Coming at BLDC motors from the theory side, my understanding has always been that they have a linear curve based on Kv, no-load current, and resistance, for a given applied voltage. Now the thing is, say they have a given "system load", like a propeller, that varies during the operation. So the load demands a certain RPM/torque combination at time A, and then a different one at time B. My understanding was that in order to achieve both combination A and B, it has to vary the supply voltage so that it's linear torque-speed curve intersects this operating point (provided this point lies below it's highest torque-speed curve).
What I can't seem to find is how this works without changing the supply voltage? If I use a PWM controller at 50% (but the supply voltage is the same), is the torque-speed curve really going to have a characteristic curve that responds as if the supply voltage was half? If not, how are these BLDC motors controller for dynamic applications where a specific torque and speed are needed at different times?