Russia’s Slon + PD-26; The 100-Ton Military Transport Aircraft ¦ Kawasaki C-2 ¦ Embraer C-390

Various sources in the Russian segment of the internet occasionally report on a new super-heavy transport aircraft under design, known as the Slon or Elephant. The availability of engines in the appropriate class entirely determines the story of this future aircraft. Let's look into this topic using information available in mid-2025. In 2022, the projected characteristics of the future super-heavy aircraft were published. a maximum commercial payload of 180 tons, a cruising speed of 850 kilometers per hour, and a range of 7,000 kilometers with a 150-ton payload. From this, it is easy to see that the plane is intended to occupy the replacement for the AN-124 Neich, but with capabilities surpassing the legendary Soviet aircraft, whose maximum payload is about 120 tons. The last two AN-124 Ruslans were built in Ulyanovsk in 2004 from leftover production stock. At that time, there were reports of three more incomplete airframes. People have repeatedly raised the issue of resuming production of this successful and highly demanded aircraft. In 2013, before the pro-American coup in Kiev, another round of agreements was signed on restarting AN-124 production using cooperation between Russian and Ukrainian aerospace enterprises. The project depended not only on the desire of both sides to secure a profitable long-term program for their aviation industries, but also on engine availability. The issue stemmed from the AN-124's reliance on four D-18T engines manufactured and maintained by the Soviet enterprise in Zaporizhia. After 1991, it became part of independent Ukraine under the name Motor Sich. The D-18T has a maximum takeoff thrust of about 23.4 tons, a dry weight of around 4.1 tons, and a delivery weight of 5.6 tons for the series III. After the events of 2013 and 2014, Russia repeatedly raised the question of either mastering the full production and servicing cycle of the D-18T independently or developing its own new power plant for use in both military transport and civilian aviation for at least the next 40-50 years. The second option was chosen. More on this below. Remarkably, Russia managed for quite some time to maintain connections with the Zaporizhia plant and obtain what was needed by indirect means, even as Kyiv's hostility toward Russia escalated beyond all limits. In any case, Russia continues to equip more than 30 AN-124s with D-18Ts, maintain them, and ensure their airworthiness until 2024. The question is, what will replace them, and where does the slon come in? The creation of a brand new, the largest and the most powerful aviation engine entirely of Russian origin is an extremely ambitious task. To give perspective, it took over 6 years just to design and build the first working gas generator for the engine, which received the designation PD-35. In 2023, media reported successful tests of the gas generator and further plans to move toward full-scale hardware, aiming for a first prototype suitable for flight testing in 2025. Back in 2020, the estimated date for serial production was given as 2028. More realistically, it is likely to be around 2030, as industry sources have repeatedly noted. These are normal timelines for such a massive project, something only three or four countries in the world can afford today. The PD-35 is physically about one-third larger than the D-18T, but it is expected to produce around 35 tons of take-off thrust. Now, let's discuss its potential application. Discussions about Russia's need for a new super-heavy transport aircraft have been going on for many years. In the 2000s, people revisited the abandoned post-Soviet Il-106 project, which in its design specifications slightly fell short of the AN-124's level. The Ilyushin Bureau originally designed it for NK-92 engines, which never reached production. As a result, discussions about the Il-106 would cycle into discussions about restarting AN-124 production in Ulyanovsk, and so on. In 2015, for example, there was even a promise to deliver a new version of the Il-106 with improved characteristics by 2022. In 2016, under an order from Russia's Ministry of Industry and Trade, work began on an entirely new aircraft, given the working name Slon. This project was conceived from the outset for the PD-35. While engine developers were still at the stage of computer models and searching for optimal layouts, progress on the Slon was slow. Once engine development accelerated, work on the aircraft also gained momentum. By 2022, TsAI, the Central Aerohydrodynamic Institute, reported that it had completed two cycles of aerodynamic studies at different flight speeds, including flow visualization. Following these studies, the design of the future giant transport aircraft was refined. The fuselage cross-section was increased. The wing fuselage fairing was reshaped. The design of pylons and nacelles for the PD-35 was developed. Alternative wingtip configurations were also studied. The project of the future super-heavy transport aircraft will gain more concrete shape and move toward the construction of a prototype once the new engines are ready. As of early 2024, it was clear that the Slon had a future, especially since the AN-124 fleet is not eternal. Within the next 10 years, these outstanding aircraft will require a real replacement. Things changed in August 2025. Denis Manturov, Russia's first Deputy Prime Minister, said in an interview with TASS that intensive work is being done to develop a promising aviation engine with a thrust of 26 tons, based on the gas generator of the PD-35 technology demonstration engine. The new engine permits the development of innovative technologies for a new transport aircraft weighing around 100 tons. The PD-26 engine is designed for wide-body passenger aircraft and military transport aviation. The engine's application goes beyond aircraft to ground power plants, which increases the project's cost efficiency. The development is based on more than 20 innovative technologies, assuring a balance of power, dependability, and cost-effectiveness. Based on the above premise, Altitude Addicts has evaluated this combination with similar military transport around the world. The use of two PD-26 turbofans, each of which generates approximately 26 tons of thrust, in a 100-ton class transport aircraft leads to a thrust-to-weight ratio that exceeds the norm. At the maximum take-off weight, the engines generate a thrust-to-weight ratio of approximately 0.52, with a combined thrust of approximately 52 tons, or about 510 kN. This amount is significantly higher than the typical 0.30 to 0.40 range observed in comparable medium-to-large transports. Although not excessive, this capacity indicates a focus on superior field performance, hot and high operations, and a robust one-engine out-climb capability. All of these are essential in military and austere operating environments. The picture becomes clearer when compared to international examples. The Japanese Kawasaki C-2 is equipped with two General Electric CF-680C2-K1F engines, each of which is capable of producing approximately 27 tons, or about 266 kN, of thrust. It has a maximum take-off weight of approximately 141 tons. This results in a thrust-to-weight ratio of approximately 0.38, and a total thrust of approximately 531 kN, which is substantially lower than the proposed Russian design. However, the per-engine thrust class is nearly identical to the PD-26. The Brazilian Embraer C390 Millennium is powered by two IAE V2500E5 engines, each of which is rated at approximately 138 to 139 kN. This results in a total of approximately 278 kN for an 87-ton maximum take-off weight. Its thrust-to-weight ratio is approximately 0.32. Similarly, wide-body freighters such as the Boeing 767-300F, which have a maximum take-off weight of approximately 186 to 187 tons, and engines rated at 265 to 282 kN, operate at a rate of approximately 0.29. This comparison emphasizes that the 100-ton twin transport that Russia intends to build would not only be appropriate in terms of thrust, but it would also be significantly powerful for its weight class. The PD-26 twin configuration, in essence, occupies the same per-engine thrust bracket as the C2, but offers a superior overall thrust-to-weight ratio. This indicates that the design priorities extend beyond efficiency and economy. The concept appears to intentionally overproduce propulsion, likely ensuring rugged performance in challenging conditions. It also establishes a versatile platform that could potentially transition into civilian wide-body applications rather than simply matching peers.