Sukhoi’s Stealth Killer – the PAK FA


With its new PAK FA design the Russian Sukhoi company plans to challenge the dominance of western fighters.

The Soviet Union was a major exporter of combat aircraft from the 1940s to the 80s, but that was mostly down to global politics – western-aligned states bought US or French aircraft, communist ones got Soviet. After the Cold War ended that started to change. In the last decade of the Soviet Union its designers had produced two new combat aircraft that were a match for all but the latest western designs – the MiG-29 FULCRUM and Su-27 FLANKER. These designs were fast, agile and heavily armed, and their electronics were good enough to hold their own against most possible opponents.

Su-27 Flanker
Sukhoi’s Su-27 series are capable, but the latest western designs are a generation ahead of them.

The MiG-29 has slowly lost market share, but constant upgrades have kept the big Flanker competitive. Advanced versions are in service with Russia, China, India and several other countries. No design can be upgraded forever though, and if Russia wants to stay competitive in the fighter export market – and maintain its own military capability – it’s going to have to match western developments in low-observable aircraft.

In fact the Soviet Union started looking at the next generation of aircraft as far back as the mid-1980s, but development came to a stop in the 1990s as Russia suffered crippling financial problems. Around the turn of the century things started to pick up again as oil wealth boosted the Russian economy, and now the Sukhoi design bureau’s advanced fighter programme is within a couple of years of delivering an operational aircraft.

The Sukhoi PAK FA started life as the T-50 technology demonstrator. Construction of this began in 2007 and it made its first flight on 29 January 2010. A second prototype flew in 2011, and by 2012 two fully equipped pre-production aircraft were operational. Russia is planning to have the first aircraft in service sometime in 2016. It’s also expected to be adopted by the Indian Air Force a few years later. India has contributed large amounts of funding to the project and Hindustan Aeronautics Limited (HAL) is a major partner. Initially it was believed that India would buy a partly new design derived from the T-50, but the latest announcements suggest that the IAF aircraft will be essentially identical to the Russian ones. It’s likely that the two countries will jointly market the plane for export.

The PAK FA is a relatively large fighter, in the same size class as the F-22A Raptor. The existing aircraft are all single seaters but a two-seat version is likely to be developed; as well as the training aircraft that will be required, the IAF have a preference for two-man crews on long missions. It has a family resemblance to the Su-27 in that it’s twin engined and twin tailed, and has a lifting fuselage design to enhance agility, but early reports that it used major Su-27 airframe parts now seem unlikely.

Sukhoi PAK FA
The PAK FA shares a family resemblance to the FLANKER, but it’s an entirely new aircraft.

Sukhoi say that the PAK FA has been designed for low observability, and its general shape supports this. Russia places less emphasis on stealth technology than US designers, though, possibly because Russia is a leader in long-wavelength radars that have some ability to detect low-observable aircraft. It’s believed that up to 70% of the PAK FA’s external surface is made of composite materials – and up to 25% of its total weight – which should help to reduce its radar signature, but it definitely isn’t in the same class of stealth as the F-22A. It’s more likely to be equivalent to the F-35 Lightning II. On the other hand Sukhoi have a reputation for building agile fighters and they say they’ve excelled themselves with this new model. Superior agility to the F-22A was apparently a design goal and Sukhoi were willing to accept a larger radar signature as the price for that. Leading edge vortex controllers and full 3D thrust vectoring – the F-22 has 2D vectoring – are key elements in achieving that. The engines are Saturn AL-41F turbofans, each capable of producing 33,000 pounds of thrust with a target of 39,000 pounds for the final production version. The engines are apparently based on the successful AL-31 series used in the Su-27, but are so extensively upgraded that they’re essentially a new model. They allow the PAK FA to supercruise – fly supersonic without afterburners – and are reported to have reduced radar and IR signatures.

Sukhoi PAK FA
The PAK FA is much larger – and more advanced – than the MiG-29M.

The PAK-FA will be fitted with three X-band Active Electronically Scanned Array (AESA) radars for detecting conventional aircraft; one will be mounted in the nose and one each side of the aircraft, giving 360° radar coverage. Interestingly, there will also be L-band radars built into the wing leading edges. Existing stealth aircraft are optimised against X-band wavelengths and are much easier to detect on L-band. The long wavelength reduces resolution and makes weapon targeting more difficult, so it’s likely that the PAK-FA would use the L-band radars to make an initial detection of low observable aircraft then either close in to a range where it could get an X-band lock or use its Infra-red Search and Track system to launch active-guidance missiles. As the PAK FA will be fitted with modern data links the detecting aircraft could also feed target data to another fighter, which could then close on the target without radiating until it was within X-band detection range.

Russian fighters have usually carried a heavy-calibre cannon with a relatively small but destructive ammunition load, and it’s reported that the PAK FA will be armed with at least one and possibly two GSh-301 30mm cannons. It also has two large weapon bays in the fuselage, each of which can carry three medium or long range air to air missiles. A smaller bay in each wing root can carry short-range AAMs including the advanced RVV-MD (AA-11 ARCHER.) There are also six external hardpoints. As well as AAMs both the hardpoints and main bays will be able to carry a variety of air to surface missiles and bombs.

The PAK FA isn’t going to knock the F-22A off its perch as the world’s leading stealth fighter, but India’s involvement brings that nation’s long-standing contacts in the French, British and Israeli avionics industries. It’s likely that the PAK FA will be a huge step up from previous Russian designs in terms of electronics, and with its agility and innovative radar systems it could be a genuine threat to any current stealth aircraft. It more or less goes without saying that it’s going to seriously overmatch legacy types like the F-15 and F-16, and could be a frightening opponent for a Eurofighter Typhoon. Sukhoi’s plan is for a thousand PAK FAs to be built, 200 each for Russia and India plus 600 more for export. If they achieve that, these advanced heavy fighters could be showing up in many future conflicts.