Get rid of that formula. It is grossly simplified, beside the fact that it is dead wrong!
general dependancy of thrust data:
diameter ^4
rpm^2
pitch^1
Then throw in a constant for prop pitch design and or prop blade geometry
another constant for blade airfoil and zero AoA lift
AoA changes at speed
another way to calculate the effect of the amount of power for a given prop disk

Then you are olmost done.
Did I mention pressure altitude and fuselage resistance?

Cynics please note, there is no room for prop efficiency here. This is about thrust, and nothing else.