ORIGINAL: Sport_Pilot
Once launched, as the airspeed increases and the angle of attack of the relative wind on the prop blades becomes less, the prop would then bite as you say, the load will increase suddenly, and the engine may load down again.
The load decreases as the plane speeds up, that is why the engine RPM goes up in flight, not down.
You would be correct if you were pertaining to something like a 11X6 prop. But not a 10X10, I guarantee you the engine load is greater when the plane is at 60 mph than it is static. As (if) it gets to say 150mph it will unload and the rpm will increase. It's very obvious to the ears with two totally different type engines and planes using that prop.