I still remain convinced that piston engines are power producing machines. Yes, we have to take into account a lot of losses, thermal efficiency, etc... But they deliver power per each pound per hour. That's a fact. After that you can do whatever you want with that power. Like producing pounds of thrust and speed, for instance.
You are obviously correct - pistons and crankshafts produce RPM and torque, which is of course power.
But it's the
propeller that creates thrust to make the plane accelerate. As a very rough rule of thumb, 1.0 hp from the engine creates 2.5 lb. prop thrust at static conditions. And thrust drops off as the plane accelerates.
So if we want to take that 875K# 747 and power it with enough pistons to create 198400# thrust, the answer is 198400/2.5 = 79360 shp.
The difference (79360 vs 97381 hp) is that the typical prop, at static-to-Vr conditions, is pretty efficient compared to a turbofan. At higher speeds, not so much.
