Why do brushless motors have a kv rating?
"kv Rating" has nothing to do with Torque, current, power, thrust , lift or drag
It is based on number of magnets, number of stator windings per rotation, number of phases per pole and has no indication of power.
Power is a function of current and load only is rated with EITHER a linear load or the nonlinear load of the aerodynamic prop. or an incremental linear load in terms of gm/W or gm/A
It is based on the laws of Physics defined by Maxwell and in more depth by Heaviside, and Lorenz who proved that this Force on charge q is a product of the sum of the E field and the velocity of the B field.
So the vector equations says. F=q(E+vxB)
The Lorenz force, F acting on a particle of electric charge q with instantaneous velocity v, due to an external electric field E and magnetic field B. This force is what we call the Electromagnetic Force and is matched by the Back EMF at no load.
The Angular Velocity per Volt is a more complex one with the number of stator poles and rotor poles giving a ratiometric conversion and the commutation of the motor current is automatically reversed just an adequate number of arc seconds after the null magnetic field to ensure no dead stop. ( design/process failure)
Thus the magnetic charge velocity is proportion to the Field strength which is due to Voltage