Value of stealth aircrafts

ahmedfire wrote:F-22 Raptor Loses $79 Billion Advantage in Dogfights: Report

Pentagon’s big budget F-35 fighter ‘can’t turn, can’t climb, can’t run’

nemrod wrote:

ahmedfire wrote:F-22 Raptor Loses $79 Billion Advantage in Dogfights: Report

Pentagon’s big budget F-35 fighter ‘can’t turn, can’t climb, can’t run’

Thx Ahmed.
Nevertheless, the F-22's link is 2 years old, and F-35's link is 6 months old.

Before I registered in this forum, I used to consider that F-22 is the king of the sky, and F-35 will be far better.
Several years of investigations about US military's past wars, chieftly regarding Iraq, and in Serbia, revealed me the cause of US superiority is subject to controversies, and benefited, exceptionnal historical circumstances.
Once the analysis was done, and objectives informations  are availlable, we could consider that neither the F-22, or F-35 are in position of suprematy.
For a long time ago, I used to ask question, why the SU-35 has not AESA's radar ? The response is simple, russians are well aware what's the AESA's technology worth, and they bet on Irbis-E to detect the F-22, it could easily detect every stealth fighter.
Furthermore, russian air force has the Mig-35 with its AESA radar, and I think it is enough.

victor1985 wrote:I wanna ask something:invisibility of aircrafts like f22 is somehow poitless? Because he do reflect waves in a specific angle. Put a aircraft to rearch in that angle and he will find f22. Lets thinks having aerian radars at rational heights so that intercept returning waves.  And bum. Even iranians can do that.

Stealth Countermeasures.
The Billion Dollar Boondoggle,
by Steven J. Smith

1.0
Introduction:
Everybody's seen them.  Those ominous looking black aircraft, like something straight out of a science fiction movie.  We've all been told how stealth technology makes aircraft invisible to radar, and thereby improves the safety and survivability of our military pilots.  Those of us who are technologists have watched the cute animations showing how radar beams are deflected away from the radar receiver by skillful use of aircraft geometry, or soaked up by special radar absorbing materials.  What a wonderful job of public relations!  A Madison Avenue advertising agency couldn't have dreamed up more impressive looking machines, or done a better job of selling them.  This is America's military at its best, winning the hearts and minds of its citizens, and of course striking fear and terror in the enemies of democracy, no matter where they are hiding.  Even the American navy (not to be out done by their rivals in the air force) is building stealth warships.

Too bad its all based on a lie...

Yes, stealth technology renders an aircraft (or ship) invisible to conventional radar, when that radar is used in a conventional manner.  Yes, during the gulf wars stealth aircraft flew with impunity into Iraq, and evaded 1980s era Russian made radars.  All of this is indisputably true.  However as I shall elaborate, a multiplicity of stealth countermeasures are both feasible and practical.  As you are about to discover, when flying against these countermeasures, stealth aircraft (and ships) are nothing more than very expensive scrap metal.  In other words, an extravagant waste of taxpayer money.


1.1.1
Stealth basics:
A quick review of how stealth technology works will prove helpful in understanding stealth countermeasures.  Those readers already familiar with the techniques embodied in stealth technology may skip this section.  Stealth aircraft and ships are dependent upon three distinct classes of technology.

   Radar diversion geometry.
   Radar absorbent materials.
   Infrared signature suppression.

Radar diversion geometry depends on the shape of the aircraft or ship to deflect the radar beam away from the radar receiver.  If the radar receiver fails to detect any reflected microwave energy from a target, that target is effectively rendered "invisible".  Radar absorbent materials (RAM) as the name implies, absorb the transmitted radar beam, thereby greatly attenuating reflected microwave energy available to the radar receiver.  By analogy, this is equivalent to painting an object black, making the object harder to see at night.  Infrared signature suppression is actually an adjunct technology that seeks to lower the temperature of jet engine exhaust gases.  Its useful because many contemporary anti-aircraft missiles are "heat seeking".  In other words, the missile is guided to the target by hot exhaust from the jet engine.

Each of these stealth technologies can be circumvented by employing appropriate technologies and/or strategies.  I shall address each stealth technology separately (below).


1.2.1
Radar diversion countermeasures:
The use of geometry to deflect radar return (bounce) energy away from the radar receiver represents the corner stone of modern stealth technology.  This technique is employed on such diverse platforms as the American F117 Nighthawk aircraft (figure 1), and the DDG (Arleigh Burke class) Aegis guided missile destroyer (figure 2).  The technique is based on the fact that only those surfaces parallel to the electromagnetic wave front will reflect the wave back to the receiver.  In optical terms this is stated as: "The angle of reflection is equal and opposite to the angle of incidence".  In other words, only a wave front incident at 90 degrees to a surface will be reflected back to the source (radar transmit/receive antenna).  By angling all surfaces with respect to the probable direction of incoming radar emissions (in most cases, the horizon), the radar wave is reflected away from the receiver.  Thereby rendering the aircraft or ship invisible to radar.


F117 Stealth Fighter
Figure 1 (courtesy USAF)

Aegis Guided Missile Destroyer
Figure 2 (courtesy USN)

The scientific paradigm that underlies this technique is known as ray trace optics, and is based on Pierre Fermat's principle of least time.  From the perspective of ray trace optics, it would seem there is no method by which this form of stealth technology can be circumvented.  However, there is a more sophisticated optical paradigm, known as quantum wave mechanics, that allows us to draw a rather different conclusion...

Those who are familiar with the operational principals of phased array radar systems understand the wave front represented by the "ray" in ray trace optics, is in reality just the in phase portion of multiple superimposed independent waves.  This is graphically illustrated in figure 3.

Figure 3

Referring to figure 3, the wave front appears to converge on the focal point because this point is the only location where all in phase waves originating at the incoming wave front plane, are in phase after reflection by the mirror.

Phased array radar systems (also known as electronically scanned arrays) make use of this principal by precisely controlling the phase (timing) relationships among a multiplicity of microwave transmitters and receivers.  By introducing a progressive set of time delays across the width and/or height of the microwave transmitter array, the in phase plane of the combined array can be rotated through any arbitrary 2D angle, relative to the physical antenna plane.  The focal plane of the microwave receiver array can also be adjusted in a similar manner.  Under normal operation, the focal planes of both the transmitter array and receiver array are adjusted to the same 2D angle, thereby causing the receiver array to exhibit maximum sensitivity at the 2D angle of the expected target return signal.  However, it must be stressed that although the transmitted microwave energy appears to exist only along a single axis (the ray) normal to the in phase plane, that in reality quantum wave mechanics dictates the transmitted microwave energy exists at ALL points surrounding the antenna array.  An appreciation of this fact is central to understanding return diversion countermeasures.  Consider the situation depicted in figure 4.


Figure 4

Referring to figure 4, the microwave transmitter array is phased such that the wave front plane (shown in yellow) is off axis from the antenna array.  Now consider the target plane (shown in red).  Because the transmitted microwave energy exists at all points (not just the in phase plane), AND the target plane angle is complimentary to the wave front plane angle, the resulting reflected wave plane (from the target plane) will be parallel to the antenna array plane.  In other words, by pre-distorting the transmitted radar pulse so the wave front plane is complimentary to the target plane, the reflected wave plane will be in phase at the antenna array, and therefore detectable by the radar receiver array.

The concept presented in the preceding paragraph represents the basic method of implementing radar return diversion countermeasures.  Of course the radar system must have some prior knowledge of the expected range of target angles in order to pre-distort the transmitted microwave pulse.  However once a set of actual angles are obtained by painting the target, this represents additional signature information that can be used to identify the type of target.  There are two additional advantages to this method.

   The radar pulse used to paint the target is not in phase at the target.  Therefore standard ECM (electronic counter measures) suites will fail to detect it.  In other words, the target will not know it has been acquired by the phased array radar system!  (a stealth radar)
   Currently, stealth platforms represent a minority of available delivery systems, and are therefore more likely to represent high value targets.  Since the techniques presented in this section allow the target to be categorized as to the degree of return diversion stealth technology employed, it follows that use of this technique facilitates prioritizing of target value.

Currently, most phased array radar systems use hundreds, and in some cases, thousands of transmit/receive channels in the array, and are therefore large and very costly.  However, these systems were designed and built in an era when computer technology was still relatively crude by the standards of today.  With the advent of small, fast, inexpensive computers, the number of microwave transmit/receive channels required for an effective stealth countermeasure phased array radar would be less than sixty, and with fine tuning of the computer hardware, software and antenna geometry, might be as few as ten.  Obviously these systems would be both very portable, and inexpensive to build in mass production.  Figure 5 shows the phased array radar used on the F/A 22 Raptor.  This radar employs approximately 2000 microwave transmitter/receiver pairs, each the size of a pack of chewing gum.


Figure 5 (courtesy USAF)

A word of caution to any nation contemplating the manufacture and/or deployment of stealth aircraft and/or ships.  The author has every reason to believe the American F/A 22 Raptor phased array radar (shown in figure 5) is capable of operation in the stealth detection mode as described in this section.


1.2.2
Radar absorption countermeasures:
Radar absorbent materials are based on the principal of converting coherent electromagnetic energy (radio waves) into incoherent electromagnetic energy (heat).  And when viewed from this perspective, the term "radar absorbent material" represents a subtle form of disinformation.  The material itself is a liquid composite, formed from low Q ferrite particles, suspended in a radar transparent organic binder, applied to surfaces in a manner similar to conventional paint.

The low Q ferrite particles act as lossy (low efficiency) resonators, thereby transforming incident microwave energy into heat.  A wide range of particle sizes are used to allow the material to function across a broad spectrum of frequencies.  However, the spectrum of frequencies over which the material will convert microwave energy into heat is not unlimited.  In particular, the lower end of the microwave band (200Mhz - 800Mhz) is NOT effectively absorbed.  This compromise was considered acceptable, since modern radar systems employ frequencies several octaves higher.

Here is the Achilles heel of radar absorbent materials.  Lower frequencies require larger ferrite particle sizes, and these in turn require a thicker coating, resulting in surface imperfections (bumps), which impair aerodynamic performance.

As a side note, the only F117 ever lost in combat was detected using this very same technique. The wreckage is still on display, available for public viewing at the aviation museum in Belgrade Serbia.

Click Here to read Wikipedia article on F117 combat loss (opens in a new browser window).

Therefore, the use of low frequency radar, especially when coupled with computer based aperture synthesis to compensate for the lower image resolution is an effective countermeasure to radar absorbent materials.


1.2.3
Infrared signature suppression countermeasures:
Infrared stealth is accomplished by mixing hot exhaust gases with air at ambient temperature, prior to release into the atmosphere.  A related technique involves spreading the hot exhaust gas plume over a large area as it's released into the atmosphere.  Both methods are designed to lower the effective temperature of the exhaust plume, thereby making infrared detection more dificult.  However, the exhaust plume has other characteristics that are detectable, and when coupled with absence of heat, shout "this is a stealth platform!"

The detectable signatures of the exhaust gas plume fall into two broad categories.

   Chemical signatures.
   Physical signatures.

The chemical signatures of exhaust gas plumes result form the combustion process itself, and include elevated levels of oxides of carbon and nitrogen (along with water vapor), relative to the surrounding atmosphere.  These chemical signatures are detectable with properly designed radar systems.  For instance nitric oxide (NO) has a resonance at 1.665 GHz, and carbon monoxide has a resonance at 9.361 GHz.  A dual band backscatter search radar operating at these frequencies, in conjunction with a coaxial mounted focal plane infrared detector would make an ideal detector for stealth platforms.  The use of multi-wavelength backscatter Lidar offers nearly unlimited flexibility in chemical signature analysis of exhaust gas plumes.

The physical signatures of the exhaust gas plume result from the large velocity differentials relative to the surrounding atmosphere.  This is especially true for jet aircraft.  Currently, backscatter Doppler radar in the 500MHz to 1500Mhz region is used to directly measure the motion of the atmosphere in the study of weather related phenomena.  Since these systems can accurately measure atmospheric motion in the 10 kilometers per hour range, the measurement of jet exhaust plumes at 100 to 600+ kilometers per hour range will prove very easy to accomplish.  As with chemical signature analysis, the use of a coaxial mounted focal plane infrared detector will confirm the stealth nature of the platform.  The Chilbolton ACROBAT (Advanced Clear-air Radar for Observing the Boundary layer And Troposphere) is an example of backscatter clear air Doppler radar technology.

Click Here for general information on the Chilbolton ACROBAT radar (opens in a new browser window).

Click Here for Chilbolton ACROBAT radar system block diagrams (opens in a new browser window).

Note: The Chilbolton system actually measures backscatter from moisture suspended in the atmosphere, however since exhaust gas contains large amounts of H2O generated by the combustion process, use of backscatter Doppler radar for stealth platform detection presents no insurmountable problems.  A Doppler frequency gate will be able to discriminate between normal atmospheric processes (rain, snow, hail, etc) and the much higher velocities associated with jet exhaust gas plumes.  The use of several small (< 4 meter) dishes, under servo control, and fed from a common RF source to maintain phase coherence will result in the same (or better) angular resolution as achieved by the 25 meter dish at the Chilbolton installation.


1.2.4
Miscellaneous countermeasures:
Another method of physical detection is worthy of mention.  Although widely used in WWII, it seems acoustic signature analysis has fallen out of favor in recent decades.  While most stealth aircraft are very quiet during approach, the authors first hand experience with an over flight by a B2 bomber indicates this is certainly NOT the case as the aircraft was departing.  This observation may not appear to be useful, until you consider the situation depicted in figure 6.


Figure 6

Two acoustic sensors (1 & 2) are sequentially triggered by over flight of the stealth aircraft.  Since the distance between acoustic sensors 1 and 2 is known, the time interval between triggers of sensors 1 and 2 yields the velocity of the stealth aircraft.  Knowing the aircraft velocity, and the distance between sensor 2 and the countermeasure weapon, allows the weapon to be triggered in advance of stealth aircraft over flight.  When employed at a natural choke point such as a long narrow valley, or an artificial choke point such as the mid point between two conventional search radars, the utility of the tactic becomes self evident.  A typical countermeasure weapon would consist of multiple mortar launched shells, containing small metal fragments dispersed by a high explosive charge, directly in the flight path of the oncoming stealth aircraft.  This countermeasure system has the added advantage of being completely passive, and therefore undetectable by the stealth aircraft.

The later generations of stealth aircraft have tried to strike a balance between stealth capabilities and conventional aerodynamic capabilities.  This was necessary because the ideal geometry (shape) for maximum stealth is NOT the ideal shape required to achieve maximum aerodynamic performance.  Consider the F/A 22 Raptor, America's newest stealth aircraft shown in figure 7 (below) as an example of compromise between stealth performance and aerodynamic performance.


Figure 7 (courtesy USAF)

From this angle, there isn't much area for reflection of a radar beam.  Next, look at figures 8 and 9.


Figure 8 (courtesy USAF)


Figure 9 (courtesy USAF)

Notice how the large flat vertical tail fins (shown in figure and the jet engine air intake side panels (shown in figure 9) make ideal targets for radar diversion countermeasures (as discussed section 1.2.1).  Judging from the multiple angled surfaces incorporated into the side panels of the air intake, F/A 22 designers were also concerned about radar reflection from this surface.  Obviously this aircraft is optimized for maximum frontal stealth, and side stealth has been sacrificed for aerodynamic performance.  Just what one would expect for an air superiority fighter aircraft.  However as the F/A designation implies, the F/A 22 Raptor is also intended to function in a ground attack mode.

Now suppose a mobile anti-missile battery equipped with a diversion countermeasure style radar (1.2.1 above) is physically separated from a conventional targeting radar located at the installation these systems are defending.

Consider the F/A 22 Raptor executing a ground attack mission against this target.

As the F/A 22 attacks the defended installation, its onboard systems will detect the conventional targeting radar (located at the installation) and to present the smallest possible radar target, it will keep its nose pointed directly at the conventional targeting radar.  However, the anti-missile battery (and stealth countermeasure radar) located some distance away and at right angles to F/A 22 flight path, will have a clear unobstructed view of the vertical tail fins and air intake side panels (figures 8 & 9 above).  Furthermore, as discussed in section 1.2.1, electronic countermeasure systems (ECM onboard the F/A 22) won't even detect the anti-aircraft missile battery stealth countermeasure radar.  Consequently, the first indication of a trap will be when infrared detectors onboard the F/A 22 inform the pilot of a missile launch.  Well, at least the F/A 22 has super cruise (Mach 1.7 without afterburners) so perhaps it will be able to out run the missile, providing the pilot reacts fast enough.  Of course this means the F/A 22 will have to break off from its attack of the ground target.  And of course the mobile anti-missile battery will be quickly relocated to preclude any follow on attempt to destroy it, preparatory to a second F/A 22 attack on the primary target.

A similar situation could be implemented using two aircraft.  One acting as bait, and a second aircraft some distance away, equipped with stealth countermeasure radar.  This would be especially effective if the second aircraft could use a digital radio link to direct the flight path of a missile launched from the "bait" aircraft.

As the scenarios (above) illustrate, even the newest, most advanced stealth aircraft are NOT invulnerable when appropriate technologies and tactics are employed.


1.2.5
Countermeasure deployment:
The effectiveness of stealth countermeasures and tactics discussed herein can be enhanced by the careful selection of deployment locations.  Since radar and infrared stealth DO NOT mean complete absence of detectable signature, but only greatly reduced signature.  If follows that stealth platforms will chose penetration and egress routes that either avoid close approach to traditional detection systems (search radars, etc.) or use natural terrain features to reduce the chance of detection.  These facts can be used to advantage in choosing deployment locations for stealth countermeasure systems.  As an example, conventional search radars are generally deployed with a slight overlap at the limit of the detection range.  This area of overlap, near the limit of detection range is where a stealth platform will naturally chose for it's penetration and egress corridor(s), and represents an ideal location for stealth countermeasure deployment.  Long sinuous valleys that terminate near high value targets and act as natural barriers to radar would represent another useful penetration and/or egress route for stealth platforms, and therefore another logical deployment location for stealth countermeasures.

Stealth naval platforms will employ the hide-in-plain-sight strategy.  Since their radar signature will be comparable to that of a small fishing boat, the use of a conventional marine search radar, coupled with advance phased array techniques (1.2.1) will serve to uncover the "shark among the minnows".  A conventional search radar would be used to locate targets, each of which would then be examined with the phased array system.  Since the (phased array) radar pulse used to paint the target is not in phase, standard ECM suites will fail to detect it, and the stealth platform will not know it's true nature has been exposed.


1.3.1
The politics of stealth:
As defensive weaponry has become ever more accurate and therefore more lethal, offensive delivery platforms (ships, aircraft, missiles, etc) have become increasingly dependent upon on various forms of stealth to achieve mission objectives.  This trend of deploying stealthy offensive weapons platforms has disturbing political consiquences.  Political restraint is largely based on the perceived risk/reward ratio of military action.  And stealth technology has the effect of lowering the perceived political risk of belligerent behavior.  Therefore a government in possession of stealth weapons platforms is far more likely to embark upon a course of aggression.  When viewed from this perspective, it becomes apparent that stealth technology represents a shift away from traditional military defense, to a more offensive military posture.  As a consequence, the widely held belief that stealth technology enhances pilot safety and mission survivability is false.  Since any added margin of safety provided by stealth technology is more than offset by the tendency of political leaders and military planners to employ stealth aircraft on missions and in environments that would be considered suicidal for any conventional aircraft.  Even a cursory examination of America's deployment and use of stealth technology lends ample credence to these conclusions.

Furthermore, as I have so amply demonstrated herein, stealth technology represents a false promise of invulnerability.  Therefore governmental appropriations for additional development and/or deployment of stealth weapons platforms is both wasteful of taxpayer money, and ultimately counterproductive to the goal of national security.

Some commercial (aerospace) corporations and governmental agencies will no doubt try to accuse me of revealing classified (secret) information.  However, when the Serbian military were capable of successfully attacking and destroying an F117 stealth fighter in March of 1999, it becomes blatantly obvious it is NOT the effect my disclosures will have on the military balance of power that worries these corporations and governmental agencies.  To the contrary, it is the damage my disclosure will do to their carefully choreographed PR campaign that motivates their cries of outrage.  A PR campaign aimed not at Belgrade, Moscow or Beijing.  Rather a PR campaign aimed squarely at you, the American voter and tax payer.  Make no mistake, military planners in Moscow and Beijing are fully aware of stealth technology limitations and flaws.  This is why there has been no great rush by these nations to emulate America's growing dependency on stealth technology.  Contrary to popular myth, America didn't win the cold war with superior military technology.  America buried the Soviet Union with video games, fax machines, and Chevrolets.  It was economic collapse that doomed the communists, not military defeat.  And sadly, as America squanders untold billions of dollars on weapons that will never live up to their promise, and further billions on wars it has no chance of winning, it becomes increasingly apparent that economic collapse will be the ultimate demise of America as well...


Those who cannot remember the past are condemned to repeat it.

-George Santayana-


1.3.2
Summary:
As I have shown, stealth platforms are far from invulnerable when the appropriate countermeasure technology and tactics are employed (1.2.1, 1.2.2, 1.2.3 & 1.2.4).  Many of these countermeasure techniques are inexpensive, and stealthy in and of them selves (1.2.1, 1.2.4).  Furthermore the mere possession of such countermeasure technology will, if known to the aggressor, serve as a deterrent against potential future aggression.  In part 2, we shall examine some practical engineering examples.


1.3.3
Disclaimer:
ALL information contained herein is derived from public sources, widely accepted scientific principles, and/or authors first hand experience.  The author has NO written or verbal agreement with ANY governmental agency forbidding disclosure of the information contained herein.  In disclosing this information, the author is exercising his right to free speech as a private citizen of the United States of America.


End.
Stealth Countermeasures

Value of stealth aircraft

Posted by picard578 on March 30, 2013

Introduction

Unlike US Navy and every other air force across the world, USAF has decided to transit to an all-stealth air force.

But due to the Moore’s law, processing power doubles every 18 months – which means not only improvements in sensors that are already very capable of detecting stealth aircraft, but also that, as time passes, stealth aircraft is ever less capable against systems it was designed to counter – namely, active radars.

Air-to-air combat

Stealth vs radar

Stealth relies on processing gain advantage over radar, by reducing return below treshold of what can be detected by radar itself. However, due to the Moore’s law, radars are becoming ever more capable. Further, stealth fighters are designed with minimum nose-on RCS, which means that they are easier to detect by aircraft flying in wall formation. At the same time, jammers benefit from Moore’s law too, which enables fighter-based jammers to rapidly close the effectiveness gap with stealth, or even surpass it.

This purely theoretical thought exercise is not likely to be very relevant, however, as radar – being an active sensor – automatically gives position of aircraft using it away far before it can detect opposing aircraft, meaning that pilots will start shutting it down in combat as soon as losses due to its use start to mount due to radars’ use giving very important advantage of surprise to the opponent. Against both enemy aircraft and SAMs, dedicated jamming aircraft – ranging in size from converted medium-weight fighters to converted heavy bombers – are avaliable, and far more effective since they also protect other aircraft.

Stealth vs IRST

Most discussions about value of IRST against stealth focus on airframe being heated due to air friction. This, however, is wrong for a very simple reason: any time a gas is compressed, it heats. And compression of gasses in front of moving object is a normal, unavoidable occurence – only difference is scale of compression, which depends on object’s speed.

While aircraft do heat up less in rarer atmosphere, less atmosphere also means that more IR radiation – especially of longwave variety – reaches the infrared sensor. Further, at high altitudes – where stealth aircraft are required to operate – temperatures range from -30 to -50 degrees Celzius. At the same time, fighter supercruising at Mach 1,7 creates shock cone with temperature of 87 degrees Celzius. While PIRATE IRST can detect subsonic fighters from 90 km from front and 145 km from rear according to (somewhat outdated) publicly avaliable information, this range is 10% greater against supercruising fighter. At the same time, OLS-35 can detect subsonic fighter from 50 km from front and 90 km from rear. PIRATE’s own range is already comparable to that of fighter radars against 1m2 targets. (Note: Data used for both PIRATE and OLS-35 dates from 2008; it is possible that both have been improved in the mean time). Prototype Russian stealth aircraft PAK FA uses QWIP-based OLS-50M, so it is possible that QWIP technology may find its way into Su-27 family of aircraft. Identification can be carried out at 8 to 10 kilometers.

Parts of aircraft’s exhaust plume are also visible from front, which should present no problem for modern IRSTs that are capable of detecting AAM release due to missile’s nose cone heating.

Some IRST systems have laser rangefinder coupled with them, which means that they can be used to gain gun firing solution without usage of radar. While IRST is mostly immune to “beam turn” used to break radar lock, laser rangefinder may not be. Rangefinder, though shorter-ranged compared to IRST, would also have increased range at higher altitudes. IRST could also use sensitivity model (Atmospheric Propagation Model) to roughly estimate range and velocity of target without using any active sensors.

(Interesting to note is that Soviet MiG-31s were able to target SR-71 by using IRST; at speeds both aircraft were flying at in these situations, MiG-31s front surfaces would heat up to 760 degrees Celzius due to aerodynamic friction. SR-71 was not much better off; fortunately, order to attack was never given).

Astronomic IR telescopes can detect velocity of star down to 1 meter per second. This kind of precision would not be required for air-to-air combat, however, as closure rates between fighters could be up to 1 700 meters per second.

This means that stealth aircraft has no escape – if it attempts to increase effective range of its missiles, it has to increase speed – but this increases IR signature and allows it to be detected from larger distance. If it attempts to avoid detection, it has to reduce speed, which means that it has to come closer to IRST-equipped fighter.

USAF is obviously concerned about it – while IRST-equipped Super Tomcat was slated to be retired in 2008, it was hurriedly retired in 2006 under neoliberal stealth proponent Donald Rumsfeld. Both PAK FA and F-35 have IRSTs, but unlike PAK FA, F-35s IRST is optimised for air-to-ground missions, and is thus operating in appropriate wavelengths, reducing its range against aerial targets.

QWIP IRST such as PIRATE or OSF has some very useful advantages over “legacy” IRST. Aside from longer range, they can be tuned for sensitivity in certain IR band. While normal IRST operates in microwave to longwave IR bands, QWIP IRST can operate in very longwave bands, allowing for easy detection of objects that are only slightly hotter than the background, with difference being in single digit degrees of Cenzius. It can also use several bands in paralel, getting “best of the both worlds”.

While F-22 was designed to operate at high altitudes, as high as 15-20 kilometers, clouds only go up to 14 kilometers in some cases, with majority being below 4 500 meters – and even that only in tropics. All other stealth air superiority aircraft are similarly expected to operate at high altitudes.

Countering SAMs

Ground radars have to be above any obstacles to radar beam, which means that areas such as small valleys and canyons are usually not covered. Anti-radiation missiles and cruise missiles are very reliable against stationary radar sites; ARMs are better against mobile radars, as there is no radar that can pack up and leave in the time that ARM requires to reach it. SAMs are no different in that regard, and as such they can be kept shut down by use of anti-radiation missiles.

Without these two factors, however, stealth aircraft can be detected easily enough by long-wavelength radars, which completely ignore any practical amount of stealth coating, and are far less affected by stealth shaping measures than shorter-wavelength radars. These, then, can be used to guide IR SAM or IRST-equipped aircraft close enough for their IR systems to detect stealth aircraft.

Numerical issues

Numerical issues are probably the worst drawback of stealth. Stealth aircraft cost more and are harder to maintain than non-stealth ones. To demonstrate the actual impact, I will compare F-22 to two twin-engined aircraft designed to carry out similar mission to F-22s, but without stealth.

While F-22 costs 250 million USD per aircraft flyaway, cost for Tranche 3 Typhoon is 121,5 million USD, and cost for F-15C is 108,2 million USD. As such, 50 billion USD gives 200 F-22s, 411 Typhoons or 462 F-15Cs.

Sortie rate stands at maximum of 0,52 sorties/aircraft/day for F-22, 1,2 sorties/aircraft/day for F-15 and 1,2 – 2,4 sorties/aircraft/day for Typhoon (later value only assuming that design goals have been met). Thus, force bought would be able to support 104 sorties/day for F-22, 554 sorties/day for F-15C and 493 – 986 sorties/day for Typhoon.

Historically, quality of aircraft was always unable to compensate for force disparity once latter was above 3:1. As such, it can easily be seen that F-22 is, strategically, worse choice than Typhoon or F-15. And while all numbers are not yet avaliable, it cannot be expected that F-35 will perform any better in this crucial area relative to Gripen and F-16 than F-22 did relative to Typhoon and F-15. Me-262, while by any measure a revolutionary aircraft, was not used in large enough numbers to have impact against Allied fighters. In the end, Me-262 shot down no more than 150 Allied fighters, with 75 of them being lost in turn, in large part due to Allied superior numbers allowing them to catch Me-262 on take-off or landing.

BVR combat

Stealth aircraft are built under assumption that BVR radar-based combat trumps WVR combat. However, that assumption is unproven; neither AMRAAM or other BVR missiles were ever used beyond distance of 40-50 kilometers. In case of AMRAAM, usage was against aircraft with no radar, no IRST, no radar warners, no ECM, with badly trained pilots that were in most cases unaware they were under attack (and were not maneuvering as a consequence). Yet even in such perfect conditions, AMRAAM achieved 6 kills in 13 BVR launches, or Pk of 0,46.

During Desert Storm, in conditions identical to above, USAF F-15s launched 12 Sidewinders for 8 kills, for Pk of 0,67. For same F-15s, AIM-7 Sparrow achieved 23 kills in 67 shots, for Pk of 0,34.

Thus we have to take a look back at Vietnam. Why Vietnam? Simply because it was the last time US have fought somewhat competent opponent in the air. Even experience with IR missile suggests that Pk in combat against competent opponent will be far lower than above: AIM-9B achieved Pk of 0,65 in tests, which fell to 0,15 in Vietnam, to be improved to 0,19 with AIM-9D and J, whereas G model does not offer large enough sample for drawing conclusions. Yet even this was better than Pk for BVR missiles. While majority of AIM-7 shots were taken within visual range, during 1971-1973 in Vietnam, 28 BVR shots were made, resulting in 2 kills, one of which was a fratricide against an F-4 – a Pk of 0,071, as opposed to predicted Pk of 0,9 or more. During entire war, AIM-7D achieved 8% Pk, AIM-7E achieved 10% Pk and AIM-7E2 achieved 8% Pk. At the same time, guns had Pk of 0,28.

In fact, summary by Burton of kills made during Cold War has found that, out of 407 missile kills he studied, 73 were made by Sparrows in 632 firings, a kill rate of 11%. Sidewinder achieved 308 kills in around 1 000 firings. Out of all radar-guided missile kills, only four were made at BVR – two already described shots in Vietnam that were carefully staged outside of combat, and two similarly staged shots by Israeli air force. His summary of these 407 shots concluded that most targets were unaware and fired from the rear, and that there were almost no head-on BVR shots due to high closing rates. Only way to positively identify the target was by the eye.

When we take a look at the data above, a clear pattern begins to emerge: while Pk against incompetent opponent is significantly higher than against competent one, by a factor of almost five, relative weapons’ effectiveness remains unchanged: IR missiles achieve half the Pk of gun, and radar-guided missiles achieve half the IR missile’s Pk. Further, visual identification of target is still important, and is likely to remain so. In fact, during First Gulf War, majority of US casualties were due to the friendly fire, while in 1973 war Israeli pilots considered an on-board radar “essentially useless”, with Sparrow achieving one or no kills in that war.

This situation will even worsen for BVR-oriented aircraft in the future, as IRIS-T has capability to intercept and destroy BVR missiles. While it definetly will not be perfect, it will reduce number of missiles aircraft actually has to evade.

Time has also shown that maximum simplicity weapons and countermeasures, such as guns and flares/chaff, are usually most effective. This is unlikely to change.

Training issues

Pilot competence was always dominant issue in Air to Air combat. During German invasion of Poland, several Polish pilots became aces in 362 kph open cockpit fighters, when fighting against 603 kph Me-109, an early warning about importance of pilot skill. This was again shown when German fighters fought outnumbered in invasion of France, when higher-performance Spitfires and equal-performance Hurricanse fared poorly against Me-109s, which were flown by far more experienced pilots using tactics derived from actual combat as opposed to air shows and unrealistic peacetime exercises. Late in the war, Luftwaffe was unable to mount serious opposition not due to the lack of air frames – Allied bombing did not have major effect on German industry – but due to the lack of pilots.

Yet stealth aircraft’s large maintenance downtime prevents pilots from becoming familiar with their aircraft, and training enough in them. Modern fighters are also more complex than World War II ones, so lack of fighters is a very real possibility. AIMVAL tests, despite bias towards BVR, have also shown that ground controller assistance was more important to more complex and automated aircraft, and off-boresight missiles offered only slight improvement in results.

Conclusion

Stealth aircraft are expensive, and do not provide bang for the buck, in good part due to them being built on flawed reasoning and inaccurate assumptions. While they can be very useful against backward coutries, even in these cases larger numbers of cheaper aircraft will perform better. Assumptions behind stealth ignore lessons of combat to date, including the fact that pilot skill tended to dominate air combat (especially when combined with numerical superiority), as well as existing counter-stealth technologies.

Game-changing technologies were always simple in idea and execution, as relatively inexpensive. For comparision, stealth F-22 has cost of 12 690 USD per kg, F-35A costs 14 812 USD per kg, F-15C costs 8 504 USD per kg, F-16C costs 8 168 USD per kg, and Eurofighter Typhoon costs 10 942 USD per kg in its most expensive variant. It should be noted that F-22 lacks IRST and some of Typhoon’s systems, whereas F-35A is most loaded with electronics of aircraft listed. As such, stealth requirements add – without counting weight increase – 1 000 – 3 000 USD per kg. If the fact that F-22 is heavier than F-15C at least 7 000 kg is counted, stealth coating itself likely cost around 50 million USD, almost as much as my estimated flyaway cost of Gripen NG. IRST, on the other hand, costs around 1 million USD, and is far more useful than radar stealth.

nemrod wrote:

Introduction
Unlike US Navy and every other air force across the world, USAF has decided to transit to an all-stealth air force.
But due to the Moore’s law, processing power doubles every 18 months – which means not only improvements in sensors that are already very capable of detecting stealth aircraft, but also that, as time passes, stealth aircraft is ever less capable against systems it was designed to counter – namely, active radars.

victor1985 wrote:My point is that stealth is useless.

SOC wrote:


Low-band radars like the VHF-band 55Zh6 can see most LO aircraft much easier, yes. Until recently, there wasn't enough acuracy within a low-band radar to make it really mean anything. Now you've got digital VHF-band AESAs like the 55Zh6 that are significantly more capable. Shorter wavelength systems, such as fire control radars, are what the bulk of LO measures are intended to defeat (things like serrated panel edges, faceting, the intake grill of the F-117, etc.). That includes fighter radars, SAM engagement radars, etc. There's only one aircraft capable of defeating both short and long wavelength systems, and that's the B-2. It's big enough to employ LO measures against the much larger VHF-band type wavelengths, and has various LO features tailored to the smaller fire-control wavelengths as well. An F-22, F-35, or T-50 is too small to do anything relevant against a VHF-band system, short of putting a meter thick coating of RAM on the things. Given the number of advanced long-wavelength systems appearing and their ability to interface directly with SAM units, the F-35 is a hilarious waste of time. The T-50, not so much, as the US has never really put much effort into VHF-band systems. You need big-ass transmitters for one, making them unsuitable for airborne or naval use.

SOC wrote:

Arrow wrote:

But B-2 can be detected by OTH radar ?

By an OTH-B system while flying in international airspace.  The OTH-B uses a different signal path geometry than a ground-based radar, which could help, and also uses a larger wavelength than a VHF-band system like the 55Zh6, which could also help for the same reasons that your X-band LO features don't affect a larger VHF-band wavelength.  Plus, weren't they claiming to have picked up the wake turbulence and not the actual airplane at one point?  Although either way you've "detected" it.  Being in international airspace also means they fly around with all of the transponders and whatnot on I think.  Pretty sure they didn't turn that crap off until they were over the Med when heading for the FRY, for example.  Transponders are cheating anyway as you track without a skin paint!

max steel wrote:
....fighters such as the Su-30SM, Su-35S and MiG-31BM can also be involved in pursuing “ghosts.” It is this fact that makes the B-2....

Value of stealth aircraft

Posted by picard578 on March 30, 2013

Introduction

Unlike US Navy and every other air force across the world, USAF has decided to transit to an all-stealth air force.

But due to the Moore’s law, processing power doubles every 18 months – which means not only improvements in sensors that are already very capable of detecting stealth aircraft, but also that, as time passes, stealth aircraft is ever less capable against systems it was designed to counter – namely, active radars.

Air-to-air combat

Stealth vs radar

Stealth relies on processing gain advantage over radar, by reducing return below treshold of what can be detected by radar itself. However, due to the Moore’s law, radars are becoming ever more capable. Further, stealth fighters are designed with minimum nose-on RCS, which means that they are easier to detect by aircraft flying in wall formation. At the same time, jammers benefit from Moore’s law too, which enables fighter-based jammers to rapidly close the effectiveness gap with stealth, or even surpass it.

This purely theoretical thought exercise is not likely to be very relevant, however, as radar – being an active sensor – automatically gives position of aircraft using it away far before it can detect opposing aircraft, meaning that pilots will start shutting it down in combat as soon as losses due to its use start to mount due to radars’ use giving very important advantage of surprise to the opponent. Against both enemy aircraft and SAMs, dedicated jamming aircraft – ranging in size from converted medium-weight fighters to converted heavy bombers – are avaliable, and far more effective since they also protect other aircraft.

Stealth vs IRST

Most discussions about value of IRST against stealth focus on airframe being heated due to air friction. This, however, is wrong for a very simple reason: any time a gas is compressed, it heats. And compression of gasses in front of moving object is a normal, unavoidable occurence – only difference is scale of compression, which depends on object’s speed.

While aircraft do heat up less in rarer atmosphere, less atmosphere also means that more IR radiation – especially of longwave variety – reaches the infrared sensor. Further, at high altitudes – where stealth aircraft are required to operate – temperatures range from -30 to -50 degrees Celzius. At the same time, fighter supercruising at Mach 1,7 creates shock cone with temperature of 87 degrees Celzius. While PIRATE IRST can detect subsonic fighters from 90 km from front and 145 km from rear according to (somewhat outdated) publicly avaliable information, this range is 10% greater against supercruising fighter. At the same time, OLS-35 can detect subsonic fighter from 50 km from front and 90 km from rear. PIRATE’s own range is already comparable to that of fighter radars against 1m2 targets. (Note: Data used for both PIRATE and OLS-35 dates from 2008; it is possible that both have been improved in the mean time). Prototype Russian stealth aircraft PAK FA uses QWIP-based OLS-50M, so it is possible that QWIP technology may find its way into Su-27 family of aircraft. Identification can be carried out at 8 to 10 kilometers.

Parts of aircraft’s exhaust plume are also visible from front, which should present no problem for modern IRSTs that are capable of detecting AAM release due to missile’s nose cone heating.

Some IRST systems have laser rangefinder coupled with them, which means that they can be used to gain gun firing solution without usage of radar. While IRST is mostly immune to “beam turn” used to break radar lock, laser rangefinder may not be. Rangefinder, though shorter-ranged compared to IRST, would also have increased range at higher altitudes. IRST could also use sensitivity model (Atmospheric Propagation Model) to roughly estimate range and velocity of target without using any active sensors.

(Interesting to note is that Soviet MiG-31s were able to target SR-71 by using IRST; at speeds both aircraft were flying at in these situations, MiG-31s front surfaces would heat up to 760 degrees Celzius due to aerodynamic friction. SR-71 was not much better off; fortunately, order to attack was never given).

Astronomic IR telescopes can detect velocity of star down to 1 meter per second. This kind of precision would not be required for air-to-air combat, however, as closure rates between fighters could be up to 1 700 meters per second.

This means that stealth aircraft has no escape – if it attempts to increase effective range of its missiles, it has to increase speed – but this increases IR signature and allows it to be detected from larger distance. If it attempts to avoid detection, it has to reduce speed, which means that it has to come closer to IRST-equipped fighter.

USAF is obviously concerned about it – while IRST-equipped Super Tomcat was slated to be retired in 2008, it was hurriedly retired in 2006 under neoliberal stealth proponent Donald Rumsfeld. Both PAK FA and F-35 have IRSTs, but unlike PAK FA, F-35s IRST is optimised for air-to-ground missions, and is thus operating in appropriate wavelengths, reducing its range against aerial targets.

QWIP IRST such as PIRATE or OSF has some very useful advantages over “legacy” IRST. Aside from longer range, they can be tuned for sensitivity in certain IR band. While normal IRST operates in microwave to longwave IR bands, QWIP IRST can operate in very longwave bands, allowing for easy detection of objects that are only slightly hotter than the background, with difference being in single digit degrees of Cenzius. It can also use several bands in paralel, getting “best of the both worlds”.

While F-22 was designed to operate at high altitudes, as high as 15-20 kilometers, clouds only go up to 14 kilometers in some cases, with majority being below 4 500 meters – and even that only in tropics. All other stealth air superiority aircraft are similarly expected to operate at high altitudes.

Countering SAMs

Ground radars have to be above any obstacles to radar beam, which means that areas such as small valleys and canyons are usually not covered. Anti-radiation missiles and cruise missiles are very reliable against stationary radar sites; ARMs are better against mobile radars, as there is no radar that can pack up and leave in the time that ARM requires to reach it. SAMs are no different in that regard, and as such they can be kept shut down by use of anti-radiation missiles.

Without these two factors, however, stealth aircraft can be detected easily enough by long-wavelength radars, which completely ignore any practical amount of stealth coating, and are far less affected by stealth shaping measures than shorter-wavelength radars. These, then, can be used to guide IR SAM or IRST-equipped aircraft close enough for their IR systems to detect stealth aircraft.

Numerical issues

Numerical issues are probably the worst drawback of stealth. Stealth aircraft cost more and are harder to maintain than non-stealth ones. To demonstrate the actual impact, I will compare F-22 to two twin-engined aircraft designed to carry out similar mission to F-22s, but without stealth.

While F-22 costs 250 million USD per aircraft flyaway, cost for Tranche 3 Typhoon is 121,5 million USD, and cost for F-15C is 108,2 million USD. As such, 50 billion USD gives 200 F-22s, 411 Typhoons or 462 F-15Cs.

Sortie rate stands at maximum of 0,52 sorties/aircraft/day for F-22, 1,2 sorties/aircraft/day for F-15 and 1,2 – 2,4 sorties/aircraft/day for Typhoon (later value only assuming that design goals have been met). Thus, force bought would be able to support 104 sorties/day for F-22, 554 sorties/day for F-15C and 493 – 986 sorties/day for Typhoon.

Historically, quality of aircraft was always unable to compensate for force disparity once latter was above 3:1. As such, it can easily be seen that F-22 is, strategically, worse choice than Typhoon or F-15. And while all numbers are not yet avaliable, it cannot be expected that F-35 will perform any better in this crucial area relative to Gripen and F-16 than F-22 did relative to Typhoon and F-15. Me-262, while by any measure a revolutionary aircraft, was not used in large enough numbers to have impact against Allied fighters. In the end, Me-262 shot down no more than 150 Allied fighters, with 75 of them being lost in turn, in large part due to Allied superior numbers allowing them to catch Me-262 on take-off or landing.

BVR combat

Stealth aircraft are built under assumption that BVR radar-based combat trumps WVR combat. However, that assumption is unproven; neither AMRAAM or other BVR missiles were ever used beyond distance of 40-50 kilometers. In case of AMRAAM, usage was against aircraft with no radar, no IRST, no radar warners, no ECM, with badly trained pilots that were in most cases unaware they were under attack (and were not maneuvering as a consequence). Yet even in such perfect conditions, AMRAAM achieved 6 kills in 13 BVR launches, or Pk of 0,46.

During Desert Storm, in conditions identical to above, USAF F-15s launched 12 Sidewinders for 8 kills, for Pk of 0,67. For same F-15s, AIM-7 Sparrow achieved 23 kills in 67 shots, for Pk of 0,34.

Thus we have to take a look back at Vietnam. Why Vietnam? Simply because it was the last time US have fought somewhat competent opponent in the air. Even experience with IR missile suggests that Pk in combat against competent opponent will be far lower than above: AIM-9B achieved Pk of 0,65 in tests, which fell to 0,15 in Vietnam, to be improved to 0,19 with AIM-9D and J, whereas G model does not offer large enough sample for drawing conclusions. Yet even this was better than Pk for BVR missiles. While majority of AIM-7 shots were taken within visual range, during 1971-1973 in Vietnam, 28 BVR shots were made, resulting in 2 kills, one of which was a fratricide against an F-4 – a Pk of 0,071, as opposed to predicted Pk of 0,9 or more. During entire war, AIM-7D achieved 8% Pk, AIM-7E achieved 10% Pk and AIM-7E2 achieved 8% Pk. At the same time, guns had Pk of 0,28.

In fact, summary by Burton of kills made during Cold War has found that, out of 407 missile kills he studied, 73 were made by Sparrows in 632 firings, a kill rate of 11%. Sidewinder achieved 308 kills in around 1 000 firings. Out of all radar-guided missile kills, only four were made at BVR – two already described shots in Vietnam that were carefully staged outside of combat, and two similarly staged shots by Israeli air force. His summary of these 407 shots concluded that most targets were unaware and fired from the rear, and that there were almost no head-on BVR shots due to high closing rates. Only way to positively identify the target was by the eye.

When we take a look at the data above, a clear pattern begins to emerge: while Pk against incompetent opponent is significantly higher than against competent one, by a factor of almost five, relative weapons’ effectiveness remains unchanged: IR missiles achieve half the Pk of gun, and radar-guided missiles achieve half the IR missile’s Pk. Further, visual identification of target is still important, and is likely to remain so. In fact, during First Gulf War, majority of US casualties were due to the friendly fire, while in 1973 war Israeli pilots considered an on-board radar “essentially useless”, with Sparrow achieving one or no kills in that war.

This situation will even worsen for BVR-oriented aircraft in the future, as IRIS-T has capability to intercept and destroy BVR missiles. While it definetly will not be perfect, it will reduce number of missiles aircraft actually has to evade.

Time has also shown that maximum simplicity weapons and countermeasures, such as guns and flares/chaff, are usually most effective. This is unlikely to change.

Training issues

Pilot competence was always dominant issue in Air to Air combat. During German invasion of Poland, several Polish pilots became aces in 362 kph open cockpit fighters, when fighting against 603 kph Me-109, an early warning about importance of pilot skill. This was again shown when German fighters fought outnumbered in invasion of France, when higher-performance Spitfires and equal-performance Hurricanse fared poorly against Me-109s, which were flown by far more experienced pilots using tactics derived from actual combat as opposed to air shows and unrealistic peacetime exercises. Late in the war, Luftwaffe was unable to mount serious opposition not due to the lack of air frames – Allied bombing did not have major effect on German industry – but due to the lack of pilots.

Yet stealth aircraft’s large maintenance downtime prevents pilots from becoming familiar with their aircraft, and training enough in them. Modern fighters are also more complex than World War II ones, so lack of fighters is a very real possibility. AIMVAL tests, despite bias towards BVR, have also shown that ground controller assistance was more important to more complex and automated aircraft, and off-boresight missiles offered only slight improvement in results.

Conclusion

Stealth aircraft are expensive, and do not provide bang for the buck, in good part due to them being built on flawed reasoning and inaccurate assumptions. While they can be very useful against backward coutries, even in these cases larger numbers of cheaper aircraft will perform better. Assumptions behind stealth ignore lessons of combat to date, including the fact that pilot skill tended to dominate air combat (especially when combined with numerical superiority), as well as existing counter-stealth technologies.

Game-changing technologies were always simple in idea and execution, as relatively inexpensive. For comparision, stealth F-22 has cost of 12 690 USD per kg, F-35A costs 14 812 USD per kg, F-15C costs 8 504 USD per kg, F-16C costs 8 168 USD per kg, and Eurofighter Typhoon costs 10 942 USD per kg in its most expensive variant. It should be noted that F-22 lacks IRST and some of Typhoon’s systems, whereas F-35A is most loaded with electronics of aircraft listed. As such, stealth requirements add – without counting weight increase – 1 000 – 3 000 USD per kg. If the fact that F-22 is heavier than F-15C at least 7 000 kg is counted, stealth coating itself likely cost around 50 million USD, almost as much as my estimated flyaway cost of Gripen NG. IRST, on the other hand, costs around 1 million USD, and is far more useful than radar stealth.

max steel wrote:B-2 IS LARGE ENOUGH TO EM0LY LO MEASURES AGAINST L BAND , VHF AND UHF RADARS. Read above.

Airborne IRST properties and performance

Posted by picard578 on June 16, 2015

Introduction

IRST is a sensory device which uses IR (infrared) radiation for detection and targeting purposes. IR radiation has wavelength of 0,75 to 1.000 microns (micrometers), longer than wavelengths of color red in the visible spectrum (visible spectrum ranges from 0,39 to 0,7 microns, with violet at 0,4 and red at 0,7 microns). It is given off by all objects above absolute zero, though objects that are below average temperature of their surroundings will absorb far more IR radiation than they will give out. Unlike FLIR which is a targeting device, IRST can be used for initial detection as well.

Infrared radiation is divided into near infrared (0,75 – 1,4 microns), shortwave infrared (1,4 – 3 microns), midwave infrared (3 – 8 microns), longwave infrared (8 – 15 microns) and far infrared (15 – 1.000 microns). These have different properties. For example, glass is opaque to LWIR band but transparent to SWIR band, and significantly degradess image in MWIR band. MWIR sensors are far better at penetrating fog and clouds than other wavelengths, while LWIR sensors have superior atmospheric performance. As a result, while SWIR sensors can use glass, MWIR and LWIR sensors have to use exotic materials such as germanium and sapphire. 5-7 micron band suffers 100% absorption by water particles.

IR bands are also associated with temperatures of bodies producing radiation. Visible light is associated with temperatures above 1.000 *C. Next come IR bands: 0,7-4 microns (1.000 – 400 *C); 5-25 microns (400 – -150 *C) and 25-350 microns (this is a civilian, not military, division). Bodies at room temperature have radiation peak at around 10 microns, while 3-5 micron band is used in civilian applications for its effectiveness in tropical conditions.

In civillian purposes, astronomers use IR telescopes to penetrate dusty regions of space that block off visible light. NASA also has an airborne IR system – SOFIA (Stratospheric Observatory for Infrared Astronomy) which is flown at altitudes of over 41.000 ft, allowing 85% of the entire IR spectrum to reach it. Its service ceilling is 45.000 ft.

First IRSTs were deployed in 1950s on F-101, F-102 and F-106 interceptors. They were also used in F-8E, F-4 (B and C models only) and Swedish J-35A and J-35F-2 (1965-1967). However, they were primitive and were slaved to the radar, as opposed to modern-day independent systems. Any IR radiation falling on the sensor would generate a blip; consequential high false alarm rate meant that IRST was typically only used for (manual) radar targeting.

In 1960s and 1970s, Soviets deployed IRST units on their MiG-23, MiG-31, Su-27 and MiG-29 fighters. This was intended to provide passive BVR surveillance capability to fighters, and also as a way of countering Western advantage in radar technology and countermeasures. In fact, MiG-23 and MiG-31 interceptors were able to track the SR-71 recon aircraft from large distance, possibly up to 100 kilometers. This was despite the fact that the system was rather primitive, and that MiG-31s own skin and canopy would reach temperatures of over 760 degrees Celsius during the intercepts. MiG-23 had an IRST capable of detecting the F-16 at 35-40 km head on and 60 km from the rear. Later developments of Su-27 and MiG-29 families all have internal IRST.

General IRST properties

Due to relatively shorter wavelength, IRST is more sensitive than radar to adverse weather conditions. Much of the infrared radiation is absorbed by water vapor, carbon dioxide, methane and ozone. However, there are two wavelength “windows” in which very little infrared radiation is absorbed by the atmosphere. These windows are at 3-5 and 8-12 microns. Both modern IRSTs and modern IR missile seekers typically operate in both bands. 3-5 mM band is optimized for detection of aircraft in afterburner, while 8-12 mM band is better suited for detection of subsonic or supercruising aircraft through aerodynamic heating of skin. More specifically, afterburner exhaust plume is more prominent in midwave than in logwave band, with most emissions being in 2-8 mM wavelength band, while emissions from nonafterburning plume are only useful in 4,15-4,2 mM band. Blackbody radiation from a warm object is most prominent in 10-15 mM band, and only objects above ~300 K give appreciable MWIR emissions (still inferior to to LWIR band). As a result, LWIR detectors have good sensitivity against targets at ambient temperatures.

Unlike other IR bands, these two bands are comparatively altitude-insensitive when it comes to detection performance, as it can be seen from an IR absorpion chart in the next section; they are also less affected by water content. Comparing both bands, 3-5 mM band is less affected by aerosoil while 8-12 mM band has longer detection range and is less affected by clouds. Consequently, up until appearance of dual-band systems, midwave band was preferred for ground attack while longwave band was preferred for air-to-air usage.

While IRSTs can detect even relatively cool targets through thin cloud cover, detection range is reduced (more than it is in case of radar), and thicker clouds can significantly degrade detection range. As a result, IRST is most useful for air superiority fighters, which typically operate at 30.000 ft and above – well above normal cloud cover and in relatively thin atmosphere.* ** Only clouds typically present at altitudes above 8 km (~26.000 ft) are those of cirrus variety, which are IR transparent. While dense cumulonimbus clouds can reach extreme heights (60.000-75.000 ft), it is very rare; vast majority does not reach above 20.000 ft. They are also very hazardous to aircraft (especially those of stealth variety), with frequent lightning discharges and large hailstones ranging from 0,5 to 5 cm in diameter, which can damage aircraft’s skin.

contrails

Septemberimage10

Due to its passive nature and shorter wavelength, IRST has major advantages over radar regarding ID capabilities and ground attack performance due to increased resolution. In particular, IRST has better ability to project image of the target (to either cockpit displays or HMD), thus giving a fighter aircraft ability to ID other aircraft at longer ranges than would be possible with radar NCTR modes. IRST also has beter capability for differentiating aircraft in formation than radar does due to better angular resolution – possibly up to 40 times more accurate than radar’s. Still, IRST might have a regular magnified optical sight added for help with identification in clear weather.

Type and location of IRST is indicative of aircraft’s mission. Air superiority fighters will have dual band or longwave system positioned in front of the canopy on upper nose surface, while ground attack aircraft will have a dual band or midwave system positioned below the nose. Dual band system is preferable in both cases as it helps eliminate clutter, though it is not as beneficial for ground attack aircraft as it is for air superiority fighters.

Major advantage over the radar is that it cannot be easily jammed. As a result, actual tracking and engagement range of IRST can be expected to be greater than that of radar, even if latter has a major advantage in initial detection range. Jamming IRST with an infrared laser is a possibility (in theory), but it is very difficult if not impossible to pull off against a maneuvering aircraft. Operating modes are similar to radar: multiple target track (permitting engagement of multiple targets; similar in nature to radar’s track while scan), single target track and slaved acquisition (where IRST is slaved to another sensor, such as radar or RWR).

Being a passive sensor, IRST alone has issues with range finding. There are some workarounds. Obvious one is laser rangefinder, but being an active sensor it means that the target is warned of the impending attack (IRST still retains its passive surveillance advantage over the radar). Second one is triangulation, which can be done in several ways: datalinking two or more aircraft together, flying in a zig-zag / weaving pattern and measuring apparent target shift, or flying in straight line perpendicular to the target while doing the same. First two are usable against aircraft, while last one is only practical against ground-based targets. Target motion analysis can also be combined with atmospheric propagation model and/or apparent size of the target in order to provide a more accurate rangefinding, or these modes can be used as standalones. Radiance difference between target and the background is also a possibility. Doppler shift may be used to provide estimate of target’s speed relative to the fighters, which can be used to help with rangefinding; this is still questionable as it does not show up well at short distances, measurement may be impeded by the atmosphere, and is typically used by platforms and against targets with relatively predictable paths, which fighters are not. Exception is radar ranging, but in this case wavelength is already known beforehand to a great degree of precision. That being said, the only determinant for Doppler shift is relative speed of sensor compared to the object emitting radiation – and modern IR sensors used in astronomy can measure velocity of a star down to 1 meter per second (relative to Earth). For comparison, speed of sound at >=40.000 ft is 294,9 meters per second, and two closing fighters will be doing it at relative speeds between Mach 1,5 and 3,6. It is questionable wether Doppler shift is, or may, be used in airborne IRST.

It should be noted that while not knowing range of the target limits maximum engagement range, it does not preclude beyond visual range engagement, as missile can fly along the line of sight towards the target. This does create issues with end-game engagement, though a missile with active radar head is capable of pulling a lead, and even one with IR head might be capable of doing so albeit with less precision. Such engagement profile is in some ways superior to the classical one, as IRST’s greater angular precision will mean less possibility of a missile flying past the target without acquiring it.

Imaging IRST can also be used as a landing aid in no or poor visibility conditions (night, fog, rain etc.). While helpful for any aircraft, this is especially important for fighter and ground attack aircraft expected to operate from austere air strips.

It should be noted that IRSTs detection range is range at which probability of detection exceeds ~95% treshold, in clear-sky conditions. Actual range at which target is detected can be higher or lower. Also, heating of sensor due to friction during high-speed flight can degrade its performance somewhat.

While modern QWIP IRSTs offer the best performance, they have to be cooled to extremely low temperatures: 65 K is not uncommon. Quantum well is a potential well in which electrons are trapped. When excited, they can be ejected from the well, and produce current if external voltage is applied. QWIP photodetector / IRST can measure how much light comes from various sources by measuring the current. The longer the wavelength of light, the less energy the light has to give the electrons and the colder the detector must be to avoid excessive thermal excitations.

IRST can use scanning or staring array. Staring sensor uses one detecting element for each part of the image within field of view. This means that all detecting elements are simultaneously exposed to the image of the object, or a frame. Standard frame rate is 30 Hz, and dwell time is equal to the frame rate (1/30 of a second). Longer dwell time results in a more sensitive detector and less noise.

Scanning system can use a single element, which then sequentially scans the instantaneous field of view (determined by the aperture). Scanning system is typically a rotaring mirror. This system is cheaper than a staring array. Its output is serial as only IFOV is directed on the detector at any one time. Dwell time is determined by both frame rate and number of pixels in the image; a system with 30 Hz refresh rate and standard VGA monitor of 640×400 pixels has a dwell time of 1/7.680.000 od a second, which leads to increased noise in the system and reduced sensitivity.

(Note that a staring array still can be mounted in a turret which can scan the area in front of the aircraft).

*French Dassault Rafale has an optronics suite (IR+visual) and radar. Radar is considered primary air-to-ground sensor, while OSF is considered primary air-to-air sensor.

** F-35, a ground attack aircraft, will also typically fly at 30.000 ft during ingress/egress.

Counter-stealth performance

It is a general wisdom that IRST is of limited usefulness due to its sensitivity to adverse weather conditions. However, most modern stealth fighters (excepting the F-35 and J-31 tactical bombers) are intended to operate at high altitudes – above 50.000 ft – where ambient temperatures range from -30 to -60 degrees Celsius, which helps provide excellent contrast. Air at this altitude is also very dry, with 99,8% of the atmospheric water being below 45.000 ft. Combined with low air density and low aerosoil content, this means that there is very little atmospheric absorption of IR radiation. This applies especially to the longwave band, but detection capability is significantly improved in most bands as can be seen from the image below.

SofiaMauna

Stealth aircraft are designed to have certain IR signature reduction measures, but effectiveness of these is rather limited due to basic physics. To fly, aircraft has to overcome two basic forces: gravity and drag. Drag is created due to friction with air, compressibility effects and lift. To overcome gravity, aircraft needs lift. To generate lift, aircraft has to move forward and overcome drag. As a result, aircraft has to perform work – which creates heat. Indeed the largest IR sources on the fighter aircraft are its engines. Jet engines work by burning fuel in order to heat up huge quantities of air, which is then propelled out of the rear in order to push the aircraft forward. This leads to significant heat – engine itself is very hot (especially turbines), as is the exhaust nozzle. Engine heats up airframe surrounding it, which can be detected. Exhaust plume is also very hot, though much of the radiation is typically absorbed by the atmosphere (this depends on the altitude – refer to the image before this paragraph).

Other than the engines themselves and their exhaust, there are other sources of IR radiation. Any moving objects have to push the air out of the way. If object is fast – for example, an aircraft flying at high subsonic or supersonic speeds – air cannot move out of the way quickly enough. This leads to compression of the air in front of the aircraft, which in turn leads to heating of said air. At Mach 1,7, a supercruising fighter generates shock cones with stagnation temperature of 87 degrees Celsius. As the air moves out of the way for the aircraft, it also creates significant friction with the aircraft itself, leading to heating of the aircraft’s skin. In a jet fighter, hottest parts of the airframe other than the engine nozzles are tip of the nose, front of the canopy, as well as leading edges (of wings, tail(s) and air intakes).

hotspot_jet

As mentioned before, MiG-31 would heat up to 760 degrees Celsius during intercepts due to aerodynamic heating alone. Airframe temperature due to friction can reach 54,4 degrees Celsius at Mach 1,6 and 116,8 degrees Celsius at Mach 2,0. F-22 has two pitot tubes – one at each side of the nose – which are heated to 270* C during flight operations to prevent them from icing at high altitude. Avionics have to be cooled – especially radar. Heat exhaust is typically located at fighter’s upper surface – just behind the cockpit in Gripen, and about one canopy length behind it for the F-22. F-35 is in even worse situation since it uses fuel as a coolant, and said fuel completely surrounds its engine. This has the effect of increasing its IR signature as well as the possibility of bursting into flames if hit.

These temperatures can be compared to the ambient air (Standard US Atmosphere). F-22 achieves maximum cruise speed of Mach 1,72 at ~38.000 ft without afterburner, and maximum speed of Mach 2,0 at between 38.000 and 58.000 ft with afterburner. Above cca 53.000 ft it requires afterburner to fly, and can achieve maximum altitude of ~64.000 ft, where it is limited to maximum speed of Mach 1,6-1,8. Ambient temperature is -44,4 *C at 30.000 ft, -54,2 *C at 35.000 ft, -56,5 *C at 40.000 ft to 60.000 ft, and -55,2 *C at 70.000 ft. That is to say, difference between shock cone of a M 1,7 F-22 and ambient air will be around 130-145 * C, while temperature difference between airframe and ambient air will be cca 111 * C at Mach 1,6 and cca 172 * C at Mach 2,0.

While fighter’s IR signature can be reduced by reducing speed, such course of action also has the effect of reducing one’s own weapons range, as well as making a rear-quarter surprise more likely. In either case, fighter will get detected by modern QWIP IRST before it reaches missile effective range (10-40 km for AIM-120D at most, and can be as low as 2 km).

It is possible to apply IR absorbent paints to a fighter in order to reduce IR emissions from systems inside it. This, at best, does not have any impact on aerodynamic heating. Some IR absorbent paints cause more friction than would otherwise be the case, increasing aerodynamic heating. RAM coatings also can increase friction. While it is not a significant factor in MWIR band, LWIR detectors can detect aircraft by detecting sunshine reflections from its surfaces, such as canopy.

Modern IRST systems can even detect missile launch from its nose cone heating – this is in fact a significant advantage for IR MAWS, as UV MAWS cannot detect missiles that have spent fuel. They are also sensitive enough for planets, birds, and (in air-to-ground) barbecue grills to be sources of clutter.

Note that even if an object is at the exact same temperature as its environment, it still emits blackbody radiation, most of it at longer wavelengths.

Tactical impact

Unlike radar, IRST is primarily a passive system. This allows a fighter aircraft, or a fighter group, to detect and track the enemy without latter being aware of their presence, thus gaining a significant initial advantage in the OODA loop. Even when the enemy is aware of the fighter’s presence, he has no way of knowing wether he has been detected, or is being targeted, until a significant shift in fighters’ posture (such as painting target with a rangefinder or shifting flight path or formation). For comparison, just turning on the radar warns the aircraft in very large area of scanning fighter’s presence – and said area is far larger than one covered by the radar. Not only does it give away fighter’s presence, but if the enemy has good enough listening equipment, it is possible to triangulate location and even identify the target through its unique radar signals. Even radio communications and datalinks can serve the same purpose.

If the enemy is using radar, it is possible to use data from radar warner to generate a bearing, after which IRST can be used in a “stare” mode – continuous track, during which photon impacts are combined over prolonged timeframe to detect a target at greater distances than would normally be possible. This mode is also present in radar systems, and like IRST, radar also has to be cued by other sensors to make use of it. But while using radar in such a manner basically guarantees than the enemy with a competent RWR will detect radar transmissions, IRST is undetectable. Even a short radar burst can allow the passive fighter to generate such bearing, albeit it will somewhat limit the precision.

If radars are jammed, or more likely turned off for fear of detection, first indication of IRST-equipped fighter’s presence that the enemy aircraft will get may be alarm from a missile warning system (or radar warning system if missile is using an active seeker), thus allowing only a short time for defensive reaction. (Simulated trials of ECR-90 have shown that its airborne detection range could be cut to less than 9 kilometers by jamming). If both sides have IRST, it comes down to sensor quality and IR signature differences.

Aircraft equipped with IRST, and using IR MAWS, can remain completely silent during the mission. If the enemy has no IRST, then he will have to turn on his own radar(s), allowing the passive aircraft excellent situational awareness, well beyond what using radar in addition to IRST would allow. Further, active usage of radar will allow geolocation of radar emitters, allowing the passive fighter to use IRST to engage such targets with high precision – thus gaining a “see first, strike first” capability. IRST-equipped aircraft is also not vulnerable to anti-radiation missiles. (Note that such missiles are not very hard to make, with basically all air-to-air engagement radars being in X band).

IRSTs shortcomings can be compensated for by using datalinks to network the fighter with other assets, such as other IRST-equipped fighters and radar-equipped AWACS. As a result, radar is not the primary onboard sensor any more, and is not actually even required.

Using datalink from AWACS (though AWACS is unlikely to survive for long in a shooting war) or ground radars, fighter can then approach the enemy from side or rear, in order to prevent detection by enemy’s own radar and maximize IRSTs detection range. Once target is acquired on IRST, fighter can pursue engagement completely independently. Of course, if enemy fighter uses its own radar, no AWACS is required. It should be noted that most, possibly all, fighter aircraft today lack the datalink capable of transferring amount of data necessary for a firing solution. Even if such datalink is deployed, it will be easy to jam. As a result, fighters have to rely on onboard sensors to create a firing solution (when Rafale shot down a target at 6 o’clock, shot was done with onboard sensors and within visual range; F-35 may have a similar capability).

Large radar-based fighters – such as the F-15, F-22, Flanker variants – can act as AWACS of sorts, providing radar image to smaller IRST-only fighters, which can then use such image to achieve optimal position for a surprise attack. This in turn will allow IRST-equipped fighters to focus the IRST and achieve detection ranges larger than could normally be achieved. Even if radars are jammed, radar-based fighters should be able to roughly tell positions of enemy fighters, unless DRFM, active cancellation or standoff jamming is used. Using IRST to generate a firing solution, and then launching an IR BVRAAM or ramjet RF BVRAAM (or, ideally, a ramjet IR BVRAAM, though such missile does not exist in Western inventory) at a surprised opponent will allow far higher kill probabilities than using an obvious radar for firing solution.

Still, using an AWACS with a huge IRST plus extensive ESM arrays might allow the same tactics without a drawback of warning the enemy that he has been detected, and without suffering vulnerability to decoys and jamming that radar has. Additional advantage of such system is that its effectiveness will not be significantly degraded even against VLO targets. On the other hand, while bad weather degrades IRSTs performance, it also degrades performance of stealth coatings (assuming that stealth fighters can safely enter storm clouds), thus combining radar AWACS with IRST-equipped fighters does make some sense, as does using both types of AWACS.

IRST is the best solution for engaging stealthy aircraft and cruise missiles. As it can be seen from the previous section, is impossible to significantly reduce IR signature of a high-speed, highly maneuverable aircraft, and even low-performance aircraft that do have very extensive IR signature reduction measures are still detectable at large distances by new QWIP imaging IRSTs. Even against “legacy” aircraft its is a better choice than radar, as radar cannot separate valid contacts from decoys except at very short range – especially if it is being jammed. As a result, only IRST-equipped fighters can effectively engage modern fighters at beyond visual range.

IRST can be used as a relatively cheap way of turning an old, possibly even WVR-only, platform into one capable of BVR combat. With PIRATE + MICA IR combination, even an old F-86 would gain a capability to shoot down enemy fighters from beyond visual range (that being said, issues of low cruise speed, deficient acceleration by today’s standards and no defense suite at all would remain, and would mean that even against the F-35, F-86 would not achieve positive kill/loss ratio).

Analytic simulations indicate that an IRST-equipped aircraft will have 230% better exchange ratio than a non-IRST equipped aircraft against a “legacy” target, and 370% better against a LO target.

Specific IRST systems

PIRATE

PIRATE is used by Eurofighter Typhoon, and it entered service in 2007. Its lead contractor is Selex ES. Selex holds the bulk of Western experience in IRST systems, and is also a sole supplier of the Skyward G IRST. Thales, another member of the Eurofirst consortium, also has extensive experience in the area.

PIRATE is a dual-band system (3-5 and 8-10 microns), combining long range detection capability of the longwave IRST with high resolution and all-weather performance of midwave one. It can track more than 200 targets, and has 140* field of regard in azimuth, with -15* depression angle. Sensor head weights 48 kg, with 60 kg (?) total weight.

Detection range against a subsonic fighter-sized target is 90 km from the front and 145 km from the rear. It has an ID range of 40 km, and can track a maximum of 200 targets. It is stated to be capable of passive ranging. Its ability to provide infrared image (which can be shown on cockpit displays and HMD) can, aside for ID purposes, also be used to help with flight operation in low visibility conditions.

(Note that range figures for Western IRSTs are most likely measured/estimated against Su-27, a massive aircraft with no IR signature reduction measures.)

Skyward G

Skyward G is a new IRST intended for use in Gripen E/F, and represents a technological improvement (in both hardware and software) over older PIRATE IRST it is based on. It is a staring imaging IRST. It is also smaller, with sensor head weighting 30 kg. Like PIRATE, it is a dual-band system covering midwave and longwave infrared bands, and can provide IR image on pilot’s helmet. Scan coverage is 160* in azimuth and 60* in elevation.

Skyward is stated to be capable of detecting all aircraft flying faster than 300-400 kts from skin friction alone – irrespective of any exhaust plume or engine IR signature reduction measures. Range for such detection is unstated.

OSF

OSF is an optical sensors suite used by Dassault Rafale. It consists of an IRST sensor and a video camera. Like PIRATE, its IR sensor is dual-band, using 3-5 and 8-12 micron bands.

Detection range against a subsonic fighter-sized target is 80 km from the front and 130 km from the rear (at 20.000 ft; 110 km at low altitude). Optical camera has ID range of 45 km, while IRST has an ID range of 40 (?) km. It was reported to have locked on a turboprop Transall through thin cloud cover.

EOTS

EOTS is a staring IR sensor. Unlike above IRST systems, it is primarily intended for ground attack, as a replacement for various IR targeting pods. As a result, it is a single-channel midwave IR system, limiting its detection performance against nonafterburning targets and in air-to-air role but providing all-weather performance. It weights 200 lbs / 90,7 kg.

It is also obsolete when compared to modern IR pods used by US Navy (in particular, newest versions of Sniper and Litening pods), being more than a decade old as of 2015. In fact, it is basically an internal version of Sniper XR pod which entered service in 2006, and has low resolution and detection range when compared to the Legion pod. From Sniper XR demo, it appears that identification range is 24 kilometers against fighter aircraft, though the aircraft in question was on the ground, and 45 kilometers against an airborne business jet, showing ID performance at most comparable to PIRATE. This suggests lower maximum detection range as PIRATE likely uses midwave channel for identification, but also has longer-ranged longwave channel. That being said, actual detection range performance may be better than suggested here. Its configuration also allows it quicker scan speeds than with traditional IRSTs.

OLS-27

OLS-27 is used on Su-27 fighter, and has a maximum range of 70 km.

OLS-30

OLS-30 is used on Su-30 fighters. Maximum detection range might be as high as 90 km, and weights 200 kg.

OLS-35

OLS-35 is a scanning array IRST used on Su-35 fighters. Detection range is 50 km head on and 90 km from the rear against a subsonic fighter-sized target. It can track 4 targets. Sensor head weights 60 kg.

OLS-50

OLS-50 is IRST for T-50/PAK FA fighter. It is the first QWIP system deployed on Russian fighters, which suggests far higher detection range than earlier systems as well as the ability to identify targets.

IRST-21

IRST-21 is a podded system in use with US military. It has field of regard of +-70 degrees (140 degrees) in both azimuth and elevation, and total weight of 67-83 kg. Like other Western IRST systems (and presumably most Russian systems listed), it is capable of generating weapons-quality tracks.

Conclusion

While historically IRST had major performance issues, modern IRST systems, especially Western ones, have mostly solved these issues. As a result, IRST can be expected to become a primary sensor in any air war between competent opponents, for the same reasons as those that led to night vision googles being used for night fighting in place of flashlights.

While US Department of Defense has a very long history of being “late to the party” when it comes to introducing simple, yet effective (even transformative) systems*, US military is currently taking baby steps to rectifying its lag in development and application of airborne IR sensors. This can be clearly seen from the F-35s inbuilt IRST (though that decision was only made on insistence of US Navy, which was also the first service to introduce the Legion pod, and generally has better understanding of passive IR systems than USAF**), and procurement of IR pods for the F-15C, F-16 and F-18 fleets. Legion pod procured is capable of generating weapons track. US Navy is also the service that initiated development of AIM-9X Block III, which is basically a BVR missile, with a range of 42 km.

One of reasons why United States have not put funds into developing IRST, and are even now using almost exclusively systems geared for air-to-ground performance that happen to have air-to-air option, is that IRST was seen as a threat to the AWACS program, and later on also to stealth fighters. Both of these were high-budget programs that USAF could not allow to disappear. With average price of 1 million USD per unit, it would take only 3,2 billion USD to equip the entire US inventory of tactical aircraft with modern IRST systems. Allowing it to threaten the multi-billion AWACS or stealth aircraft programmes was simply unacceptable.*** For this reason, USAF is still acting as if IR sensors have not advanced past Vietnam-era sensors with their range, weather and targeting limitations. Same reason is also likely behind the decision to retire the IRST-equipped F-14 just before the F-22 started entering service (F-14s were retired in mid-2006, while the F-22 started entering service in 2007).

This might be changing as USAF agressors are starting to use IR sensors during Red Flag exercises. US’ Northrop Grumman has also signed a deal with SELEX which will bring Europe’s more advanced IRST technology to United States. This will help overcome US technological lag in field of IR systems when compared to Europe.

* Examples are assault rifles, carrier catapults, IR sensors, helmet mounted sights, HOBS IR missiles.

** US Navy was also the first service to deploy IR Sidewinder missile in 1956. US Air Force deployed a Falcon missile the same year, but it had both IR and RF variant, and unlike Sidewinder, it was primarily intended for bomber self-defense and not for usage on fighters. Even though it was later deployed on fighter aircraft as well, USN Sidewinder proved superior and became preeminent US IR air-to-air missile.

*** E-3 Sentry program cost is 26,73 billion USD, F-22 program cost is 79,48 billion USD and F-35 program cost is estimated at 323 billion USD, though it is likely to be higher.

Ye cannae change the laws of physics! – Scotty

Further reading

http://fas.org/man/dod-101/navy/docs/es310/EO_image/EO_Image.htm

http://foxtrotalpha.jalopnik.com/infrared-search-and-track-systems-and-the-future-of-the-1691441747

Austin wrote:AW&ST : Measuring Stealth Technology's Performance

http://aviationweek.com/defense/measuring-stealth-technologys-performance

Austin wrote:What do you make out of this , Any Rebuttal ?

An F-35 pilot explains why Russia and China's counterstealth can't stop him

http://www.businessinsider.in/An-F-35-pilot-explains-why-Russia-and-Chinas-counterstealth-cant-stop-him/articleshow/58694948.cms