Bratukhin G-4

The first Soviet helicopter with the engines purposely designed, with cooling fan and front gearbox giving vertical and lateral outputs for the rotor and for transverse coupling shaft. The transmission was provided with centrifugal clutch; overall drive ratio 0.27 (540 rotor rpm). The main rotor had an inbuilt twist of 6 deg 45 min along the blade, and blade spar were extruded instead of folded sheet. Two prototypes were built, the first flown in October 1947 by M.K.Baikalov and second a month later. In January 1948 the first G-4 was damaged in the course of autorotational descents and deadstick landings typically at 12 m/s descent along 15.5-16 deg glide path.
The first prototype did not meet expectations (some calculated parameters were not reached). The second prototype had an improved rotor blade airfoil passed the extended test program without problems. Gliding (autorotation) rate was 12m/s, with gliding angle 16°. In this case landing speed was 80-90km/h with 10-15m roll.
The second G-4 was the first helicopter in the Soviet Union to meet its stipulated life for dynamic parts (in this case 100h). A small series constructed 1947-48, according to one account four flying out of ten ordered.

A G-4 and two G-3s participated in Aviation Parade in 1947.

G-4
Engine: 2 x AI-26GR pistone engine, 370kW
Rotor diameter: 7.7m
Take-off weight: 3002kg
Empty weight: 2364kg
Max speed: 148km/h
Ceiling: 2400m
Range: 233km
Crew: 1