On December 19, 1944, the Yak-3 M prototype reached 463 mph (745 km/h) powered by one 1,800 hp. VK-108 V-12. It was the fastest of all piston-engine Soviet airplanes only surpassed at the time by the American prototypes XP-47J, XP-72, XP-51F and XP-51G, but this experimental engine showed constant overheating and vibration problems, and flight testing was halted on March 8, 1945. Despite its excellent performance the Yak-3 M project was abandoned in favor of a new class of mixed power plant fighters.
Yak-3 M technical data
Wingspan: 30 ft. (9.2 m), length: 28 ft. (8.55 m), height: 7.9 ft. (2.42 m), wing surface: 165 sq. ft. (14.85 sq. m), take-off weight: 5,464 lb. (2,896 Kg).
The Soviet industry proved to be unable to build efficient turbo-superchargers during the war and all the programs for the construction of the high-altitude interceptors (MiG-7, MiG-11, Polikarpov ITP, M, Sukhoi Su-1, Su-3 and Yak-9PD) were affected by that.
In 1943 one Lavochkin LaGG-3 PVRD of the 11th Series was tested with two Bocharev ramjets mounted in the underwings bomb racks. The speed gain over the LaGG-3 standard was only 19 mph, but the ramjets imposed 31 mph drag penalty when not operating.
Lavochkin LaGG-3 PVRD technical data
Wingspan: 32 ft. (9.8 m), length: 28.8 ft. (8.81 m), height: 14.4 ft. (4.4 m), wing surface: 188 sq. ft. (17.5 sq. m), take-off weight: 6,543 lb. (2,968 Kg).
In March 1944 the Yak-7 PVRD (Nº 820803) was flown with two wing mounted Merkulov DM-4C ramjets, the speed gain was 12 mph.
Yak-7 PVRD technical data
Wingspan: 32.8 ft. (10 m), length: 27.9 ft. (8.5 m), height: 9 ft. (2.75 m), wing surface: 190.5 sq. ft. (17.15 sq. m), take-off weight: 6,675 lb. (3,024 Kg).
In August 1946 the Lavochkin La-7S/D-10 PVRD prototype was tested with two Tchelomei RD-13 pulsejets (the Soviet version of the Argus As 109-014 captured at Berlin-Reinichendorf) mounted under the wings. The aircraft was expected to reach 497 mph but could not exceed 416 mph due to the drag.
Lavochkin La-7S/D-10 PVRD technical data
Wingspan: 32 ft. (9.8 m), length: 28.4 ft. (8.67 m), height: 9 ft. (2.7 m), wing surface: 189.3 sq. ft. (17.59 sq. m), take-off weight: 8,170 lb. (3,701 Kg).
Also in September 1944, the Lavochkin La-9 PVRD (La-126) experimental airplane flowed, fitted with two wing mounted Bondaryuk PVRD-430 ramjets.
The 430 was aerodynamically cleaner than the Merkulov 45, proving better performance, but the speed gain of both prototypes was 40 mph only, with 37 mph drag.
Lavochkin La-9 PVRD technical data
Wingspan: 32 ft. (9.8 m), length: 28.3 ft. (8.63 m), height: 11.7 ft. (3.56 m), wing surface: 197 sq. ft. (17.72 sq. m), take-off weight: 7,230 lb. (3,275 Kg).
The Lavochkin La-9 RD, with two RD-13/D-10 pulsejets, 419 mph top speed and 37 mph drag was tested in March 1947. The RD-13 only worked acceptably at low altitude, losing power very quickly above 9,000 ft. The operation of two pulsejets could not be synchronized, generating severe vibrations and worsening the handling.
Lavochkin La-9 RD technical data
Wingspan: 32 ft. (9.8 m), length: 28.3 ft. (8.63 m), height: 11.7 ft. (3.56 m), wing surface: 197 sq. ft. (17.72 sq. m), take-off weight: 7,024 lb. (3,182 Kg).
The ramjet’s thrust failed to exceed the aerodynamic drag of the engine nacelle, because the high-temperature internal deformation caused turbulence, produced during the combustion process, and dynamic instabilities in flight.
Trials were discontinued in 1948 when the GIRD scientist finally admitted that the thrust produced by the ramjet boosters was outweighed by the drag when not operating.
An evolutionary dead-end.