Yakovlev Yak-46

Yakovlev Design Bureau

Industry	Aerospace, Aircraft design
Founded	1934 (as OKB-115)
Headquarters	Moscow , Soviet Union / Russia
Key people	Alexander Sergeyevich Yakovlev (founder)
Products	Aircraft including conceptual designs such as the Yak-46

Template:Infobox aircraft

The Yakovlev Yak-46 was a conceptual aircraft derived from the Yak-42, featuring twin rear-mounted contra-rotating propellers on a propfan engine. The Samara turbofans designated for this design were specified to produce thrust in the range of 11,000 kg (24,250 lb). Although introduced during the 1990s, the Yak-46 project did not advance to production.

Design and development

During the 1987 Paris Air Show, the Soviet Union presented scale models of several upcoming aircraft, including a 150-seat model equipped with two pusher propfan engines positioned on the aft fuselage. This aircraft had not been named at that time, but it was revealed that development was underway by the Yakovlev Design Bureau. Later that year, the Soviet civil aviation minister confirmed Yakovlev's work on a twin-propfan airliner concept based on the existing Yak-42. By 1989, Yakovlev aimed to conduct flight tests of the D-236 propfan engine developed by the Ivchenko-Progress engine bureau (also known as Progress, Lotarev, Muravchenko, ZMKB, and Zaporozhye) using a Yak-42 testbed before year-end.

In early 1990, Yakovlev disclosed further information about its propfan project, officially named Yak-46, targeting entry into service by 1997. Alongside the Yak-42M—a stretched version of the Yak-42 intended for introduction in 1994—the Yak-46 was planned to incorporate advanced features such as fly-by-wire (FBW) controls, an electronic flight instrument system (EFIS), and a supercritical wing with increased aspect ratio, span, and sweep. Both aircraft were designed to accommodate at least 150 passengers and include new engines capable of thrust reversal. Unlike the Yak-42 and Yak-42M's three aft-mounted turbofan engines (one integrated into the vertical stabilizer), the Yak-46 would utilize two exposed propfan engines mounted on the rear fuselage. Additionally, Yakovlev proposed an unnamed intermediate model between the Yak-42M and Yak-46 featuring two underwing engines based on a contra-rotating integrated shrouded propfan (CRISP) concept; however, due to significant airframe modifications required, its production prospects were uncertain.

Configured for seating between 150 and 162 passengers in a six-abreast single-aisle layout, the Yak-46 was designed for a maximum range of approximately 1,540 nautical miles (2,850 km; 1,770 mi) and cruising speeds between 445 to 460 knots (800 to 850 km/h). Propulsion would come from two Lotarev D-27 propfan engines with a diameter of about 3.8 metres (12 ft; 3,800 mm; 150 in), featuring contra-rotating propellers—eight blades forward and six blades aft. These engines were expected to deliver roughly 9,700 kilowatts (13,000 hp) of power with a thrust output near 11,200 kgf (24,700 lbf; 110 kN) and achieve a thrust specific fuel consumption (TSFC) of approximately 0.44 lb/(lbf⋅h) (12 g/(kN⋅s)). The fuel efficiency per available seat kilometer was estimated at 13.8 grams per kilometre (0.78 oz/mi), outperforming both an underwing engine variant at 14.5 g/km (0.82 oz/mi) and the already more efficient-than-predecessor Yak-42M at 21 g/km (1.2 oz/mi). Although airlines showed interest in the Yak-46 concept, no firm orders were recorded; meanwhile, negotiations were underway for Aeroflot to acquire 200 units of the Yak-42M—the world's largest airline at that time.

By October 1990, two variants of the Yak-46 were competing against the 102–126 seat Tupolev Tu-334, which similarly offered an interim turbofan version and a final propfan configuration intended to replace aging fleets of Tupolev Tu-134 aircraft operated by Aeroflot. To facilitate development of the Yak-46, Yakovlev established a joint venture with Ivchenko Progress and the Soviet Ministry of Civil Aviation. Aeroflot agreed to contribute funding toward prototype construction slated to begin in early 1991 if selected. Projected annual production could reach up to 100 aircraft through 2005.

Flight testing of a single D-236 propfan engine mounted on a Yak-42E-LL testbed commenced on March 15, 1991—marking the first Soviet design bureau-led propfan flight program. This testbed was later publicly displayed at the June 1991 Paris Air Show. The D-236 engine featured contra-rotating fans with an eight-bladed front and six-bladed rear propeller assembly measuring approximately 4.2 m (14 ft; 4,200 mm; 170 in) in diameter. It produced around 8,195 kW (10,990 hp) power with thrust estimated between 10.5–11 tf (10,500–11,000 kgf; 23,000–24,000 lbf; 103–108 kN), although limited thrust was applied during testing since it exceeded that of its predecessor, the Lotarev D-36 engine.

File:Yakovlev Yak-42LL, Aeroflot AN0916963.jpg

To aid development of its Yak-46 concept, Yakovlev operated a modified Yak-42E-LL testbed powered partly by an experimental Progress D-236 propfan.

Conflicting reports emerged regarding the definitive powerplant choice for the Yak-46: one source indicated that the D-236 would be adopted eventually; another suggested that Yakovlev was deliberating between a gearless unducted fan offering fuel consumption near 12 g/km (0.68 oz/mi) and a ducted fan alternative with an ultra-high bypass ratio ranging from 20 to 27—though less efficient but considered more feasible at that time. By August, updates revealed that an initial version designated as Yak-46-1 would feature two Progress underwing engines inspired by the International Aero Engines (IAE) SuperFan design; a subsequent variant named Yak-46-2 would revert to aft-fuselage-mounted D-27 engines. A Soviet aviation publication identified this initial engine as the Progress D-627, characterized as a quiet turbofan with super-high bypass ratio incorporating ducted contra-rotating fans driven via differential gearing. The D-627 delivered takeoff thrust around 11,000 kgf (24,000 lbf; 110 kN), with cruise TSFC not exceeding 0.5 lb/(lbf⋅h) (14 g/(kN⋅s)) at Mach 0.8 altitude near 11,000 m (36,000 ft), corresponding to approximately Mach 0.8 speed (~850). Fuel consumption per passenger kilometer using this engine was estimated at 15.5 g/km (0.88 oz/mi). The later production variant would retain previously mentioned performance metrics associated with the D-27 engine but improve cruise TSFC to roughly 0.47 lb/(lbf⋅h) (13 g/(kN⋅s)) at speeds near 850. The projected operational lifespan for the Yak-46 was approximately 60,000 flight hours based on an average annual utilization of 3,000 hours. As of November 1991, construction of a wooden mockup had commenced. By August 1992, plans included potential co-production arrangements in South Africa.

By March 1993, only one development order had been placed for the Yak-46 project—a contract that temporarily prevented bankruptcy for Yakovlev. In mid-1994, Progress engine bureau explored creating a turbojet derivative based on its D-27 model intended for use on this aircraft. Later that year, reports indicated plans for equipping the Yak-46 with two high-bypass turbofan Progress D-727 engines without mention of maintaining a propfan configuration. However, by 1996 an updated aircraft registry still referenced both versions: a Yak-46-1 fitted with D-727 underwing engines followed by a Yak-46-2 featuring T-tail empennage-mounted D-27 units. Due to ongoing challenges in engine development, neither model was anticipated to achieve flight prior to 2000.

See also

• Antonov An-180
• Boeing 7J7
• McDonnell Douglas MD-94X
• MPC 75
• Tupolev Tu-334