The early helicopter and radial piston engine were a meeting of minds. Unlike airplanes of the time, which required a crank-shaft lying prone driving a propeller, helicopters would need a drive-shaft in the perpendicular and the pancake outline of the radial engine was ideal for laying flat on the floor as can be seen here on the left in one of the earliest helicopters in the shape of the Bristol Sycamore; in fact it could be argued that the radial engine was a better fit in helicopters than in fixed-wing aircraft.
Nonetheless pitched around the centre of gravity it clearly occupied much of the space that might be given over instead to payload, and as a solution to this problem in another early helicopter in the form of the Wessex Whirlwind it occupied the nose instead, from where its drive-shaft passed between the two crew: with the benefit it took up less space altogether. And though it would add a deal of weight forward, this would be compensated by the rearward extension of that area given over to payload in the form of additional crew or passengers.
Looking at each installation however ~ and notwithstanding the gear-box at the top end beside a complex rotor-head and tail-rotor assembly ~ one can see how simple an electrical multi-copter is instead. Given an analogy I would say it is like comparing the movement of a conventional watch with the quartz oscillator and battery that more or less replaced it, except among those who wear unnecessarily complex watches by way of an investment or fashion statement.
Perhaps this is the fate of the conventional helicopter?
