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Tu-124

Successful operation of Tu-104 has confirmed the economic feasibility of the use of passenger aircraft with turbojet engines not only en the air routes of 2,000-2,900 km length, but also on the lines of a relatively small length of 800-1,000 km. However, despite all the advantages of Tu-104, a special short-range aircraft of smaller dimensions was required for short routes, which could successfully combine in operation high flight performance and comfort of Tu-104 with satisfactory takeoff and landing characteristics, which made it possible to provide mass air transportations on inter-republican lines by jet airplanes, with good economic and operational performance.

In 1958, designing of such passenger plane was started in the Tupolev Design Bureau. Tupolev’s proposal for creation of a new short-range passenger aircraft on the basis of the common aerodynamic and structural layout of Tu-104 has been worked out under the leadership of S.M. Eger, D.S. Markov, L.L. Kerber, K.V. Minkner, B.M. Kondorsky, I.B. Babin. Dimensions of the new aircraft had to be reduced in comparison with Tu-104 by 25%, and takeoff weight – reduced twice, while the estimated passenger capacity was reduced to 50-60 persons. Due to the decrease in weight and size parameters of the new aircraft, it became possible to use turbojet engines with lower thrust: instead of turbojet engine with a maximum thrust of 8,570-9,500 kg, a transition to engines with a maximum thrust of 5,000-5,500 kg each was performed. Such engine, designated D-20P was being designed in the Bureau of P.A. Soloviev, based on the D-20 bypass engine intended for military airplanes. For the first time in the practice of the Tupolev Design Bureau, scaled methods of strength calculations proposed by A.M. Cheriomukhin which allowed reducing significantly the time of design, were used in development of a new passenger airplane which got "124" (Tu-124) designation within the Bureau. Equipment department of the Bureau proposed to fit the plane with flight and navigation equipment which met the requirements to the corresponding class of airplanes of the late 50's - early 60’s. The center-wing of the aircraft was completely redesigned, - it became structurally and technologically integrated with the engine nacelles – it became possible to eliminate the air flow separation in the engines’ air intakes. These two design innovations had been already tested on four-engine modification of Tu-104 - Tu-110.

On July 18, 1958, the Council of Ministers of the USSR issued a decree № 786-378, according to which the Bureau was obliged to design and build Tu-124 high-speed passenger aircraft with two turbofan D-20P engines with the following performance: maximum speed of 950 km/h, cruising speed at an altitude of 10,000-12,000 m - 750-900 km/h, range with fuel reserve of 30 minutes of flight at cruising speed – 1,350-1,500 km, maximum service range – 2,000 km, take-off run and landing roll - not more than 800 meters, payload of 5,000 kg, number of passengers - 36-40 persons, crew - 4 persons. Conversion of Tu-124 in ambulance version equipped Tu-124TS aircraft with a load capacity of 5,000 kg was also provided. The aircraft was to be operated from unpaved airfields and take off with one inoperative engine. Batch production of Tu-124 was to be mastered at the plant № 135 in Kharkov, and the first production plane was to be released in late 1959. Additionally, a system of boundary layer blowing was provided for implementation on the airplane that could reduce run and roll to 600-700 m. The D-20P engines (with take-off thrust of 5,400 kg) and their D-20-PO version with bleed air system for boundary layer blowing were to pass checks and refinement on the modified Tu-110 (Tu-110B). During discussions with the customer on the mock-up committee, number of seats was increased to 44, with the following development for 56 and 60 seats. "Section" variants (business class section, economy class section and etc.) for special passenger services were also in the development.

Since the second half of 1958 till early 1959, the design bureau together with its branches had prepared the design documentation for Tu-124, then, handed it to the prototype production and the plant № 135. Thus, construction of the prototype aircraft has begun in Moscow with simultaneous deploying batch production in Kharkov. A.N. Tupolev imposed management of all the works on the aircraft and its modifications on D.S. Markov.

By the beginning of 1960, the first prototype was finished. Factory tests of the airplane began on March 24, 1960. On March 29, 1960, Tu-124 prototype aircraft performed its first flight piloted by the crew headed by test-pilot A.D. Kalina. Factory tests continued until June, 1961. In May 1960, first Tu-124 production airplane came out of the shops of the plant № 135, and till the end of the year, another 4 production planes were built, which then went to the factory and field tests. Overall evaluation of the aircraft was positive. However, the tests revealed some shortcomings of the first airplanes.

Thus, improvements were made to the design, in particular, navigator’s cabin was changed, the wing dihedral angle was reduced, etc. The modified version of the aircraft was transferred to the state joint tests that were being performed from July 1961 to September 1962, and according to their results Tu-124 has been recommended for passenger transport. In the same period, 10 production airplanes took part in the field tests. In addition to basic flight tests Tu-124 has successfully passed the following tests: on takeoff and landing on unpaved airfields; in conditions of low and high temperatures; on flying at critical angles of attack; on continued and rejected takeoff with one engine out, etc.

Tu-124 performed its first passenger flight on October 2, 1962 en the Moscow-Tallinn route. So, successful operation of the aircraft on the routes of Aeroflot began.

In order to improve the economic efficiency of the aircraft the design bureau together with the production plant and the CAF carried out a large amount of work on its modification aimed at increasing passenger capacity, range and improving comfort. After it, comfortable cabin of the new layout could accommodate 56 passengers. This modification was designated Tu-124V and was the most mass produced of all variants of Tu-124. Also, a version for 60 passengers had been worked out, but was not put into operation, as well as intermediate variants for 48 and 52 seats. For government flight squadrons of the USSR and other countries Tu-124K VIP-versions have been designed and batch produced which, with some changes in the equipment, were operated by the Air Force, as command airplanes. For flying and air navigation schools of the Air Force Tu-124Sh training version was batch produced. Also, there were following attempts to improve the power plant: in 1963, Tu-124B with D-20P-125 engines similar to those of Tu-124A (Tu-134) was produced; there was a project of refitting Tu-124 with D-30 engines.

 Modifications and variants of the aircraft:

 - Tu-124 - production version for 44 passengers, was being produced till 1963, then, almost all the airplanes were converted for 56 passengers;

 - Tu-124 - a project for 48 or 52 passengers;

 - Tu-124 - for 60 passengers - only one airplane was reequipped;

 - Tu-124V - production version for 56 seats - batch produced since 1964;

 - Tu-124B - three production airplanes with D-20P-125 engines, produced in 1963;

 - Tu-124K - Tu-124K-1 and Tu-124K-2 VIP-versions with different number of passengers and level of comfort;

 - Tu-124TS - standard conversion of Tu-124 production airplane in medevac aircraft;

 - Tu-124 (SPS) - project of Tu-124 with boundary layer blowing system;

 - Tu-124 (VTOL) - a project of the aircraft with vertical or short takeoff and landing with RD-36-35 or RD-36-35P lift jet engines installed in the landing gear fairings and the fuselage;

 - Tu-124Sh - navigational training production aircraft for training staff for the Air Force and Navy aviation. The airplane was produced in two versions: Tu-124Sh-1 for training navigators for long-range bombers and Tu-124Sh-2 - for training navigators for front-line bombers;

 - "127" (Tu-127) - the project of conversion Tu-124 airplane in military transport variant.

In total, the production plant № 135 had produced 110 Tu-124 and Tu-124V by the second quarter of 1966. Moreover, the plant has delivered 55 Tu-124Sh to the Air Force in the period from 1962 to 1968. From 1964 to 1966, 13 airplanes were sold abroad - they were delivered mostly in the "section" variants.

In the early 70's, Tu-124s were flying on routes connecting in total about 50 cities of the USSR. In 1964, the aircraft entered international lines of the Aeroflot: it flew from Moscow to Warsaw, East Berlin and Prague. In Aeroflot, Tu-124 and Tu-124V were in operation till the beginning of the 80s, up to the moment when they were finally replaced by Tu-134A. During the years of operation, fleet of Tu-124 has carried about 6.5 million passengers.

Tu-124 has gone down in history of the Soviet aircraft engineering as the first passenger jet that brought comfort and speed to the Soviet country towns. Tu-124 is the world's first passenger aircraft with turbofan engines.


Basic characteristics of Tu-124 production aircraft with two 2D-20P engines:

• aircraft length, m - 31.578;
• wing span, m - 25.55;
• aircraft height, m - 8.082;
• wing area, m2 - 119.37;
• take-off weight, kg - 38,000;
• payload weight, kg - 6,000;
• maximum speed at an altitude of 8,000 m, km/h - 970;
• cruising speed at altitudes of 8,000-11,000 m, km/h - 750-850;
• service ceiling, m - 11,500;
• range at an altitude of 10,000 m, cruising speed of 780-800 km/h
and a payload of 5,000 kg, km - 2,000-2,100;
• number of passengers, persons - 44-56;
• crew, persons - 4-5