Yakovlev Yak-40

Yakovlev Yak-40

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Yak-40

Aeroflot Yak-40 at Bromma Airport in 1971
Role	Regional jet/ VIP transport
National origin	Soviet Union
Manufacturer	Yakovlev
First flight	October 21, 1966
Introduction	September 1968 (Aeroflot)^[1]
Status	Operational
Primary user	Aeroflot
Produced	1967-1981
Variants	Yakovlev Yak-42

A lineup of Yak-40s at Zhulyany Airport in Kiev.

The Yakovlev Yak-40 (NATO reporting name: Codling) is a small, three-engined airliner that is often called the first regional jet transport aircraft. It was introduced in September 1968 with Aeroflot.

History

The Yak-40 was developed to meet a desire by Aeroflot to replace the Ilyushin Il-12, Il-14 and Lisunov Li-2, which, along with the An-2 biplane, served Aeroflot's regional and local routes. By the 1960s all these aircraft had become obsolete, and Aeroflot desired a single modern replacement aircraft for all of them to ease operating costs and maintenance. Aeroflot believed that a turboprop aircraft would best serve this need, and Yakovlev produced various studies using a variety of turboprop arrangements. In 1964 Yakovlev came to the conclusion that a STOL jet would better suit Aeroflot's needs, despite the fact that there was no desire for high speed, the emphasis instead being on reliability and the ability to operate in ICAO Category II weather conditions and from Class 5 airfields (unpaved strips shorter than 700m, 2,300 ft).

Development

In order to achieve the STOL capability desired Yakovlev initially spent considerable effort exploring a VTOL arrangement (Yak-40 VTOL). Designs were studied that incorporated dedicated lift jets in pods mounted mid-wing, as well as designs incorporating the lift jets within the fuselage. Ultimately the concept of a VTOL aircraft was abandoned, being judged impractical.

In 1964 the OKB received a GVF (civil air fleet) agreement to build a conventional 20/25 seat regional jet with unswept wings, powered by three new turbofans being developed by A I Ivchenko at Zaporozhye in the Ukraine. R S Petrov and M A Shcherbina were appointed chief engineers along with the founder's elder son, Sergei A Yakovlev, who was given his first major responsibility as a chief designer.

The design evolved into a relatively slow jet transport, though this idea seemed to offer the best merger of simplicity, reliability, and low purchase and operating costs. Among the designs features was a 30,000-hour operating life, independence of sophisticated airport facilities, and the ability to meet foreign certification requirements.

The final design was unusual in that the passenger compartment was ahead of the wing. Behind the wing was a short rear fuselage housing the three engines. The large tail features a leading edge sweep of 50 degrees, not for high-speed, but rather to move the high tailplane further back. Indeed, the tailplane does not extend to the fin's leading edge, but is mounted about one fifth the way back. Because of its short movement arm the the fin itself had to be somewhat huge.

The wing was made of left and right halves joined at the centerline, with the main spar running from wingtip to wingtip, and auxiliary spars front and rear. Virtually the entire wing between the main and front spars formed internal fuel tanks with a capacity of 3,800 liters (839.9 gallons).

The fuselage was a simple ring frame with stringers and measured 2.4m (94.5in) in diameter. The nose section was made separately, with a cockpit floor slightly higher than the cabin floor. The cockpit was arranged for two pilots, with a wide center console. The cabin was fully pressurized, and initially measured 6.7m long on the prototype, but was later extended aft with an extra window being added on each side, to a length of 7.07m (23 ft 2 3/8 in). Seating was for twenty-four passengers in a two-plus-two configuration, with a luggage bay and toilet at the rear. A shelf for carry-on bags was located along the right side. An outward opening service door was located in front on the left, and eight circular windows were installed on each side, the rearmost being escape hatches. The main passenger door was located in the rear pressure bulkhead, allowing passengers to board and exit the aircraft from the rear down a hydraulically operated rear stairway.

The three AI-25 engines were especially designed for the aircraft, and featured a two-shaft turbofan with an eight-stage compressor and a bypass ratio of 2.15. Takeoff thrust was rated at a mere 1,500 kg (3,307lbs), a very low thrust figure for a commercial airliner. Dry weight was 320 kg (705lb). The engines had no jetpipes, and initially no thrust reversers.

The undercarriage was a conventional tricycle arrangement. Each wheel had a multi-disc brake with the latest anti-skid control systems, while the tires were wide, low pressure units for operations on unpaved runways. The wheels had no fairings when retracted, and almost met at the centerline.

Testing

The first of five prototypes (SSSR-1966) was first flown on 21 October 1966 by Yakovlev test pilots A I Kolossov and Yu B Petrov. This aircraft was followed by 19661, 1967, 19671 and 19672. With so many flying prototypes it was possible to achieve certification by 1968. One year earlier, in 1967, large orders were place at the factory at Saratov, supported by Smolensk producing specific parts. Initial series production aircraft differed from the prototypes mainly in having the longer cabin and a back-sloping inlet to the number 2 engine.

The ASCC reporting name is "Codling".

Second series

The second series was introduced in 1969 and featured clamshell thrust reversers on all three engines. The main undercarriage was strengthened, and a ninth row of seats was installed, bringing the seating capacity to twenty-seven. The fuel tank capacity was also increased to 3,910 liters (860 gallons).

Third series

Introduced in 1973, the third series was cleared to significantly higher weights, giving customers the option of an interior for thirty-two passenger. The upper tailplane bullet fairing was removed from this and all subsequent models.

Forth series

The final series was introduced in 1975. Payload was increased to 3,200 kg (7,055lb), and the interior could be arranged into two classes of seating, or for rapid conversion from passengers to cargo.

Yak-40K

A few of the forth series were built as a special cargo version with a door measuring 1.6 by 1.5m (63 by 59in) on the left side behind the service door.

Operational history

Passenger service began on 30 September 1968.

By the time production ended in 1981 the factory at Saratov had produced 1,011 aircraft. By 1993 Yak-40s had carried 354 million passengers. Between 1967 and 1976 the OKB had demonstrated the aircraft for sale in seventy-five countries. In 1972 it was certified in Italy and West Germany. Certification was completed in the U.K. but the document was not issued. A total of 130 aircraft were exported to Afghanistan, Angola, Bulgaria, Cambodia, Cuba, Czechoslovakia, Equatorial Guinea, Ethiopia, Germany, Hungary, Italy, Laos, Malagasy, Poland, Syria, Vietnam, Yugoslavia and Zambia.

Czechoslozak pilots flying a Yak-40 set twelve world class records.

Since the demise of the old Aeroflot, many have been converted from passenger service layout to more luxurious corporate layouts and are in use as corporate and private aircraft.

Most of the Yak-40s in active service fly in the former Soviet Union. Some are flying in Europe, but are rare because of noise restrictions.

Summary

Despite its many shortcomings, including obsolete and inefficient engines, primitive avionics, and a cruise speed below many contemporary turboprops, the Yak-40 must be considered a very successful aircraft. The design pioneered the concept of the regional jet, a type now essential to virtually all airline operations. That 40% of all Yak-40s built are still operating nearly three decades after the last one rolled off the assembly line is impressive. More impressive still is that these aircraft are largely operating in poor, underdeveloped countries where parts and maintenance are often lacking, a testament to the Yak's planned durability. With the demise of Yakovlev as an independent company, in retrospect the Yak-40 must be considered Yakovlev's most successful design based on its safety record, hours of operation and passengers flown.

Variants

Yak-40 - The first production model.
Yak-40-25 Military conversion with the nose of a MiG-25R and SRS-4A Elint installation.
Yak-40 Akva (Aqua) - Military conversion with nose probe, pylon-mounted sensors, a fuselage dispenser and underwing active jammer pods.
Yak-40DTS - Only known by the designation. Possibly a long-range cargo version.
Yak-40EC - Export version.
Yak-40 Fobos (Phobos) - Military conversion with two dorsal viewing domes and a removable window on each side.
Yak-40K - cargo / convertible / combi version with a large freight door.
Yak-40 Kalibrovshchik - Military Elint conversion with a "farm" of blade, dipole and planar antennas.
Yak-40L - Proposed version with two Lycoming LF507-1N turbofans, a joint program between Skorost and Textron (now Allied-Signal) Lycoming. The original design would have had a slightly swept wing.
Yak-40 Liros - Military conversion with nose probe carrying air and air-data sensors.
Yak-40M - Proposed 40-seat stretched passenger version.
Yak-40 M-602 - Flying testbed with a Czechoslovak M 602 turboprop installed in the nose.
Yak-40 Meteo - Military conversion with multipole dipole antennas and fuselage dispenser.
Yak-40P - Yak-40L with large nacelles projecting ahead of the wings.
Yak-40REO - Military conversion with large ventral canoe for IR linescan. Lateral observation blister on right side.
Yak-40 Shtorm - Military conversion with multiple probes and sensors on the forward sidewalls.
Yak-40TL - Proposed American version, to be powered by three Lycoming LF 507 turbofan engines.
Yak-40V - Export version powered by three AI-25T turbofan engines.
Yak-40VTOL - Two designs proposed capable of vertical takeoff and landing.