Yes, theorically, the acceleration should not change ; it remains at zero. The engine has theorically constant speed and so the aircraft. If the acceleration is at zero, then the "F" in you formula will be zero (the weight of the prop do not change anything).

In real world, you must gently rock the throttle to stay there and you help torque rolling when the prop accelerates (now you formula enters the scene) but as soon as you accelerate the engine, you must slow it down so you don't gain altitude, so the prop decelerates and in turn, slowing the torque roll until you get equilibrum.

The only way to gain torque on a given engine is to prop it so it turns in its peak torque range. A better way is to get a 4-stroke which for the same thrust, get higher torque since it is turning slower.