Stealth and counter-stealth on show at MAKS
More details of the Sukhoi T-50 stealth fighter emerged at the MAKS air show at Zhukovsky, outside Moscow, last week. It was confirmed that the T-50 is being designed to carry heavy, long-range missiles internally, its engines incorporate built-in features to reduce radar cross-section and infrared signature and a new engine for the aircraft, offering improved supercruise performance, is under development.
The initial service-entry engine for the T-50 is the United Engine Co. 117. It was not shown at MAKS but a UEC engineer confirmed it is very similar to the 117S engine for the Sukhoi Su-35S, that was. Both engines are derived from the AL-31F series used on the Su-27 and other members of the Sukhoi family. In particular, the stealth technology applied to the 117S will be carried over and improved for the 117.
The inlet casing and guide vanes, as well as the spinner of the 117S, are coated with a new radar-absorbent material developed by the Russian Academy of Sciences, the UEC engineer tells Aviation Week. To reduce the engine's infrared (IR) signature, the nozzle features a new air-cooling system. Also, the thrust-vectoring nozzles can be deflected to provide partial line-of-sight blockage to the rear of the engine, with the aircraft's aerodynamic controls being used to counter the resulting pitch moment.
The 117S has an inlet diameter of 932 mm (36.7 in.) versus 905 mm for the AL-31F, providing more thrust (32,000 lb. maximum versus 27,500 lb. for the basic AL-31F), and has a digital control system. UEC has also developed an upgraded AL-31F, the 29,750-lb.-thrust Series 42 variant for the Su-27SM upgrade program being implemented by the Russian air force.
The aerodynamic design of the T-50's 117 engine is similar to the 117S, the UEC engineer says, but it is further uprated to 33,000 lb. thrust, has a new digital control system and incorporates new materials. The weight is reduced, but the most important change is that the hot-end temperature limits are increased, to allow the engine to sustain maximum non-afterburning thrust to higher speeds. Combined with the T-50's aerodynamic design, this is intended to meet the fighter's supersonic cruise goal. The 117 also features additional signature-reduction measures.
The 117 will be used on initial production T-50s, but an all-new successor engine identified as Type 30 is in full development. It will be lighter, more powerful and fuel-efficient than the 117, and offer a further improvement in supersonic cruise speed. Other details remain secret, including whether the Type 30 incorporates variable-cycle technology.
It was also confirmed at MAKS that the T-50 has been designed to carry larger weapons than will fit in theand . Tactical Missiles Corp. showed a video of the T-50 carrying the Kh-58UShE anti-radar missile, a highly modified version of a weapon in service since the 1970s, with folding wings for internal carriage. It has a shorter radome than the original Kh-58, inertial mid-course guidance and a broadband seeker where earlier Kh-58s were fitted with different seekers for different targets.
Also likely to be carried internally by the T-50 is the RVV-BD (long-range air-to-air missile), a modernized version of the Vympel R-37 that was designed for the MiG-31M Foxhound-B but never put into production. Its total external dimensions are within centimeters of the Kh-58UShE with wings folded. It seems likely that the T-50 forward bay has been designed around the minimum-risk RVV-BD, with the Kh-58 being modified to fit the same envelope.
Both weapons are long-range types. The Kh-58UShE is a 1,400-lb., Mach 4 weapon with a range up to 130 nm from a 65,000-ft. launch altitude, and the RVV-BD has a claimed maximum range of 110 nm against a head-on target. This indicates a different operational philosophy from U.S. stealth aircraft, for which a key principle has been to use stealth to permit the use of short-range, low-cost weapons.
Also exhibited here was the T-50's helmet-mounted display (HMD), comprising a module attached to the custom-fitted pilot's helmet and incorporating light sources for the optical head-tracking system. A unique feature is that the HMD has two visors—a seamless outside visor for physical protection, and an inner visor on which binocular, wide-angle symbology can be projected. The Zvezda company exhibited the T-50's ejection seat, the K-36D-5, which incorporates a fully electronic control system and an improved parachute-deployment mechanism that is designed to meet the same “expanded-pilot population” standards as recent Western seats, accommodating pilots weighing 55-125 kg (121-275 lb.).
Future air-launched weapons for the T-50 and other combat aircraft may have new propulsion systems, according to Tactical Missiles Corp. General Director Boris Obnosov. Responding to questions about the company's ramjet effort, Obnosov said it is moving away from ramjet/scramjet propulsion “because it is not possible to design a universal propulsion system,” a simple, scalable technology for different missile requirements and flight profiles. Asked whether this meant the company was looking at higher-energy solid propellants (Russia in the Cold War era had a large program to produce such a fuel, ammonium dinitramide or ADN), Obnosov told Aviation Week, “We don't have enough scientists for that” and said the company is looking at new liquid-fuel systems.
Liquid fuels have higher energy than solid propellants, but complexity, storability and harsh carriage environments have precluded their use in tactical air-launched weapons. Obnosov declined to say what approach Tactical Missiles Corp. is taking to solve those problems.
While pursuing development of its own stealth fighter, Russia's defense industry is maturing counter-stealth radars. The Nizhny-Novgorod Research Institute (NNIIRT) brought the newest configuration of its multi-band 55Zh6ME radar complex, designed to support the Almaz-Antey S-400 Triumph surface-to-air missile system. It also used the show to unveil the new 55Zh6UME, a single-unit, dual-band system designed for customers with more modest needs and budgets.
The 55Zh6ME comprises three truck-mounted radar “modules,” operating in metric (VHF), decametric (L) and centimetric (S) bands, all with active, electronically scanned array (AESA) radars. The VHF unit has an antenna area of 235 sq. meters (2,530 sq. ft.), carrying 168 VHF transmit-receive modules, and is claimed to be able to detect a target with a radar cross-section of 1 sq. meter at 510 km range and 30,000 meters altitude in jamming conditions. The radars can be deployed in 15 min., NNIIRT says.
The new 55Zh6UME has a smaller VHF array (with a 430-km range under the same conditions) with an L-band AESA trailer-mounted on the same structure, facing the opposite direction.
Stealth targets that claim radar cross section of less than 1 sq. meter do not achieve those numbers in the VHF band, according to NNIRT engineers. For instance, the Chinese Dongfeng-15 short-range ballistic missile has a 0.002-sq.-meter radar cross section in X-band, but is a 0.6-sq.-meter target in VHF, company officials tell Aviation Week. This is because radar waves are scattered by a “resonant” mechanism (rather than specular reflection, which stealth shaping is designed to manage) when the dimensions of the target, or its parts, are similar to the wavelength of the radar. They are not affected by shape or by surface coatings.
The S-400 and the 55Zh6ME are in service with the Russian armed forces, while the 55Zh6UME is now on offer for export.