This article will compare upcoming Russian PAK FA with US F-22, since both air single-purpose heavyweight air-to-air fighters. However, since PAK FA is still in a prototype stage, article will by its nature be incomplete. I should also note that while some use the term “Raptorski” for PAK FA, it is entirely inaccurate. In fact, while the F-22 clearly draws its basic design from its F-15 predecessor, utilizing some aerodynamic advances introduced by the F-16 (such as aerodynamically unstable design and LERX), PAK FA in the same measure draws its basic design from Su-27. F-22, like the F-15, has two closely set engines, air intakes on sides of the cockpit and classical wing-tail surfaces with shoulder-mounted wing. Both have standard armament of eight missiles and M61 20 mm rotary gun. Su-27 and PAK FA on the other hand both utilize large LERX, wing-body blending and spaced podded engines. They also have basic standard armament of six missiles and 30 mm revolver cannon. If comparison should be drawn, then F-22 can be described as a stealth!F-15, and PAK FA as a stealth!Su-27, as neither presents clear design departure from their predecessor that the F-16 did. They are also both hugely complex to produce due to their stealth designs, and as a result both US and Russia have decided to supplement them with large fleets of 4,0 (and, in Russia’s case, 4,5) generation fighters.
Impact on pilot’s skill
Most important factors in fighter design are ones that directly affect pilot: sortie rate / maintenance downtime, operating cost, user interface and reliability. Good enough pilot will compensate for aircraft’s weaknesses and focus on strengths, and even if aircraft is inferior across the board, he will be able to beat the opponent through tactics. How important training is was shown clearly in Vietnam: early on, USAFs F-4s achieved negative 2:1 exchange ratios against NVAF MiG-19 and MiG-21. Once USAF put some effort into pilot training, they started regularly achieving positive 2:1 exchange ratios. This is despite the fact that in dogfight, angles fighter (MiG) has no inherent advantage over the energy fighter (F-4) – or the opposite. In fact, MiGs had advantage in Vietnam due to smaller size and less smoky engines.
Both F-22 and PAK FA are twin-engined heavy stealth fighters, which means that they will be harder to maintain than any non-stealth fighters. F-22 can fly one hour every two days, and PAK FA will likely do better than that due to lesser focus on stealth; still, it is unrealistic to expect more than one hour per day. Neither is likely to delover 30 hours per month that pilots need to stay proficient, but PAK FA is in the better position due to less focus on radar stealth.
F-22 has only an X-band AN/APG-77 radar in the nose, with 120* coverage and 1.956 T/R modules. It also has IR/UV MAWS and RWR sensors providing spherical coverage. PAK FA has an IRST sensor on the nose, forward-looking AESA radar with 1.552 T/R modules, two side-mounted AESA radars with 358 T/R modules each, with 240* total (?) coverage; it may also have a tail boom radar, providing for a 360* coverage. It also has turreted DIRCM sensors on the dorsal spine and lower fuselage as well as UV MAWS and RWR sensors. F-22 has 190,5 degree vertical and 345 degree horizontal cockpit visibility, with 4,5 degrees aft being blocked in vertical by airframe. PAK FA has 181 degree vertical and 310 degree horizontal cockpit visibility, with 14 degrees aft being blocked in vertical by airframe. Overall, F-22 has advantage in cockpit visibility while PAK FA has advantage in passive surveillance and sensors coverage. PAK FA may also have L-band radars in wing leading edges, though those may as well just be IFF systems; they can be used for EW purposes.
Stealth can be divided into several areas: visual, radar and IR. Visual stealth refers to how easy is to to see the aircraft with Mk.I eyeball. Radar stealth can refer to two things: aircraft’s radar cross section (RCS), and aircraft’s radar emissions (EMCON). IR stealth refers to aircraft’s IR signature.
In terms of visual signature, PAK FA is flatter than the F-22 and has smaller frontal signature. There will be no great difference in side or top signature, and both aircraft are very large.
In terms of radar signature, F-22 will be detected first as it has to use radar to have hope of BVR detection, while PAK FA can stay passive and use IRST and RWR to keep track of the F-22. Average (not frontal!) RCS is 0,5 m2 for PAK FA compared to 0,3 m2 for F-22. Frontal RCS is 0,0014 – 0,025 m2 for PAK FA (tennis/golf ball to 1/40 of Su-35S) and 0,00018 m2 for F-22. Most likely RCS for PAK FA is 0,01 m2, as estimated by Air Power Australia. AN/APG-77 has range of 193 km vs 1 m2 target, whereas PAK FAs radar may achieve range of 350-400 km vs 3 m2 target; lower range is more likely as Irbis E achieves 425 km vs 5 m2 target. Using radar, F-22 will detect PAK FA at 37-77 km, while PAK FA will detect F-22 at 30-35 km. F-22 will achieve 30-62 km tracking range vs PAK FA, while PAK FA will achieve 24-28 km tracking range against F-22. In presence of jamming, F-22 will achieve 5-12 km tracking range, and PAK FA will achieve 5 km tracking range. Going by APA estimates, F-22 will detect PAK FA at 61 km, leading to tracking range of 49 km, or 9 km if jamming is present. F-22 uses its own radar for jamming, and also has expendable jammers. PAK FA can also use its radar for jamming, and will likely have internal jammer as well. That being said, PAK FAs uneven underside will increase its RCS vs ground radars, or if maneuvers expose it to airborne radars. PAK FA also has non-stealthy engine nozzles. This however is not a major issue, especially in air combat, since PAK FAs significant supercruise capability will make it relatively immune to chase shots.
However, using radar will allow detection of radar’s signals at far larger distance, possibly up to several hundred kilometers and most likely not less than 100-200 km. This, of course, depends on quality of radar warning sensors. As a consequence, radars will typically stay off. This means a major disadvantage for the F-22, as it does not have onboard IRST and will thus have to rely on offboard sensors and datalinked data – and datalinks can be jammed to uselessness, especially if they are transferring large amounts of data. PAK FA has OLS-50, an advanced version of Su-35s OLS-35. OLS-35 can detect a subsonic fighter-sized target from 50 km head-on and 90 km tail-on; since OLS-50 is assumed to be a QWIP sensor, it is likely to offer significantly improved performance – possibly even on par with PIRATE (90 km head on, 145 km tail-on vs subsonic fighter aircraft). Head-on tracking range will thus likely be between 40 and 70 km, allowing PAK FA to launch missile from 30-60 km, while F-22 will only be able to launch missile from maybe 10 km, or 20-50 km if jamming is not present.
In terms of IR signature, primary factors are size, speed and engine emissions. F-22 is 18,9 m long, 5,08 m high with 13,56 m wing span. It has 21.319 kgf of dry thrust and cruise speed of Mach 1,75. PAK FA is 19,8 m long, 4,74 m high with 13,95 m wing span. It has 19.051 kgf of dry thrust and cruise speed of Mach 1,6. While PAK FA, as it is, uses round engine nozzles, F-22s flat nozzles allow for some IR signature reduction. Overall, there should be no major difference in IR signature, though F-22 might have slight advantage.
F-22 can cruise at Mach 1,75 with 8 missiles, while PAK FA can achieve Mach 1,6 with 6 missiles. However, while F-22 has fuel fraction of 0,29, PAK FA has fuel fraction of 0,36, suggesting significantly superior supersonic endurance. At subsonic speeds, maximum combat radius on internal fuel is 1.166 km for the F-22 and 1.700 km for PAK FA, which also shows PAK FAs superior endurance. PAK FAs LEVCONS might improve supersonic performance when compared to the F-22, in a similar way to what close coupled canards do (by reducing supersonic pressure point shift). Both aircraft also have sharp LERXes, which reduce supersonic drag by producing a shock in front of the wing leading edge.
F-22 has wing loading of 317,4 kg/m2 and TWR of 1,35 at combat weight. PAK FA has wing loading of 272,84 kg/m2 and TWR of 1,4 at typical combat weight and wing loading of 306,09 kg/m2 and TWR of 1,24 at heavy combat weight. PAK FA will have less drag and better lift/drag ratio during cruise when compared to the F-22 due to large flat area between engines, where BVR missile bay is located, and overall more slender airframe. However, PAK FA has more wetted area and a number of sharp transitions between engine nacelles and fuselage, resulting in increased drag, which will reduce drag difference. While its higher wing sweep (46,5* vs 42*) will help reduce drag during cruise and allow slower drag rise with increased Mach as well as compressed transonic region, it will also increase drag during maneuvering flight. Span loading is 1.835 kg/m for F-22 and 1.541 kg/m at standard combat weight / 1.729 kg/m at heavy combat weight for PAK FA, counteracting adverse effects of higher wing sweep. Overall, PAK FA can be expected to drag less, but difference will not be great.
However, F-22s engines are placed close together while PAK FA has widely separated engines. Consequently, F-22 has significantly lower roll inertia, resulting in superior roll performance – in particular, roll onset rate can be expected to be superior for the F-22. While PAK FAs differentially vectored engines may compensate for this somewhat, these have far slower response than control surfaces (20 deg/s TVC vs 60-70 deg/s tails/ailerons in F-22). PAK FA consequently uses differential deflection of LEVCONS to improve roll onset, but it will stll have sluggish roll performance when compared to the F-22.
Overall, PAK FA is likely to have better turn rates (with difference being rather minor at heavy combat weight) while F-22 will have better roll performance. However, PAK FA will – at heavy weight at least – have significantly superior combat endurance.
PAK FA will have initial climb rate of 361 m/s, compared to F-22s 350 m/s. If these figures are correct, it means that PAK FA will have minor advantage in regaining energy during dogfight, as well as slight superiority in BVR engagement. PAK FAs higher wing sweep in any case suggests superior acceleration.
Both F-22 and PAK FA are likely to have good post-stall maneuverability thanks to thrust vectoring. Both aircraft have very sharp LERX devices (cca 70* sweep) which promote strong wortex flows at high angles of attack, improving turn rates. Both aircraft are also likely to have similar supersonic maneuverability.
Overall, dogfight performance will be similar, with edge to the F-22; PAK FA will have a small edge in BVR maneuvering performance.
F-22 has AIM-120 for beyond visual range engagement and AIM-9X for within visual range engagement. AIM-120D is a RF BVR missile with 180 km maximum aerodynamic range. It has 40 g maneuvering capability at Mach 4. AIM-9X is an IR missile with 26 km maximum aerodynamic range and 50 g maneuvering capability at Mach 2,7. AIM-9X Block III was supposed to provide a limited-capability IR BVRAAM with 42 km range, improving F-22s lethality in beyond visual range combat. However, its development was cancelled. F-22s lack of IRST means that it is still dependant on radar for firing solution. Consequently, it sacrifices surprise against a competent opponent, significantly limiting F-22s beyond visual range capability.
PAK FA has R-77 for beyond visual range engagement and R-73 for within visual range engagement. R-77 is a BVR missile with 110 km maximum aerodynamic range (possibly up to 150 km). However, its lattice controls make it more maneuverable than the AIM-120D. It also has the advantage of three variants – in addition to standard RF head, it also has IR and anti-radiation options avaliable. This diversity presents a challenge to opponents. While PAK FA will have to defeat only RF AIM-120D when fighting the F-22 or other US fighters (with RF Meteor and RF/IR MICA added to the mix when facing European fighters), F-22 pilot will have to defeat RF, IR and AR variants. Last (antiradiation) variant is a major challenge to the entire concept of the F-22, as it can force the opponent to completely shut down the radar. Combination of IRST and passive missiles also allows PAK FA completely passive BVR engagement capability, significantly improving its lethality in beyond visual range combat.
Overall, IIR missiles are extremely hard to jam or decoy. They are also ideal for engaging low-RCS targets, as all high-speed aircraft will have significant IR signature regardless of any reduction measures. Anti-radiation missiles meanwhile can home on the enemy radar, while active radar missiles force the enemy to use jamming and thus provide additional source for anti-radiation missiles. While modern DRFM jammers can safely jam enemy radars without worrying about anti-radiation missiles, these are still a significant threat for any fighter aircraft with no IRST.
F-22 has a standard loadout of 6 RF BVRAAM, 2 IR WVRAAM and 5,5 1-second bursts, with a possibility to carry RF BVRAAM instead of Sidewinders. PAK FA has a standard loadout of 4 RF BVRAAM, 2 IR WVRAAM and 5,2 1-second bursts, but RF BVRAAM can be replaced with IR or AR variants; using different missiles in a single salvo has a potential to improve salvo effectiveness over that consisting of missiles with single seeker type. PAK FA has an advantage in gun department in that it has two guns, giving it 30/60 30 mm rounds per burst, compared to the F-22s 37/96 20 mm rounds per burst. Consequently, throw weight per burst is 4,8/9,6 kg with 0,6/1,19 kg of HEI while F-22 has throw weight of 3,77/9,79 kg with 0,39/1,01 kg of HEI, giving overall similar performance with slightly edge in lethality to PAK FA in one-second bursts and higher edge in half-second bursts. In number of total onboard kills, F-22 has 2,1 to 2,2 onboard kills while PAK FA has 2,2 to 2,3 onboard kills, depending on weapons selection. However, as discussed before, any single salvo by PAK FA has a potential to be more effective than F-22s BVR salvo, somewhat increasing difference.
Numbers in the air
PAK FA will likely have a unit flyaway cost of 120-135 million USD, compared to the F-22s 170-200 million USD, giving it a 1,4:1 to 1,5:1 numerical advantage. However, PAK FA will likely have slightly lower maintenance downtime due to lesser emphasis on stealth, increasing numerical difference. A 50% advantage in numbers is a safe assumption.
Response to attacks
Combination of lower wing loading, LEVCONS and TVC will likely give PAK FA significantly better STOL performance. Its higher fuel fraction and combat radius will also enable it to be based at locations further away than what F-22 is capable of, and likely enable superior supersonic endurance.
PAK FA supercruises at Mach 1,6 with 6 missiles, compared to F-22s cruise speed of Mach 1,75 with 8 missiles. Assuming that 40% of the fuel can be used for supercruise, PAK FA can supercruise for 15,7 minutes at dry thrust, compared to 9,87 minutes for F-22 (going by static sea level figures). At 40.000 ft, this means that PAK FA can cover 444 km compared to 306 km for F-22.
Engagement kill chain performance
Kill chain consists of following steps:
- detection capability
- identification capability
- cruise speed
- maximum speed / mach on entry
- altitude on entry
- lock on / firing solution range
- missile seeker diversity
- endgame countermeasures (inbuilt, towed, disposable; jammers, decoys, chaff, flares)
- defeat the missile / disengage
- airframe agility
- sensors coverage
- mach on egress / fuel reserves on afterburner
- BVR missile seeker diversity
- BVR missile agility
- BVR missile warhead lethality
- WVR missile agility
- WVR missile warhead lethality
- gun lethality
PAK FA has a major initial detection advantage with its IRST. By using IRST, PAK FA can detect the F-22 at beyond visual range without radiating any signals. Conversely, F-22 pilot has to choose wether to limit himself to Mk.1 eyeball or use radar, giving his position at far longer distance than it will be able to detect the PAK FA at. This is made worse by PAK FA having extensive RCS reduction measures, making work easier for its radar warners. Since PAK FA will likely have RCS of 0,01 m2, F-22s radar will receive cca 0,01% of the signal that PAK FA receives. Even when aperture size difference between RWR and radar is accounted for, PAK FA will detect F-22s radar signal at 50 times the distance that PAK FA will appear on the F-22s scope, possibly more. If radar is not used, F-22 pilot will have to accept just as great disadvantage in detection range due to PAK FAs possession of IRST. If PAK FA is equipped with imaging IRST (such as QWIP IRST), it will also have significant advantage in identification range, giving it a true BVR combat capability, while the F-22 pilot will have to come within cca 400-1.000 meters from target to establish positive VID. NCTR works at longer ranges, but is very unreliable and can be disabled by jamming or by target maneuvering. For this reason, 82% of the enemy aircraft engaged during Desert Storm had to be identified with help of AWACS, which will not be avaliable against a competent opponents as comlinks will be jammed, and AWACS aircraft will not survive for long in a shooting war.
F-22 has a cruise speed of Mach 1,75 with 8 missiles, while PAK FA has cruise speed of Mach 1,6 with 6 missiles. Top speed is Mach 2,0 for both F-22 and PAK FA due to lack of variable geometry intake. Consequently, F-22 will have advantage in cruise speed and thus missile energy in standard conditions, while top speeds are equal. This cruise speed difference may give the F-22 some advantage in dictating terms of engagement, but that is limited due to low fuel fraction and PAK FAs superior acceleration.
F-22 has service ceilling of 65.000 ft; that of PAK FA is identical. Consequently, neither aircraft can count on altitude advantage in BVR engagement. Engagement range will come down to sensor capabilities, missile capabilities and closure speed. PAK FAs possession of IRST will likely give it superiority in engagement range (7-19 vs 40-70 km). This is further reinforced by its greater selection of missile types and seeker heads.
That being said, if PAK FA manages 75.000 ft service ceilling, it will give it an advantage over the F-22.
Defeat the missile / disengage
Once warned of a missile launch, first reaction is to properly position the aircraft for evasion. At beyond visual range, it is oftentimes enough to turn the aircraft away from the missile. At shorter ranges (near-visual and visual range), pilot has to quickly position the missile to the aircraft’s 3 or 9 o’clock and then turn into the missile once close enough. Both of these require high instantaneous turn capability, as well as acceleration / climb to recover lost energy and good transient performance. PAK FA has inferior roll performance to the F-22, but similar or superior turn performance and superior climb performance. Consequently, F-22 may have slight advantage when evading missiles due to superior transient performance, but this is at least partly compensated for by PAK FAs superior turn performance and acceleration.
Both PAK FA and F-22 have 360* coverage with radar and missile warners. However, F-22s only BVR sensor is AN/APG-77 X-band AESA radar which covers 120* arc to front of the aircraft. PAK FA has an IRST covering frontal sector and either 240* or 360* coverage with X-band AESA radars. Consequently, F-22 will have to keep the target within 60* off the nose in order to maintain radar track, forcing the pilot to choose wether to fly into enemy missile(s) or break the track in order to initiate proper evasive maneuvers. PAK FA will be able to keep track of the enemy while flying away from any possible missiles thanks to its side AESA arrays; however, against stealth fighters there will be a limit on this due to maximum effective detection range. Using IRST is an obvious solution, but it presents the PAK FA pilot with the same dilemma as the F-22 pilot has with using radar.
When it comes to fuel reserves for afterburner, it will be assumed that both aircraft have 40% of fuel avaliable. This however heavily penalizes PAK FA due to its significantly greater combat radius on internal fuel, which means that it will have greater percentage of internal fuel avaliable for maneuvers at same combat radius. At 40% internal fuel, F-22 has 3.280 kg of fuel avaliable, compared to the PAK FAs 4.120 kg. Fuel consumption at maximum afterburner is 60.894 kg/h for F-22 and 68.178 kg/h for PAK FA. This gives endurance of 3,23 minutes for F-22 and 3,63 minutes for PAK FA. However, since PAK FA with 50% of full internal fuel has TWR of 1,24, compared to F-22s 1,35, effective endurance may be higher for the F-22 as it will not require full afterburner to achieve same thrust-to-weight ratio.
In terms of countermeasures, both F-22 and PAK FA have standard load of chaff and flares. AESA radars that both aircraft use are capable of jamming enemy radars; here, PAK FA has a major advantage in coverage, as F-22 will have to keep the enemy within 60* off the nose to jam their radar while PAK FA will be able to keep up (less powerful) jamming even when facing away from the enemy. Neither uses, or is likely to use, classic omnidirectional RF jamming, or even directional AESA jammers as present on e.g. Rafale, since these are incompatible with all-aspect LO/VLO design. Answer to this problem may be provided with disposable jammers, which are present on the F-22 and may be present on PAK FA as well. While PAK FA will be able to jam F-22s radar and radar-guided missiles, PAK FA is immune to jamming due to presence of IRST and IR BVRAAM.
At beyond visual range, F-22 can use RF missiles, while PAK FA can also use IR and anti-radiation missiles. While AIM-9X Block III was supposed to have a maximum range of 40 km, but was cancelled. R-77 has a range of 110 (150?) km, and anti-radiation as well as IR variant. This gives PAK FA a significant advantage in surprise attacks from long range; while F-22s cruise speed advantage will reduce its disadvantage in missile range – 100 knot speed advantage reduces missile range 5 to 25%. At 40.000 ft, Mach 0,15 speed advantage that the F-22 has over the PAK FA translates into 86 knot difference, and 4,3% missile range difference. Hence, AIM-9X will achieve effective range of 1-2 km and R-77 will achieve effective range of 5,3 – 7,2 km. If F-22 uses AIM-120D, it will suffer from greater vulnerability to countermeasures but will achieve effective range in rear-quarter attacks of 9,4 km. Compared to AMRAAM, R-77 has the advantage of anti-missile capability, but it will be more limited than that of more maneuverable WVR missiles such as IRIS-T; however, neither aircraft carries IRIS-T.
When it comes to WVR missiles, F-22 has AIM-9X while PAK FA uses R-73/74. R-74 has range of 40 km, making it a BVR missile; AIM-9X Block II has range of 26 km. R-74 has 75* off-boresight capability, compared to 90* for AIM-9X. Seeker head FoV is 90* for AIM-9X and 120* for R-73 (likely similar for R-74).
In terms of gun lethality, PAK FA uses GSh-30-1 linear action gun and F-22 uses M61A2 rotary gun. GSh-30-1 fires 400 g projectile with 12,4% HEI content (~50 g) at 860 m/s muzzle velocity. M61A2 fires 102 g projectile with 11% HEI content (~11 g) at 1.050 m/s muzzle velocity. Crossectional density is 56,59 g/cm2 for GSh-30-1 and 32,47 g/cm2 for M61A2. Despite this, higher muzzle velocity may give M61 greater effective range. GSh-30-1 will fire 12 projectiles weighting 4,8 kg (0,6 kg HEI) in first 0,5 seconds, while M61 will fire 37 projectiles weighting 3,77 kg (0,4 kg HEI) in first 0,5 seconds, giving GSh-30-1 greater lethality.
F-22 has a minimum takeoff distance of 480 m, compared to 300 m for PAK FA. F-22 has wing span of 13,56 m and PAK FA has wing span of 13,95 m; both way too large for proper road basing. However, PAK FA has robust undercarriage, allowing for more demanding landings. PAK FA will also have lower fuel consumption. Overall, PAK FA has advantage in ground survivability.
Capabilities of both aircraft are similar, with overall edge going to PAK FA. In the end, victory will most likely go to a pilot who plays to his aircraft’s strengths. Overall, F-22 is the only US fighter capable of matching PAK FA in one-on-one combat; F-15, F-16, F-18 and F-35 may win against PAK FA if deployed in superior numbers – which will not be a problem for teen-series fighters (especially F-16), but will be very problematic for F-35. However, F-22 still requires IRST to be truly effective.
Links of interest