This article provides an analysis of the capabilities of the two aircraft. You have to remember that the PAK-FA is still a prototype, details and information on it are subject to change.
Before I start comparing the stealth characteristics of the F-22 Raptor and the PAK-FA, it is important to know how stealth works and to know which different aspects make these aircraft stealthy. There are many different methods to prevent being detected in combat, the first and most important one is to hide from the enemy’s radar, the main sensor of a fighter. To achieve stealthiness against enemy radar, an aircraft has to feature paralleled edges in its design, called “planform alignment“, for example if the leading and the trailing edges of an aircraft’s main wing and its control surfaces have the same sweep angles, thus, the radar waves are scattered by the shape and do not return back to their source. But of course not every single part of a fighter can be made in planform alignment, so that Radar Absorbing Material (RAM) and special radar absorbing coatings are used to absorb the radars waves which are not scattered by the shape. Obviously, radar is not the only way of detecting aircraft, another one is Infrared, as every aircraft gives off heat, mainly generated by its engines, but also by their electronic systems. These infrared emissions can be detected by Infrared Search and Track Sensors (IRST), at ranges of up to 50 km. So to make an aircraft stealth in IR, a special nozzle design is used, which spreads out the hot exhaust, but the ability to supercruise is an important factor as well, because such a fighter does not need to use its afterburner to reach supersonic speeds, so there are no large and hot flames coming out of the engines and which would make it a very easy target for IRST sensors. Furthermore the surfaces and the systems of the aircraft are cooled down, providing a significant reduction in terms of IR detectability. The next important thing is to minimize the chance of being detected through the signals given off by an aircraft. For example Low Probability of Being Intercepted capability of an aircraft’s radar, such as the APG-77 of the F-22 Raptor, changing its frequency over 1,000 times a second and it does only use as much energy as necessary to detect, to minimize the chance of being intercepted by passive radar emitters. In addition to that, an aircraft can be detected through its communication systems, the F-22 uses a stealthy low power datalink for stealthy communication. In fact this is the reason why the F-22 is currently only able to communicate with other Raptors, as this stealth data link is only used by the F-22 Raptor itself. This does basically describe all stealth features of the F-22 Raptor. "Where the PAK-FA falls well short of the F-22A and YF-23 is the shaping design of the lower fuselage and side fuselage, where the general configuration, wing/fuselage join angles, and inlet/engine nacelle join angles" - Air Power Australia, 2010 When now taking a look at the PAK-FA it does also feature these however its radar lacks advanced LPI, its whole systems aren’t stealthy and it is not stealthy in IR at all. The F-22 Raptor features a significantly better planform alignment than the PAK-FA has, especially on the tail section of the PAK-FA is no planform alignment and another factor sacrificing the stealth of the PAK-FA is that its engine blades are not hidden, also the RAM coatings are less advanced than of its US counterpart, as a result it’s radar cross section can’t get less than 0.5 to 0.01 square metres, while the F-22 Raptor has an RCS of 0.0001 m². In addition to that, the PAK-FA has no IR reduction measures (however this does not provide an advantage for the F-22, because it doesn’t have IRST). "The aircraft that flew today is a prototype - and it does not show visible features like a frameless canopy and panel alignment that you'd expect on a production aircraft. Other not-very-stealthy-looking features include the gaps around the inlet (compare the YF-23) and a spherical infrared search and track housing in front of the windshield. And, of course, the nozzles are round." - Bill Sweetman, 2010 In summing up, the PAK-FA fails to compete with the F-22 Raptor in terms of stealth.
The F-22 Raptor is equipped with a low observable, APG-77 Active Electronically Steered Array radar, made of about 2000-2200 transmit/receive modules, the APG-77 is having a detection range of about 240 km versus a 1 m² target. The PAK-FA will be equipped with an improved AESA derivative of the Irbis-E radar of the Su-35, the PAK-FA AESA outranges the APG-77 of the F-22 Raptor, as it has a detection range of about 400 km against a 3 m² target, so that it can be assumed that the range against a target with a RCS of 1m² is about 260-300 km, however these numbers are pure speculation and were never proved to be correct and it is unclear whether the radar will achieve this performance or not. Another important point is that the PAK-FA will have 360 degree radar coverage, as it will be equipped with an L-Band radar on each wingtip, as well as with a small X-Band radar mounted on the tail of the aircraft, so that the PAK-FA uses 5 radars at all, the X-band on the won’t ever be able to detect VLO aircraft like the F-22, as it is simply much too small to make a detection, the reason why the two low band radars on the wingtips, which are ought to detect stealthy aircraft due to a different wavelength, won’t provide an advantage at all, will be explained below. <
Low wavelength radars on the PAK-FA
The Low Band radars featured on the wingtips of the PAK-FA are not an advantage in combat against Very Low Observable Fighter aircraft such as the F-22 Raptor, the reasons for that are that a Low Band radar has to be very large to allow accurate detection of a target, which is only possible if these are ground based, but if mounted on an aircraft, it is clearly not possible to reach a sufficient size, to allow proper detection or a missile lock on. Furthermore, these radars give off high power emissions, making them a very easy target for passive sensors.
Radar Warning Receivers and other Passive Detection systems
The F-22 Raptor is equipped with the ALR-94, which is the most advanced Radar Warning Receiver (RWR) in existence, having a maximum detection range of 463 km , which is even greater than the radar. It is able to coorporate with the APG-77 by delivering target information, allowing the radar to work passively and to detect a target with a narrow beam, which then can be taken out when coming into missile range. This provides a massive increase in stealthiness for the F-22 Raptor, as it doesn’t give off any signal, which could make it visible for the enemy. "High-priority emitters -- such as fighter aircraft at close range -- can be tracked in real time by the ALR-94. In this mode, called narrowband interleaved search and track (NBILST), the radar is used only to provide precise range and velocity data to set up a missile attack. If a hostile aircraft is injudicious in its use of radar, the ALR-94 may provide nearly all the information necessary to launch an AIM-120 AMRAAM air-to-air missile (AAM) and guide it to impact, making it virtually an anti-radiation AAM." - Bill Sweetman The PAK-FA will be equipped with an updated derivative of the Khibiny M RWR of the Sukhoi Su-35. Not much information is known on it, however it won’t match the performance of the ALR-94 at all. The PAK-FA will however, feature an upgraded OLS-35 Infrared Search & Track Sensor, such a system was not installed on the F-22 Raptor, due to budget cuts. The IRST will allow the PAK-FA to detect targets passively through their IR-emissions, like the hot engine exhaust, at ranges of up to 50 km (this may vary depending on the aircraft, against the F-22 for example, it will be much lower, as it features IR-emission reduction measures, like a special nozzle design spreading out the hot exhaust, or several cooling mechanisms).
Low Probability of Being Intercepted
Low Probabilty of Being Intercepted or LPI, is the ability of an aircraft’s radar, prevent itself from being detected by passive sensors, the APG-77 of the F-22 changes frequency over 1,000 times a second and it does only use as much energy as needed to detect the enemy, as a result th chance of being intercepted by passive radar emitters is minimalized. The PAK-FA’s radar will lack an advanced LPI mode, giving the F-22 a clear advantage in this area.
There are some general conclusions that can be made concerning the manoeuvrability of an aircraft:
- Low wing loading results in great manoeuvrability
- The higher the thrust-to-weight ratio, the better the turning performance
- Thrust vectoring control provides the advantage of greatly improved turning performance at both, low and high speeds
Both aircraft have excellent manoeuvre capability, the PAK-FA features 3D thrust vectoring engines having a range of 15 degrees in pitch axis and 8 in yaw axis, fully movable LERX and a very aerodynamic design. Therefore, the F-22 Raptor has larger control surfaces, but only 2D thrust vectoring, however with 20 degrees range in pitch axis. In a dogfight the PAK-FA may have slight advantages caused by the 3D TVC engines, however the F-22 Raptor has a better thrust to weight ratio, this combined with a greater TVC range, may give the F-22 better performance in pitch axis.
Both, the F-22 Raptor and the PAK-FA carry their weapons in internal bays, this greatly improves stealth and reduces drag, as a result better manoeuvrability and higher speeds can be achieved. The F-22 Raptor carries 8 missiles internally, six of them are AIM-120D AMRAAM medium range missiles and two AIM-9M or AIM-9X Sidewinders. It can be assumed that the PAK-FA carries about eight missiles in its internal weapons bays as well.
Missile kill probability
There are many different factors determining the kill probability of a missile, some of them are the kinetic energy of the missile (in other words, the missile’s speed), the missiles turning capability, the turning capability of the target, the countermeasures the target uses and (if it’s an heat-seeking missile) how well the target is shielded against the seeker-head of the missile. A fighter capable of supercruising adds additional kinetic energy and range to a launched missile, for example, if in a combat situation a F-22 Raptor and a F-15 Eagle detect a hostile aircraft and lock on with an AIM-120D AMRAAM missile, the chance that the missile launched by the F-22 gets the kill is higher (both aircraft don’t use their afterburners, as this would burn fuel too fast), due to the fact that it is able to supercruise, so that the AIM-120, when launched, is already flying at speeds of Mach 1.8, while the missile launched by the F-15 still has to speed up, giving the enemy more time to react and the missile will have less speed when reaching the enemy. Another point is the altitude at which a missile is launched, as a missile launched from a lower altitude at a higher flying target still has to “climb the hill“.
AIM-120D and R-77 BVR missiles
So when now comparing the AIM-120D and the R-77 the AIM-120D has with a range of 180km a much higher range than the R-77 with only 55 km, however in the era of stealth combat such high ranges have less importance than 20 years ago, as detections are made much later. The AIM-120D matches the R-77 in terms of jamming resistance, kinetic energy (as it is with a speed of Mach 4 faster than the Vympel with a speed of Mach 3), but the thrust vectoring R-77 is more manoeuvrable than the AIM-120, to be able to follow the target’s turnings, while the AIM-120D is more ought to kill the enemy quickly through kinetic energy. The probability of kill of a BVR missile is about 17 % (http://www.ausairpower.net/APA-NOTAM-270109-1.html). Which is certainly very low, so that multiple missile salves have to be fired to get a Beyond Visual Range kill.
AIM-9X and R-73WVR Missiles
The AIM-9X missile of the F-22 Raptor is superior to the R-73 Archer of the PAK-FA, mainly because of superior off-boresight capability, as it is able to engage targets up to 90 degrees off-boresight, while the R-73 has 60 degree off-boresight capability. The probability of kill of WVR missiles is about 74.6 per-cent (http://www.ausairpower.net/APA-NOTAM-270109-1.html). This means that who gets first look in a dogfight, does usually win.
One aspect, which is often completely ignored, are the guns, in a classical dogfight or knife fight, a better guns can provide a decisive advantage. Back to Vietnam, it turned out to be serious issue for the F-4 Phantom not to be equipped with a gun, as it was assumed that the F-4 won’t need one due to the use of BVR missiles. The gun was added to the aircraft at a later point.The F-22 Raptor is equipped with a 20 mm M61A2 Gatling gun, the PAK-FA prototypes don’t have a gun, however it is more than most likely that the final aircraft will be equipped with a 30 mm GSh-30-1 cannon, as all important Russian fighters produced, are equipped with the GSh-30-1. Despite the use of smaller 20 mm rounds, the M61A2 of the F-22 outperforms the 30 mm GSh-30-1 of the PAK-FA, as the 20 mm rounds are less heavy, giving them with a muzzle velocity of 3,300 ft/sec a clear advantage over the GSh-30-1 with 2883 ft/sec thus they are more suitable for supersonic dogfights. Furthermore, the single barrel GSh-30-1 overheats much faster than the multiple barrel M60A2 Gatling gun, meaning that the sustained firing performance of the M61A2 is clearly superior, giving it a much higher chance to hit. The next advantage resulting of the Gatling design is the rate of fire, which is another essential factor during high speed dogfights, the GSh-30-1 fires 1,500 rounds/sec, the M61A2 fires 6,600 rounds at the same time. As gun kills are a matter of seconds the PAK-FA may have problems getting gun kills due to the high risk of seriously overheating the gun, as it can then only attack in small bursts, but once the F-22 has pointed its nose on to the PAK-FA, it will easily get a gun kill, due to its superior rate of fire and the fact that overheating is nothing to worry about and it can fire as many bullets as needed.
Both aircraft, the F-22 Raptor and the PAK-FA will dominate the skies for at least the next decade. With the introduction of the PAK-FA and Chinese 5th Generation Fighters like the J-20, the F-22 isn’t the only “superfighter“ anymore.
Beyond Visual Range combat
Beyond Visual Range combat is usually won by the aircraft which detects its enemies before being detected.
If radar is used:
Raptor detects PAK FA with 0.01m², using the APG-77 at ~40 nautical miles. PAK FA detects Raptor with 0.0001m² at ~15 nautical miles.
If IRST is used:
If the PAK-FA would use its IR-sensor (50 km maximum range), it would detect the IR-shielded F-22 at a maximum distance of 20 nautical miles. The F-22 is not equipped with an IRST.
If passive radar emitters are used:
The F-22 Raptor would also be able to use its ALR-94 passive radar emitter, to operate the APG-77 passively and thus detect it using a narrow beam, which would make it impossible to detect the F-22 with any passive sensor, as its radar does then not give off any signal, which could be detected by the PAK-FA’s upgraded Khibiny M sensor. And detecting the 5 AESAs used on the PAK-FA would actually be pretty simple for the ALR-94, as the PAK-FA for example can’t properly hide its L-bands. But of course, the PAK-FA could also turn its radars off just like the F-22, however its passive radar emitter would have trouble detecting the F-22, due to its much more advanced LPI capabilities. The Russians most likely don't have the same experience on LPI as the Americans have. In summing up, the F-22 would have first look in a combat situation.
Visual Range Combat
In a visual range combat situation, the outcome depends a lot on manouevrability, the use of advanced off-boresight missiles, gun lethality and of course pilot skill. The PAK-FA has an advantage due to its 3D TVC and advanced LERX, the F-22 has therefore better thrust to weight, however this will change with the definite PAK-FA fighter, which will be equipped with new engines, delivering up to 170 kN of thrust on afterburner. Furthermore the Raptor is equipped with more advanced off-boresight missiles, unfortunately the Scorpion helmet was cancelled, which is needed to make use of off-boresight capability, however the AIM-9X features helmetless high-off boresight capability, which compensates the resulting disadvantage to a certain degree. All in all both aircraft are very capable dogfighters, however the definite version of the PAK-FA will be slightly superior, as more powerful engines will be added, giving it a better Thrust to weight than the F-22, thus making it more manoeuvrable. However WVR combat still depends a lot on pilot skill.