeds without using an afterburner. The Aircraft also emphasizes agility through the use of thrust vectoring nozzles and a sophisticated fly-by-wire control system.

ii.

Other advanced systems aboard the Raptor include an integrated avionics suite built around a powerful flight computer with three times the memory and 16 times the speed can be used and also uses a navy/attack system that incorporates artificial intelligence to filter information to the pilot reducing his workload as well as improving his situational awareness.

iii.

The Aircraft can be advanced by incorporating Nano-materials rather than other materials which increases the strength and reduces the weight hence it can carry more pay load.

iv.

The contouring of a stealth aircraft is so designed to avoid reflecting a radar signal directly back in the direction of the radar transmitter from both side of bi-static radars. [9]

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Stealth and Camouflage: Techniques and Materials

8

CONCLUSION

The word ‘Stealth’ has a heavy weight in contemporary weapon systems. Stealth or low observable technology which has come up is trying to face many challenges. Although primarily the technology is intended to defy detection of fighter aircraft and bombers by radar, it has to counter detection by visible, near IR, thermal infrared, acoustic, electrical, magnetic, etc. depending upon the actual situation. Conventional methods of camouflage and deception cater for only the preliminary stages of the stealth technology. Starting from the design stage of the military object, stealth technology has to take into consideration all aspects - shape, structure, surface materials and surface appliques - to reduce all possible signatures to levels from which they cannot be detected. As stealth technology advances further, it is imperative that technologies to counter stealth should also be developed. These developments involve more powerful and versatile sensors. The new stealth technology may create false signatures to confuse the sensors. Further, the weapon platforms, weapons and weapon delivery systems may have characteristics which may change depending upon the requirements. These variations in the characteristics may make the task of the sensors difficult. On the whole, the world of camouflage and deception, or in its modern terminology, ‘countermeasures’ or ‘low observables’, has to face greater challenges in future. It demands a thoughtful combination of research in a variety of basic sciences, their application to specific situations, development of newer materials to cater to a wide variety of rigorous specifications, innovative design techniques, and cost-effective production technologies. It is a never-ending battle of wits between advances in sensor technology and corresponding countermeasures!

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BIBLIOGRAPHY

[1] V. KAPUR, STEALTH TECHNOLOGY AND ITS EFFECT ON AERIAL WARFARE, New Delhi: Institute for Defence Studies and Analyses, 2014. [2] J. R. Rao, INTRODUCTION TO CAMOUFLAGE AND DECEPTION, Delhi: Director, DESIDOC, Metcalfe House, Delhi-1 10 054, 1999. [3] K. Zikidis, A. Skondras and C. Tokas, “Low Observable Principles, Stealth Aircraft and AntiStealth Technologies,” Journal of Computations & Modelling, vol.4, no.1, 2014, 129-165, vol. 4, no. 1792-8850, pp. 129-165, 2014. [4] S. Cadirci, RF STEALTH (OR LOW OBSERVABLE) AND COUNTER RF STEALTH TECHNOLOGIES, Turkey: NAVAL POSTGRADUATE SCHOOL, 2009. [5] “How Stuff Works,” [Online]. Available: http://science.howstuffworks.com/question69.htm/printable. [Accessed March 2016]. [6] “Wikipedia - Stealth Technology,” [Online]. Available: https://en.wikipedia.org/wiki/Stealth_Technology. [7] Ashwin.V and Abirami.K, “STEALTH TECHNOLOGY: For Military Aircrafts using Composite Materials,” P.S.G. College of Technology, Peelamedu., Coimbatore, 2013. [8] “TWI,” [Online]. Available: http://www.twi-global.com/technicalknowledge/faqs/material-faqs/faq-what-are-carbon-carbon-composites/. [Accessed March 2016]. [9] I. KUMAR, “6th GENERATION STEALTH AIRCRAFT,” International Journal of Research In Science & Engineering, vol. 1, no. 2, pp. 07-15, 2015. [10] S. Arora and R. Kaur, “Stealth Technology And Counter Stealth Radars: A Review,” International Journal Of Engineering And Science, vol. 3, no. 12, pp. 15-19, 2013.

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