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

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.

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.

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 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.

Operators

• Soviet Union – The Yakovlev EG was designed with the intent of serving the Soviet Union. The EG was evaluated by Yakovlev OKB but was deemed to be unfit for service due to the excessive vibration and loss of stick control and phugoid instability when the helicopter reached speeds around 20 mph (30 km/h).

Gallery

Sources

• Gordon, Y., Kommisarov, D., & Kommisarov, S. (2005). OKB Yakovlev: A History of the Design Bureau and its Aircraft. Hinckley: Midland Publishing.
• Gunston, B., & Gordon, Y. (1997). Yakovlev Aircraft Since 1924 (Putnam). London: Putnam Aeronautical Books.
• Yakovlev EG / Sh / Yak-M11FR-1. (n.d.). Retrieved from http://www.aviastar.org/helicopters_eng/yak.php
• Colorized Image by Amazing Ace
• Illustrations by Ed Jackson