Thrust of a propeller has nothing to do with the weight or position of the motor/plane or propeller. It is simply the force that a propeller will exert at a given altitude density and is directly related to its RPM.

Static thrust is just that, the amount of force generated from a static position and zero wind speed in any direction. Measured using a strain gauge with the engine/plane held level in place.

Dynamic thrust is directly related to the speed through the air mass. At a certain point after the prop unloads the max rpm will become constant. The faster the plane moves through the air mass the lower the Dynamic Thrust will be until the sum of the drag on the aircraft balances out the dynamic thrust then maximum airspeed on the straight an level is achieved. We measured this with the same strain gauge with the engine mounted on a sliding test stand in a wind tunnel. Air speed was set with a manometer calibrated for air speed to 60 mph. Dynamic thrust fell off in direct proportion to airspeed.

In a climb or dive the mass of the aircraft will be a contributing factor to the max speed but only as long as the dive or climb is maintained. Returning to straight and level flight will return to the balance of Dynamic thrust and sum of the drag and the previous airspeed.