Experimental fighter Yak-140

Developer: OKB Yakovlev
Country: USSR Built: 1955

The Yak-140 is an experimental fighter developed by the Yakovlev design bureau. Created in the mid-1950s, the Yak-140 fighter remained a mystery to both Western and domestic aviation historians until recently. And this is not surprising, because the machine not only did not take part in air shows, which were held regularly at that time, but never even took off, although it was built and taxied at the LII airport in Zhukovsky. Further interest in the Yak-140 is due to the fact that this lightweight first-line fighter could compete well with the well-known MiG-21.

Jak-140 with AM-9D engine. January 1955

 

The main idea of the creators of the Yak-140 is clearly defined in the concept - the first official document submitted to higher authorities in July 1953. Specifically, it says: "The present design of the AM-11-engined front-line fighter is a further development of the light fighter idea, which has been carried out for many years. The proposed fighter successfully combines the characteristics of a small light aircraft and provides excellent flight and combat characteristics guaranteed by an unsurpassed thrust-to-weight ratio ... Flight data: climb rate at ground level 200 m/s and at 15 000 m - 30 m/s; practical range exceeds 18 000 m; maximum speed at altitudes of 10 000-15 000 m reaches 1700 km/h. Due to the low wing area loading and high thrust-to-weight ratio, the light interceptor has excellent manoeuvrability both vertically and horizontally. "

During preliminary investigations, Yak-140 designers studied several alternative propulsion options, including: the VK-3, TRD-I, AM-11. The best results were achieved with the lightest AM-11, which at the time was characterized by very high specific performance and later became one of the most successful Soviet aircraft engines (serially produced under the designation R-11, installed on MiG-21, Yak-28).

The time when the Yak-140 was designed was characterized by a very dynamic development of combat aviation, with flight speed becoming extremely important. Rapid advances in aerodynamics and aircraft engine design opened up prospects that until recently seemed fantastic. In just 5-6 years the speed of fighters nearly doubled, and in many ways this pursuit of speed came at the expense of maneuverability. Aviation specialists' ideas about aerial combat have undergone serious changes, largely due to the emergence of air-to-air missile weapons. The most prominent example is the Lockheed F-104 Starfighter, which was one of the fastest and least maneuverable fighters.

 

The designers of the Yak-140 took a different route. They deliberately sacrificed speed for good maneuverability. To do this, the wing of the Yak-140 was made slightly larger than was usual for high-speed aircraft of this class. At the same time, the top speed was reduced by 150-200 km/h, but maneuverability and takeoff and landing characteristics were greatly improved. The low values of specific wing loading (250 kg/m² on take-off and 180 kg/m² on landing) and low wheel ground pressure (6.0 kg/cm²) allowed the aircraft to operate from unpaved airfield surfaces. In addition, the vertical rate of descent was significantly reduced, making it easier to land the interceptor with the engine stopped, which the designers considered an important element in improving safety and survivability.

The interceptor was also able to land with the engine stopped.

The Yag-140 was supposed to have a phenomenal thrust-to-weight ratio for its time, which was calculated to be slightly more than 1 (!), equivalent to the performance of the modern F-15, F-16, MiG -29 or Su-27. For comparison, this indicator for the MiG-21F (1958) was 0.84 and for the F-104A was 0.83. Such a thrust-to-weight ratio combined with the relatively low specific wing loading would give the Yak-140 a clear advantage in maneuverable aerial combat. Importantly, modern fighters, designed to achieve air superiority, are characterized by their prioritization of these qualities.

In designing the Yak-140, no less attention than to flight characteristics was paid to ease of mass production, simplicity and ease of maintenance. The design of the main units and their subdivision into panels were made to ensure the possibility of assembly on the line. Molding and casting were widely used. The arrangement of equipment and weapons adopted, as well as the large openings in the hull, facilitated operation. The control rods and engine controls, as well as a significant portion of the wiring, were located under an easily accessible ridge. The rear of the fuselage was detachable for the purpose of engine replacement. The design and layout of the Yak-140 was done taking into account the experience gained in the creation of the Jak-50 light fighter.

Jak-140 (based on a 1953 design) was a self-supporting all-metal semi-spar mid-airplane with a canopy, arrow wing and tail. The wing consisted of two separate brackets carried by a strong fuselage spar. Its power structure consisted of two spars and ribs placed perpendicular to the front spar. The wing sweep along 25% of the depth was 55.5°. The relative thickness of the root profile was 6.3%, and the end profile was 8%. The transverse V of the wing was -4.5°. The wing was equipped with extendable flaps and weight-compensated ailerons. Two aerodynamic ridges were installed on the upper surface of each cantilever.

In the front of the fuselage was an unregulated cone that housed the radio rangefinder units. Fuel (1275 kg) was placed in tanks located behind the cockpit and in the aft fuselage. The cockpit was sealed, with an ejection seat. In the event of an emergency jettison of the cockpit canopy, the air brakes located on the sides of the fuselage were automatically opened, increasing the safety of ejection. The fighter's armament consisted of three 30 mm guns with 50 rounds per barrel and 16 unguided 57 mm RS.

How-140 in the cut

The bicycle-style chassis consisted of a main, front and two underwing supports. Damping was pneumohydraulic, and the construction of all legs was lever-type. The main strut was fitted with two 600 × 200 mm braked wheels and the front was hydraulically controlled around a 480 × 200 mm wheel. The underwing struts with 250 × 110 mm wheels were inserted into the fairing located at the wing tips. PVDs were installed on the same fairings. Extension and retraction was performed by a hydraulic system (node unlocking - pneumohydraulic). The front and main landing gear were folded downstream, which guaranteed their release even at low system pressure.

In 1953, the Soviet Union began a program to create a new generation of fighters that featured high supersonic speed. The design bureau of A. S. Yakovlev and A. I. Mikoyan relied on the A engine to create such aircraft. A. Mikulin AM-11 and on the "firm" P. O. Sukhoi - on the much more powerful and inherently heavy AM Ljulky AL-7 engine. In fact, the AM-11 and AL-7 did not exist in 1953-1954, they were developed in parallel with the aircraft. However, it turned out that the pace of work on the Yak and MiG fighters was higher than on the AM-11 engine. After that, both design bureaus decided to build experimental models for the lower thrust AM-9B production engine (additional combustion thrust of 3300 kg) or its modification AM-9D. Thus the Yak-140 with AM-9D appeared, as well as the Mikoyan E-2 and E-4 with AM-9B.

The Yak-140 with AM-9D was quite similar to the main version with AM-11. The only differences were in the elements associated with the propulsion and in the armament, which consisted of two 23mm NR-23 guns. The radio rangefinder was not installed. It is clear that it was not planned to achieve the declared flight performance. The machine was intended for testing and fine-tuning of systems and units, with the identification of features that would accelerate the entry into service of the main version of the machine.

This experimental fighter was built in late 1954. In January 1955, its ground tests began: taxiing to limit speed, etc. Meanwhile, CAGI conducted static tests of the main version of the Yak-140. It turned out that the wing of the aircraft needed to be strengthened, but this did not interfere in the least with the first phase of flight tests. In February 1955, however, work on the aircraft was stopped literally on the eve of the first flight and was not resumed. No satisfactory explanation for this has yet been found, except that there was no official decision by the Ministry of Aeronautics to restrict work on the Yak-140. The need to redesign the wing cannot be considered a serious reason for cancelling the aircraft, as such cases have often happened before. The technical problems that arose in this case were usually resolved quickly and quite successfully.

Interesting information illuminating this story was told to the author by a KB veteran. When asked about the fate of the Yak-140 by A. S. Yakovlev, many years after the events described, he replied that the then USSR Minister of Aviation Industry, P. V. Dementyev, had informed him, without any explanation, of the futility and pointlessness of the design bureau's attempts to continue work on the Yak-140 because another aircraft would be preferred anyway. Now one can only guess what motives guided the Minister. Yakovlev, who was well aware that without the support of MAP management the design bureau would not be able to achieve success, ordered all work on this aircraft to stop.

Thus, in February 1955, the Yak-140 was discontinued, and from then on the Yakovlev Design Bureau never returned to light frontline fighters.

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Yak-140
Wingspan, m		8.00
Length, m		12,95
Height, m		3,96
Wing area, m2		17.20
Weight, kg	empty aircraft	3400
	normal take-off	4850
	maximum take-off	5200
Engine	1 × TRD AM-11
Train, kN	max	1 x 39.0
	fornage	1 x 49,0
Maximum speed, km/h	with afterburner	1715
	without afterburner	1360
Practical range, km		1900
Max climb rate, m/min		6900
Practical access, m	with afterburner	18300
	without afterburner	16800
Crew		1
Equipment	3 × 30mm NR-30 cannon with 50 rounds per cannon
	16 × 57mm NURS ARS-57

Sources used:
History of aircraft designs in the USSR 1951-1965.
Aviation and Time. Konstantin Kosminkov. Not listed in reference books
Site "Corner of the sky". 2004 page: Yakovlev Yak-140.