Radar absorbent material technology. How absorbent a Radar absorbent material , or RAM, is a class of materials used in Stealth technology. radar absorbment material is depends upon the frequency of radar used on the particular material. RAM cannot be said to perfectly absorb radar on any frequency, but they do have greater a bsorbancy on some frequencies than others. Different radar absorbent materials will have different frequency ranges that they absorb best, so theres no one RAM that is suited to absorption of all radar frequencies. A common misconception is that RAM ma!es an ob"ect invisible to radar. A radar absorbent material can significantly reduce an ob"ects radar cross section in section in specific radar frequencies, but it does not result in #invisibility# #invisibility# on any an y frequency. $ad weather may contribute to deficiencies in stealth capability% a particularly disastrous e&le occurred during the 'osovo war , in which moisture on the surface of () of () **+ ighthaw!s allowed ighthaw!s allowed long)wavelength radar to trac! and shoot them down. RAM is only a part of achieving stealth.
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* Hi Hist stor ory y / 0ypes of RAM /.* 1ron bal balll pain paintt o /./ (oa (oam m abs absorb orber er o /.2 3aumann absorber o 2 Se Seee al also so 4 Refe Referen rences ces
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History 0he earliest forms of RAM were the materials called Sumpf and and Schornsteinfeger , a coating used by 7ermans during the 8orld 8ar 11 for 11 for the snor!els snor!els of of submarines submarines,, to lower their reflectivity in the /9) centimeter radar band the Allies used. 0he material had a layered structure and was based ongraphite on graphite particles and other semiconductive materials embedded in a rubber matri&. matri&. 0he materials efficiency was -*--/ -* partially reduced by the action of sea water . 7ermany also pioneered the first aircraft to use RAM, in the form of the Horten Ho //:. //:.-2 1t used a carbon)impregnated plywood that would have made it e&tremely stealthy to $ritains crude radar of the time. 0he same flying wing design can be seen in the ;S $)/ Spirit, Spirit, and it is no coincidence. 0owards 0owards the end of 8orld 8orld 8ar 8ar 11, the ;S captured the Ho //: and a nd sent it to orthrop, who later developed the $)/. 7ermany can be said to have ha ve been the forefather of RAM technology, technolog y, and stealth aircraft. aircraft.
Types of RAM Iron ball paint
0he iron particles in the paint are obtained by decomposition of iron pentacarbonyl and may contain traces of carbon, o&ygen and nitrogen. =arbonyl iron is also used as a catalyst and in medicine as an iron supplement, even though it is to&ic in higher doses. A related type of RAM consists of neoprene polymer sheets with ferrite grains or carbon blac! particles >containing about 29? of crystalline graphite@ embedded in the polymer matri&. 0he tiles were used on early versions of the ()**+A ighthaw! , although more recent models use painted RAM. 0he painting of the ()**+ is done by industrial robots with the plane cov ered in tiles glued to the fuselage and the remaining gaps filled with iron ball paint. 0he ;nited States Air (orce introduced a radar absorbent paint made from both ferrofluidic and non) magnetic substances. $y reducing the reflection of electromagnetic waves, this material helps to reduce the visibility of RAM painted aircraft on radar.
Foam absorber Foam absorber is used as lining of anechoic chambers for electromagnetic radiation measurements. 0his material typically consists of a fireproofed urethane foam loaded with carbon blac!, and cut into long pyramids. 0he absorber is applied to the chamber walls with the tips of the pyramids pointing inward or toward the radar. As a radar wave stri!es a pyramid, it e&periences a gradual transition from free space at the tip of the pyramid to absorbing foam at the base.
Jaumann absorber A Jaumann absorber or Jaumann layer is a radar absorbent device. 8hen first introduced in * :42, the 3aumann layer consisted of two equally)spaced reflective surfaces and a conductive ground plane.
i.e. it uses wave interfering to cancel the reflected wave@, the 3aumann layer is dependent upon the BC4 spacing between the first reflective surface and the ground plane and between the two reflective surfaces >a total of BC4 BC4 @. $ecause the wave can resonate at two frequencies, the 3aumann layer produ ces two absorption ma&ima across a band of wavelengths >if using the two layers configuration@. 0hese absorbers must have all of the layers parallel to each other and the ground plane that they conceal. More elaborate 3aumann absorbers use series of dielectric surfaces that separate conductive sheets. 0he conductivity of those sheets increases with pro&imity to the ground plane.
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Radar cross section Stealth technology Salisbury screen Stealth aircraft
References *. ^ Hepc!e, 7erhard. #The Radar War, 1930-1945# >ED(@. Radar 8orld. /. ^ 0he History of Radar (Enlis!" >H0MF@. $$= >/992)9+)*4@.
2. ^ Horten Ho //: (Enlis!" >H0MF@. All6&perts.
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8ave absorber ) patent 5:5/:52
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Radar cross section (rom 8i!ipedia, the free encyclopedia
3ump toG navigation, search Radar cross section >R=S@ is a description of how an ob"ect reflects an incident electromagnetic wave. (or an arbitrary ob"ect, the R=S is highly dependent on the radar wavelength and incident direction of the radio wave. 0he usual definition or R=S differs by a factor of 4 I from the standard physics definition of differential cross section at *J9 degrees. $istatic radar cross section is defined similarly for other angles.
0he R=S is integral to the development of radar stealth technology, particularly in applications involving aircraft and ballistic missiles. R=S data for current military aircraft are almost all highly classified.
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Measurement Measurement of a targets R=S is performed at a radar reflectivity range or scattering range. 0he first type of range is an outdoor range where the target is positioned on the pylon some distance down)range from the transmitters. Such a range eliminates the need for p lacing radar absorbers behind the target, however multi)path effects due to the ground must be mitigated. An anechoic chamber is also commonly used. 1n such a room, the target is placed on a rotating pillar in the center, and the walls, floors and ceiling are covered by stac!s of radar absorbing material. 0hese
absorbers prevent corruption of the measurement due to reflections. A compact range is an anechoic chamber with a reflector to simulate far field conditions.
Calculation Luantitatively, the R=S is an effective surface area that intercepts the incident wave and that scatters the energy isotropically in space. (or the R=S, is defined in three)dimensions as
8here is the R=S, P i is the incident power density measured at the target, and P s is the scattered power density seen at a distance R away from the target. 1n electromagnetic analysis this is also commonly written as
where E i and E s are the incident and scattered electric field intensities, respectively. 1n the design phase, it is often desirable to employ a computer to predict what the R=S will loo! li!e before fabricating an actual ob"ect. Many iterations of this prediction process can be performed in a short time at low cost, whereas use of a measurement range is often time)consuming, e&pensive and error)prone. 0he linearity of Ma&wells equations ma!es R=S relatively straightforward to calculate with a variety of analytic and numerical methods, but changing levels of military interest and the need for secrecy have made the field challenging, none the less. 0he field of solving Ma&wells equations through numerical algorithms is called computational electromagnetics, and many effective analysis methods have been applied to the R=S prediction problem. R=S prediction software are often run on large supercomputers and employ high)resolution =AD models of real radar targets. High frequency appro&imations such as geometric optics, Ehysical method of moments@, finite difference time domain method >(D0D@ and finite element methods are limited by computer performance to longer wavelengths or smaller features. 0hough, for simple cases, the wavelength ranges of these two types of method overlap considerably, for difficult shapes and materials or very high accuracy they are combined in various sorts of hybrid methods.
Reduction R=S reduction is chiefly important in stealth technology. 8ith smaller R=S, aircraft and other military vehicles may better evade radar detection, whether it be from land)based installations or other vehicles.
%urpose S!apin Eurpose shaping is an R=S reduction technique in which the shape of the targetNs reflecting surfaces is designed such that they reflect energy away from the source. 0he aim is usually to create a O cone)of) silenceP about the aircraftNs direction of flight. ote that due to the energy reflection, this R=S reduction method is defeated by using Eassive >multistatic@ radars.
Eurpose)shaping techniques can be seen in the design of surface faceting on the ()**+A ighthaw! stealth fighter. 0his aircraft, designed in the late *:+9s though only revealed to the public in *:JJ, uses a multitude of flat surfaces to reflect incident radar energy away from the source. Que suggests that limited available computing power for the design phase !ept the number of surfaces to a minimum. 0he $)/ Spirit stealth bomber benefited from increased computing power, enabling its contoured shapes and further reduction in R=S. 0he ()// Raptor and ()25 3oint Stri!e (ighter continue the trend in purpose shaping and promise to have even smaller monostatic R=S.
Acti&e Cancellation 1n active cancellation techniques, the target aircraft generates a radar signal equal in intensity but opposite in phase to the predicted reflection of an incident radar signal >similarly to noise canceling ear phones@. 0his creates destructive interference between the reflected and generated signals, resulting in reduced R=S. 0o incorporate active cancellation techniques, the precise characteristics of the waveform and angle of arrival of the illuminating radar signal must be !nown, since they define the nature of generated energy required for cancellation. 6&cept against simple or low frequency radar systems, the implementation of active cancellation techniques is e&tremely difficult due to the comple& processing requirements and the difficulty of predicting the e&act nature of the reflected radar signal o ver a broad aspect of an aircraft, missile or other target.
RAM 0he third R=S reduction technique for aircraft and missiles is the use of radar absorbing material >RAM@ either in the original construction or as an addition to highly reflective surfaces. 0here are at least three types of RAMG resonant, non)resonant magnetic and non)resonant large volume. Resonant but somewhat OlossyP materials are applied to the reflecting surfaces of the target. 0he thic!ness of the material corresponds to one)quarter wavelength of the e&pected illuminating radar)wave. 0he incident radar energy is reflected from the outside and inside surfaces of the RAM to create a destructive interference pattern. 0his results in the cancellation of the reflected energy. Deviation from the e&pected frequency will cause losses in radar absorbence, so this type of RAM is only useful against radar with a single, common, and unchanging frequency. on)resonant magnetic RAM uses ferrite particles suspended in epo&y or paint to reduce the reflectivity of the surface to incident radar waves. $ecau se the non)resonant RAM dissipates incident radar energy over a larger surface area, it usually results in an increase in surface temperature, thus reducing R=S at the e&pense of an increase in infrared signature. A ma"or advantage of non)resonant RAM is that it can be effective over a broad range of frequencies, whereas resonant RAM is limited to a narrow range of design frequencies. Farge v olume RAM is usually resistive carbon loading added to fiberglass he&agonal cell aircraft structures or other non)conducting components. (ins of resistive materials can also be added. 0hin resistive sheets spaced by foam or aerogel may be suitable for space craft. 0hin coatings made of only dielectrics and conductors have very limited absorbing bandwidth, so magnetic materials are used when weight and cost permit, either in resonant RAM or as non)resonant RAM.
'ptimiation met!ods 0hin non)resonant or broad resonance coatings can be modeled with a Feontovich impedance boundary condition. 0his is the ratio of the tangential electric field to the tangential magnetic field on the surface, and ignores fields propagating along the surface within the coating. 0his is particularly convenient when using boundary element method calculations. 0he surface impedance can be calculated and tested separately. (or an isotropic surface the ideal surface impedance is equal to the 2++ anisotropic@ coatings, the optimal coating depends on the shape of the
target and the radar direction, but duality, the symmetry of Ma&wells equations between the electric and magnetic fields, tells one that optimal coatings have 9 * T 2++/ U/, where 9 and * are perpendicular components of the anisotropic surface impedance, aligned with edges andCor the radar direction. A perfect electric conductor has more bac! scatter from a leading edge for the linear polariation with the electric field parallel to the edge and more from a trailing edge with the electric field perpendicular to the edge, so the high surface impedance should be parallel to leading edges and perpendicular to trailing edges, for the greatest radar threat direction, with some sort of smooth transition between. 0o calculate the radar cross section of such a stealth body, one would typically do one dimensional reflection calculations to calculate the surface impedance, then two dimensional numerical calculations to calculate the diffraction coefficients of edges and small three dimensional calculations to calculate the diffraction coefficients of corners and points. 0he cross section can then be calculated, using the diffraction coefficients, with the physical theory of diffraction or other high frequency method, combined with Ehysical
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Shaeffer, 0uley and 'nott. Radar ross Section. Sci0ech Eublishing, /994. 1S$ *)J:**/*)/5)*. Harrington, Roger (. Time-!armonic E"ectromagnetic #ie"ds. Mc7raw)Hill, 1nc., *:K*. 1S$ 9+9/K+45K. $alanis, =onstantine A. $d%anced Engineering E"ectromagnetics. 8iley, *:J:. 1S$ 9)4+*) K/*:4)2. OA Hybrid Method $ased on Reciprocity for the =omputation of Diffraction by 0railing 6dgesPDavid R. 1ngham, &EEE Trans' $ntennas Propagat', 42 o. **, ovember *::5, pp. **+2V J/. ORevised 1ntegration Methods in a 7aler!in $oR ErocedureP David R. 1ngham, $pp"ied omputationa" E"ectromagnetics Societ( )$ES * +ourna" *9 o. /, 3uly, *::5, pp. 5V*K. OA Hybrid Approach to 0railing 6dges and 0railing 6ndsP David R. 1ngham, proceedings of the $ES S(mposium, *::2, Monterey. O0ime)Domain 6&trapolation to the (ar (ield $ased on (D0D =alculationsP 'ane Qee, David 1ngham and 'urt Shlager, &EEE Trans' $ntennas Propagat', 2: o. 2, March *::*, pp.4*9V4*2. Oumerical =alculation of 6dge Diffraction, using ReciprocityP David 1ngham, Proc' &nt' onf' $ntennas Propagat', 1W, May *::9, Dallas, pp.*5+4V*5++. O0ime)Domain 6&trapolation to the (ar (ield $ased on (D0D =alculationsP'ane Qee, David 1ngham and 'urt Shlager, invited paper, Proc' RS& onf', *:J:, San 3osX .
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1ndoor Microwave Measurement (acility at System Elanning =orporation lucernhammer R=S Erediction Software by 0ripoint 1ndustries, 1nc.
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Radar cross)section (RCS" reductions *of stealt!+ Radar avoidance technology was first used on a large scale during the 7ulf 8ar in *::*. However, () **+A Stealth (ighters were used for the first time in combat during the ;nited States invasion of Eanama >a!aG
,e!icle s!ape 0he possibility of designing aircraft in such a manner as to reduce their radar cross)section was recognised in the late *:29s, when the first radar trac!ing systems were employed, and it has b een !nown since at least the *:K9s that aircraft shape ma!es a very significant difference in how well an aircraft can be detected by a radar. 0he Avro Wulcan, a $ritish bomber of the *:K9s, had a remar!ably small appearance on radar despite its large sie, and occasionally disappeared from radar screens entirely. 8e now !now that it had a fortuitously stealthy shape apart from the vertical element of the tail. A0< reporting name $ear@ appeared especially well on radar. 1t is now !nown that propellers and "et turbine blades produce a bright radar image% the $ear had four pairs of large >5.K metre diameter@ contra)rotating propellers. Another important factor is the internal construction. $ehind the s!in of some aircraft are structures !nown as re)entrant triangles. Radar waves penetrating the s!in of the aircraft get trapped in these structures, bouncing off the internal faces and losing energy. 0his approach was first used on SR)+*. 0he most efficient way to reflect radar waves bac! to the transmitting radar is with orthogonal metal plates, forming a corner reflector consisting of either a dihedral >two plates@ or a trihedral >three orthogonal plates@. 0his configuration occurs in the tail of a conventional aircraft, where the vertical and horiontal components of the tail are set at right angles. Stealth aircraft such as the ()**+ use a different arrangement, tilting the tail surfaces to reduce corner reflections formed between them. 0he most radical approach is to eliminate the tail completely, as in the $)/ Spirit. 1n addition to altering the tail, stealth design must bury the engines within the wing or fuselage, or in some cases where stealth is applied to an e&isting aircraft, install baffles in the air inta!es, so that the turbine blades are not visible to radar. A stealthy shape must be devoid of comple& bumps or protrusions of any !ind% meaning that weapons, fuel tan!s, and other stores must not be carried e&ternally. Any stealthy vehicle becomes un)stealthy when a door or hatch is opened. Elanform alignment is also often used in stealth designs. Elanform alignment involves using a small number of surface orientations in the shape of the structure. (or e&le, on the ()//A Raptor, the leading edges of the wing and the tail surfaces are set at the same angle. =areful inspection shows that many small structures, such as the air inta!e bypass doors and the air refueling aperture, also use the same angles. 0he effect of planform alignment is to return a radar signal in a very specific direction away from the radar emitter rather than returning a diffuse signal detectable at many angles. Stealth airframes sometimes display distinctive serrations on some e&posed edges, such as the engine ports. 0he Q()/2 has such serrations on the e&haust ports. 0his is another e&le in the use of re)entrant triangles and planform alignment, this time on the e&ternal airframe.
Shaping requirements have strong negative influence on the aircrafts aerodynamic properties. 0he ()**+ has poor aerodynamics, is inherently unstable, and cannot be flown without computer assistance. Some modern anti)stealth radars target the trail of turbulent air behind it instead, much li!e civilian wind shear detecting radars do. Shaping does not offer stealth advantages against low)frequency radar. 1f the radar wavelength is roughly twice the sie of the target, a half)wave resonance effect can still generate a significant return. However, low)frequency radar is limited by lac! of available frequencies which are heavily used by other systems, lac! of accuracy given the long wavelength, and by the radars sie, ma!ing it difficult to transport. A long)wave radar may detect a target and roughly locate it, but not identify it, and the location information lac!s sufficient weapon targeting accuracy. oise poses another p roblem, but that can be efficiently addressed using modern computer technology% =hinese #antsin# radar and many older Soviet)made long)range radars were modified this way. 1t has been said that #theres nothing invisible in the radar frequency range below / 7H#. -* Ships have also adopted similar techniques. 0he Wisby corvette was the first stealth ship to enter service, though the earlier Arleigh $ur!e class destroyer incorporated some signature)reduction features -/.
-on)metallic airframe Dielectric composites are relatively transparent to radar, whereas electrically conductive materials such as metals and carbon fibers reflect electromagnetic energy incident on the materials surface. =omposites used may contain ferrites to optimie the dielectric and magnetic properties of the material for its application.
Radar absorbin paint Radar absorbing paint or radar absorbent material >RAM@, is used especially on the edges of metal surfaces. 0he RAM coating, !nown also as iron ball paint, contains tiny spheres coated with carbonyl iron ferrite. Radar waves induce alternating magnetic field in this material, which leads to conversion of their energy into heat. 6arly versions of ()**+A planes were covered with neoprene)li!e tiles with ferrite grains embedded in the polymer matri&, current models h ave RAM paint applied directly. 0he paint must be applied by robots because of issues relating to solvent to&icity and tight tolerances on layer thic!ness. 1n a similar vein, it is !nown that coating the coc!pit canopy with a thin film transparent conductor >vapor)deposited gold or indium tin o&ide@ helps to reduce the aircrafts radar profile because radar waves would normally enter the coc!pit, bounce off something random >the inside of the coc!pit has a comple& shape@, and possibly return to the radar Y but the conductive coating creates a controlled shape that deflects the incoming radar waves away from the radar. 0he coating is thin enough that it has no adverse effect on the pilots vision.
Salisbury screen 0he Salisbury screen is maybe the first ever anti)radar or, to be more precise, anti)reflective concept% the so called RAM >radar absorbent material@. 1t was first described in *:5/ and was ap plied in ship radar cross section reduction >R=S@. 0here have been many design refinements over the years especially because of the increasing interest for stealth planes, but the principles remain the same.
0he most easy to understand salisbury screen design co nsists of a ground p"ane which is the metallic surface that needs to be concealled, a lossless dielectric of a given thic!ness >a quarter of the wavelength that will be absorbed@ and a thin lossy screen. 0he principle is thisG *. 0he incident wave >which we will consider to be made up by parallel beams@ is split into two >equal in intensity@ waves that have the same wavelength >B@ /. 0he first wave is reflected by the e&terior surface >the thin lossy screen@ while the second beem travels through the dielectric, and it is reflected by the ground plane >which is the most inner layer of the sailsbury screen@ 2. 0he reflected waves interfere and cancel each otherNs electric fields >radar is an electromagnetic beam)microwave and 1R @ 0o e&plain the phenomenon, we need to loo! at the interference theory. 0wo waves that arecoherent interact, they combine to form a single output wave and if their pea!s coincide, the output intensity is the sum of the two intensities. However, if the two waves are completely out of ph ase the two intensities cancel each other out >that only happens when the two waves are offset by one half a wavelength@. 0he second wave >in step /.@ travels twice >once from and once to the e&terior thin lossy screen@ the distance equal to one quarter a wavelenth, for a total distance of one half a wavelength. 0hus the two waves cancel each other. 0he incidence angle the waves that are canceled do not come from the same e&act incident wave. However, they are all similar thus they are coherent and interfere.
0here are a few disadvantages inherent to this model >some of which have been solved@. in the aerospace applications@, reaserches are being made for ultrathin salisbury screens involving Sievenpiper H17E>high impedance ground plane@ >sourceG8iley Eeriodicals, 1nc. Microwave
Stealt! aircraft
;SA( stealth bomber orthrop 7rumman $)/ Spirit. A stealt! aircraft is an aircraft which has been designed to absorb and deflect radar >via stealth technology@% these are not completely #invisible# to radar, they are simply harder to detect than conventional technology. 1n general the goal is to allow a stealth aircraft to e&ecute its attac! while still outside the ability of the opposing systems detection. Stealth aircraft were most notably used during the 7ulf 8ar >*::*@. Although stealth technology has since become less effective, the ;nited States, Russia, =hina, 1ndia, and several other nations continue to develop stealth aircraft.
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$enefits of stealth aircraft designs Drawbac!s of stealth aircraft designs How stealth aircraft could potentially be detected ;se of stealth aircraft Fist of stealth aircraft 5.* Manned o 5./ ;nmanned >full stealth@ o o
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A smaller number of stealth aircraft may replace a large fleet of conventional attac! "ets with the same or increased combat efficiency, possibly resulting in longer term savings in the military budget. A stealth aircraft stri!e capability may deter potentional opponents from ta!ing action and !eep them in constant fear of stri!es, since they can never !now if the attac! planes are already underway. 0his may ma!e them more willing to accept a diplomatic solution, although the moral reasoning behind this is disputed. Raids on important point targets, while maintaning a cover of plausible denial. Since no)one could detect the attac!ers or at least identify them, the stealth operator would simply refuse to comment and hope to avoid war. 0he production and fielding of a stealth combat aircraft design may force an opp onent to pursue the same aim, possibly resulting in significant wea!ening of the economically inferior party. 0he *:J9s American Strategic Defense 1nitiative >#Star 8ars#@ program served a similar purpose against the ;SSR .
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Stationing stealth aircraft in a friendly country is a powerful diplomatic gesture. 1t emphasies close relations between the allies and e&presses high confidence in their governments and competence of security services, as stealth planes incorporate high technology and military secrets. 0he ;SA has stationed squadrons of ()**+ ighthaw!s in $ritain.
/ra0bac$s of stealt! aircraft desins
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Stealth aircraft are designed with a focus on minimal R=S >radar cross section@ rather than aerodynamic perfection. Highly stealth aircraft >the ()**+ and $)/@ are aerodynamically unstable on all three a&is and require constant flight corrections from the fly)by)wire system to stay airborne. Most modern non)stealth fighter aircraft >()*K, Su)/+, Rafale@ are unstable on one or two a&is only. Stealth aircraft need to have highly redundant fly)by)wire systems for safety, which adds e&tra cost and weight to the design. 1n case of a strong electromagnetic pulse >e.g. atmospheric nuclear e&plosion@, loss of flight control computers would affect stealth aircraft more seriously, possibly causing them to crash, but this is highly unli!ely due to electronic hardening that is implemented by the ;nited States Air (orce. Stealth aircaft are seriously handicapped in combat o nce located by the enemy. 6&isting fully stealth designs >namely the ()**+ and $)/@ lac! afterburners, whose hot e&haust would increase the R=S and infrared footprint of the plane. Stealth aircraft are thus unable to e&ceed the speed of sound and flee rapidly. 0his ma!es them vulnerable to fighter interceptors, which can reach Mach / or higher speeds using afterburners. 0he peculiar shape of stealth aircraft reduces their agility in a dogfight, thus they may be destroyed by autocannon fire from a traditional "etfighter, even if their low R=S and effective infrared shielding prevents a successful missile loc!. either the ()**+ nor the $)/ Spirit carry any anti)aircraft armament for self)defense. 0he high level of computeriation and large amount of electronic equipment found inside stealth aircraft ma!es them vulnerable to passive detection. 0he =ech)developed, field)mobile 0amara system snoops on very wea! electromagnetic #lea!s# emanating even from the most shielded aircraft. 0amara detectors provide general range C distance information to active air defence radars, which would then loc! onto targets using highly focused scanning. Stealth aircraft are high)maintenance equipment. 0he condition of the aircrafts s!in determines stealth efficiency, either by diverting radar impulses due to specific geo metry of the airframe andCor absorbing electromagnetic waves in a graphite)ferrite microspheres based surface paint layer. 0he coc!pit windows are shielded with delicate gold and indium foil layers. 1f the planes s!in is punctured by a pebble thrown from the runway or heavy rain damages the paint layers, the R=S could be dramatically increased. Stealth planes are preferably operated from homeland bases, where air conditioned shelters provide optimal maintenance and storage conditions. Although airframe maintainability and availability progressed dramatically during the late *::9s, the cost of aircraft procurement, establishment of high) standard home base facilities, and the comple&, long range sorties conducted from the homeland against overseas targets still places a serious economic burden on stealth aircraft operators. Stealth aircraft are still vulnerable to detection immediately before, during and after using their weaponry. Since stealth payload >reduced R=S bombs and cruise missiles@ are not yet generally available, all armament must be carried internally to avo id increasing the radar cross section. As
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soon as the bomb bay doors are opened, the planes R=S will be multiplied and even older generation radar systems will be able to locate them. Stealth aircraft pilots receive special training to minimie weapon dispatch intervals to *5)/5 seconds. 1n case of 4th and 5th generation #reduced R=S# >semi)stealth@ fighter)bomber designs, air)to)ground armament is mainly carried on e&ternal pylons, accepting the higher ris! of detection. 0he internal weapon bays are reserved for various anti)aircraft missiles. Since fully stealth aircraft carry all armament internally, the available military payload is limited. 0he ()**+ carried only two laser)guided bombs onboard, requiring highly reliable intelligence for a successful attac!. transonic@ speed, resulting in *J to /4 hour long missions when it flies half)way around the globe to attac! overseas targets. 0herefore advance planning and receiving intelligence in a timely manner is of paramount importance for a successful sortie. 1n case mobile targets will be attac!ed, the Spirit will need to rely on satellite data or forward placed observers to guarantee a successful engagement. 1n 3uly *::: two days prior to the Royal 1nternational Air 0attoo at RA( (airford ;', a single $/A Spirit penetrated ;' airspace at 9*.29 hours. Eassing overhead reporting point 8his!y Delta / at appro&. /59 feet it was travelling at "ust above stalling speed and was completely silent. 0he anterior half of the aircraft structure was covered in a green)white cond ensation cloud. Stealth aircraft are an air traffic haard unless flying in restricted training airspaces or fitted by e&ternally mounted radar reflectors and light beacons to avoid collisions. Due to the great sie of continental ;SA and general availability of sparsely populated areas this is not a significant training problem in practice. Stealth aircraft have a limited operational envelope. 8hile the $)/ Sp irit can put ordinance on any square foot of the planet within */ hours it is operationally crippled by the following factorsG 1ts e&orbitant replacement cost e&ceeds the 7DE of some countries, resulting in a challenging ris!Cbenefit analysis when considering its deployment. 1t is still vulnerable to the mar! * eyeball, ma!ing its deployment dependent on weather and time of day. Fong range missions and the avoidance of radar facilities ma!e its approach and departure vectors more predictable. 8hile the aircraft may be stealthy, the ordinance delivered will more than adequately advertise its e&istence.
Ho0 stealt! aircraft could potentially be detected
$)/ Spirit stealth bomber side view. A number of methods to detect stealth aircraft at long range have been developed. $othAustralia and Russia have announced that they have developed processing techniques that allow them to detect the turbulence of aircraft at reasonably long ranges >possibly negating the stealth technology@. Eassive >multistatic@ radar and bistatic radar systems are believed to detect stealth aircraft better than conventional monostatic radars, since stealth technology reflects energy away from the transmitters line of sight, effectively increasing the radar cross section >R=S@ in other directions, which the passive radars monitor. 1n addition, it has been suggested that use of low frequency broadcast 0W and (M radio signals as the illuminating source produces a much higher R=S than high frequency monostatic radars as the long wavelengths cause whole structural portions of the targets to resonate. 0arget detection, even at very low
signal)to)noise ratios is theoretically possible. 0arget trac!ing, in three)dimensional position and velocity should be more accurate with a multistatic system than with a monostatic system, using either triangulation or hyperbolic >or both@ target location strategies. 8ide usage of such broadca st signals >esp. in inhabited regions@ means a continuous and reliable coverage and source of energy, that cannot easily be neutralied by an attac!er. Researchers at the ;niversity of 1llinois at ;rbana)=hampaign with support of DAREA, have shown that it is possible to build a synthetic aperture radar image of an aircraft target using passive multistatic radar, possibly detailed enough to enable Automatic 0arget Recognition >A0R @. Ro!e Manor Research in the ;nited 'ingdom announced an e&perimental system that uses the signals broadcast from cellular telephone towers to trac! aircraft, although it is not clear if this method is actually practical or offers any significant counter)stealth advantage. A general feature of these systems is that they use a large number of low)accuracy radar systems >or signal sources@ combined with heavy computer processing to generate trac!ing information. (or this reason they tend to be useful only in the early warning role, and have limited applicability to g uidance radars for missile systems, and are rarely portable. 0he problem of successfully countering stealth aircraft on the battlefield remains essentially unsolved. Stealth aircraft could also be passively detected from their electromagnetic emissions >terrain)following radar , radio communications, missile guidance communications etc.@ if they broadcast such emissions. Stealth aircraft typically attempt to minimie these emissions >using low probability of intercept radars, satellite communications etc.@. 0o this date, the only systems that have been shown to successfully detect stealth aircraft are very old, and use long wave radar systems that have a low resolution. 0he shooting down of an ()**+ over Qugoslavia was attributed to the trac!ing of the vortices produced by the poor aerodynamic shape of stealth aircraft. 1t was also reported that the ()**+ was downed due to the use of an #electro)optical# >0W@ trac!ing system used in con"unction with the missile battery. 0he aircraft may be hard to detect using radar, but it is still visible to the na!ed eye. An ()**+ was also detected by a $ritish ship during the first 7ulf 8ar, in this case because the wavelength of the radar was twice the length of the aircraft. 0his caused the entire aircraft to act as a dipole, leading to a very strong radar return.-citation needed 0he Dutch company 0hales ederland, the former company Holland Signaal, developed a Stealth detection radar called SMAR0)F. So far the company has been unable to test it on a Stealth vehicle. 0he only chance was an airshow in Feeuwarden >the etherlands@ where an ;SA( $)/ would attend, but at the last moment the $oeing aircraft was withdrawn from the show. So, instead of testing the radar on a $) /, they used tennis balls instead. (our Dutch and three 7erman frigates are equipped with this type of radar.
1se of stealt! aircraft
0o date, stealth aircraft have been used in several low) and moderate)intensity conflicts, including or even before it@, before other aircraft had the opportunity to degrade the opposing air defense to the point where other aircraft had a good chance of reaching those critical targets. Stealth aircraft in future low) and moderate)intensity conflicts are li!ely to have similar roles. However, given the increasing prevalence of e&cellent Russian)built surface)to)air missile systems on the open mar!et >such as the SA)*9, SA)*/ and SA)/9 >S)299ECWCEM;@ and SA)*5 >:'22*C22/@@, stealth aircraft are li!ely to be very important in a high)intensity conflict in order to gain and maintain air supremacy, especially to the ;nited States who is li!ely to face these types of systems. 1t is possible to cover ones airspace with so many air defences with such long range and capability that conventional aircraft would find it very difficult #clearing the way# for deeper stri!es. (or e&le, =hina license)builds all of the previously mentioned SAM systems in quantity and would be able to heavily defend important strategic and tactical targets in the event of some !ind o f conflict. 6ven if anti)radiation weapons are used in an attempt to destroy the SAM radars of such systems, or stand)off weapons are launched against them, these modern surface)to)air missile batteries are capable of shooting down weapons fired against them. 0he surprise of a stealth attac!, and the ability to penetrate the air defences and survive, may become the only reasonable way of ma!ing a safe corridor through which conventional bombers and other aircraft can enter the enemys airspace.
2ist of stealt! aircraft Manned (ully stealth designsG • • • • • •
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Have $lue ) Foc!heed >developed into ()**+@ 0acit $lue ) orthrop >technology demonstrator reconnaissance plane@ ()**+ ighthaw! ) Foc!heed ) fighter)bomber >in service@ $)/ Spirit ) orthrop)7rumman ) strategic bomber >in service@ A)*/ Avenger 11 ) McDonnell)Douglas C 7eneral Dynamics >cancelled@ M$$ Fampyridae ) 8est 7erman stealth fighter prototype >cancelled during wind tunnel tests in *:JJ@ $ird of Erey ) $oeing >technology demonstrator@ Reduced R=S designsG
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Horten Ho //: ) a 7erman design of *:44, and perhaps the first basic stealth design orthrop Q$)4: ) li!e the Ho //:, this ;SA( bombers stealthy characteristics were not the result of intentional design De Havilland Mosquito ) $ritish light bomber and ground attac! plane of wooden construction, low R=S against early radars. Antonov An)/ ) 8ooden propellor and canvas wings give it a minimal radar signature. SR)+* $lac!bird ) Foc!heed Advanced Development Ero"ects High)speed reconnaissance aircraft. R=S equal to or better than the $)*$
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6urofighter ) 6ADS >in service@ ()// Raptor ) Foc!heed)Martin C $oeing >in service@ Q()/2 $lac! 8idow 11 ) orthrop C MDD >prototype built, lost competition to Q()//, almost full stealth, may resurrect as a fast bomber@ ()25 3oint Stri!e (ighter ) Foc!heed)Martin >under development@ Dassault Rafale ) (rench air force and naval fighter bomber Medium =ombat Aircraft ) Hindustan Aeronautics Fimited >under development@ 1ndian Air (orce stealthy 5th generation combat aircraft optimised for stri!e missions. Mi7 Ero"ect *.44 #(latpac!# ) Mi!oyan)7urevich >prototype@, possibly full stealth with plasma shield 3)*9 ) =hengdu Aircraft 1ndustry =orporation >pro"ected twin engine design for stealth missions@ 0)59 C EA')(A ) Su!hoi >under development, Russian)1ndian counterpart of ;S ()// Raptor, possibly plasma shielded@ ()*K =CD and 6C( ) from $loc! 29 has got reduced R=S to about * m/ (CA)*J =CD and 6C( ) both have reduced R=S, believed be to similar to ()*K=s, but (CA)*J 6C( is believed to have more advanced technology, but the aircraft is larger so the aircraft might >and might not@ have the same R=S as (CA)*J=CD Mi7)/: SM0 ) has got similar to ()*K=CD reduced R=S
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$oeing [)45 ) $oeing ) based on the manned $oeing $ird of Erey demonstrator >technology demonstrator@ RL)2 Dar! Star ) Foc!heed C S!un! 8or!s >cancelled@ Dassault AW6)D Eetit Duc ) Dassault Aviation >tactical ;AW@ Dassault n6;Rtechnology demonstrator@ (uture and current wor! into ;AWs and ;=AWs feature great focus into stealth technology.
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Mi$oyan Mi3)45 Y #irefo F)56 3!ostrider Y 0estors Mi$oyan Mi3)47 Y 0estors F8A)47 Talon Y Stea"th .lac$bird Y .-/en 3eneral 3ala#y 9F):5 Y /across P"us
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