Russia’s aerospace industry is delaying a full-scale launch of a second-generation supersonic transport aircraft (SST2) while intensifying efforts to work out key technologies needed to deliver on that ambition. The change in course was confirmed in a high-level government meeting last month when President Vladimir Putin himself approved a proposal by state-backed companies to develop the new Strizh (Swift) supersonic technology demonstrator to be powered by Klimov RD-93MA turbofans (a no-afterburning derivative of the MiG-35 fighter engine).
With a takeoff weight of 16 tonnes (35,273 pounds), the Strizh would serve as a platform to evaluate a package of new technologies such as pro-bionic structural airframe design (instead of classic frames and ribs) and engineering advances on engine/airframe integration to deliver a lower noise footprint around airports.
Having completed wind-tunnel and hot-gas testing on scaled models, the industry now awaits a government response to its proposal to build the 125-foot-long vehicle able to accelerate to speeds of up to Mach 1.8. If Kremlin funding materializes in a timely manner, construction and flight testing would take place between 2022 and 2026.
Heavier and faster than the NASA/Lockheed-Martin X-59 so-called Quiet Technology Supersonic Transport (QueSST), the Strizh features a wedge-shaped nozzle and an inverted-V wing to reduce sonic boom and noise levels. The features would allow it to cruise at Mach 1.7 at an altitude of 51,000 feet while producing a sonic boom quieter than 85 dB. Although that doesn’t match the overall performance targeted by some in the aviation sector for a future supersonic business jet, and by extension a supersonic airliner, Russian developers feel the Strizh would serve as the next step forward toward a viable supersonic future.
Developers of both the American X-59 project and the Strizh intend for community-response flight tests to enable ICAO's Committee on Aviation Environmental Protection meeting (CAEP13) to establish a sonic boom standard in 2025. Without such a standard and SST2 certification rules covering tolerable sonic boom intensity over populated areas and cities, starting any commercial supersonic aircraft development in earnest would likely become too risky.
Those considerations appear to have spurred the Russian government’s decision to spend more time and money on fundamental research and technology maturation. In September 2020, the administration approved of the formation a special consortium of national scientific centers to address the issue.
That led to the launch in December 2020 of the new so-called world-class Sverkhzvuk Scientific Center (known more commonly as TsNTU Sverkhzvuk or the Supersonic Center). The Russian industry and trade ministry committed around $34 million in funding through 2025 on the condition that six industry partners contribute at least $7.6 million from their own resources.
The TsAGI research institute (the Central Aero Hydra Dynamics Institute named after Zhukovsky) leads the consortium with a workforce of 4,600 manning over 60 wind tunnels and other testing devices. The primary goal centers on setting a set of standards and critical technologies to enable the development of an SST2, as well as necessary supporting infrastructure, and to give the Russian aviation industry a shot at taking the lead in the 21st-century supersonic race.
However, the roughly $41 million budget allocated so far is only a fraction of the estimated costs for getting the SST2 off the ground. The development of a suitable engine alone likely will take another $640 million, according to estimates. The required parameters for the propulsion system include an exhaust gas velocity below 1,300 feet per second at takeoff and specific fuel consumption (SFC) of one pound of thrust per pound of fuel used in one flight hour.
By comparison, the CFM56-7B turbofan commonly used on Western narrowbody airliners has an SFC ratio of around half a pound of thrust per pound of fuel used in an hour, but it carries a more efficient bypass ratio of 5.1. On that basis, the SFC for the powertrain of the envisioned Russian SST2 aircraft would be quite a technical achievement at speeds of Mach 2 by 2030.
But the initial funding does at least give Russia’s SST team a fresh start. Over the next six years, the Supersonic Center has received a mandate to run no fewer than 131 conferences and 43 educational programs, publish 78 scientific articles of Q1/Q2 level to the Scopus/Web of Science Core Collection, and nurture 349 young aerospace scientists for the industry. Plans call for its team of scientists to grow from 39 today to 50 in 2025.
The new initiative’s aircraft design goals include an increase in the lift/drag ratio for a possible SST 2 in sustained cruise by 20 to 25 percent, a reduction in fuel burn by 15 percent and sonic boom intensity by 7- to 10 dB, and ensuring at least a 5-to 7 dB margin with current ICAO Chapter 14 noise limits.
“We speak not only of pure science and technologies, but the certain level of system integration which finds reflection in a proposed aircraft design of a current iteration,” Cyril Sypalo, head of both TsAGI and the new Supersonic Center told a conference during July’s MAKS air show in Moscow. “Shaping aircraft design is a very important issue to us. We have already moved from the R0 to R1 configuration and will continue to refine the aircraft design to at least R5 as the technologies and methods become more mature. Our work shall not come to an end in 2025 with the presentation of the results to the ministry. Instead, we will move from scientific research into research and development.”
The specifications for the R1 supersonic design would include a gross weight of 121,250 pounds (large enough for between 4 and 18 passengers), a Mach 1.8 speed, an operating ceiling of between 49,000 and 58,000 feet, and sonic boom noise levels of between 65 and 69 dBA.
The Supersonic Center team hopes that in 2025 the level of technologies will allow them to plan on delivering an SST2 with all-electric systems onboard and technical vision/augmented reality cabin for a single pilot (with second crew member functions to be reassigned to some kind of artificial intelligence-backed technology). The aircraft would also feature a lift-to-drag ratio of 10, a 0.45 ratio between empty weight and maximum takeoff weight, a 5- to 7-EPNdB noise margin within ICAO’s Chapter 14 limits, and a time between major overhauls of 15,000 flight hours.
Managing expectations, the Russian industry stakeholders have advised that they likely will not deliver either a supersonic airliner or a business jet with such performance any time before 2030.