First Soviet helicopter with engine designed for such duty. Cooling fan and fron gearbox giving vertical and lateral outputs for rotor and for transverse coupling shaft. Transmission provided with centrifugal clutch; overall drive ratio 0.27 (540 rotor rpm). Rotor diameter slightly increased, inbuild twist of 6°45' along blade, and blade spar extruded instead of folded from sheet. Two prototypes, first flown Oct 1947 by M.K.Baikalov and second a month later. In Jan 1948 first G-4 damaged in course of exhaustive autorotational descents and deadstick landings typically at 12 m/s descent along 15.5-16° glide path. Second G-4 first in Soviet Union to meet stipulated life for dynamic parts (in this case 100h). Small series constructed 1947-48, according to one account four flying out of ten ordered.
Bill Gunston "The Osprey's Encyclopedia of Russian Aircraft", 2000
Equipped with domestic AI-26GR, G-4 was slightly bigger than G-3.
First G-4 was flight-tested in October 1947 by test-pilot M.K.Bajkalov. Helicopter was capable to fly horizontally with one engine shot down, and land safely in autorotation regime. The first prototype did not meet expectations (some calculated parameters were not reached). As a result of incomplete pilot instructions, it was crashed.
The second prototype with 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.
Powerplant and rotors passed 100 hours resource test (performed for the first time on helicopter in the USSR).
G-4 and two G-3 participated in Aviation Parade in 1947.
Small series of G-4 were built.