Indian Defence Review

China’s ‘Sharp Sword’ stealth UAV

The stealth muscle in the air threat vehicles of today is one dimension of survivability that is fast becoming a nightmare to air defence warriors. Why so? Because survivability directly translates into lethality. The relationship is fairly simple. Stealthy machines, by managing to become near invisible to the sensors of the adversary, not only survive by avoiding the onslaught of the defender’s air defence arsenal, but also, with all the smart and intelligent arsenal at their disposal, cause disproportionate damage, by getting to attack the defender’s vulnerabilities nearly unchallenged (read undetected). Shadow boxing of sorts! Detection of stealthy air threat vehicles is, therefore, an operational compulsion.

The stealth muscle in the air threat vehicles of today is one dimension of survivability that is fast becoming a nightmare to air defence warriors. Why so? Because survivability directly translates into lethality. The relationship is fairly simple. Stealthy machines, by managing to become near invisible to the sensors of the adversary, not only survive by avoiding the onslaught of the defender’s air defence arsenal, but also, with all the smart and intelligent arsenal at their disposal, cause disproportionate damage, by getting to attack the defender’s vulnerabilities nearly unchallenged (read undetected). Shadow boxing of sorts! Detection of stealthy air threat vehicles is, therefore, an operational compulsion.

What Stealth Threat Do We Face Today?

Has stealth threat arrived at our door? Yes, for a one-word answer, if we were to examine some features of the frontline aircraft with our Northern neighbour that are fast approaching operationalisation and are making waves in professional circles. The case in point is Chengdu J-20 (Black Eagle) that is a stealth Fifth Generation Fighter Aircraft (FGFA) with the People’s Liberation Army Air Force (PLAAF) optimised for long range strike. Starting its first flight on January 11, 2011, it was planned for induction in January 2018. In March 2017, Chinese media reported the aircraft has entered initial operational capability phase with the PLAAF.1,2 In September 2017, it was reported that the J-20 had officially entered service with the PLAAF.3 In October 2017, Chinese media reported that Chengdu Airspace Corporation (CAC) had initiated series production of J-20 and was on a path to achieving full operational capability with the PLAAF.4 Though very few details are available, the stated (and unstated/analysed) stealth muscle of the J-20 may run like this:

A careful inspection of the aircraft structure shows the leading edges of the wing and the tail surfaces at the same angle. Same is the case with other small structures, viz. the air intakes, bypass doors and air-refuelling apertures. This design feature is called Planform Alignment (also in F-22 Raptor). This sort of alignment returns defenders the radar signal in a very specific direction away from radar emitter (thus avoiding detection) rather than returning a diffused signal which can be detected by several anti-stealth radars (Bi-Static, Multi-Static).

Though the latest prototype rolled out only wearing the yellow factory fuselage primer, the Black Eagle/Soaring Dragon will, in all probability, get a state-of-the-art Radiation Absorbing Material (RAM) coat in order to get the minimalistic RCS signature. One of the earlier pictures of the aircraft is reminiscent of Haze paint RAM which was used on the F-16s. Open sources reported in November 2015, that the Chinese Huazhong University of Science has developed a RAM wherein, a metal slab sits over a layer of thin metal honeycomb under which there are several layers of ultra thin active frequency selective surface materials each optimised to absorb a range of radar frequencies. Will such a thing find its way onboard the J-20? While that could be a ‘yes’ or ‘no’, it is very likely, the RAM will feature cutting edge features such as use of nano-materials and active carbon coats or even plasma-driven stealth coat.

Also to note are the very sharp edges, vertical cuts and an equally sharply pointing nose with a frameless canopy. These are deliberate design features which ensure that the incident radar energy of the defender’s radars is never returned to the radar in a conventional mode but is invariably deflected at an angle away from the mother radar making detection difficult. A YouTube video of this aircraft in flight throws up an interesting observation. It is seen that throughout its flight (except for a brief moment when the aircraft is overhead and offers a fleeting view of its underbelly), the shape of the aircraft is such that it never offers a flat perfectly reflecting surface in manoeuvre. The axi-asymmetric nozzles with jagged edges are low observables and effectively conceal the engine exhaust, the main aiming point of the IR-seeking SAMs. These features not only make the aircraft almost invisible to defenders radars, but also make the aircraft a very difficult target for the heat-seeking SAMs fired at it in the visual/BVR domain.

Supersonic combat jets have another issue. The current technology Gas Turbine Engines (GTEs) which require constant air inlet flow are unable to handle supersonic air speeds, since it causes shock waves. This may result in dangerous vibrations in the turbine blades which not only can result in reduced thrust, but also may lead to a catastrophic engine failure. The air required for the GTEs which is resident at the aircraft boundary (boundary layer) has, therefore, to be reduced from supersonic to subsonic speeds. This is done by using diverter (splitter) plates. These attachments next to aircraft skin serve as perfect reflecting bodies for the incident radar energy giving away the location of the aircraft. Technology has now got rid of the diverter plates in offering Diverter-less air Inlets (DSI). The J-20 has a DSI where a bump and a forward swept inlet cowl deflect the boundary layer (supersonic) air flow away from the aircraft engine. This makes the aircraft a real low-observable machine.

There used to be a time when the external strong points under the aircraft fuselage carrying a known inventory of armaments were a sure giveaway of the aircraft’s identity. As the idea of stealth caught on, the aircraft pulled in their weapons load into their internal bays. However, during the precise moments of firing (also the same moments when the defender’s sensors and weapons were ticking), the weapon bays used to open to permit firing. This again opened the entire arsenal load at a critical time. Then came the canted trapeze. When it was time for firing, the canted trapeze would lower one missile into the air stream at a time without directly exposing the entire bay. If the missile has to achieve a lock-on-before-launch, it will be lowered till lock on is achieved. For lock-on-after-launch missiles, the lowering duration will be shorter (F-22 Raptor). When the canted trapeze is lowered, the weapon bay is open. The J-20 does one better in the design of the trapeze; it permits the weapons bay to be closed before the firing is to take place thus permitting only one missile exposure at a time. This adds to the stealth muscle of the aircraft.

Another smart idea is to have two types of weapon bays. One main weapon bay storing one lot of short and long range AAMs [PL9 (22Km), PL12 (70 Km) C/D and PL 21 (> 100 km)] and another two smaller lateral weapon bays (smartly tucked behind the air inlets, in the low visibility domain) containing only the short range P-9 AAMs. The logic of smaller bay yielding smaller exposure and quicker reaction cannot be missed.

Subject Matter Experts (SMEs) are pairing the stealthy muscle of the J-20 with the likes of the F-22 Raptor, the F-35 Joint Strike Fighter, the Su-57, the Japanese ATX or the Korean KAI KF-X (the last two still under development). The question is not which aircraft tips the other or otherwise, the grave fact is that the stealth threat in a tangible measure has arrived at our door. An expert analysis has opined that the J-20 has the potential for development into a high performance stealth aircraft. What about the ever strengthening military bond between our neighbours on the North and West and the likelihood of seeing these machines on our West as well. Need I answer?

The Shenyang J-31 Gyrfalcon or Falcon Hawk is also maturing alongside as a Fifth Generation twin-engine, mid-size, stealthy, multi-purpose medium fighter. Starting with its first flight in October 2012, the aircraft is due for induction in 2018-2019. The aircraft is likely to have comparable stealth features as quoted above – DSI bumps, stealth weapons bays, matt-finish RAM, to name a few.5

If that is the shape of things firming up, where is the doubt that the stealth threat has indeed arrived at our door? Also having discussed the stealth capability of the PLAAF, is there any doubt that the same will over time also make its unwelcome appearance on our Western border?

Dealing with the Stealth Threat

If we have to counter the deadly threat from such multi-role stealth fighters such as the J-20, the J-31 and others, we need to have sensors that can detect them in the first place. Thanks to many a state-of-the-art stealth technologies onboard (Planform Alignment, latest RAM, stealth exterior engineering, stealth weapons bays and more) stealth aircraft will be undetectable by the old conventional radars. Also, since most of such class of aircraft have long stand-off capabilities, these are likely to strike while remaining in the Beyond Visual Range (BVR) domain. If therefore these machines have to countered, they must be detected electronically by our sensors at long range. How do we do it? Basically, when the EM waves from the surveillance and other radars of the defender fall on the stealth (also called Low Observable) aircraft like the above, these aircraft either absorb or dilute the radar energy incident on them or deflect it in one or multiple directions away from the mother radar. This results in the mother radar getting a very weak or no reflected signal from the aircraft, resulting in the radar’s inability to detect the aircraft and paint it on its screen.

Air Defence warriors the world over are working to break the above trick one way or the other, going by the name of Counter Very Low-Observable (CVLO) technologies. This is very briefly, the world snapshot of the CVLO scene:

•  The Russians in the forefront, followed by Americans, Israelis and French are working on radar frequency bands that are optimised to detect stealth targets. Experts have realised that lower frequency bands (VHF and low UHF ranging from 0.2-0.5 GHZ) make much better CVLO radars than the higher frequency band I/J/K or X/Ku/K Band (8-20 GHZ) which are conventionally most popular radar bands for military application.6

•  In rudimentary terms, the equation is simple. While higher band radars are more accurate, and are more responsive with smaller antennae, their power handling capability is limited. Also, their waves suffer far more atmospheric attenuation and absorption than low-band radars. Due to this, high-band radars do not make good stealth radars simply because detection of stealth requires the waves incident on the target to have good signal power with minimum attenuation by the atmosphere. Why? The waves must have adequate residual reflective power after a big chunk of them is either absorbed or is attenuated by the stealth aircraft. VHF and low UHF band radars make a good CVLO choice because, firstly, they can handle large transmission power and secondly, the waves exhibit minimal absorption/attenuation by the atmosphere. The price to be paid is in the form of huge and unwieldy antennae and less accuracy in target resolution.

•  The Russian 55Z46M Nebo M 3D Radar or the Chinese KJ 2000 and KJH 200 are CVLO radars in this category. In fact, these radars go a step further. These feature not one, but multiple bands. Low band (VHF) for anti-stealth and high band (L and X bands 40 GHZ+) for other accuracy driven tasks such as illuminating the target or tracking it, post detection. These are thus also called the Multiple Input Multiple Output (MIMO) Radars.7

•  For threats that remain on the other side of the hill and use that as a stealth feature (a capability well existent with our immediate neighbours), VHF/HF radars also make good Over the Horizon (OTH) radars. These launch their waves at higher elevations over the hill escaping them out of the atmosphere and hitting the ionosphere from where these get reflected in hops covering the areas beyond the LOS obstacles.

•  Experts world over are also exploiting the lasers for detection of stealth targets. Laser waves, because of their short wave length, high beam quality, strong direction-ability and high measuring accuracy can successfully detect stealth targets. Such waves are ideal in initial identifying the target, positively displaying it and following it up with orbit recording in a continuous mode. Due to their high coherence, high resolution laser waves also possess anti-jamming capabilities. Radars using Laser waves are famously called Light Detection and Ranging (LIDAR).8

•  Since any stealth target will either try to absorb the radar energy or reflect it back in pure/diffused/altered condition away from the mother radar, two trends are prevalent to counter this trick. One, to transit from mono-static radars where the transmitter and receiver are at the same place to bi-static/multi-static configurations in which the radar receiver(s)/ is/are placed at a different location(s).

•  Going a step further, open source talks about the Chinese going in for an integrated Air Defence System hooked to a Central Information Processing Centre which features multiple radars with high altitude drones (Divine Angle) along with satellite tracking. Based on the theme that a target cannot remain stealthy at all angles, this system claims that stealth targets can ‘RIP’.9

•  Another prevalent concept is Passive Detection or more precisely, Passive Coherent Location (PCL). In this, the radars do not transmit any radar energy themselves, but achieve detection of targets based on receiving EM waves that strike the stealth targets from multiple domains such as FM, Digital Audio Broadcast or DAB and DAB-T (terrestrial). Lockheed Martin’s Silent Sentry ushered in the era of PCL. In 2013, EADS displayed its Cassidian PCL radar at the Paris Air Show. According to a report in Defence News, the Chinese are claiming that their DWLoo2 Passive Detection Radar System will make the stealth features of front-runners like the F-22 and F-35 obsolete.10,11

•  There is yet another niche development called the Quantum Radar which holds the future promise of a strong anti-stealth sensor. It makes use of the quantum properties of photons. Normally, a stealth target alters the radar signal and sends a spoofed signal making the defender believe that either the target is harmless (say, sending back a bird signal) or it is elsewhere. Moment spoofing is attempted on photons, these particles undergo a high degree of polarisation. The measure of the strength and extent of polarisation lets out the invisibility of stealth machine.12

Focus India

While much is happening all round the world, what does this mean in our scenario? A possible way forward is suggested as under:

As per details in the open source sources (www.forceindia.net) the legacy air surveillance radars in service with the IAF, viz. THD 1955, PSM 33, TRS 2215, Indra, Rohini and Reporter are generally not in the anti-stealth optimised bands (exact frequency bands not quoted).

It is, however, fortunate that the later version surveillance, tactical and missile guidance radars, viz. 3D CAR, 3D TCR, LLWR and more have significant technological ability to detect stealth targets. Such capabilities are not band-specific alone (high band/low band). Frequency bands and exact features not quoted.

Since a large number of Ground Based Air Defence Weapon Systems (GBADWS) are at various stages of the procurement cycle (VSHORAD, SRSAM, QRSAM, MRSAM), it needs to be ensured that the associated sensors that come along with these futuristic GBADWS, must have the anti-stealth muscle.

Several legacy Tactical Control Radars (those that can electronically designate target tracks to other radars), Early Warning Radars (those which carry out only surveillance with no capability to designate targets to other sensors), Fire control Radars (controlling the fire of terminal GBADWS like guns and VSHORADS) and Missile Guidance radars of Army AD (exact names not quoted) are giving way either to their successors or to their product improved versions. It is to be ensured that the incoming radars have a degree of anti-stealth muscle which does not necessarily mean only lower band radars.

Certain legacy SAM system of Russian origin held with Army AD still possess the old vintage P series of radars (P12, PRV 11, PRV 16, P15, P18). Some of these are low band VHF radars. Even if the main equipment gets obsolete and is to be de-inducted, these anti-stealth gems need to be kept and exploited till it is possible.

Over a period of time Electronics & Radar Development Establishment (LRDE) and Defence Research and Development Laboratory (DRDL), both under the DRDO and Bharat Electronics Limited (BEL) have gained considerable clout in design and production of a whole spectrum of radars. It is time for them to focus on radars with anti-stealth capability. A beginning can be made by developing a Bi-Static radar. Future R&D areas could be along the path of PCL and LIDAR. In this it is not necessary to re-invent the wheel as a headstart is available along multiple routes of JV or MoUs or ToT, thanks to the opening up of the DPP regime.

What is true of DPSUs is also true of the private industry. Since the stealth muscle in our scenario is just about maturing, it is only going to become an increasingly prominent feature of the futuristic air threat. Opportunities to develop stealth detectable radars for indigenous consumption as well for the export market either in the ‘go alone’ mode or through technological tie ups et al, is thus an emerging business opportunity.

At Def Expo 2016, OIS AT displayed four radars claimed to be developed by them (bird detection, multi-mode UAV detection with a sense-n-avoid function, foliage penetration and portable ground surveillance). There is a need to diversify by sensing the demand in-house and in the export market.

Such is the exciting and dynamic field of stealth and anti-stealth. The eternal cause-effect duel between the prosecutors of air threat and defenders there from, is only going to become more intense and interesting in so far as it pertains to the ‘magic of invisibility’ on the one end and the resolve to find the invisible on the other.