Hesham, once more, and again, and again - READ something BEFORE you post something STATING something.
You are posting pic of compound twin engine VM-6 and saying it was single-engined earlier version. IT WAS NOT.
DO YOU UNDERSTAND THAT CHANGE IN REQUIREMENTS (MAX PAYLOAD INCREASE +50%, SPEED UP TO 400 KM/H) LEAD TO initial project GROWTH IN SIZE, ADDITION_OF_THE_SECOND_ENGINE AND THEN _OPTIONAL_WINGS_AND PROPULSORS_ TO REACH REQUIRED SPEED, MAKING VM-6 AN COMPOUND? DO YOU UNDERSTAND THAT THERE _WERE_NOT_ SINGLE ENGINE COMPOUND VM-6?