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An explanation of some of the PAK-FA's avionics, from the Key Publishing Forums.  I can't vouch for accuracy, but it seems reasonable.

 

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This is the 101KS-O DIRCM (Directional Infra-Red Counter Measure) turret.  There are two such turrets on the PAK-FA; one is underneath the nose, and the other is the astromech droid-looking thing behind the canopy:

 

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This is a defensive jammer that works by blinding heat-seeking missiles with an infra-red laser beam.  Here is some test footage of a similar DIRCM system made by Northrop Grumman:

 

 

This sort of defense is likely to be very effective against older heat-seeking missiles with reticle seekers.  This includes the FIM-92 Stinger, the 9M38 Igla, all AIM-9 variants except the AIM-9X, all Soviet-designed heat-seeking air to air missiles, Israeli-designed heat-seeking missiles up to Python 4, et cetera.  Newer heat-seeking missiles with imaging infrared seekers like IRIS-T, ASRAAM, AIM-9X and the as-yet unseen K-74M2 will be harder to fool.  When hit with DIRCM they can enter a Home-on-Jam mode which steers the missile towards the jammer.

 

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This is the MAWS (Missile Approach Warning System).  This is believed to be an ultra-violet based system that detects UV light from rocket motors.  The pilot is then warned of the approaching missile, and the DIRCM can begin jamming it.  These MAWS sensors are scattered all over the PAK-FA to give complete coverage, but you can see one of them behind the cockpit on the side of the aircraft:

 

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This is an infra-red targeting pod.  This will be attached externally to the PAK-FA when it is performing ground attack missions.  It looks very similar to Lockheed Martin's Sniper pod:

 

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This pod likely contains a high-resolution, high magnification, stabilized infra-red camera as well as a long-range laser designation beam (perhaps also a laser system for beam-riding air to surface ordnance.  Russians love laser beam riding missiles.)  Russian optoelectronics generally lag their Western counterparts by a decade or two, but it is probably at roughly as capable as the LANTIRN pod:

 

 

This system will be very useful for finding and designating ground targets as well as reconnaissance and surveillance.  This sort of thing would be extremely useful in the current Syrian conflict.  The PAK-FA could overfly a suspicious sector of the conflict with its radar in Ground Moving Target Indication mode (GMTI).  In this mode the radar detects the Doppler shift of returned radar waves to filter ground clutter noise from signals returning from moving vehicles.  The PAK-FA's software could then point the targeting pod at the moving vehicles so that the pilot or an intelligence officer in a bunker somewhere, watching the feed from the aircraft's data link, could then scrutinize the images.  If it turns out to be a large fleet of jihadotas then the strafing runs can begin.

 

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This is the IRST (Infra-Red Search and Track) system.  This one is easy to identify, it's the big, metallic marble in front of the canopy:

 

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This system is a wide-angle infra-red sensor that supplements the radar in the air-to-air role.  It serves to detect and track the heat signatures of enemy aircraft.  Because it is a passive system, there is no possible way for enemy aircraft to know that they are being tracked by the IRST.  The IRST also has a built-in laser rangefinder.

 

Various Western defense analysts made a big deal about the MiG-29 carrying an IRST system.  However, when Western pilots finally got their hands on former East German MiG-29s, they were not particularly impressed with the IRST.  Compared to radar, IRST is shorter ranged, and its range drops even further when there are clouds in the sky (radar is basically unaffected by clouds).  Radar can perform its scan of the sky faster, especially PESA and AESA radars because their electronically scanned antennae are not limited by mechanical movement speeds.  Finally, the IRST on the MiG-29 was non-imgaging; it just detected anything that was hot in front of it, but it had no way to inform the pilot what the hot thing was.  The system on the PAK-FA is supposed to be much better, although whether it is so much better that it is actually useful has yet to be seen.

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Sputnik News has a blurb on the PAK-FA's IFF systems.

 

The big antennae in the leading edges of the PAK-FA's wing roots are probably part of the IFF system:

 

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In some parts of the internet, enthusiastic, shall we say, commentators suggested that the wing antennae on the PAK-FA were some sort of super-duper stealth-busting L-band AESA system.  This is a completely stupid idea.  While it is true that L-band radars work better against stealth aircraft than X-band radars typically used in fighters, an L-band radar small enough to fit into the wings of the PAK-FA would have such poor resolution that it would be useless.

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Here's a look at the integrated avionics suite of the PAK-FA.  Some highlights:

 

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The T-50 fighter prototype furnished with the latest avionics and microprocessor has conducted its maiden flight in winter this year. According to Dmitry Gribov, chief designer and avionics suite integration director, Sukhoi, the advanced platform is designed to replace the computer system wrapped around the Baget digital computer system and developed as far back as 2004. The development of the advanced IMA BK (Russian for ‘integrated modular avionics of combat complexes’) system was kicked off four years ago, with the Russian Industry and Trade Ministry among the customers. The computer system is based on Russian-made multicore chips and a real-time operating system that is Russian-made too.

 

So until very recently, all flying PAK-FA prototypes were not using flight control computers that were representative of the mass-produced type.

 

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In the T-50’s integrated avionics suite, the central computer controls the aircraft systems, weapons employment and self-defense and provides multifaceted intellectual support for the pilot. The central computer triple-hatted as electronic pilot, electronic navigator and electronic flight engineer, performs real-time automatic target identification and prioritization, optimal route plotting, optimal weapons use and self-defense, and system reconfiguration in case of failure. The cutting-edge control system assumes control of almost all key instruments of the fighter - the radars, navaids and comms, while each of the systems of the preceding aircraft prototype called for a computer of its own.

 

My understanding is that most combat aircraft are headed in the direction of integrated electronics suites to manage all of their subsystems.  Furthermore, some modern avionics are flexible enough that they can perform more than one role.  The AESA radar of a stealth fighter, for instance, can reasonably double as a jammer.  The F-35 is supposed to be able to use its radar as a jammer when appropriate, and there has been discussion (on Key Publishing, mostly) that the PAK-FA will have similar capability.

 

If the integrated avionics suite is responsible for handling the radar, then it is possible the radar will get a major boost in performance thanks to strong signal processing.

 

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The data exchange in the IMA BK is via fiber-optic lines. The transition from the copper cable to the fiber-optic one has boosted the data rate and throughput several-fold, slashed the weight of the cables by an order of magnitude and boosted the immunity to natural clutter and electronic countermeasures drastically. While the data transfer via the ubiquitous copper cable is at a rate of 10-100Mbps, it is almost 1,000 times higher via the fiber-optic cable - 8Gbps. The system’s networked structure increases the reliability of all instruments: if a computer malfunctions, the systems automatically switch over to another, and the introduction of the centralized processor has almost halved the device’s weight. The central digital computer’s performance has surged by more than 10 times and its fail-safety by over four times.
 

 

Sounds like the PAK-FA will also be following other aircraft in transitioning from fly-by-wire to fly-by-light.  This isn't new; the Boeing 787 has some fiber optics in its avionics already, but it shows that Sukhoi is at least trying to keep pace.

It would be interesting to know what these massively higher data transfer rates would allow the aircraft to do that it would otherwise not be able to do.  Can it tolerate greater margins of instability?  Does it allow the PAK-FA to perform maneuvers like the F-35's 28 degree/sec J-turn?

 

 

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In some parts of the internet, enthusiastic, shall we say, commentators suggested that the wing antennae on the PAK-FA were some sort of super-duper stealth-busting L-band AESA system.  This is a completely stupid idea.  While it is true that L-band radars work better against stealth aircraft than X-band radars typically used in fighters, an L-band radar small enough to fit into the wings of the PAK-FA would have such poor resolution that it would be useless.


Producer itself state it's L band AESA radar. Also apparently it's already implemented in other SU planes. And generally they(Russians) have experience in L band radars.

http://www.niip.ru/eng/index.php?option=com_content&view=article&id=22:-l-&catid=30:esa-with-ebs&Itemid=42

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Conformal+L-Band+AESA+array+for+Super+Su
 

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It's an Actively Electronically Scanned Array (AESA), but that does not mean it is a radar.  AESA is just a type of antenna, it doesn't necessarily mean it's a radar antenna.  It could be a transmit-only antenna, or a receive-only antenna.

 

It can't be a radar.  Or if it were, it would be the world's most singularly useless radar.  This isn't a matter of experience or design finesse, this is a matter of fundamental radar antenna physics.  That is not a large enough antenna relative to the wavelength it's operating in.

It is almost certainly an IFF system, but one that uses an AESA.

 

The way IFF works is that the aircraft with the IFF system gets pinged by a radar, and the radar sends a coded interrogation signal.  The aircraft that receives this signal sends back a coded response, which identifies it to friendly forces.

 

The problem with this for a stealthy jet is that the IFF system is broadcasting radio waves, which is decidedly un-stealthy and could allow any radar with a passive seeker mode to get a bearing fix on the aircraft.

 

The solution Sukhoi is using here is an AESA IFF system.  Instead of a regular antenna, the response IFF signals are transmitted through the AESA, which allows it to confine the signal to a very narrow beam.  AESA has extremely high gain and very small sidelobes, so it can make the IFF beam much narrower than a conventional antenna.  That makes it much less likely that an enemy eavesdropper will detect these signals and use them to locate the PAK-FA.

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But does size rly matter? It's not simple antenna. And generally the more complex system get the more it can "bend physics". I'm quite sure there are many ways to made antennae much much smaller while not loosing resolution or even gaining by design complexity. Also after getting data from antenna then come insane amount of mathematics(imagining theories, algorithms, AI, whatever) that probably can made from seemingly useless data, perfectly usable thing.

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1 minute ago, tomtom said:

But does size rly matter? It's not simple antenna. And generally the more complex system get the more it can "bend physics". I'm quite sure there are many ways to made antennae much much smaller while not loosing resolution or even gaining by design complexity. Also after getting data from antenna then come insane amount of mathematics(imagining theories, algorithms, AI, whatever) that probably can made from seemingly useless data, perfectly usable thing.

 

Maximum angular resolution is a function of beam width.  Beam width is a function of antenna size and operating wavelength.  An AESA might be able to wring a slightly smaller beam width out of a given antenna size and a given wavelength, but it is still subject to these same limitations.  It's fundamental physics; you see similar-looking equations if you look into the maximum focal range of laser weapons.

 

L band is an order of magnitude longer wavelength than X band.  Wing antennas are narrower than nose-mounted radars.  This supposed "wing mounted L band AESA radar" is going to have less than a tenth the resolution of the nose radar.

 

Computer signal processing do a much better job of finding useful signals.  A more capable computer can find information that a weaker computer would have to throw away as noise.  But there are information theoretic limits.  Computers cannot create information that they weren't given in the first place.  Computers aren't magical.  They cannot improve the resolution of a grainy photo to show the face of the killer reflected in a raindrop.

If a radar has a small antenna relative to its operating wavelength then its beam will be quite wide.  If there are two targets within that beam width at the same distance moving at the same speed then there is no possible way that the computer will be able to tell whether it's one target or two.  There simply is not enough information for the computer to dig through to find out what is going on.

 

Likewise, if a radar has a wide beam and it's engaging a moving target, it is going to have a hard time figuring out where exactly in this wide beam the returns are coming from.  It can move the beam around until it stops getting return signal, but the edge of a radar beam isn't a clean and abrupt end, and if the target is moving it won't be able to do this quickly enough to get a precise location anyway.

 

These are fundamental problems with the amount of information that the antenna can provide the computer.  The computer won't be able to fill in the blanks.

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