File:Yak-42D (4322116300).jpg

The Yakovlev Yak-42 (NATO reporting name: Clobber) is a 100/120-seat three-engined mid-range passenger jet. It was designed as a replacement for several obsolete Aeroflot jets as a mid-range passenger jet. It was also the first airliner produced in the Soviet Union to be powered by modern high-bypass turbofan engines.

The Yak-42 was designed as a replacement for several earlier Aeroflot aircraft, including the twin-engined Tupolev Tu-134, An-24 and An-26, and the Il-18, as well as various smaller aircraft serving routes experiencing significant growth, and where airports and runways had been expanded to accommodate a more advanced aircraft. To meet this requirement Yakovlev developed the largest, heaviest, and most powerful aircraft it had ever designed.[2]

To save design time Yakovlev conducted a detailed study of all foreign aircraft in the same category. In addition, an unprecedented amount of research was performed by Yakovlev as well as CAHI and CIAM, as well as other organizations to support the program. A major manufacturing plan was drawn up under which the aircraft was to have parts constructed at Saratov, with final assembly at Smolensk, in reverse of the Yak-40 program.[2]

The project started with a scaled-up Yak-40 with an unswept wing, and seating for 114 passengers in nineteen rows of three plus three.[2]

This design was soon rejected as uncompetitive with western counterparts. In addition, western aircraft were now employing high-bypass turbofan engines, and the decision was made to introduce a similar engine to the new aircraft. As a result, at Zaporozhye Vladimire Lotarev designed a three-shaft engine with a bypass ratio of 5.4/5.6 specifically for the Yak-42. In late 1972 Yakovlev decided to place three of the engines on the aircraft, as had been done with the Yak-40 (he was also influenced by the Boeing 727 and Hawker Siddeley Trident). Lotarev designed the new engine, designated D-36, to deliver 6,500 kg (14,330lb) of thrust.[2]

The full-scale mock-up was revealed to western aviation writers in June 1973. It was essentially a greatly enlarged Yak-40 with 120 seats in twenty rows of three plus three. Compared with the Yak-40 the Yak-42 was roughly four times as heavy, and would require a much larger and better developed runway.[2]

Considerable debate took place over the sweep back of the wings. As a result the first prototype was built with an 11-degree sweep, while the second prototype possessed a 25-degree sweep, that was later changed to 23-degrees before its first flight.[2]

The pressurized fuselage had a circular diameter of 3.8m (149 5/8in). Like the Yak-40 it was of simple ring/stringer construction and was semi-monocoque. Also like the Yak-40 it was designed with an expected lifespan of 30,000 one-hour flights. Unlike the Yak-40 the passenger compartment extended back behind the wing, though the rear fuselage was very similar. Also like the Yak-40, the aft pressure bulkhead incorporated the main cabin door, which led to powered airstairs which hinged down under the tail.[2]

The side engines were attached quite high on the fuselage, with short fan ducts and initially no reversers. Again like the Yak-40, the number 2 (center) was fed by an S-duct. The center engine fairing extended back over the TA-12 APU (auxiliary power unit), which provided compressed air to start the engines and also ground cabin air-conditioning, giving the Yak-42 the same ability to operate independent of airport facilities that the earlier Yak-40 enjoyed. The large fin housed the one-piece rudder. At the top of the fin was the fully-powered tailplane, with a span of 10.8m (35ft 5in). The prototype had a bullet fairing extending from the front of the tailplane, but this was removed from series production. Unlike the Yak-40, the tailplane extended to the forward edge of the fin.[2]

The undercarriage also experienced revision, with the prototype possessing a single large tire on each main unit, while production aircraft incorporated a bogie with four tires similar in size to the nose wheel. The main gear retracted inward, while the nose wheel retracted forward. All wheels were equipped with the latest multi-disc brakes with anti-skid control.[2]

The passenger cabin had an interior diameter of 3.6m (11ft 9 3/4in), while height along the center aisle was 2.03m (6ft 8in). Functional length behind the cockpit was 19.89m (65ft 3in). The fuselage had twenty windows on each side, four housing emergency escapes.[2]

In addition to the rear airstair there was an additional airstair located on the forward left side, and a service door opposite. Allowing for galley and toilets early aircraft were designed for 100 seats. Cargo and baggage holds were located under the floor with doors on the right side, and on series aircraft, six chain conveyors in the forward hold and two in the rear for moving standard containers.[2]

The cockpit seated the two crew members, and included a SAU-42 autopilot, with advanced avionics and radar. The overall avionics packaged was designed with the goal of landing in bad weather on an unpaved runway measuring 30 by 400m (98 by 1,312ft). As of late 1995 this goal had still not been achieved.[2]

All fuel storage was inside the main wings. In prototypes and early series aircraft the capacwas 15,795 liters (3,474.4 gallons). In 1981 this was increased to 23,175 liters (5,098 gallons).[2]

Current models include the Yak-42 base version, the Yak-142 with a higher gross weight, and the Yak-42D-100 with western avionics that never entered serial production. Late in 1997, Yakovlev announced the development of the Yak-42A, an improved version of the Yak-42D featuring a higher range and a modernised cabin interior (see variants).

General characteristics

   * Crew: two pilots
   * Capacity: up to 120 passengers (But usually 8 first class and 96 economy class)
   * Length: 36.38 m (119 ft 4 in)
   * Wingspan: 34.88 m (114 ft 5 in)
   * Height: 9.83 m (32 ft 3 in)
   * Wing area: 150.0 m² (1,615 ft²)
   * Empty weight: 33,000 kg (72,752 lb)
   * Max takeoff weight: 57,500 kg (126,765 lb)
   * Powerplant: 3× Lotarev D-36 turbofan, 63.75 kN (14,330 lbf) each

Performance

   * Maximum speed: 810 km/h (437 knots, 503 mph) (maximum cruise)
   * Cruise speed: 740 km/h (399 knots, 460 mph) (economy cruise)
   * Range: 4,000 km (2,158 nmi, 2,458 mi) (with maximum fuel)