Soviet Mixed Power Experimental Fighter Aircraft Piston-Liquid Propellant Rocket Engine/Piston-Ramjet/Piston-Pulsejet & Piston-Compressor Jet Engine Designs of the 1940's The intent of this research paper is to provide an overview of the Soviet experimental fighter aircraft programs employing mixed power plants - piston-liquid propellant rocket engine, piston-ramjet, piston-pulsejet and piston-compressor jet engine accelerator technology, in the World War II and early post war period of the 1940's. A number of piston fighter aircraft types were converted for experimental roles from the Design Bureaus of Lavochkin and Yakovlev to test liquid propellant rocket engines and ramjet accelerators to increase maximum speed of in-service fighter aircraft, Sukhoi also developing the purpose designed Su-7 as a piston-liquid propellant rocket engine powered aircraft. Lavochkin also tested pulsejet accelerators on the La-7 and La-9 piston engine fighter families whilst Mikoyan, Sukhoi and Yakovlev tested piston-compressor jet engine accelerators. The latter employed a conversion from a serial piston engine fighter whist Mikoyan and Sukhoi developed new designs for their respective piston-compressor jet engine accelerator test programs. As no design provided the necessary combination of speed performance and reliability, the respective piston-liquid propellant rocket engine, piston-ramjet, piston-pulsejet and piston-compressor jet engine development programs, all of which were unreliable and over complex in their operation, would fall by the wayside due to the promise of better performance from the first generation exclusively jet powered fighter aircraft designs.