Yakovlev | Plane-Encyclopedia

USSR (1939)
Light Bomber – 90 to 100 Built

Following the failure of the Yak-2, Yakovlev attempted to salvage the project. One of the attempts that saw limited production was the Yak-4. While it would be powered by a somewhat stronger engine, it too would prove to be a failure and only some 100 aircraft would be built by 1941.

The Yak-2 Failure

While the Yak-2 prototype initially had excellent flying characteristics, once it was actually fully equipped with its military equipment, its performance dropped dangerously. A large number of issues, like overheating, poor flight stability, and problems with its hydraulics, were also noted during the development phase. Despite this, some 100 aircraft would be built and some were even issued for operational use.

Yak-2 side view. [Gordon & Khazanov, Soviet Combat Aircraft]

One of the many weak points of the Yak-2 was its problematic Klimov M-103 engine. The Soviet designers decided to replace this with the more powerfulr M-105 engine. Two basic designs emerged, one for a dive bomber and one for a short-range bomber. During its first test flight, the dive bomber variant proved to be so disappointing that the project was canceled. The bomber version, however, showed to be somewhat promising and the green light for its development was given.

Development History

The development of the BB-22bis (also known as Izdeliye 70bis) prototype was given to Factory No.1, and the Yak-4 designation was officially adopted only in December 1940. Engineers at Factory No. 1 started to build the prototype in early 1940 and it was completed by March the same year. This was not a new aircraft, but a modified Yak-2,serial number 1002) . That same month, Factory No.1 was instructed to produce additional prototypes for testing the aircraft’s performance by the Army, which had to be completed by the start of July 1940. The Army requested a maximum speed of 590 km/h (366 mph) at 5,000 m (16.400 ft)be , an operational range of 1,200 km (745 miles), and a service ceiling of 11,000 m (36,090 ft).

The modified Yak-2 (serial number 1002) aircraft that served as the base for the BB-22bis prototype. [Y. Gordon, D, Khazanov and S. Komissarov OKB Yakovlev ]

Following the completion of the first prototype, a series of test flights were carried out. During one of the test flights, carried out on the 12th May, a maximum speed of 574 km/h (356 mph) was achieved. On 23rd May, however, there was an accident and the pilot was forced to crash land at a nearby airfield, damaging two other bombers and the prototype’s wing in the process. Given the extensive damage to the aircraft’s wing, the prototype had to be written off. Due to this and delays in production, the first two trial aircraft could not be completed before the end of 1940. Interestingly enough, these were actually produced by the Moscow Aircraft Factory No.81, which started the production of the Yak-4 during October and November 1940. At that time, the type had not yet received official approval from the Soviet Army.

The damage suffered by the first prototype during its hard landing was so severe that it had to be scrapped. [Y. Gordon, D, Khazanov and S. Komissarov OKB Yakovlev]

The two trial aircraft were given to the Army for testing on 10th December 1940. These tests were held at the end of January 1941. The results were once again disappointing, as these aircraft had worse performance than the prototype. With the added weight of equipment and fuel, the maximum speed was reduced from 574 km/h (357 mph) to 535 km/h (332 mph). The cockpit was described as being too cramped, and with the full bomb load, the plane proved to be difficult to control even by experienced pilots. The commission that examined the two aircraft insisted that the Yak-4 should not be accepted for service. In late February 1941, the Director of Factory No.81 gave a report to the Soviet People’s Commissar of the Aircraft Industry, A. Shakhoorin, that the production of the Yak-4 was to be stopped and replaced with the Yak-3. Interestingly enough, while the Yak-2 was developed by Alexander Sergeyevich Yakovlev, he did not direct the design process of the Yak-4.

Technical Characteristics

The Yak-4 was an overall copy of its predecessor, the Yak-2, but there were still some differences. The most obvious change was the introduction of new engines. The older M-103 ,960 hp, was replaced with a stronger M-105 1050 hp engine. The installation of the two new engines also introduced a number of internal improvements to the ventilation and fuel systems. New 3.1 m (122 in) long VISh-22Ye type propellers were also used on this model. The landing gear retracted to the rear into the engine nacelles, but was not fully enclosed. These consisted of two pairs of 700×150 mm wheels.

The rear parts of the fuselage were lengthened and redesigned, and it was less bulkier than the Yak-2. The cockpit was improved in order to provide the crew with a slightly better overall view. The rear gunner received a completely new pivoting canopy. He operated the TSS-1 mount armed with two 7.62 mm (.30 caliber) ShKAS types machine guns.

The maximum bomb load was increased to 900 kg (1,980 lbs). In addition, there was an option of mounting two 90 (20 gallons) or one 250 liter (54 gallons) auxiliary fuel tanks under each wing. There were six fuel tanks placed in the wings. These had a total capacity of 1,120 litres (244 gallons) of fuel.

A front view of the Yak-4 with its new and stronger M-105 engines. [Y. Gordon, D, Khazanov and S. Komissarov OKB Yakovlev]

In Combat

The Yak-4, together with the Yak-2, was allocated to the 314th and 316th Reconnaissance Regiments in the western district. Some were given to the 10th, 44th, 48th, 53rd, 136th and 225th short to medium range Bomber Regiments. The main problem for the units that operated the Yak-2 and Yak-4 was the slow delivery of these aircraft. For example, only a few pilots from the reconnaissance units had a chance to fly on these new aircraft. By 10th June 1941, only limited numbers of Yak-4s were available for service. A shipment of some 10 new aircraft was meant to arrive but did not due to the war’s outbreak.

Pilots from the 314th Reconnaissance Regiment performed several flights over the border with Germany just prior to the Invasion of the Soviet Union while flying Yak-4s. The Germans responded by sending the Bf 109E to intercept them, but they failed to do so. However, once the war started, the German Luftwaffe destroyed many Soviet aircraft on the ground. This was also the case with the Yak-4, with the majority lost this way. Some did survive though and offered limited resistance to the Germans. By September 1941, on the Northern front, there were still fewer than 10 operational Yak-4s. To the South, there were still some 30 or so Yak-4s which were still operational by October 1941. There is no information of the use or losses of the Yak-4 after 1942. According to Y. Gordon, D, Khazanov and S. Komissarov OKB Yakovlev , at least one Yak-4 was still operational and used by the 118th Reconnaissance Regiment in 1945.

Most of the Yak-4s were destroyed on the ground by the advancing Germans. [Y. Gordon, D, Khazanov and S. Komissarov OKB Yakovlev]

The advancing Hungarians, who were supporting the Germans during the Invasion of the Soviet Union, managed to capture at least one Yak-4 aircraft during 1941. The use of this aircraft by them would be limited at best, due to the scarcity of spare parts and general poor performance.

Production

The production of the Yak-4 was only carried out at Factory No.81. The production lasted from November 1940 to April 1941. Around 90 to 100 aircraft would be built, with the last 22 Yak-4s being delivered for use by late April 1941.

Operators

Soviet Union – Operated some 90 aircraft
Hungary – Managed to capture at least one Yak-4 aircraft

Conclusion

Despite attempts to resolve a number of issues noted on the previous version, the Yak-4 in general failed to do so. The problem was the overall poor design of the original Yak-2 which offered little room for improvement. The inability to improve the aircraft to the satisfaction of the Soviet Air Force led to the cancelation of the Yak-4 project after only a small number of aircraft was built.

Yak-4 Specifications
Wingspans	45 ft 11 in / 14 m
Length	33 ft 4 in / 10.18 m
Wing Area	316.4 ft² / 29.4 m²
Engine	Two M-105 hp engines
Empty Weight	10,050 lbs / 4,560 kg
Maximum Takeoff Weight	13,481 lbs / 6,115 kg
Climb Rate to 5 km	In 6.5 minutes
Fuel load	1,120 litres (244 gallons)
Maximum Speed	332 mph / 535 km/h
Cruising speed	284 mph / 458 km/h
Range	460 miles / 740 km
Maximum Service Ceiling	31,824 ft / 9,700 m
Crew	Pilot and the rear gunner.
Armament	Two 7.92 mm (.30 caliber) machine guns 400 to 900 kg (880 to 1.980 lbs) bombs

Gallery

Illustrations by Ed Jackson

Yak-4, 118th Independent Reconnaissance Aviation Regiment, Northern Fleet, 1943

Yak-4, 314th Reconnaissance Aviation Regiment, 1941

Yak-4 from the 314th Reconnaissance Aviation Regiment, Babruysk, Belarus, June 1941

Credits

Written by: Marko P.
Edited by: Stan L. & Henry H.
Illustrations by Ed Jackson

Sources

D. Nešić (2008), Naoružanje Drugog Svetskog Rata SSSR, Beograd
B. Gunston and Y. Gordon (1977)Yakovlev Aircraft Since 1924, Putnam Aeronautical Books.
Y. Gordon, D, Khazanov (1999) Soviet Combat Aircraft, Midland Publishing
Y. Gordon, D, Khazanov and S. Komissarov (2005) OKB Yakovlev, Midland
G. Sarhidai, H. Punka and V. Kozlik. (1996) Hungarian Air Forces 1920-1945, Hikoki Publisher

USSR (1946)
Coaxial Rotor Helicopter – 1 Built + 1 Incomplete

The modified Yakovlev EG prototype in flight. (Yakovlev OKB) Colorization by Amazing Ace

The EG (also known as the Yak-M-11-FR-1, Sh or Yak-EG) was a prototype helicopter designed in 1946 by the Yakovlev OKB. The EG was designed with a coaxial rotor configuration and had an ambitious performance estimation. Through manufacturer testing, it was revealed that the EG had very undesirable handling characteristics and excessive vibrations when the helicopter reached around 20 mph (30 km/h). These flaws caused the cancellation of the EG project and the completed prototype was converted to an aerosani in 1955 and donated to a farm in the Kazakh SSR. The Kamov OKB would later go on to develop the coaxial rotor configuration further.

History

Lessons of the Second World War showed the world the importance of adopting and developing modern technologies. Throughout the war, autogyros and helicopters became increasingly relevant with several countries’ militaries and saw a dramatic increase in development. The Soviet Union had a very limited selection of these machines during the war, and looked to develop this technology and expand their arsenal. In 1946, the esteemed Yakovlev OKB initiated a project for an experimental coaxial rotor helicopter design. The project was given the nickname of “EG”, for “Experimental Helicopter” (Экспериментальный Геликоптер / Eksperimentahl’nyy ghelikopter). When the task of designing the EG was first announced to the design team, a flabbergasted staff member exclaimed “Shootka?” (шутыш), which roughly translates to “Are you kidding?”. This then led the EG to unofficially be referred to as the “Sh”, a running joke in the design team. Another designation which referred to the EG was “Yak-M-11FR-1”, which referred to the engine that the helicopter would use. The origin of this designation is unknown, but it does not appear to be official.

A detailed cutaway drawing of the modified Yakovlev EG prototype. (Yakovlev OKB)

Responsibility over the project was given to chief designer S.A. Bemov, with I.A. Erlikh as his aide. The EG was envisioned as a coaxial rotor configuration while powered by a 5-cylinder air-cooled Shvetsov M-11FR-1 radial engine producing 140 hp. When the initial design was completed in early 1947, the design team built a flying scale model of the EG to prove the viability of the coaxial rotor design. The scale model was given the designation of ED 115, with the digits referencing OKB-115, the plant designation for Yakovlev OKB.

The modified prototype Yakovlev EG sits on the Yakovlev OKB’s premise with it’s rotor fins folded. (Yakovlev OKB)

After verifying the EG’s design, construction of the actual prototype commenced. The prototype was completed sometime in the summer of 1947 and was promptly subjected to manufacturer’s trials. The EG prototype performed 40 tethered flights (total of 5 hours flight time) before being authorized to perform the first free flight test on December 20, 1947. Through extensive testing, it was revealed that the center of gravity was too far to the rear, which led the team to remove the tail and tailskid and relocate the oil tank behind the cockpit. In early 1948, the M-11FR-1 engine was removed, replace by an experimental M-12 radial engine, a development of the M-11. The first test flight with this engine was conducted on April 9th, but the engine proved troublesome and forced the team to refit the M-11FR-1 engine. Flight tests continued until July 8, 1948, with a total of 75 free flights conducted (total of 15 hours flight time).

Despite the EG showing relatively decent results, it suffered from excessive vibration, loss of stick force and phugoid instability once the machine approached 20 mph (30 km/h). This severely restricted the EG’s practicality and thus warranted the project’s cancellation. The coaxial rotor design configuration was given to Kamov OKB to further develop, while the Yakovlev OKB moved onto more conventional helicopter configurations. A second prototype was in construction but was never completed and was scrapped when the program was canceled. The sole completed prototype was preserved at the Moscow Aviation Institute for a couple of years before being converted to an aero-sleigh by students between 1954 and 1955. The converted sleigh was then donated to a farm in the Kazakh SSR and the fate beyond that is unknown. Photos of this new conversion do not exist. Though ultimately ending up as a failure, the EG was an important stepping stone in Soviet helicopter development and was quite special in the sense that it was the Yakovlev OKB’s first helicopter design.

Design

The original configuration of the Yakovlev EG with a horizontal tail, tail bumper and endplate fins. (Yakovlev OKB)

The Yakovlev EG was a coaxial rotor helicopter powered by a 5-cylinder air-cooled Shvetsov M-11FR-1 radial engine producing 140 hp. The engine drove co-axial two-bladed rotors using a transmission system which featured a centrifugal clutch, a 90-degree gearbox and a cooling fan. Fuel tanks were placed under the gearbox while the oil tank was next to the engine. The rotors (made of laminated pine and hardwood) spun in opposite directions at 233 rpm. Both collective and cyclic pitch control was provided through the rotor’s fully articulated hub mount. The EG’s fuselage consisted of simple welded steel tubes which had D1 duraluminium skin all around except for the engine compartment. The rear fuselage, which was covered with fabric, gradually tapered off to form a fin which was accompanied by a horizontal stabilizer supplemented by two endplate tips. The tail and the horizontal stabilizer would be removed later on in the test phase due to the offset center of gravity. The EG had a non-retractable tricycle landing gear with vertical shock absorber struts. The glazed cockpit compartment could house two pilots, which would enter through doors on either side of the fuselage.