Some Key Facts About Su-75 Checkmate

The new Russian single-engine fighter T-75 may not be in the F-35 class—a field that is getting crowded—echoes designs dating back to the Joint Strike Fighter competition of the 1990s; ironically, borrowing most from the two concepts that lost that contest. The internal project designated as T-75, once it enters service with the Russian Aerospace Forces serve, it will be renamed Su-75.

The US intelligence community proposed a NATO Code Name “Screamer” for Su-75 Checkmate.

The Checkmate fighter from Sukhoi is officially unveiled at the MAKS airshow near Moscow on July 2021.

Fact# 1 Imitation of X-32 Inlets

The images show an aircraft with a large angular chin inlet reminiscent of Boeing’s X-32 contender in the JSF contest ultimately won by Lockheed Martin’s F-35 and also on China’s J-10B.

Top Boeing X-32. Bottom Su-75

Checkmate also seems to have a short, clipped delta wing, which does not extend to the tail; again, like the X-32.

Fact#2 Imitation of Ruddervators

The jet has two canted elevons rather than a standard empennage of stabilizers and elevators, harkening to both the X-32 and McDonnell Douglas’s JSF entrant, as well as to the YF-23 on which McDonnell Douglas was partnered with Northrop. The YF-23 lost out to the Lockheed Martin F-22 in the Advanced Tactical Fighter competition, and McDonnell Douglas’s loss in the must-win JSF contest was a major factor in the company’s 1996 merger with Boeing.

The new fighter’s tail arrangement offers reduced radar cross section—with a lower profile and fewer tail surfaces to harmonize with other aircraft edges—as well as potentially high agility. A chine beginning on the jet’s nose and inlet becomes a shallow leading edge root extension (LERX).  

Fact#3 Elements of MiG LMFS

From a genetic point of view, the Su-75 is a bit like a hybrid of the Sukhoi Bureau’s early LFI S-21 project and the Mi-type LMFS project. From the appearance point of view, with the United States that year to bid JSF project defeated Boeing X-32 is also quite similar , but “lore” of the body seems to be more slender, both in terms of aerodynamic configuration of the intake and so there are no small way The difference.

Top S-21 and Bottom MiG LMFS

Fact#4 Lore in foreign buyers

Unlike the previous Su-57, which was mainly targeted for domestic sales, the Su-75 is an “entry-level” “affordable aircarft” destined for foreign buyers. Its market positioning is locked in some third-world countries that are eager to obtain the fifth-generation machine but are shy in the pocket.

Su-75 Cockpit

In the propaganda film of the aircraft, many potential customers appeared in Vietnam, India, and the UAE. I don’t know who is willing to be the first “guinea pig” this time.

The Su-75 and China’s Shenfei FC-31 are basically fighters of the same level. Earlier there was news that FC-31 may also be introduced to the international market, so if the Su-75 is mass-produced, there will inevitably be a competitive relationship between the two. Here we might as well make a simple comparison of the two fighters.

Chinese FC-31 is in direct competition with Su-75.

Fact#5 Potential Development Flaws

In order to reduce the risk, the aircraft plans to use a 117S engine with a maximum afterburner thrust of 14.5 tons in the flight test phase, and wait until the “Product 30” with a thrust of 18 tons (open afterburner)/14.5-16 tons (conventional) matures. Product 30 is in the developmental phase.

The Checkmate is expected to use a variant of the Saturn AL-41F1 engine used by the Su-57; much as the F-35’s Pratt & Whitney F135 engine derives from the F119 powerplant on the F-22.

The aerodynamic layout of the Su-75 has made some progress compared with the previous Russian fighters. It has begun to reduce the wing surface and use the engine with vector propulsion to compensate for the mobility problem.

The leading edge of the Su-75 main wing adopts a medium sweep angle design, the outer edge is horizontal, and the trailing edge is basically perpendicular to the longitudinal axis of the fuselage. This design is very abnormal in the fifth-generation aircraft, because the main wings of ordinary stealth fighters are mostly designed with trapezoidal wings, with the leading edge designed to be swept backward (about 10 degrees), and the trailing edge to be swept forward (about 10 degrees). Moreover, the position of the flaps of the aircraft is too forward, which may result in insufficient control torque and affect the agility of the aircraft.

The main wing of the Su-75 adopts a small sweep angle design with a relatively large chord, and the sweep angle is estimated to be between 20-30 degrees.

Due to the cancellation of the horizontal tail, the aircraft uses two trapezoidal camber full-motion vertical tails that are responsible for the pitch and yaw of the fighter. The two vertical tails of the aircraft are arranged relatively rearward, and they are relatively separated, possibly in order to avoid mutual interference.

Compared with a single vertical tail, a double vertical tail is not only more conducive to the control of the aircraft, but require sophisticated flight control systems which Sukhoi is to develop a FCS for Su-75.

Read More   Indian Air Force Wouldn't Buy Russia's Su-57 Says Air Chief Marshal Rakesh Bhadauria

With a thick wing root and heavy twin “booms” under the twin tails, the aircraft may have high fuel capacity. No external stores or fuel tanks were shown on the aircraft.

Fact#6: Radar Problem

 It is not yet known which radar the Su-75 will be equipped with, but according to outsiders’ speculation it may use NIIP products. The NIIP is yet to develop a functional radar for any aircraft of Russian origin.

More images of the aircraft will allow a better analysis of whether it is intended to have all-aspect stealth—unlikely, given that its more expensive stablemate, the Su-57, is not stealthy in all aspects—or whether it has only been optimized for forward-quarter, low, or reduced observability.

Fact#7 Limited Armaments

According to Russian officials, the Su-75 has the largest mount capability among its class fighters. According to the propaganda video at the air show, the aircraft has 3 built-in weapon bays, and its standard anti-air mission mode is 5 air-to-air missiles, that is, 1 built-in bomb bay on each side of the fuselage, and the main bomb bay on the belly can be used for 3 missiles.

In addition to air superiority missions, Su-75 can also perform air-to-surface attack missions. At this time, two air-to-surface missiles or smaller precision-guided bombs can be mounted in the main bomb bay of its belly.

In addition, there are 4 external pylons under the Su-75 wing, which can mount a number of ground attack weapons.

At present, the airborne weapons available for Su-75 include: R-77 air-to-air missile, R-74M air-to-air missile, Kh-31PD anti-ship missile, Kh-35UE anti-ship missile, Kh-38MLE (MTE) air-to-surface missile, Kh-58USHKE air-to-surface missiles, Kh-59MK stealth anti-ship missiles, Grom-E1 air-to-surface missiles, various guided and unguided bombs, and even the ancestral S-8 and S-13 rockets.

The major design difficulty of the single-engine lightweight fifth-generation machine lies in how to fit a larger-sized magazine in a relatively narrow body.

Fact#8 When can Su-75 achieve IoC?

Finally, inferring from the current state of the Su-57, it is still not small for the aircraft to finally achieve mass production and enter the military. It took 21 years for Sukhoi to deliver first production variant Su-57 to Russian air force with inferior engine and phased array radar. No one can certainly say that Russia or any other country can develop and deliver an aircraft with pre-defined time frame.

Fact#9 Slide back canopy

Like its larger Su-57 stablemate, the Checkmate has a bubble canopy that slides back, and its infrared search and track feature is mounted on the windscreen, as it is on all recent MiG and Sukhoi fighters. However, UAC has shown images online in recent weeks of a faceted electro-optical aperture like the F-35’s, seemingly mounted on the underside of an aircraft. Other images that have circulated on the internet showing portions of the Checkmate have revealed sawtooth edges on the otherwise round exhaust, very similar to those on the F-35’s F135 engine.

A KH-59MK anti-ship missile is also visible in the airshow image, but it’s not clear if its presence is meant to indicate it’s a primary weapon of the Checkmate. The missile might just fit in the Checkmate’s narrow side weapons bay.

The MAKS mockup is painted in a blue-gray “spatter” scheme not very similar to those seen on previous Russian jets, such as the Su-57. The scheme bleeds slightly over the sharp edges onto the light blue underside. 

The Checkmate joins a lengthening list of aircraft competing in the F-35’s category. Korea is developing a twin-engined F-35 lookalike called the KF-21, billed as a generation 4.5 fighter but lacking internal weapons bays. Turkey’s twin-engined developmental TF-X also resembles the F-35, as does China’s twin-engined FC-31. Britain’s Tempest combat jet design is similar to the F-35 in its nose area but has more of a delta wing. Japan’s F-X fighter is more in the F-22 class, and a consortium (France, Germany, and Spain) is developing the Future Combat Air System, billed as an advancement over the F-35, which in mockup form resembles a more streamlined and flatter F-22.

The Su-75 is long way from the developmental phase to initial operational capability, it is expected to be beyond the scheduled operational date 2026.

To Summarize, Russia never built a Ruddervators, which require sophisticated flight-control systems to be developed by Sukhoi as the functionality does not exist in Su-35 and Su-57 fighters. The Flight Control System is the major weakness of the existing Su-57 aircraft. Russia does not have an operational Active Electronically Scanned Array (AESA) Radar. The future of Su-75 depends on export commitment from buyers to invest in the development of the technology. If this does not have then, Su-75 will face the same fate as the Sukhoi Design Bureau’s early LFI S-21 project and the Mikoyan’s LMFS project.

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