Russia has devised a new iteration of the Slon (English: Elephant) next-generation outsized cargo aircraft, an intended replacement for the An-124-100 Ruslan from Ukraine's Antonov. On July 7, the Central Aero Hydrodynamics Institute (TsAGI) issued a statement on the completion of the third “research cycle” on the Slon, concentrating on aerodynamics at various flight modes and speeds.

TsAGI has received a contract from Russia’s Ministry for Industry and Trade under the “Transport Technologies – 2” scientific research project for the work.

Draft specifications call for transportation of heavy outsized cargo loads at a distance of 7,000 km (3,778 nautical miles) at a cruise speed of 459 kt with takeoffs and landings on runways as short as 9,843 feet. The maximum commercial payload capacity totals 180 tonnes, or one-third more than the respective figure for the An-124-100 (120 tonnes). The increase results from the intended use of the PD-35 turbofan, which produces nearly 50 percent more thrust (35 tonnes) than the Ivchenko-Progress/Motor Sich D-18T on the Ruslan.

As a result of the third iteration, TsAGI has introduced a number of corrections from the previous Slon layout. The most significant change involves an enlarged fuselage cross-section to accommodate bulkier cargo loads.

The aerodynamic fairing for wing-to-fuselage attachment points has become smaller. Designers also improved the shape of the engine pylons and nacelles to better house the PD-35.

A refined aerodynamic model for wind testing incorporates the changes. It features a wingspan of 5.9 feet and a length of about 6.56 feet. Engineers used complex 3D technologies on computer-aided manufacturing tools to make the parts for the model.

Despite the stated completion of the third research cycle, TsAGI intends to carry on with additional wind testing before year-end focused on typical cruise flight conditions. For that, the institute will use of its T-106 wind tube running at different modes, including variable air density. The scaled model will undergo testing with a few alternative versions of the winglets.

TsAGI characterizes the Slon as “optimized primarily for civil applications,” whereas the Ruslan has served both air forces and commercial airlines. “Thanks to the latest decision to enlarge the fuselage cross-section, we will be able to offer our customers a better solution to do with the transportation of larger-volume cargoes at distances they specified,” TsAGI representative Alexander Krutov said. “Besides, the wing with improved winglets will provide a higher lift to drag ratio.”

Russia’s development of the Slon comes as most Ruslans in military and commercial service have begun to approach the end of their lifespans. TsAGI has led the project since its inception in 2016, but the role of the dedicated scientific-research organization is limited to suggesting and refining the airplane’s aerodynamic layout before responsibility gets handed over to an established aircraft manufacturer. Ilyushin has emerged as the most likely candidate given it has won a number of government contracts on technical support of Russia’s Ruslan fleet.