Russian Partners Set To Fly Hybrid-electric Airliner Testbed

 - April 16, 2021, 11:42 AM
A consortium of Russian companies and scientific agencies is preparing to start flight tests with a Yak-40 airliner converted to a hybrid-electric propulsion system. (Photo: N.E. Zhukovsky Scientific Research Center)

A 1970s vintage Yak-40 regional jetliner serves as the platform for what could become the Russian aerospace industry’s biggest step yet towards hybrid-electric propulsion. Developers are now preparing the testbed aircraft for an imminent first flight at the Siberian Scientific Research Academy (SibNIA) and plan to exhibit it to the public for the first time at Moscow’s MAKS 2021 air show in July.

The project, which enjoys high-level backing from the Russian government, is mainly being led by electric motor pioneer SuperOx and the Ufa State Aviation Technology University, which is providing a generator to power the motors and recharge a lithium-ion battery. The partners have removed the original three Ivchenko-Progress AI-25 turbofans, replacing them with a pair of Honeywell’s TFE731-5BR engines and a Klimov TV2-117 turboshaft, which drives the generator. 

Weighing around 100 kg (220 pounds), the generator produces between 400 and 500 kW (up to around 680 hp) of power per tonne, running at 2,500 rpm. The combined electrical power output totals about 800 volts, which the partners say is the highest achieved yet by Russian propulsion companies.

SuperOx’s battery primarily gives the Yak-40 a boost during takeoff. During cruise flight, it accumulates surplus energy while powering the company’s new electric motor, which drives a six-blade propeller at the front of the aircraft.

Under a project called “Contour,” underway since December 2016 and sponsored by Russia’s Fund for Perspective Research, SuperOx seeks to develop a completely integrated propulsion system that could be used to convert existing aircraft, or potentially for new designs. At a media event on February 5 in Novosibirsk, FPI head Andrei Grigoriev said that the government is fully committed to supporting the development of a new all-electric aircraft.

Moscow-based SuperOx is a specialist in applications for high-temperature superconductivity technology, which is also being used for industrial power supply and other transportation uses such as trains. SuperOx also partnered with the Central Institute for Aviation Motors (TsIAM) based in Baranov, which also is contributing to another project—called simply “Electric Aircraft”—that has support from Russia’s Ministry for Industry and Trade. The N.E. Zhukovsky Scientific Research Center also contributes to the Electric Aircraft project.

According to Anton Vavilov, who leads TsIAM’s hybrid-electric division, the Yak-40 flight tests will boost the Russian industry’s efforts to transition aviation away from propulsion based entirely on fossil fuel.

SuperOx chairman Andrei Vavilov said that his company and TsIAM have already done extensive development work to test wiring arrangements on a dozen or so different experimental engines. He said the configuration resulting from the work is now ready to be evaluated in flight. The aircraft also features some cryogenic technology used for cooling the propulsion system.

Even though the Yak-40 airframe is outdated, it has already proved useful as a testbed for the re-engined Yak-40MS model, featuring the TFE7321 turbofans. It has also served as a platform for the development of a new version of the trijet with a high-lift composite wing (the STR-40DT).

The partners expect to complete flight trials by the end of 2022. If they prove successful, SuperOx says it will produce a higher-powered electric motor with an output of around 1 MW per tonne (around 1,360 hp). It plans to fit two of the motors onto an Ilyushin Il-114 aircraft, replacing its TV7-117 turboprops.

The converted 68-seat model will be all-electric and act as a potential prototype for Russia’s next-generation regional airliners. SuperOx has yet to specify how its system will generate enough power to support such a large aircraft.