|Yakovlev EG / Sh / Yak-M11FR-1|
Also said to have been called EG (Eksperimentalnyi Gelikopter), and widely known as the Yak-M11FR-1, this was the OKB's first essay into the field of helicopters, in 1946. The chief engineer was S.A.Bemov, assisted by I.A.Erlikh. From the outset it was planned as the smallest practical machine to solve basic problems. The engine was a 140hp M-11FR-1 mounted in the normal attitude with the drive taken through a cooling fan and centrifugal clutch to a 90deg bevel gearbox to co-axial vertical shafts. These turned two-blade rotors in opposite directions, at 233 rpm. After studying the possible use of pilot controlled tabs or auxiliary surfaces behind the blade tips the choice wisely felt on a fully articulated hub with swashplates giving collective and cyclic pitch control. A unique feature was a spring-loaded hydraulic coupling which, upon failure of the drive torque, automatically moved the collective linkage to autorotative pitch.
The rotor blades were laminated pine and hardwood, covered in glued fabric, held in a hub of steel and duralumin. The fuselage was a simple truss of welded steel tube, with Dl skin as far back as the rear of the engine compartment, where an aft-facing gap allowed fan-induced cooling air to escape. The fuel tank was under the main gearbox and the oil tank next to the engine. For better stability in cruising flight a light fabric-covered rear fuselage with twin fins and a tailskid was added behind this point. The welded truss was extended at the front and sides to three vertical shock struts with single wheels, the nose unit having levered suspension. Track was 2.8m and wheelbase 2.68m. The side-by-side cockpit had a door on each side and the largest possible window area.
The Sh was completed in early 1947. The chief pilot was V.V.Tezavrovskii, who with others made forty tethered tests (total 5hr) followed by seventy-five free flights (total 15hr). Ground resonance, then little known, was avoided by pure chance. The centre of gravity was clearly too far aft, so the tail (and for a time the tail-skid) were removed and the oil tank relocated behind the cockpit bulkhead. Eventually the Sh hovered under good control, but as soon as forward speed exceeded about 30km/h vibration and progressive loss of control were encountered, and this configuration was abandoned.
Bill Gunston & Yefim Gordon "Yakovlev Aircraft since 1924", 1997
The Yakovlev OKB started development of helicopters after the war and designed an experimental machine, the Yak-EG with a coaxial rotor system. A prototype of this helicopter was tested in 1947/48 following which it was decided that the coaxial rotor layout should be developed by the Kamov bureau, and Yakovlev moved on to other helicopter configurations. They produced a design designated Yak-100 which was externally similar to the Sikorsky S-51. The first of two prototypes of this helicopter flew in 1948, but the Mi-1 was adopted as the standard light helicopter for the Soviet forces and the Yakovlev design was dropped.
OKB formed helicopter group in 1946, and assigned design management to Igor A. Erlikh. Adopted coaxial configuration with pair of two-blade rotors with max vertical separation. Maximum help from CAHI, and OKB engineers also visited Breguet which had flown Dorand coaxial machine before war and was completing prototype G-IIE. No direct liaison with Kamov but GUAP provided funds and oversaw both teams, which (except for pilot controls) did come to similar conclusions. Rejecting TE outrigger tabs considered at start, rotor fully articulated with friction dampers and controlled by modern cyclic/collective levers acting via oil dashpots on swash-plates, with yaw control by pedals giving differential collective to upper/lower rotors. Blades built up laminated hardwood and pine with ply covering overlain by glued fabric. Simple fuselage based on welded steel truss with D1 sheet from nose to rear of engine compartment, fabric at tail. To seats side by side in nose (not known if dual control) with door each side. Radial engine in normal attitude with forward drive via cooling fan and centrifugal clutch to bevel box and rotor shafts, with hydraulic coupling and additional oil-depressed spring which on failure of drive forced blades into autorotative pitch. Tricycle landing gear with vertical oleo struts; ground resonance avoided by pure chance. Completed early 1947 with long fabric-covered rear fuselage carrying twin-finned tail and tailskid. Tested by V.V.Tezavrovskii who made 40 tethered hovers followed by 75 flights for total airborne time of 20 hours. EG (Eksperimentalnyi Gelikopter) flew, but CG too far aft and tail removed; oil tank moved from engine compartment to rear cockpit bulkhead, skid removed and rear fuselage re-faired. Normal rotor rpm 233, severe vibration, and though positive control never lost, stick force and phugoid instability worsened beyond 30km/h forward speed, severely limiting practical value of EG. After prolonged investigation Yak decided to leave this configuration to Kamov.
Bill Gunston "The Osprey Encyclopedia of Russian Aircraft", 2000