Yakolev ordered the development of a practical helicopter capable of being built in two forms, as a transport carrying a pilot and two passengers, or equivalent cargo, and as a two-seat, dual-control trainer. Design began in June 1947, this machine being one of several which were given out-of-sequence type numbers. The Yak-100 was externally similar to the Sikorsky S-51. The OKB team, under Erlikh, designed this single-rotor machine retaining similar dynamic parts the to EG. The drive and hub mechanism with damped flapping, feathering and drag hinges and hydraulic-dashpot control via swashplate were similar with three main blades of hardwood and pine as before, with ply skin and glued fabric overall. Root of each blade in upper/lower halves of bolted D1, steel hub. Main change in engine installation was vertical engine mount with several changes to enable engine to run in this attitude. Cooling fan, clutch/freewheel and reduction gear and angle box for tail rotor were more Sikorsky than scaled-up EG, though pilot controls and control system retained OKB belief in spring and oil vibration dampers (this time with pilot adjustment) and in spring-loaded actuation of pitch into autorotation following loss of drive torque. Pedal control of tail-rotor pitch. Airframe based on welded steel-tube frame carrying landing gear, seats, rotor hub and engine. Skin riveted D1, and cranked tailboom D1 monocoque. Basic design completed late 1947 as tandem trainer or as transport with single pilot in front and two-seat divan or other payload behind.

The engine was Ivchyenko’s AI-26 seven-cylinder radial, the version chosen being the 575hp AI-26GRFL designed to operate with crankshaft vertical. This drove via a cooling fan and centrifugal clutch to a main gearbox which turned the single main rotor at 232 (not 233) rpm, with a bevel drive to a shaft carried on external trunnions along the top of the long tail boom to a 2.6m three-blade tail rotor. The latter counteracted the main-rotor drive torque and provided yaw (directional) control, driven by pedals. Both rotors were again of fabric-skinned wood laminates, the main rotor having manual control via swash-plates, with spring-loaded automatic autorotative control following loss of drive torque.

The fuselage was again based on a welded-tube truss, with unstressed D1 skin, but the tail boom was a D1 semi-monocoque. The main gearbox was housed in a large mast fairing above the engine compartment, with a front air inlet for the fan-assisted oil cooler. Again the undercarriage was a simple tricycle, with a castoring levered-suspension nosewheel and triangular-braced main units with oleo shock struts pinned to the upper longerons. Track was 3m and wheelbase 2.865m. The entire front of the fuselage was transparent, with sliding doors on the right for the pilot and on the left for the backseater (who had dual control in the first prototype). The transport version was to have a two-seat divan at the rear.

Two prototypes built, first with VVS funds and bearing VVS insignia. The first prototype was tested from November 1948. Initially suffering from severe vibration and apparent blade flutter, the lades given ground-adjustable TE tabs and eventually modified with CG further aft, behind flexural axis. These blades first fitted to No.2 Yak-100, which began test July 1949. Gradually problems with vibration and flutter were solved, and a second prototype was built with modified blades with the cg behind the flexural axis which greatly improved behaviour without complicated damper systems. This dubler, first flown in July 1949, had a more-fully enclosed engine bay with grilled panels and an internally mounted tail-rotor drive shaft. NII-VVS testing took place in the second half of 1950.

Factory test complete June 1950 and NII tests successfully accomplished later same year, but Mi-1 already adopted and Yak-100 project was lost dropped.

Yak-100
Total length: 13.91m
Main rotor diameter: 14.50m
Tail rotor diameter: 2.60m
Empty mass: 1805kg
Max take-off weight: 2180kg
Max. speed: 170km/h
Static ceiling: 2720m
Dynamic ceiling: 5250m
Range: 325km
Crew: 1-2

The Yakolev OKB started development of helicopters after the war and designed an experimental machine in 1946, the Yak-EG (Eksperimentalnyi Gelikopter) with a coaxial rotor system, and widely known as the Yak-M11FR-1.
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 was 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. Following testing it was decided that the coaxial rotor layout should be developed by the Kamov bureau, and Yakolev moved on to other helicopter configurations.

EG
Engine: M-11FR-1 5-cylinder air cooled piston, 140 hp
Rotor diameter: 10.0m
Length: 6.53m
Max take-off weight: 1020kg
Empty weight: 878kg
Payload: 142kg
Fuel: 50kg
Max speed at sea level: 150km/h
Max speed reached: 70km/h
Hovering ceiling: 250m
Service ceiling: 2700m
Service ceiling reached: 180m
Range: 235km