Multichannel communication with Arduino and HC-12 transmitter
I believe you are misunderstanding what it means by channels. The HC-12 can transmit on up to 100 channels, which means different frequencies under the 433 MHz band. For example 433.05 MHz or 433.15 MHz. This is so multiple HC-12 modules can be used next to each other and only the module receiving on the channel of the transmitter will receive the data broadcast.

What you need to do for your quadcopter is send an array of bytes that begins with a constant, followed by the data you need (a packet). Example:

byte packet[] = {0x00, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01}

// in your loop
packet[1] = ; HOW MUCH THE ENGINE IS THROTTLED
packet[2] = ; HOW FAR THE CONTROL TO GO FORWARD IS DEPRESSED
// etc


Iterate through this array writing the data through the serial port to the HC-12. Whenever your receiver detects the constant (in this case 0x00) read the values that follow as the controls for the quadcopter.