Stealth in the air

Introduction

While “stealth” is normally used as short for “radar stealth”, it actually means proper suppression of all following signatures: visual, radar, infrared, electromagnetic and sound.

Stealth vs sensors

Visual

Visual stealth depends on several factors: airframe size and contrast, presence/absence of smoke and visibility conditions.

Airframe stealth is achieved by small size and masking colors – usually light gray. Early F-16s and Gripens were delivered with a black radome, which was quickly repainted grey when it was realized how much impact it has on visual signature. Visual signature also changes depending on aspect – it is smallest from the front and largest from top/bottom.

Smoke can have a very large impact on detection range – F-104 smoked so heavily that it was detectable at twice as long range as required to see aircraft itself. However, modern fighter aircraft use engines designed to minimize smoke, so it may not be a factor, older aircraft such as F-14 and F-15 excepted.

Visual stealth is especially important for ground attack aircraft, since visually-aimed AAA has always been the greatest threat (caused 38% of casualties in the Gulf War), followed by IR SAMs (31%) and only then by radar-guided SAMs (16%) and radar-aimed AAA (15%).

Radar

Radar stealth depends on multiple variables: aspect to radar, radar’s frequency, materials aircraft is made of. For all fighter aircraft, radar signature is lowest head-on, and higher from all other angles; and due to the shape, they are only truly stealthy few degrees from horizontal. Frequency-wise, any RAM coatings are only effective against X-band radars; radar-transparent materials are effective against all frequencies, but it is impossible to make entire fighter aircraft from them – Rafale’s fin is made from radar-transparent material, but nothing else.

Aircraft with datalink may be able to pick up reflections from radars by other fighters and thus detect stealth aircraft; at very least Gripen and Typhoon have that capability. This reduces impact of shaping, as all stealth fighters (and stealth aircraft in general) are optimized for the minimum nose-on RCS. F-16s have also frequently picked up F-117s on radar; signal would come and go, but pilot would know there is something around worth looking at, and where to look at.

Actual effectiveness of radar stealth is questionable at best. F-117s during Gulf War have flown in presence of jammer support, and only at night. Two night-flying squadrons of A-10s have flown as many sorties as F-117s and suffered same number of losses: none. In Gulf War and Kosovo War, A-10s suffered 4 losses in 12.400 sorties, compared to 2 losses in 2.600 sorties suffered by F-117s. Basically, A-10 was as 2,4 times as survivable as F-117 (survivability can only be compared by using loss rate, that is number of losses relative to number of sorties). In Kosovo war, F-16 suffered 1 loss in 4.500 sorties, for loss rate of 0,02%, and F-117 suffered 2 losses in 1.300 sorties, for loss rate of 0,15% – that is, F-16 was 7,5 times as survivable as F-117. It should be noted that Close Air Support flown by the A-10 was a far more dangerous mission than missions flown by F-16 and the F-117, with A-10 often using its gun.

IRST

IRST works by detecting IR emissions. This is a problem, since all aircraft heat up when flying. Greatest source of heat is aircraft’s engine and its emissions, but there are also skin friction and electronics, particularly radar. Airframe heating is not the only source of the IR signature. There is also air compression in front of the airframe, as well as shock waves created when aircraft is supersonic.

irranging7ek

Impact of airframe heating can be reduced somewhat by use of materials, but it will always be a major source of IR emissions. Shock waves and air compression effects are however made worse by the radar-stealth measures, since latter involve heavy aerodynamic compromises.

Only way to hide from the IRST is by using clouds. However, most clouds extend to no more than 6-14 kilometers (6 on poles, 14 on equator; this would give ~10 kilometers in Central and Western Europe and United States), where fighter aircraft typically operate at altitudes of 9-18 kilometers. Cumulonimbus clouds are dense and can extend very high up, but they are also hazardous to aircraft due to very strong turbulences (upwards and downwards drafts can exceed 1 km per minute) as well as frequent thunderstorms, large hailstones and tornadoes. These effects can damage stealth aircraft’s coating -hailstones can be as large as grapefruit or ananas, and F-35 is actually banned from flying within 40 km from thunderstorms as its fuel could ignite due to the lightning. Icing may also form on aircraft’s skin, compromising its radar stealth.

Problems with hiding at high altitude can be clearly seen in following photo of F-15s intercepting MiG-29s:

contrails

RWR

Modern RWRs can detect even so-called “LPI” radars; as a result, only defence against them is to turn off the radar. Even worse, aircraft such as Rafale and F-22 can use opponent’s radar emissions for completely passive target acquisition. Missile warners are also usually radar-based (Dassault Rafale and F-22, possibly other “stealth” fighters too, are an exception), which means that their emissions can also be detected by the RWR; and missile warners are constantly active.

Acoustic

Aircraft are comparably loud, especially when supersonic. This can be exploited by using a network of ground-based acoustic sensors to detect and locate aircraft by using its acoustic signature. In this area, aircraft built for radar stealth are at disadvantage due to their unaerodynamic configuration. This disadvantage is however mitigated to the extent by the fact that stealth aircraft carry missiles internally; but while this reduces noise due to the air flow turbulences around the aircraft, it means that aircraft in question needs stronger engines – which are bout hotter and louder.

Conclusion

Stealth is a scam, with idea of stealth and its effectiveness being spread by a mindless repetition ad nauseum: say a lie once, and some will believe it. Say it often, and many will believe it after some time. F-35 for example has lower RCS than the F-16, but is larger, hotter and louder than it; F-16 only needs IRST to become stealthier than the F-35 in real terms.

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40 replies

  1. I wonder if a very sensitive IR sensor with 360 spherical protection could be used to detect incoming missiles from a distance. That would allow for a truly all passive aircraft.

  2. Passive missile approach warning for Gripen E.

  3. Another interesting question – detecting an airplane directly to the rear of your fighter; how would this be affected by engine heat? That could be an issue.

    Somewhat OT, but if you want to see a long documentary (series of 4) about the Russians and what influenced the Su-27, it’s worth looking at this one:

    It is somewhat pro-Soviet/Russian, but still an interesting watch.

  4. “That is true, but what is blocked to the sensor at the bottom won’t be to two on the top.”

    True I suppose. Top would have to double up for rear.

    Also, since we’re talking about radar stealth, from the other thread, the link on flying wing canards:
    http://www.google.com/patents/USD588976

    Click on the pictures for a closer look. I don’t know if this will ever be made into a production aircraft though.

    Apparently the new F-16V variant may also get IRST. Here is a picture:

    • “Apparently the new F-16V variant may also get IRST. Here is a picture:”

      Finally.

      • Although Lockheed won’t admit this one, they have a back up because they know that the F-35 will not work out very well.

        Anyways, the upgrade plan are

        – IRST
        – AESA radar
        – Fully glass touchscreen cockpit (like that on the F-35)

        Judging by the picture, there’s probably a lot of other electronics underneath and conformal fuel tanks (probably add quite a bit of drag).

  5. @chris
    From that picture with the conformal tanks on I see also a little bit of radar stealth shaping.

    • Yeah it looks like it.

      Anyways, there were plans done in the 1990s even to modify the inlet:

      A bloated plane overall, but I suppose it beats the JSF any day.

  6. @Chris

    Actually that was the test plane for the divertless inlet used on the F-35. Could probably have led to a stealthier variant of the F-16.
    Here is something to discuss. I find it that achieving radar stealth through the use of conformal weapons/fuel tanks like the F-15 Silent Eagle concept it’s a much more sound approach then F-35. I mean if you want to conduct a deep strike mission and are worried about ground based radars you strap on the conformal tanks (which allow both for fuel and weapon carriage) and become a bomber that can be somewhat stealthy to ground radars. If you want air-superiority you leave the tanks at home and you have a streamlined high performance air-superiority fighter.
    It would also allow for the stealth characteristics of the aircraft to adapt to different radars by simply loading different conformal tanks with a different shape.
    It might also be a way to have a multi-role aircraft that can be efficient at both air superiority and CAS. The aircraft is optimized for air-superiority. For air-superiority the aircraft flies naked, and for CAS it carries special shaped conformal tanks that increase it’s low speed performance at the expense of high speed performance and also ad Armour over the engine.

    • “Here is something to discuss. I find it that achieving radar stealth through the use of conformal weapons/fuel tanks like the F-15 Silent Eagle concept it’s a much more sound approach then F-35.”

      Yeah I think that it may very well have been as you say – an F-35 test bed.

      I’m not convinced about the F-15SE as an air superiority fighter though.

      There would be trade-offs:
      1. Weapons bay would make the fuselage bigger and that adds drag
      2. Fuel fraction would have to be compromised for center weapons bay
      3. F-15’s fuel fraction already isn’t too good (0.30 for the F-15C) so that could further affect operational range

      “It might also be a way to have a multi-role aircraft that can be efficient at both air superiority and CAS.”

      Problem is you still don’t have a plane that can take ground fire the way a dedicated CAS aircraft can. Medium calibre AA would be a serious threat against an enemy with good air defenses.

      As you said, it’d be a deep strike bomber first, then anything else second. It’s certainly more sound than the F-35, but it’s not without it’s own tradeoffs.

    • “CAS it carries special shaped conformal tanks that increase it’s low speed performance at the expense of high speed performance and also ad Armour over the engine.”

      As indicated, I don’t think it’s possible to be a good CAS aircraft:

      1. Engines are spaced to close together so if one dies it’s likely to affect the other
      2. Lacks the titanium tub that you find on aircraft like the A-10 and Su-25
      3. Cannot loiter being a high speed jet for very long
      4. Would be forced to make use of a pod-mounted gun, which is not as good as internally mounted (accuracy issues and vibration)

  7. I don’t think you understood exactly what I was proposing.
    We start from the picard’s FLX. The naked version of it with it’s high fuel fraction, high thrust to weight, high maneuverability is the perfect air superiority fighter. Air-superiority squadrons use just this variant.
    Now for CAS we design a set of four conformal modules.
    First the gun module. Which is not designed just like a pod but like a detachable piece of the fuselage, so that the problems associated with podded guns don’t manifest. It carries a big cannon, and has high ammo capacity. Maybe make the revolver gun of the FLX removable and in it’s place mount more ammo for the CAS gun. This module get’s mounted just behind the nose landing gear, and also contains the armored bath tub for the pilot.
    Second and third, modules mounted at the joining of the fuselage and wing. Each of them very wide and designed so that when they are mounted they they modify the profile of the fuselage such that the aircraft practically becomes a lifting body. This I believe increases lift at low speed and thus loiter time, at the expense of an increased drag which sacrifices high-speed. The modules contain revolver launchers carrying Maverick missiles and maybe an Anti-Radiation version of the Maverick. The outside of the pods would contain fuel and armor. The fuel from this pods would be used on the approach to target so that by the time the aircraft enters combat the fuel in this pods is exhausted. The fuel tanks could thus be used to absorb damage. And they could be designed to be jettisoned once damaged so that they don’t affect performance on the way back to base.
    Fourthly. Belly armor module covering the engine and joining the wing modules at the sides and the gun module at the front. Obviously the doors of the main landing gear would not be covered by it.
    Now this configuration would be very close to the one-engined CAS proposal of Picard. Due to the high thrust to weight of the FLX the modules I propose could carry lot of armor and still leave the aircraft with high thrust to weight. Obviously when equipped for CAS the aircraft would be incapable of air combat.
    The only weakness remaining is that the aircraft would be one-engined.

    • Air superiority fighter cannot be used as a basis for CAS fighter. Air superiority fighter needs good maneuverability at medium and high subsonic speeds, which means delta wing with canards and an afterburning engine. CAS fighter needs to have good maneuverability and fuel economy at low speeds which means straight wing with commercial turbofan engine.

      • Some of the advantages of straight wing you can get with a lifting body which I proposed you achieve with the conformal modules. Something like this: http://en.wikipedia.org/wiki/Flying_Pancake . And I didn’t say it was the optimum CAS fighter just an idea to make a multi-role aircraft feasible. If for example you manage to build the FLX so cheap that it’s dual seat variant is usable as an advanced trainer, then aircraft equipped with CAS modules could supplement a dedicated CAS/FAC aircraft.

        • Multirole CAS aircraft is an oxymoron. You either have a dedicated CAS aircraft or you have no real CAS capability. Fast jets can carry out CAS, but that is extremely limited, and can only be used in situations when CAS is the least pressing (as in, enemy is not yet in direct combat with friendly troops).

  8. “Multirole CAS aircraft is an oxymoron. You either have a dedicated CAS aircraft or you have no real CAS capability. Fast jets can carry out CAS, but that is extremely limited, and can only be used in situations when CAS is the least pressing (as in, enemy is not yet in direct combat with friendly troops).”

    And I suppose that is the end of the discussion. Just for the sake of it I wasn’t talking about a fast jet, but of a jet that can be reconfigured to be fast or slow depending on the mission at hand. To bad, a fighter which changes shape might have been an good exercise of the imagination.

    • For that you would need a swing-wing fighter (a.k.a. F-14) which adds new layer of complexity and lacing performance. And even then, it will be severely lacking in the either mission: air superiority fighter needs to be as light as possible, while CAS aircraft needs to have heavy armor. Which means either an unsurvivable disaster of a CAS aircraft, or useless disaster of an air superiority fighter.

      • Did you read anything I said of the conformal modules, of actually changing the shape of the fuselage based on what conformal modules you have attached? I wasn’t talking of swing wing or other complex, expensive complication. I was trying to think out of the box and was basically proposing a LEGO fighter.

      • Only way to achieve that would be to have detachable wings, which could work but would also serve to add additional failure point. And it still doesn’t answer the issue of armor and armament.

  9. Regarding the IR signature of the F-35, a couple of months ago PW announced that they was running the F135 engine at higher temperatures then any other engines before.
    They will lower fuel consumption and increase power with a few percentage – but they will increase its IR radiation as well.
    Few percent more power, perhaps some extra nm combat radius but easier to detect. Calculated risk?

    • It is calculated risk, Id on’t think US aircraft designers really consider IR signature that important. Even F-22s flat nozzles may have been more of an attempt at RCS reduction than IR signature reduction. Quite unfortunate, as IRSTs are proliferating, but then again US do tend to lag in good ideas, despite having technology to make such ideas come true earlier than others.

  10. Picard578,

    You do sound knowledgable in the subject and I am no airpower expert.

    Regardless, you have made statements that I just can’t fathom.

    The Rafale barely won out in competitions for procurement (India & Brazil) against the F-18E/F. Only because France is willing to share its tech specs and the U.S. will not give up its secrets. The F-18E/F (although cheaper) is clearly not close to F-35 in capabilities. The world’s best air forces are willing to pay twice as much to aquire F-35’s than they would pay for Rafale/Gripen NG/Typhoon.

    Either the worlds airpower pros are all very stupid or you are full of it.

    Common sense tells me that you (like most Frenchman) are insanely jealous that someone else is better and can’t accept it. I am half French too, but the truth is the truth.

    • “The Rafale barely won out in competitions for procurement”

      Exports are not a good way to gauge aircraft’s quality, unless you think that MiG-21 was better than the F-4, F-5, Mirage III, Saab Draken?

      “The F-18E/F (although cheaper) is clearly not close to F-35 in capabilities. The world’s best air forces are willing to pay twice as much to aquire F-35’s than they would pay for Rafale/Gripen NG/Typhoon.”

      See my reply on your another comment. It has nothing to do with F-35s capabilities.

      “Either the worlds airpower pros are all very stupid or you are full of it.”

      Or you don’t know first thing about exports. I’d say it is the last one, because if you did, you’d understand that it is a matter of politics first, economies second and military capability last.

      “like most Frenchman”

      I’m Croatian.

      “but the truth is the truth.”

      And propaganda is a lie that often masks as truth.

  11. You were right I did not acknowledge properly the political factors that go into procurement.

    I still have a hard time beleiving that nations that are not very big and rich (thats every F-35 suitor except maybe Britain and Japan) and are in positions of needing to defend themselves from real enemies (S. Korea, Israel), would be willing to pay double for an aircraft that as you stated is a “piece of crap”.

    I am not disagreeing with your arguments, I just can’t seem to bring myself to believing.

    • “would be willing to pay double for an aircraft”

      I have an article “On F-35 export success”, but basically a lot of it is because US threatened them not to provide support for some other needed capabilities if they don’t buy the F-35. There are other tricks as well – Gripen uses a lot of US-made components, and during competitions in Norway and ?Netherlands, US “suggested” that if Gripen is selected, US may cease supply of these components.

  12. This is an old post so my comment may not be approved or read, but here goes.

    I don’t think it’s reasonable or fair to call stealth a scam. The manner in which it has been presented to the public and civilian decision-makers is a scam.

    The original reason for the cancellation of the B-1 was that the B-2 would be far more effective at penetrating Soviet air defenses. Do you really think the B-1 would’ve done a better job of that in 1990? Do you think Jimmy Carter had a goal of enriching defense contractors?

    If stealth were a scam, why are Russia and China now fielding stealth fighters? Why did West Germany design a stealth fighter mockup? Why are South Korea and Japan now designing stealth fighters? Why do conventional aircraft now have design features intended to reduce RCS?

    Rather, stealth, like all other aircraft design considerations, involves tradeoffs. The F-35 isn’t a dog because it’s stealth (in the frontal area only), but because it has a terrible airframe (thanks to the USMC’s VSTOL obsession) and the program was designed from the outset to enrich defense contractors.

    • “I don’t think it’s reasonable or fair to call stealth a scam. (…) The original reason for the cancellation of the B-1 was that the B-2 would be far more effective at penetrating Soviet air defenses. Do you really think the B-1 would’ve done a better job of that in 1990? Do you think Jimmy Carter had a goal of enriching defense contractors?”

      There is a difference between stealth and radar stealth, as well as its meaning and effectiveness. F-22 and F-35 are being presented as being far more effective than any other fighter in all roles because they have low RCS. That is a scam: both were designed to penetrate Soviet air defenses and either a) shoot down aircraft (F-22) or b) hit fixed targets (F-35). In those roles they would have been more effective than legacy fighters. But that is not how they are presented today, nor how the stealth is presented today. Rather than one aspect of survivability, stealth is today presented as the only measure of survivability and, oftentimes, utility – even in the missions where it was not intended for (such as air superiority, where all-aspect stealth is unnecessary, or close air support where radar stealth in general is mostly unnecessary). Further, low RCS does not automatically mean stealth, yet it is typically presented as such. To be stealthy, an aircraft has to have low visual, active and passive electromagnetic, infrared and acoustic signature. F-22 and F-35 only have low RCS; their IR signature, while reduced, is still significantly higher than is the case of say, Gripen or Rafale, and acoustic signature is enormous. And F-22, due to not having IRST, needs either an offboard platform or its own radar to engage targets – which leads to considerable electromagnetic signature on the active side, in good part negating advantages of low RCS. So stealth, as presented, is indeed a scam. It was never a golden bullet, never even intended as such, yet it is being treated that way by the media – and it seems that (as it so often happens) both US and foreign decision-makers have started to believe their own lies.

      As for the B-2 question, that depends entirely on wether Soviets back then had over-the-horizon radars. If they did, B-2 would be detected. In 1990, B-1 woudn’t have done a better job, but I don’t think it would have done a worse job either.

      And yes, Carter did have that goal.

      “If stealth were a scam, why are Russia and China now fielding stealth fighters? Why did West Germany design a stealth fighter mockup? Why are South Korea and Japan now designing stealth fighters? Why do conventional aircraft now have design features intended to reduce RCS?”

      First, as I have explained above, *radar* stealth (these fighters are not really stealthy in visual or IR spectrum) does have utility – Russia and China in particular are aiming to use their stealth fighters to neutralize US AWACS aircraft – hence a focus on frontal stealth and relatively lesser focus on side and rear stealth in their designs. And as I mentioned above, F-22 was intended to hunt enemy fighters within Soviet air defense network, and F-35 was intended to hit fixed targets and take out that very network. Hence F-22s all-aspect stealth and F-35s front-optimized stealth.

      Second, humans have a bandwagon tendency. The moment someone gets a shiny new toy, everybody else wants it, regardless of actual utility. Much like battleships pre-World War II, or aircraft carriers after that, stealth aircraft have become a symbol of prestige. Consequently, everybody wants one – even if they have no bloody idea what they are going to do with it once they fulfill their wish, or if the stealth aircraft in question is only good for a static display (F-35).

      Third, I have not discounted importance of reducing sensory footprints, RCS included. I just do not believe that doing so to an extent that other characteristics suffer – most importantly, sortie rate and logistical footprint – is a good idea. Again, stealth is being presented as being an only characteristic that matters – which is bullshit.

      You might want to read following articles for a better idea of my stance, and how it evolved (I grouped them by topics, you can see when posts were published in the URL):
      https://defenseissues.wordpress.com/2013/03/30/value-of-stealth-aircraft/
      https://defenseissues.wordpress.com/2015/08/01/stealth-evolution-of-justification/
      https://defenseissues.wordpress.com/2016/02/01/note-on-stealth-fighters/
      https://defenseissues.wordpress.com/2012/11/24/are-stealth-aircraft-really-required-for-dealing-with-air-defenses/
      https://defenseissues.wordpress.com/2014/01/17/stealth-in-the-air/
      https://defenseissues.wordpress.com/2015/06/16/airborne-irst-properties-and-performance/
      https://defenseissues.wordpress.com/2013/10/12/symmetric-and-assymetric-counters/
      https://defenseissues.wordpress.com/2014/08/02/air-superiority-fighter-proposal-6/
      https://defenseissues.wordpress.com/2013/10/19/how-stealthy-is-the-f-35/
      https://defenseissues.wordpress.com/2015/07/16/f-35-reality-check/

      “Rather, stealth, like all other aircraft design considerations, involves tradeoffs. The F-35 isn’t a dog because it’s stealth (in the frontal area only), but because it has a terrible airframe (thanks to the USMC’s VSTOL obsession) and the program was designed from the outset to enrich defense contractors.”

      Agreed.

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