Скользящая пороховая контратака
Mean piston speed Wikipedia. The mean piston speed is the average speed of the piston in a reciproing engine is a function of stroke and RPM. There is a factor of 2 in the equation to account for one stroke to occur in 1/2 of a crank revolution (or alternatively: two strokes per one crank revolution) and a ''60'' to convert seconds from minutes in the RPM term.